Human diet

CifiHjjOi. A fatly acid which is easily oxidized in air.-It occurs widely, in the form of glycerides, in vegetable oils and in mammalian lipids. Cholesieryl linoleale is an important constituent of blood. The add also occurs in lecithins. Together with arachidonic acid it is the most important essential fatty acid of human diet. 

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Of nutrient chelates in the human diet, oxalates and phytates are the most common. OxaUc acid (8), found principally in spinach, rhubarb leaves, beet leaves, some fmits, and mushrooms, is a primary chelator of calcium. Oxalate present in pineapple, kiwifmit, and possibly in other foods, occurs as calcium... 

Mycotoxias fiad thek way kito the human diet by way of mold-contaminated cereal and legume crops, meat, and milk products. Com and peanuts probably represent the most common sources of mycotoxias ki the human diet. Many mycotoxias are acutely toxic as well as being poteat carckiogeas (86). 

Epidemiologic studies in Japan indicate an increased risk of stomach cancer owing to consumption of broiled fish and meats (116). In the United States, stomach cancer incidence has steadily declined since the 1940s, whereas consumption of broiled food has increased (108). In addition, the average human intake of PAHs is only 0.002 of that required to produce cancer in half of animals fed. Test results are often contradictory (117) and many components of food, such as vitamin A, unsaturated fatty acids, thiols, nitrites, and even saUva itself, tend to inhibit the mutagenic activity of PAHs (118—120). Therefore, the significance of PAHs in the human diet remains unknown (121,109). 

Vanillin has a low potential for acute and chronic toxicity, with a reported oral LD q in rats of 1580—3300 mg/kg. Dietary doses up to 20,000 ppm adrninistered to rats for two years resulted in no adverse toxicologic or carcinogenic effects. Vanillin is classified as a GRAS substance by EEMA. Consequently, at levels normally found in the human diet, vanillin would present no significant health or carcinogenic risk to humans. 

The presence of nucleic acids ia yeast is oae of the maia problems with their use ia human foods. Other animals metabolize uric acid to aHantoia, which is excreted ia the uriae. Purines iagested by humans and some other primates are metabolized to uric acid, which may precipitate out ia tissue to cause gout (37). The daily human diet should contain no more than about 2 g of nucleic acid, which limits yeast iatake to a maximum of 20 g. Thus, the use of higher concentrations of yeast proteia ia human food requires removal of the nucleic acids. Unfortunately, yields of proteia from extracts treated as described are low, and the cost of the proteia may more than double. 

Zinc is also an essential food element in the human diet. Too Httle zinc in the diet can lead to poor health, reproductive problems and a lowered abHity to resist disease. Taking too much zinc into the body through food, water or dietary supplements can also affect health. The levels of zinc that produce adverse effects are higher than the Recommended DaHy AHowances, which are 15 mg/day for men, 12 mg/day for women, 10 mg/day for children and 5 mg/day for infants. 

Boron in the form of borate is an essential micronutrient for the healthy growth of plants and is present in the normal daily human diet at an estimated level of 3—40 mg as boron. It is not a proven essential micronutrient for animals (119). 

Most carbohydrates exist in the form of polysaccharides. Polysaccharides give stmcture to the cell walls of land plants (cellulose), seaweeds, and some microorganisms and store energy (starch in plants and glycogen in animals). They are important in the human diet and in many commercial apphcations. 

Copper is required for all forms of aerobic and most forms of anaerobic life. In humans, the biological function of copper is related to the enzymatic action of specific essential copper proteins (66). Lack of these copper enzymes is considered a primary factor in cerebral degeneration, depigmentation, and arterial changes. Because of the abundance of copper in most human diets, chemically significant copper deficiency is extremely rare (67). 

Ascorbic acid commonly known as vitamin C, is one of the most important water soluble vitamins. Ascorbic acid is involved in many biological processes and it is an essential compound in the human diet [1]. The determination of ascorbic acid has gained increase significance in pharmaceutic, clinical, and food applications. So far, different methods have been developed for determination of ascorbic acid [2, 3]. 

Pantothenic acid is found in extracts from nearly all plants, bacteria, and animals, and the name derives from the Greek pantos, meaning everywhere. It is required in the diet of all vertebrates, but some microorganisms produce it in the rumens of animals such as cattle and sheep. This vitamin is widely distributed in foods common to the human diet, and deficiencies are only observed in cases of severe malnutrition. The eminent German-born biochemist Fritz Lipmann was the first to show that a coenzyme was required to facilitate biological acetylation reactions. (The A in... 

Organic chemicals Most organic liquids, other than the stronger acids, only attack zinc slowly. Zinc is, therefore, suitable for storage tanks for liquid hydrocarbons such as motor fuels, for phenols and for trichlorethy-lene degreasers. Zinc or zinc-coated vessels are not recommended for use in contact with acid foodstuffs, but are regularly used for dry foods. Zinc in small quantities is beneficial in the human diet. 

Tykot, R.H., van der Merwe, N.J. and Hammond, N. 1996 Stable isotope analysis of bone collagen, bone apatite, and tooth enamel in the reconstruction of human diet. A case study from Cuello, Belize. In Orna, M.V., ed., Archaeological Chemistry Organic, Inorganic, and Biochemical Analysis. ACS Symposium Series 625, Washington, DC, American Chemical Society 355-365. 

Schoeninger, M.J., DeNiro, M.J. and Tauber, H. 1983 Stable nitrogen isotope ratios of bone collagen reflect marine and terrestrial components of prehistoric human diet. Science 220 1381-1383. 

Schoeninger, M.J. 1989 Prehistoric human diet. In Price, T.D., ed.. Chemistry of Prehistoric Human Bone. Cambridge, Cambridge University Press 38-67. 

Ezzo, J.A., Larsen, C.S. and Burton, J.H. 1995 Elemental signatures of human diets from the Georgia Bight. American Journal of Physical Anthropology 98 471-481. 

Nitrogen isotope ratios ( N/ " N) inerease from plants to herbivores to eami-vores and ean be used to estimate the degree of camivory in human diets. Some field studies observe a greater differenee in 5 N between trophie levels in dry, hot habitats than in wet, cool ones. Two hypotheses have been proposed to explain this variation in difference in 8 N between trophic levels. (1) Elevated excretion of -depleted urea in heat/water-stressed animals (2) recycling of nitrogen on protein-deficient diets. Both predict increased diet-tissue 8 N difference under stress. 

Small amounts of trans-unsamrated fatty acids are found in ruminant fat (eg, butter fat has 2-7%), where they arise from the action of microorganisms in the rumen, but the main source in the human diet is from partially hydrogenated vegetable oils (eg, margarine). Trans fatty acids compete with essential fatty acids and may exacerbate essential fatty acid deficiency. Moreover, they are strucmrally similar to samrated fatty acids (Chapter 14) and have comparable effects in the promotion of hypercholesterolemia and atherosclerosis (Chapter 26). 

Twenty different amino acids ate required fot protein synthesis, of which nine ate essential in the human diet. The quantity of protein required is affected by protein quahty, enetgy intake, and physical activity. 

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