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Dietary Mineral

Dietary mineral

Dietary minerals are the inorganic, indestructible elements that aid physiological processes within the body. They are chemical elements required by living organisms. They can be either bulk minerals (required in relatively large amounts) or trace minerals (required only in very small amounts). These can be naturally occurring in food or added in elemental or mineral form, such as calcium carbonate or sodium chloride. Some of these additives come from natural sources such as ground oyster shells. Sometimes minerals are added to the diet separately from food, as vitamin and mineral supplements and in dirt eating, called pica or geophagy. Appropriate intake levels of each dietary mineral must be sustained to maintain physical health. Excessive intake of a dietary mineral may either lead to illness directly or indirectly because of the competitive nature between mineral levels in the body. For example, large doses of zinc are not really harmful unto themselves, but will lead to a harmful copper deficiency (unless compensated for, as in the Age-Related Eye Disease Study). Soils in different geographic areas contain varying quantities of minerals. In human nutrition, the most important dietary minerals include (in alphabetical order):
- Chromium
- Cobalt
- Copper
- Fluorine
- Iodine
- Iron
- Magnesium
- Manganese
- Molybdenum
- Potassium
- Selenium
- Zinc Secondary dietary minerals. Standards of evidence vary for different elements, and not all have been definitively established as essential to human nutrition. Elements for which convincing scientific evidence is lacking are marked as suspect. This category includes:
- Arsenic
- Bismuth (suspect)
- Boron
- Nickel
- Rubidium (suspect)
- Silicon
- Strontium (suspect)
- Tellurium (suspect)
- Titanium (suspect)
- Tungsten (some organisms use tungsten rather than molybdenum)
- Vanadium Other elements essential to life include calcium, carbon, hydrogen, nitrogen, oxygen, phosphorus, sodium and sulfur. These are not generally considered trace elements, as they are needed in larger quantities. Iron and potassium are needed in larger quantities than the other listed minerals and are sometimes considered trace elements, and sometimes not. Sodium is needed in large quantities, but the mineral is found so commonly in food, it is not generally necessary to take additional supplements. Various other elements found in food supplies may vary from holding no known nutritional value (such as silver) to being toxic (such as mercury).

External links

- [http://www.bartleby.com/65/mi/minerald.html Bartleby Encyclopedia article on dietary minerals]
- [http://www.portfolio.mvm.ed.ac.uk/studentwebs/session2/group29/intronut.htm Metals in Nutrition] Category:Dietary minerals Category:Nutrition th:เกลือแร่

References

Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.

Chemical element

A chemical element, often called simply element, is a chemical substance that canot be divided or changed into other chemical substances by any ordinary chemical technique. The smallest unit of this kind of chemical substances is an atom. An element is a class of substances that contain the same number of protons in all its atoms.

Chemistry terminology

Earlier an element or pure element was defined as a substance which "cannot be further broken down into another compound with different chemical properties" -- which should be taken to mean it consists of atoms of one element. However, due to allotropy, the isotope effect, and the confusion with the more useful term referring to the general class of atoms (irrespective of what compound it may be in), this usage is in disfavor amongst contemporary chemists, and sees restricted, mostly historical, use. This definition was motivated by the observation that these elements could not be dissociated by chemical means into other compounds. For example, water could be converted into hydrogen and oxygen, but hydrogen and oxygen could not be further decomposed, thus "elemental". There are also many counterexamples (for example "elemental oxygen" (O₂) can be decomposed by solely chemical means into oxygen ions and atoms which have drastically different chemical properties). The remainder of this article will concern itself with the first definition.

Description

The atomic number of an element, Z, is equal to the number of protons which defines the element. For example, all carbon atoms contain 6 protons in their nucleus, so for carbon Z=6. These atoms may have different amounts of neutrons, and are known as isotopes of the element. The atomic mass of an element, A, is measured in unified atomic mass units (u) is the average mass of all the atoms of the element in an environment of interest (usually the earth's crust and atmosphere). Since electrons are light, and neutrons are barely more than the mass of the proton, this usually corresponds to the sum of the protons and neutrons in the nucleus of the most abundant isotope, though this is not always the case (notably chlorine, which is about three-quarters ³⁵Cl and a quarter ³⁷Cl). Some isotopes are radioactive and decay into other elements upon radiating an alpha or beta particle. Some elements have no nonradioactive isotopes, in particular all elements with Z >= 84. The lightest elements are hydrogen and helium. Hydrogen is thought to be the first element to appear after the Big Bang. All the heavier elements, are made naturally and artificially through various methods of nucleosynthesis. As of 2005, there are 116 known elements: 93 occur naturally on earth (including technetium and plutonium), and 94 (including promethium) have been detected so far in the universe. The 23 elements not found on earth are derived artificially; the first purportedly synthesized element was technetium, in 1937, although the trace amounts of naturally occurring technetium were not known then. All artificially derived elements are radioactive with short half-lives so that any such atoms that were present at the formation of Earth are extremely likely to have already decayed. Lists of the elements by name, by symbol, by atomic number, by density, by melting point and by boiling point are available. The most convenient presentation of the elements is in the periodic table, which groups elements with similar chemical properties together.

Nomenclature

The naming of elements precedes the atomic theory of matter, although at the time it was not known which chemicals were elements and which compounds. When it was learned, existing names (e.g., gold, mercury, iron) were kept in most countries, and national differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For example, the Germans use "Wasserstoff" for "hydrogen" and "Sauerstoff" for "oxygen," while some romance languages use "natrium" for "sodium" and "kalium" for "potassium," and the French prefer the obsolete but historic term "azote" for "nitrogen." But for international trade, the official names of the chemical elements both ancient and recent are decided by the International Union of Pure and Applied Chemistry, which has decided on a sort of international English language. That organization has recently prescribed that "aluminium" and "caesium" take the place of the US spellings "aluminum" and "cesium," while the US "sulfur" takes the place of the British "sulphur." But chemicals which are practicable to be sold in bulk within many countries, however, still have national names, and those which do not use the Latin alphabet cannot be expected to use the IUPAC name. According to IUPAC, the full name of an element is not capitalized, even if it is derived from a proper noun (unless it would be capitalized by some other rule, for instance if it begins a sentence). And in the second half of the twentieth century physics laboratories became able to produce nuclei of chemical elements that have too quick a decay rate to ever be sold in bulk. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This can lead to the controversial question of which research group actually discovered an element, a question which delayed the naming of elements with atomic number of 104 and higher for a considerable time. (See element naming controversy). Precursors of such controversies involved the nationalistic namings of elements in the late nineteenth century (e.g., as "lutetium" refers to Paris, France, the Germans were reticent about relinquishing naming rights to the French, often calling it "cassiopeium"). And notably, the British discoverer of "niobium" originally named it "columbium," after the New World, though this did not catch on in Europe. The Americans had to accept the international name just when it was becoming an economically important material late in the twentieth century.

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of one atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, which were to be used to depict molecules. These were superseded by the current typographical system in which chemical symbols are not used as mere abbreviations though each consists letters of the Latin alphabet - they are symbols intended to be used by peoples of all languages and alphabets. The first of these symbols were intended to be fully international, for they were based on the Latin abbreviations of the names of metals: Fe comes from Ferrum; Ag from Argentum. The symbols were not followed by a period (full stop) as abbreviations were. Besides a name, later chemical elements are also given a unique chemical symbol, based on the name of the element, not necessarily derived from the colloquial English name. (e.g., sodium has chemical symbol 'Na' after the Latin natrium). The same applies to "W" (wolframium) for Tungsten , "Hg" (Hydrargyrum) for mercury and "K" for potassium. Stricly taken, a symbol like Tu for tungsten or M or Me for mercury seems to be more logical. Chemical symbols are understood internationally when element names might need to be translated. There are sometimes differences; for example, the Germans have used "J" instead of "I" for iodine, so the character would not be confused with a roman numeral. The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always minuscule (small letters).

General chemical symbols

There are also symbols for series of chemical elements, for comparative formulas. These are one capital letter in length, and the letters are reserved so they are not permitted to be given for the names of specific elements. For example, an "X" is used to indicate a variable group amongst a class of compounds (though usually a halogen), while "R" is used for a radical (not to be confused with radical_(chemistry), meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of Yttrium. "Z" is also frequently used as a general variable group. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

Nonelement symbols

Nonelements, especially in organic and organometallic chemistry, often acquire symbols which are inspired by the elemental symbols. A few examples: Cy - cyclohexyl; Ph - phenyl; Bz - benzoyl; Bn - benzyl; Cp - Cyclopentadiene; Pr - propyl; Me - methyl; Et - ethyl; Tf - triflate; Ts - tosyl.

External links

- [http://www.vanderkrogt.net/elements/ Elementymology & Elements Multidict] word history and language dictionary

Chemical information

- [http://www.webelements.com/ WebElements]
- [http://www.vcs.ethz.ch/chemglobe/ptoe/ ChemGlobe]
- [http://pearl1.lanl.gov/periodic/default.htm Los Alamos National Laboratory]
- [http://www.chemicalelements.com/ ChemicalElements] ko:화학 원소 ms:Unsur kimia ja:元素 simple:Element th:ธาตุเคมี

Macromineral

Macrominerals (also known as macroelements or bulk minerals) are macronutrients that are chemical elements. They include calcium, magnesium, sodium, potassium, phosphorus and chlorine. They are dietary minerals needed by the human body in high quantities (generally more than 100 mg/day) as opposed to microminerals (trace elements) which are only required in very small amounts. Category:Dietary minerals

Food

Food is any substance that can be consumed, including liquid drinks. Food is the main source of energy and of nutrition for animals, and is usually of animal or plant origin. The study of food is called food science. In English, the term food is often used metaphorically or figuratively, as in food for thought. Food can also be a system of communication, a collection of images, a protocol of usages, situations, and behavior. Food is what brings the memory of our past into our contemporary life.

Legal definition

Western food law defines four categories of object as food:
- any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans whether of nutritional value or not;
- water and other drinks;
- chewing gum;
- articles and substances used as an ingredient or component in the preparation of food. Links to official legal definitions of food:
- [http://www.fda.gov/opacom/laws/fdcact/fdcact1.htm US federal definition of food]
- [http://www.legislation.hmso.gov.uk/acts/acts1990/Ukpga_19900016_en_2.htm#mdiv1 UK definition of food]
- [http://europa.eu.int/smartapi/cgi/sga_doc?smartapi!celexapi!prod!CELEXnumdoc&lg=EN&numdoc=32002R0178&model=guichett EU definition of food]

Human eating habits

Historical development

Humans are commonly believed to be omnivorous animals that can consume both plant and animal products. Evidence suggests that early Homo Sapiens employed Hunter-gatherer as their primary means of food collection. This involves combining stationary plant and fungal food sources (such as fruits, grains, roots, and mushrooms) with mobile animals which must be hunted and killed in order to be consumed. Additionally, it is believed that humans have used fire to prepare food prior to eating since their divergence from Homo erectus, possibly even earlier. At least ten thousand years ago, humans developed agriculture, which has Timeline of agriculture and food and altered the kind of food people eat. This has led to a variety of important historical consequences, such as increased [[population]], the development of [[cities, and the wider spread of infectious diseases. The types of food consumed, and the way in which they are prepared has varied widely by time, location, and culture.

Meals

A portion of food or the act of eating a portion of food is considered a meal. Often named and patterned, meals play a role in an important social occasion, such as the celebration of many key cultural and religious festivals. A meal can be used as means for feeding a single individual or shared and eaten simultaneously by two or more people. The number of meals consumed by individuals in a day, their size, composition, when and how they are prepared and eaten varies greatly around the world. This diversity can be attributed to a number of local factors, including climate, ecology, economy, cultural traditions and industrialisation. In societies where the availability of food has risen above subsistence levels and beyond staple foods, meals are also sold pre-prepared for immediate consumption in restaurants and other similar retail premises. Food eaten in smaller quantities between the culturally normative meals is regarded as snack food. :See also: Appetite, Buddhist cuisine, Eucharist, Fast food, Fasting, Gault Millau restaurant guide, Halaal, I-tal, Kashrut, Michelin restaurant guide, Muslim dietary laws, Potluck, Totemism.

Food production or acquisition

Food is traditionally obtained through farming, ranching, and fishing, with hunting, foraging and other methods of subsistence locally important for some populations, but minor for others. In the modern era in developed nations, food supply is increasingly dependent upon agriculture, industrial farming, aquaculture and fish farming techniques. These techniques aim to maximize the amount of food produced while minimizing the cost. The techniques include a reliance on mechanized tools, from the threshing machine and seed drill, to the tractor and combine. Developed tools have been combined with the use of pesticides to promote high crop yields and to combat insects or mammals which reduce yield. More recently, there has been a growing trend towards more Sustainable agricultural practices. This approach - which is partly fuelled by consumer demand - encourages biodiversity, local self-reliance and Organic farming methods. Major influences on food production are international policy, e.g. the World Trade Organization and Common Agricultural Policy, national government policy or law and war. Food for livestock is fodder and traditionally comprises hay or grain. :See also: mariculture, horticulture, agribusiness, gardening. gardening

From plants

- Seeds
- Cereals from grasses, including barley, maize, oats, rice, rye, and wheat
- Cereals from non-grasses, including buckwheat, amaranth, and quinoa
- Legumes, including beans, peas, and lentils
- Nuts, including coconuts, almonds, and pine nuts
- Oilseeds, including sesame, sunflower, and hemp
- Vegetables (see also list of vegetables)
- Root vegetables, including potatoes, cassava, and turnips
- Leaf vegetables, including amaranth, spinach, and kale
- Sea vegetables, including dulse, kombu, and dabberlocks
- Stem vegetables, including bamboo shoots, nopales, and asparagus
- inflorescence vegetables, including globe artichokes, broccoli, and daylilies
- Fruit vegetables, including pumpkin, okra, and eggplant
- Fruits (see also list of fruits)
- Herbs and spices (see also list of herbs and spices) list of herbs and spices

From animals

- Dairy products, including milk
- Eggs, including roe and caviar
- Insects, including honey
- Meat, including beef, frogs' legs, goat, horse, kangaroo, lamb, mutton, pork, veal, rodents, human (i.e. cannibalism)
- Offal, including blood
- Poultry, including chicken, turkey, duck, goose, pigeon or dove, ostrich, emu, guinea fowl, pheasant, quail
- Seafood, including finfish such as salmon and tilapia, and shellfish such as mollusks and crustaceans
- Snails
- Game, this includes all animals hunted for food.

From neither animals or plants

- Salt
- Mushrooms, which are a type of fungi
- Seaweed, which is a protist
- Water, including mineral water and spring (water)

Food preparation

spring (water) While some food can be eaten without preparation, many foods undergo some form of preparation for reasons of safety, palatability, or flavor. At the simplest level this may involve washing, cutting, trimming or adding other foods or ingredients, such as spices. It may also involve mixing, heating or cooling, pressure cooking, fermentation, or combination with other food. Most food preparation takes place in a kitchen. The preparation of animal-based food will usually involve slaughter, evisceration, hanging, portioning and rendering. :See also: Barbecue, Eating utensils, Frankfurt kitchen, Hangi, Oven, Microwave oven, Refrigeration, Food preparation utensils.

Food manufacture

Early food processing techniques were limited by the available food preservation, packaging and transportation. Early food processing mainly involved salting, curing, curdling, drying, pickling and smoking. An early processed food product was cheese. During the industrialisation era in the 19th century, food manufacturing arose. This development took advantage of new mass markets and emerging new technology, such as milling, preservation, packaging and labelling and transportation. It brought the advantages of pre-prepared time saving food to the bulk of ordinary people who did not employ domestic servants. At the start of the 21st century, a two-tier structure has arisen, with a few international food processing giants controlling a wide range of well known food brands; with a populous number of small local or national food processing companies. :See also: Best before, Canning, Coloring, Food quality, Snap freezing, Additives, Flavoring, Enzymes, Genetically modified food, Pasteurization, Shelf-life, Ultra-high temperature processing.

Types of manufactured food

- Drinks: beer, juice, soft drink, squash, wine.
- Bread is a staple food for many nations, being made of risen dough of wheat or other cereals.
- Cakes and cookies
- Cheese is a curdled milk product, of which many varieties exist.
- Dessert is a course, usually sweet, and generally served after the main course, e.g. Ice cream.
- French fries, Chips
- Functional food
- Jam and Jelly
- Pasta
- Pie
- Pizza
- Processed meats
- Sandwiches
- Salad
- Sauce
- Sausage

Food trade

Food is now traded on a global basis. The variety and availability of food is no longer restricted by the diversity of locally grown food or the limitations of the local growing season. Between 1961 and 1999 there has been a 400% increase in worldwide food exports. Some countries are now economically dependent on food exports, which in some cases account for over 80% of all exports. In 1994 trade liberalisation began when over 100 countries became signatories to the Uruguay Round of the General Agreement on Tariffs and Trade which included an agreement to reduce subsidies paid to farmers. This is underpinned by the WTO enforcement of agricultural subsidy, tariffs, import quotas and settlement of trade disputes that cannot be bilaterally resolved. Where trade barriers are raised on the disputed grounds of public health and safety, the WTO refer the dispute to the Codex Alimentarius Commission, which was founded in 1962 by the United Nations Food and Agriculture Organization and the World Health Organization.

Food retailing

World Health Organization The sale of surplus food traditionally took place once a week when farmers took their wares on market day, into the local village market place. Here food was sold to grocers for sale in their local shops for purchase by local people. With the onset of industrialisation, and the development of the food processing industry, a wider range of food could be sold and distributed in distant locations. Typically early grocery shops would be counter-based shops, in which purchasers told the shop-keeper what they wanted, so that the shop-keeper could get it for them. In the 20th century supermarkets were born. Supermarkets brought with them a self-service approach to shopping using shopping carts (or Trollies in Commonwealth English) and were able to offer quality food at lower cost, through economies of scale and reduced staffing costs. This was sometimes known as 'pile it high' In the latter part of the 20th century, this has been further revolutionised by the development of vast warehouse sized out-of-town supermarkets, selling an extraordinarily wide range of food from around the world. Unlike food processors, food retailing is a two-tier market in which a small number of very large companies control a large proportion of supermarkets. The supermarket giants wield great purchasing power over farmers and processors, and strong influence over consumers. Nevertheless, in 2000 only 19% of all US consumer expenditure spent on food went to farmers. Recent technological innovations such as point of sale technology - barcodes. This allows ordering of goods and food to be driven by actual sales.

Food sufficiency

Food deprivation leads to malnutrition and ultimately starvation. This is often connected with famine, which involves the absence of food in entire communities. This can have a devastating and widespread effect on human health and mortality. In 2003 it was estimated that each year, 40 million people die of hunger worldwide. Rationing is sometimes used to distribute food in times of shortage, most notably during times of war. Food deprivation is regarded as a deficit need in Maslow's hierarchy of needs and is measured using famine scales.

Food aid

Food aid can benefit people suffering from a shortage of food. Conversely, badly managed food aid can cause problems by disrupting local markets, depressing crop prices and discouraging food production. Its provision, or threatened withdrawal, is sometimes used as a political tool to influence the politics of the destination country. International efforts to distribute food to the neediest countries are co-ordinated by the World Food Programme. :See also: Fair trade, food security.

Food safety

Foodborne illness, commonly called "food poisoning," is caused by bacteria, toxins, viruses and prions. Food poisoning has been recognised as a disease of man since as early as Hippocrates. Murder by food poisoning was used during the Roman Empire. In the Middle Ages all Royal Courts had food tasters. The sale of rancid, contaminated or adulterated food was commonplace until introduction of hygiene, refrigeration, and vermin controls in the 19th century. Discovery of techniques for killing bacteria using heat and other microbiological studies by scientists such as Louis Pasteur contributed to the modern sanitation standards that we enjoy today. This was further underpinned by the work of Justus von Liebig whose work led to the development of modern food storage and food preservation methods. The two most common factors leading to cases of bacterial foodborne illness are cross-contamination of ready-to-eat food from other uncooked foods and improper temperature control. Less commonly, acute adverse reactions can also occur if chemical contamination of food occurs, for example from improper storage, or use of non-food grade soaps and disinfectants. Food can also be adulterated by a very wide range of articles (known as 'foreign bodies') during farming, manufacture, cooking, packaging, distribution or sale. For example, pests (or their feces), hairs, cigarette butts, wood chips, metal shards, plasters etc. It is possible for certain types of food to become contaminated if stored or presented in an unsafe container, such as a ceramic pot with lead-based glaze. Understanding of the causes of food-borne-illnesses and more systematic techniques for their elimination has led to the development of commercial systems such as HACCP which can, if properly implemented, identify and eliminate many, but not all, possible risks. HACCP is well suited to identifying and controlling these potential food safety risks.

Food allergies

Some people have food allergies or sensitivities to foods which are otherwise wholesome to the majority of people. The amount of the food substance required to provoke a reaction in a susceptible individual can be minute. For instance, tiny amounts of food in the air, too minute to be smelled, have been known to provoke lethal reactions in sufficiently sensitive individuals. In theory, any food may provoke a reaction, however, this most commonly involves gluten, corn, shellfish (mollusks), peanuts, and soy. Most patients present with diarrhea after ingesting certain foodstuffs, skin symptoms (rashes), bloating, vomiting and regurgitation. The digestive complaints usually develop within half an hour of ingesting the allergen. Rarely, food allergy can lead to anaphylactic shock: hypotension (low blood pressure) and loss of consciousness. This is a medical emergency. An allergen associated with this type of reaction is peanut, although latex products can induce similar reactions. Initial treatment is with epinephrine (adrenaline), often carried by known patients in the form of an Epi-pen. Food allergy is thought to develop easier in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma. The syndrome has a strong inherited component; a family history of these diseases can be indicative of the atopic syndrome.

Dietary habits

Dietary habits play a significant role in the health and mortality of all humans. For example:
- Eating disorders are a group of mental disorders that interfere with normal food consumption. They often affect people with a negative body image;
- 13% of the world's population suffer from Iodine deficiency;
- In 2003 it was estimated that vitamin A deficiency causes blindness in up to 500,000 children each year;
- Vitamin C deficiency results in scurvy;
- Calcium, Vitamin D and Phosphorus are inter-related. The consumption of each may affect the absorption of the others.
- Kwashiorkor and marasmus are childhood disorders caused by lack of dietary protein.
- Obesity, a serious problem in the western world, leads to higher chances of developing heart disease, diabetes, and many other diseases. Concerns about foodborne illness have long influenced diet. Traditionally humans have learned to avoid foods that induce acute illness. Some believe that this is the underlying rationale behind some traditional religious dietary requirements. Additionally, many people choose to forgo food from animal sources to varying degrees; see vegetarianism, veganism, fruitarianism, living foods diet, and raw foodism. The nutrient content of diets in industrialised countries contain more animal fat, sugar, energy, alcohol and less dietary fiber, carbohydrates and antioxidants. Contemporary changes to work, family and exercise patterns, together with concerns about the effect of nutrition and overeating on human health and mortality are all having an effect on traditional eating habits. Physicians and alternative medicine practitioners may recommend changes to diet as part of their recommendations for treatment. More recently, dietary habits have been influenced by the concerns that some people have about the chronic impact on health that arise through the consumption of genetically modified food. Further concerns about the impact of industrial farming on animal welfare, human health and the environment are also having an effect on contemporary human dietary habits. This has led to the emergence of a counterculture with a preference for organic and local food. :See also: Food faddism, Health claims on food labels, list of diets, Slow Food.

Nutrients in food

- Calcium
- Carbohydrate
- Essential amino acids
- Fat
- Iron
- Minerals
- Phytochemicals, including anti-oxidants, enzymes, bio-flavinoids
- Potassium
- Protein
- Sodium
- Starch
- Vitamins
- Water Category:Nutrition Category:Biology

Calcium carbonate

Calcium carbonate is a chemical compound, with chemical formula Ca C O₃. It is commonly used as an antacid, and is the active ingredient in agricultural lime. It is a common substance found as rock in all parts of the world and is the main component of seashells and the shell of snails.

Occurrence

Calcium carbonate is found naturally as the following minerals and rocks:
- Aragonite
- Calcite
- Chalk
- Limestone
- Marble
- Travertine Eggshells are composed of approximately 95% calcium carbonate.

Preparation

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. When pure calcium carbonate is required (e.g. for food or pharmaceutical use), it is prepared by passing carbon dioxide into a solution of calcium hydroxide: the calcium carbonate precipitates out, and this grade of product is referred to as precipitated. :Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Chemical properties

:See also: Carbonate Calcium carbonate shares the typical properties of other carbonates. Notably: #it reacts with strong acids, releasing carbon dioxide. ::CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O #it releases carbon dioxide on heating (to above 825 °C in the case of CaCO₃), to form calcium oxide. ::CaCO₃ → CaO + CO₂ Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate. :CaCO₃ + CO₂ + H₂O Ca(HCO₃)₂ This reaction is important in the erosion of carbonate rocks, forming caverns, and leads to hard water in many regions.

Uses

The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or as an ingredient of cement. Calcium carbonate is widely used in the pharmaceutical industry, either as an antacid, a calcium supplement, or as a base material for tablets of other pharmaceuticals. Calcium carbonate is known as whiting in ceramics/glazing applications, where it is used as a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. It is commonly called chalk as it has been a major component of blackboard chalk. Chalk may consist of either calcium carbonate or gypsum, hydrated calcium sulfate CaSO₄·2H₂O. Recently, calcium carbonate has begun to replace Kaolin in the production of glossy paper. It is also the substance from which the lens of the mammalian eye is made.

External links

-
- Category:Calcium compounds Category:Carbonates ja:炭酸カルシウム th:แคลเซียมคาร์บอเนต

Oyster

The name oyster is used for a number of different groups of mollusks which grow for the most part in marine or brackish water. Inside a usually highly calcified shell is a soft body. The gills filter plankton from the water. Strong adductor muscles are used to hold the shell closed. Oysters are highly prized as food, both raw and cooked, and have a reputation as an aphrodisiac. It is disputed whether this is true. If there is such an effect, it may be due to the soft, moist texture and appearance of the oyster; it may also be due to their high zinc content. Perhaps the definitive work on oysters as food is Consider the Oyster, by M. F. K. Fisher.

True oysters

The "true oysters" are the members of the family Ostreidae, and this includes the edible oysters, which mainly belong to the genera Ostrea, Crassostrea, Ostreola or Saccostrea. Examples are the Edible Oyster, Ostrea edulis (others are just as edible); the Olympia Oyster Ostreola conchaphila; Wellfleet oyster and the Eastern Oyster Crassostrea virginica.

Oysters as edibles

Eastern Oyster Eastern Oyster Oysters can be eaten raw, or smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, or broiled (grilled). Preparation can be as simple as opening the shell, while cooking can be as spare as adding butter and/or salt, or can be very elaborate. Like all shellfish, oysters have an extremely short shelf-life, and should be fresh when consumed. Precautions should be respected when eating them (see below). Purists insist on eating oysters raw, with no dressing save perhaps lemon juice or vinegar. Raw oysters are regarded like wines in that they have complex flavors that vary greatly among varieties and regions: some taste sweet, others salty or with a mineral flavor, or even like melon. The texture is soft and fleshy, but crisp to the tooth. Oysters are generally an expensive food in places where they aren't harvested, and often they are eaten only on special occasions, such as Christmas. Whether oysters are predominantly eaten raw or cooked is a matter of cultural preference. In the United States today, oysters are usually cooked before consumption; canned smoked oysters are widely available as preserves with a long shelf life. Raw oysters were, however, once a staple food along the East Coast of the US, and are still easily found in states bordering the ocean. Oysters are nearly always eaten raw in France. Fresh oysters must be alive just before consumption. There is a simple criterion: oysters must be tightly closed; oysters that are already open are dead and must be discarded. To confirm if an open oyster is dead, tap the shell. A live oyster will close and is safe to eat. Opening oysters requires skill, for live oysters, outside of the water, shut themselves tightly with a powerful muscle. The generally used method for opening oysters is to use a special knife (called a shucking knife), with a short and thick blade, inserting the blade (with some moderate force and vibration if necessary) at the hinge in the rear of the shell, and sliding it upward to cut the adductor muscle (which holds the shell closed). Inexperienced cooks can easily slip and injure themselves; this is said to be a significant cause of domestic accidents in the Christmas season in France. An alternative to opening raw oysters before consumption is to cook them in the shell – the heat kills the oysters and they open by themselves. Cooked oysters are savory and slightly sweet-tasting, and the varieties are mostly equivalent. A piece of folk wisdom concerning oysters is that they are only safe to eat in months containing the letter 'r.' This is because oysters spawn in the warmer months, from roughly May to August. They are safe to eat at all times of the year, although their flavor when eaten raw can be somewhat watery and bland during spawning season. Oysters from the Gulf of Mexico spawn throughout the year, and are generally best cooked.

History

Within the United Kingdom, the town of Whitstable in the county of Kent is particularly noted for oyster farming from beds on the Kentish Flats that have been used since Roman times. Similarly the seaside resort of Cancale in France is noted for its oysters which also date from Roman times. In the early nineteenth century, oysters were very cheap and were mainly eaten by the working classes in steak and oyster pies. However, increasing demands from the rapidly-growing cities led to many of the beds running short. To increase production, foreign varieties were introduced and this soon brought disease which, combined with pollution, resulted in oysters becoming rare. This rarity increased prices leading to their current status as a delicacy. In the United Kingdom, the native variety is still held to be the finest, taking five years to mature and protected by an Act of Parliament during the May-August spawning season. The current market is dominated by the larger Pacific oyster and rock oyster varieties which are farmed all year round.

Pearl oysters

All oysters (and, indeed, many other bivalves) can secrete pearls, but those from edible oysters have no market value. The Pearl Oysters come from a different family, the Pteriidae (Winged Oysters). Both cultivated pearls and natural pearls are obtained from these oysters, though some other mollusks, for example freshwater mussels, also yield pearls of commercial value. The largest pearl-bearing oyster types is the Pinctada maxima, which is roughly the size of a dinner plate. Not all oysters produce pearls. In fact, in a haul of three tonnes of oysters, only around three or four oysters produce perfect pearls. These oysters, and other mollusks, produce pearls by covering an invading piece of grit with nacre (or as most know it, mother-of-pearl). Over the years, the grit is covered with enough nacre to form what we know as a pearl. There are many different types and colours and shapes of pearl, but this depends on the pigment of the nacre and the shape of the piece of grit being covered over. Pearls can also be cultivated by pearl harvesters placing a single piece of grit, usually a piece of polished mussel shell, inside the oyster. In three to six years, the oyster has produced a perfect pearl. These pearls are not as valuable as natural pearls, but look exactly the same.

Dermo

"Dermo" (Perkinsus marinus) is marine disease of oysters, caused by a protozoan parasite. It is a prevalent pathogen of oysters, causing massive mortality in oyster populations and poses a significant economic threat to the oyster industry.

Other molluscs named "oyster"

A number of other molluscs not falling into either of these groups have common names that include the word "oyster", usually because they either taste or look like oysters, or because they yield noticeable pearls. Examples include:
- the family Spondylidae, the Thorny Oysters;
- the Pilgrim oyster, a kind of scallop.
- the Saddle oyster (Anomia ephippium)

External links

- [http://www.perlas.com.mx/Ingles/famtree.htm Family tree of Molluscs] Category:Molluscs Category:Seafood zh-min-nan:Ô-á ko:굴 ja:カキ (貝)

Geophagy

Geophagy is a practice of eating earthy substances such as clay, often to augment a mineral-deficient diet. While most often seen in rural or preindustrial societies among pregnant women, it also occurs among children and as a psychological eating disorder. Geophagy is a type of disorder known as pica. In parts of Africa and among some African-Americans, clay consumption may be correlated with pregnancy as women eat clay to eliminate nausea possibly because the clay coats the gastrointestinal tract and absorbs dangerous toxins. The clay may also provide critical calcium for fetal development. In the southeastern United States especially tasty earth (usually a chalky earth with a certain flavor) is sold in local stores or sent to friends and family who are no longer living near the source of this earth. Bentonite clay is available worldwide as a digestive aid, kaolin is also widely used as a digestive aid and as the base for some medicines. Geophagy was also practiced by Native Americans who would eat earth with acorns and potatoes to neutralize potentially harmful alkaloids. Clay was used in the production of acorn bread. Geophagy has also been observed in birds. Notably, South American macaws have been observed at clay licks in South America by scientist Charles Munn, whilst sulphur crested cockatoos have been observed ingesting clays in Papua New Guinea by Jared Diamond (Discover, 1998) as well as in the Blue Mountains of Australia by David W Cooper (Parrots Magazine, 2000)

References

- Wiley, Andrea S. "Geophagy." Encyclopedia of Food and Culture. Ed. Solomon H. Katz. Vol. 2. New York: Charles Scribner's Sons, 2003. 120-121.
- Wiley, Andrea S., and Solomon H. Katz. "Geophagy in Pregnancy: A Test of a Hypothesis." Current Anthropology 39, no. 4 (1998): 532–545.
- Lagercrantz, Sture. "Geophagical Customs in Africa and among the Negroes in America." Studia Ethnographica Upsaliensia 17 (1958): 24–81.

External link

- [http://www.uic.edu/classes/osci/osci590/8_2DirtasFood.htm Dirt as Food]
- [http://geography.about.com/cs/culturalgeography/a/geophagy.htm Eating Dirt] Category:Eating behaviors

Human nutrition

Nutrition is the study of the relationship between diet and states of health and disease. It is defined as the study of food. Absence of adequate nutrients can cause certain diseases to take hold that can potentially result in death. Between the extremes of optimal health and death from starvation or malnutrition, there is an array of disease states that can be caused or alleviated by changes in diet. Deficiencies, excesses and imbalances in the diet can produce negative impacts on health, which may result in diseases such as scurvy, obesity or osteoporosis. Also, excess ingestion of elements that have no apparent role in health (e.g. lead, mercury, PCBs, dioxins) may have toxic and potentially lethal effects depending on dose. The science of nutrition attempts to understand how and why specific aspects of diet have specific influences on health.

Overview

The human body comprises chemical compounds such as water, amino acids (proteins), fatty acids (lipids), nucleic acids (DNA/RNA), and carbohydrates (e.g. sugars). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, and phosphorus, and may or may not contain minerals such as calcium, iron, and zinc. Minerals also ubiquitously occur in the form of salts and electrolytes. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones/vitamins, phospholipids, hydroxyapatite), both in the human body and in organisms (e.g. plants, animals) that humans eat. The human body must necessarily comprise those elements that humans eat and absorb into the bloodstream. The digestive system, except in the unborn fetus, is the first step in helping to make the different chemical compounds and elements in food available for the trillions of cells of the body. In the digestive process of an average adult, about seven (7) litres of liquid, known as digestive juices, exit the internal body and enter the lumen of the digestive tract. The digestive juices help break chemical bonds between ingested compounds as well as modulate the conformation and/or energetic state of the compounds/elements. Yet many compounds/elements are absorbed into the bloodstream unchanged, though the digestive process helps to release them from the matrix of the foods where they occur. Any unabsorbed matter is eliminated in the feces. Only a minimal amount of digestive juice is eliminated this way; the intestines reabsorb most of it otherwise the body would rapidly dehydrate (hence the devastating effects of persistent diarrhea). Study in this field must take into careful account the state of the body before ingestion and after digestion as well as the chemical content of both the food and the waste. The specific types of compounds and elements that are absorbed by the body can be determined by comparing the waste to the food. The effect that the absorbed matter has on the body can be determined by finding the difference between the pre-ingestion state and the post-digestion state. The effect may only be discernible after an extended period of time in which all food and ingestion must be exactly regulated and all waste must be analyzed. The number of variables (e.g. 'confounding factors') involved in this type of experimentation is very high. This makes scientifically valid nutritional study very time-consuming and expensive, which accounts for why a proper science of human nutrition is rather new. In general, eating a variety of fresh, whole (unprocessed) foods has proven hormonally and metabolically favourable compared to eating a monotonous diet based on processed foods. In particular, fresh, whole foods provide higher amounts and a more favourable balance of essential and vital nutrients per unit of energy, resulting in better management of cell growth, maintenance, and mitosis (cell division) as well as of appetite and energy balance. A generally more regular eating pattern (e.g. eating medium-sized meals every 3 to 4 hours) has also proven more hormonally and metabolically favourable than infrequent, haphazard food intake.

Nutrition and health

Ill health can be brought about by an imbalance of nutrients, producing either an excess or deficiency which in turn affects body functioning in a cumulative manner. Moreover, because most nutrients are, in some way or the other, involved in cell-to-cell signalling (e.g. as building block or part of a hormone or signalling 'cascades'), deficiency or excess of various nutrients affects hormonal function also indirectly. Thus, because they largely regulate the expression of genes, hormones represent a link between nutrition and how our genes are expressed, i.e. our phenotype. The strength and nature of this link are continually under investigation, but observations especially in recent years have demonstrated a pivotal role for nutrition in hormonal activity and function and therefore in health. Mineral and/or vitamin (tocotrienol and tocopherol) deficiency or excess may yield symptoms of diminishing health such as goitre, scurvy, osteoporosis, weak immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health (including eating disorders). The list goes on and on; for reference, see Modern Nutrition in Health and Disease by Shils et al. As of 2005, twelve vitamins and about the same number of minerals are recognized as 'essential nutrients', meaning that they must be consumed and absorbed - or, in the case of vitamin D, alternatively synthesized via UVB radiation - to prevent deficiency symptoms and death. Certain vitamin-like substances found in foods, such as carnitine, have also been found essential to survival and health, but these are not strictly 'essential' to eat because the body can produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which have many discovered and yet to be discovered properties including antioxidant activity (see below). Other essential nutrients include essential amino acids, choline and the essential fatty acids. In addition to sufficient intake, an appropriate balance of essential fatty acids - omega-3 and omega-6 fatty acids - has been discovered to be crucial for maintaining health. Both of these unique "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins. The omega-3 eicosapentaenoic acid (EPA) (which can be made in the body from the omega-3 essential fatty acid alpha-linolenic acid (LNA), or taken in through marine food sources), serves as building block for series 3 prostaglandins (e.g. weakly-inflammation PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as building block for series 2 prostaglandins (e.g. pro-inflammatory PGE1). Both DGLA and AA are made from the omega-6 linoleic acid (LA) in the body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which partly explains the importance of omega-3/omega-6 balance for cardiovascular health. In industrialised societies, people generally consume large amounts of processed vegetable oils that have reduced amounts of essential fatty acids along with an excessive amount of omega-6 relative to omega-3. The rate of conversions of omega-6 DGLA to AA largely determines the production of the respective prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 made from AA toward anti-inflammatory PGE1 made from DGLA. Moreover, the conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as insulin (up-regulation) and glucagon (down-regulation). Because different types and amounts of food eaten/absorbed affect insulin, glucagon and other hormones to varying degrees, not only the amount of omega-3 versus omega-6 eaten but also the general composition of the diet therefore determine health implications in relation to essential fatty acids, inflammation (e.g. immune function) and mitosis (i.e. cell division). Several lines of evidence indicate lifestyle-induced hyperinsulinemia and reduced insulin function (i.e. insulin resistance) as a decisive factor in many disease states. For example, hyperinsulinemia and insulin resistance are strongly linked to chronic inflammation, which in turn is strongly linked to a variety of adverse developments such as arterial microinjuries and clot formation (i.e. heart disease) and exaggerated cell division (i.e. cancer). Hyperinsulinemia and insulin resistance (the so-called metabolic syndrome) are characterized by a combination of abdominal obesity, elevated blood sugar, elevated blood pressure, elevated blood triglycerides, and reduced HDL cholesterol. The negative impact of hyperinsulinemia on prostaglandin PGE1/PGE2 balance may be significant. The state of obesity clearly contributes to insulin resistance, which in turn can cause type 2 diabetes. Virtually all obese and most type 2 diabetic individuals have marked insulin resistance. Although the association between overfatness and insulin resistance is clear, the exact (likely multifarious) causes of insulin resistance remain less clear. Importantly, it has been demonstrated that appropriate exercise, more regular food intake and reducing glycemic load (see below) all can reverse insulin resistance in overfat individuals (and thereby lower blood sugar levels in those who have type 2 diabetes). Overfatness can unfavourably alter hormonal and metabolic status via resistance to the hormone leptin, and a vicious cycle may occur in which insulin/leptin resistance and overfatness aggravate one another. The vicious cycle is putatively fuelled by continuously high insulin/leptin stimulation and fat storage, as a result of high intake of strongly insulin/leptin stimulating foods and energy. Both insulin and leptin normally function as satiety signals to the hypothalamus in the brain; however, insulin/leptin resistance may reduce this signal and therefore allow continued overfeeding despite large bodyfat stores. In addition, reduced leptin signalling to the brain may reduce leptin's normal effect to maintain an appropriately high metabolic rate. There is debate about how and to what extent different dietary factors - e.g. intake of processed carbohydrates, total protein, fat, and carbohydrate intake, intake of saturated and trans fatty acids, and low intake of vitamins/minerals - contribute to the development of insulin- and leptin resistance. In any case, analogous to the way modern man-made pollution may potentially overwhelm the environment's ability to maintain 'homeostasis', the recent explosive introduction of high Glycemic Index- and processed foods into the human diet may potentially overwhelm the body's ability to maintain homeostasis and health (as evidenced by the metabolic syndrome epidemic). Antioxidants are another recent discovery. As cellular metabolism/energy production requires oxygen, potentially damaging (e.g. mutation causing) compounds known as radical oxygen species or free radicals may form. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds, such as certain vitamins (vitamin C, vitamin E, vitamin K and the aforementioned phytochemicals as well as other compounds, some of which the body itself produces. Different antioxidants are now known to function in a cooperative network, e.g. vitamin C can reactivate free radical-containing glutathione or vitamin E by accepting the free radical itself, and so on. It is now also known that the human digestion system contains a population of a range of bacteria which are essential to digestion, and which are also affected by the food we eat. The role and significance of the intestinal bacterial flora is under investigation.

Nutrition and sports

(Stub, please expand.) Nutrition is very important for improving sports performance. The most common means to improve performance through diet is the practice of eating large quantities of protein, usually red meat, when attempting to build muscle mass; its efficacy is doubtful, as daily protein intake even on a normal diet usually outweighs the amount of muscle protein which can be synthesized in a day, and protein is a much less efficient source of the energy needed to build new muscle tissue than are fats and carbohydrates.

Nutrition and longevity

Lifespan is somehow related to the amount of food energy consumed: this was first systematically investigated in the seminal study by Weidruch, et al. (1986). A pursuit of this principle of caloric restriction followed, involving research into longevity of those who reduced their food energy intake while attempting to optimize their micronutrient intake. Perhaps not surprisingly, some people found that cutting down on food reduced their quality of life so considerably as to negate any possible advantages of lengthening their lives. However, a small set of individuals persists in the lifestyle, going so far as to monitor blood lipid levels and glucose response every few months. See [http://www.calorierestriction.org/ Calorie Restriction Society]. Underlying this research was the hypothesis that oxidative damage was the agent which accelerated aging, and that aging was retarded when the amount of carbohydrates (and thereby insulin release) was reduced through dietary restriction. However, recent research has produced increased longevity in animals (and shows promise for increased human longevity) through the use of insulin uptake retardation. This was done through altering an animal’s metabolism to allow it to consume similar food-energy levels to other animals, but without building up fatty tissue. (Bluher et al, 2003) This has set researchers off on a line of study which presumes that it is not low food energy consumption which increases longevity. Instead, longevity may depend on an efficient fat processing metabolism, and the consequent long term efficient functioning of our organs free from the encumbrance of accumulating fatty deposits. (Das et al, 2004) Thus, longevity may be related to maintained insulin sensitivity. However, several other factors including low body temperature seem to promote longevity also and it is unclear to what extent each of them contribute. Antioxidants have recently come to the forefront of longevity studies which have included the FDA and [http://www.brunswicklabs.com/ Brunswick labs]. In 2005 the FDA issued a statement recommending that Americans should be consuming 7,000 ORAC units daily or 12 full servings of fruit in order to curb the cancer epidemic. The dietary supplement industry has responded by shifting focus away from hormone replacements to “super” antioxidants such as [http://www.proleva.com/ Proleva] which contain whole fruit extracts and ORAC scores near 5,000 units mark or two thirds of the new level set by the FDA.

Nutrition, industry and food processing

Since the Industrial Revolution some two hundred years ago, the food processing industry has invented many technologies that both help keep foods fresh longer and alter the fresh state of food as they appear in nature. Cooling is the primary technology that can help maintain freshness, whereas many more technologies have been invented to allow foods to last longer without becoming spoiled. These latter technologies include pasteurisation, autoclavation, drying, salting, and separation of various components, and all appear to alter the original nutritional contents of food. Pasteurisation and autoclavation (heating techniques) have no doubt improved the safety of many common foods, preventing epidemics of bacterial infection. But some of the (new) food processing technologies undoubtedly have downfalls as well. Modern separation techniques such as milling, centrifugation, and pressing have enabled upconcentration of particular components of food, yielding flour, oils, juices and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large scale upconcentration changes the nutritional content of food, saving certain nutrients while removing others. Heating techniques may also reduce food's content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet to be discovered substances. Because of reduced nutritional value, processed foods are often 'enriched' or 'fortified' with some of the most critical nutrients (usually certain vitamins) that were lost during processing. Nonetheless, processed foods tend to have an inferior nutritional profile than do whole, fresh foods, regarding content of both sugar and high GI starches, potassium/sodium, vitamins, fibre, and of intact, unoxidized (essential) fatty acids. In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids. A dramatic example of the effect of food processing on a population's health is the history of epidemics of beri-beri in people subsisting on polished rice. Removing the outer layer of rice by polishing it removes with it the essential vitamin thiamin, causing beri-beri. Another example is the development of scurvy among infants in the late 1800's in the United States. It turned out that the vast majority of sufferers were being fed milk that had been heat-treated (as suggested by Pasteur) to control bacterial disease. Pasteurisation was effective against bacteria, but it destroyed the vitamin C. As mentioned, lifestyle- and obesity-related diseases are becoming increasingly prevalent all around the world. There is little doubt that the increasingly widespread application of some modern food processing technologies has contributed to this development. The food processing industry is a major part of modern economy, and as such it is influential in political decisions (e.g. nutritional recommendations, agricultural subsidising). In any known profit-driven economy, health considerations are hardly a priority; effective production of cheap foods with a long shelf-life is more the trend. In general, whole, fresh foods have a relatively short shelf-life and are less profitable to produce and sell than are more processed foods. Thus the consumer is left with the choice between more expensive but nutritionally superior whole, fresh foods, and cheap, usually nutritionally inferior processed foods. Because processed foods are often cheaper, more convenient (in both purchasing, storage, and preparation), and more available, the consumption of nutritionally inferior foods has been increasing throughout the world along with many nutrition-related health complications.

Policy advice and guidance on nutrition

Most Governments provide guidance on good nutrition, and some also impose mandatory labelling requirements upon processed food manufacturers to assist consumers in complying with such guidance. Current dietary guidelines in the United States are presented in the concept of a food pyramid. There is no apparent consisteny in science-based nutritional recommendations between countries, indicating the role of politics as well as cultural bias in research emphasis and interpretation.

Current issues and challenges

Challenging issues in modern nutrition include: 'Artificial' interventions in food production and supply:
- Should genetic engineering be used in the production of food crops and animals?
- Are the use of pesticides, and fertilizers damaging to the foods produced by use of these methods (see also organic farming)?
- Are the use of antibiotics and hormones in animal farming ethical and/or safe? Sociological issues:
- How do we minimise the current disparity in food availability between first and third world populations (see famine and poverty)?
- How can public advice agencies, policy making and food supply companies be coordinated to promote healthy eating and make wholesome foods more convenient and available?
- Do we need nutritional supplements in the form of pills, powders, liquids, etc.?
- How can the developed world promote good worldwide nutrition through minimising import tariffs and export subsidies on food transfers? Research Issues:
- How do different nutrients affect appetite and metabolism, and what are the molecular mechanisms?
- What yet to be discovered important roles do vitamins, minerals, and other nutrients play in metabolism and health?
- Are the current recommendations for intake of vitamins and minerals generally too low?
- How and why do different cell types respond differently to chronically elevated circulating levels of insulin, leptin, and other hormones?
- What does it take for insulin resistance to develop?
- What other molecular mechanisms may explain the link between nutrition and lifestyle-related diseases?
- What role does the intestinal bacterial flora play in digestion and health?
- How essential to proper digestion are the enzymes contained in food itself, which are usually destroyed in cooking (see Living foods diet)?
- What more can we discover through what has been called the phytochemical revolution?

References

- Shils et al. (2005) Modern Nutrition in Health and Disease, Lippincott Williams and Wilkins. ISBN: 0781741335.
- Bluher, Khan BP, Kahn CR, Extended longevity in mice lacking the insulin receptor in adipose tissue. Science 299(5606): 572-4, Jan 24, 2003.
- The Times newspaper, January 31 2004 Could vitamins help delay the onset of Alzheimer’s? by Jerome Burne.
- The Times newspaper February 28, 2004 Autism: I can see clearly now . . . by Simon Crompton
- The Times newspaper March 10, 2004 Work up an Amish appetite by Anne-Celine Jaeger
- Das M, Gabriely I, Barzilai N.Caloric restriction, body fat and aging in experimental models. Obes Rev. 2004 Feb;5(1):13-9.
- William Eaton et al Coeliac disease and schizophrenia British Medical Journal, February 21, 2004.
- Janssen I, Katzmarzyk PT, Ross R. Waist circumference and not body mass index explains obesity-related health risk. Am J Clin Nutr. 2004 Mar;79(3):379-84.
- J Mei, SSC Yeung et al "High dietary phytoestrogen intake and bone mineral density in postmenopausal women."Journal of Clinical Endocrinology and Metabolism, 2001, Vol 86, Iss 11
- Merritt JC "Metabolic syndrome: soybean foods and serum lipids."J Natl Med Assoc. 2004 Aug;96(8):1032-41.
- Sobczak S, et al Lower high-density lipoprotein cholesterol and increased omega-6 polyunsaturated fatty acids in first-degree relatives of bipolar patients Psychol Med. 2004 Jan;34(1):103-12.
- Walter C. Willett and Meir J. Stampfer,Rebuilding the Food Pyramid, Scientific American January 2003.
- Weindruch R, et al. The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake. (Journal of Nutrition, 116(4), pages 641-54.,April, 1986.)

External links

- [http://www.unsystem.org/scn/ UN Standing Committee on Nutrition] - In English, French and Portuguese
- [http://www.nal.usda.gov/fnic/foodcomp/Bulletins/faq.html USDA Frequently asked questions]
- [http://outside.utsouthwestern.edu/chn/literature/index.htm Texas University: A review of current nutrition academic articles ]
- [http://www.nutritional-supplements-directory.com Nutrition and Nutritional Supplements Information]
- [http://www.nal.usda.gov/fnic/ Department of Agriculture's Food and Nutrition Information Center].
- [http://7nutrition.co.uk Nutrition Dictionary]
- [http://www.nismat.org/nutricor/healthydiet.html Nutrition advice for sports people from Nicholas Institute for Sports Medicine and Trauma]
- [http://www.code-interactive.com/evolution-diet/healthprofile.html Personalized Online Health Profile]
- [http://www.agr.gc.ca/misb/fb-ba/nutra/index_e.php/ Agriculture & Agri-Food Canada]
- [http://www.ifpri.org/ International Food Policy Research Institute]
- [http://www.foodfileonline.com/ Food File Online] Nutrition information for thousands of food products
- [http://www.iodinenetwork.net Network for Sustained Elimination of Iodine Deficiency]

Disclaimer

:Please remember that Wikipedia is offered for informational use only. The information is in most cases not reviewed by professionals. You are advised to contact your doctor for health-related decisions. Category:Health Category:Nutrition ja:栄養学

Chromium

Chromium is a chemical element in the periodic table that has the symbol Cr and atomic number 24.

Notable characteristics

Chromium is a steel-gray, lustrous, hard metal that takes a high polish, melts with difficulty, and tarnishes. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +4 and +5 are rare. Chromium compounds of oxidation state 6 are powerful oxidants. Chromium(0) is unstable in oxygen, immediately producing a thin oxide layer that is impermeable to oxygen and protects the metal below.

Applications

Uses of chromium:
- In metallurgy, to impart corrosion resistance and a shiny finish:
- as an alloy constituent, e.g. in stainless steel used in cutlery, etc.,
- in chrome plating,
- in anodized aluminium (literally turning the surface of aluminium into ruby).
- As dyes and paints.
- Chromium(III) Oxide is a metal polish known as Green rouge.
- Chromium salts color glass an emerald green.
- Chromium is what makes a ruby red, and therefore is used in producing synthetic rubies.
- As a catalyst.
- Chromite is used to make molds for the firing of bricks.
- Chromium salts are used in the tanning of leather.
- Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e. a fixing agent) for dyes in fabric.
- Chromium(IV) oxide (CrO₂) is used to manufacture magnetic tape, where its higher coercivity than iron oxide tapes gives better performance.
- In well drilling muds as an anti-corrosive.

History

In 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the material was in fact lead chromate (PbCrO₄), now known as the mineral crocoite. In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red "lead" mineral that had very useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow made from crocoite became a very fashionable color. In 1797, Nicolas-Louis Vauquelin received samples of crocoite ore. He was able to produce chromium oxide (CrO₃) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious gems, such as ruby, or emerald. During the 1800s chromium was primarily used as a component of paints but now the primary use (85%) is for metal alloys, with the remainder used in the chemical industry and refractory and foundry industries. Chromium was named based on the Greek word "chroma" meaning color, because of the many colorful compounds made from it.

Biological role

See Chromium deficiency.

Occurrence

Chromium is mined as chromite (FeCr₂O₄) ore. Chromium is obtained commercially by heating the ore in the presence of aluminium or silicon. Roughly half the chromite ore in the world is produced in South Africa. Kazakhstan, India and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa. Approximately 15 million tons of marketable chromite ore were produced in 2000, and converted into approximately 4 million tons of ferro-chrome with an approximate market value of 2.5 billion US dollars. Though native chromium deposits are rare, some native chromium metal has been discovered. The Udachnaya Mine in Russia produces samples of the native metal. This mine is a kimberlite pipe rich in diamonds, and the reducing environment so provided helped produce both elemental chromium and diamond.

Compounds

Potassium dichromate is a powerful oxidizing agent and is the preferred compound for cleaning laboratory glassware of any possible organics. Chrome green is the green oxide of chromium, Cr₂O₃, used in enamel painting, and glass staining. Chrome yellow is a brilliant yellow pigment, PbCrO₄, used by painters. Chromic acid has the hypothetical structure H₂CrO₄. Neither chromic nor dichromic acid is found in nature, but their anions are found in a variety of compounds. Chromium trioxide, CrO₃, the acid anhydride of chromic acid, is sold industrially as "chromic acid".

Isotopes

Naturally occurring chromium is composed of 3 stable isotopes; 52-Cr, 53-Cr, and 54-Cr with 52-Cr being the most abundant (83.789% natural abundance). 19 radioisotopes have been characterized with the most stable being 50-Cr with a half-life of (more than) 1.8E17 years, and 51-Cr with a half-life of 27.7025 days. All of the remaining radioactive isotopes have half-lifes that are less than 24 hours and the majority of these have half lifes that are less than 1 minute. This element also has 2 meta states. Chromium-53 is the radiogenic decay product of ⁵³Mn. Chromium isotopic contents are typically combined with manganese isotopic contents and have found application in isotope geology. Mn-Cr isotope ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system. The isotopes of chromium range in atomic weight from 43 amu (43-Cr) to 67 amu (67-Cr). The primary decay mode before the most abundant stable isotope, 52-Cr, is electron capture and the primary mode after is beta decay.

Chromium and the quintuple bond

Chromium is notable for its ability to form quintuple covalent bonds. Writing in science, Tailuan Nguyen and coworkers of the University of California describe how they synthesized a compound (which does not appear to have a common name) of chromium and a hydrocarbon radical; X-ray diffraction showed unambiguously that the compound had a quintuple bond joining the two central chromium atoms. The compound had chemical formula :

\rm Ar-Cr-Cr-Ar

where

\rm Ar

is the aryl group

\rm C_6H_3\mbox2,6(C_6H_3\mbox2,6\mboxPr^i_2)_2

(

\rm Pr^i

is isopropyl). (ref: Science, Vol 310, Issue 5749, 796-797, 4 November 2005)

Precautions

Chromium metal and chromium(III) compounds are not usually considered health hazards, but chromium (VI) (hexavalent) compounds can be toxic if orally ingested or inhaled. The lethal dose of poisonous chromium (VI) compounds is about on