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HEALTH AND DISEASE

foods that enhanced dietary nutrient profiles. Indeed, in the postagricultural period, food-processing techniques became crucial for reducing the negative health impacts of reliance on a few foods. Native populations of the Americas that had a long tradition of reliance on maize (corn) prepared it in such a way as to avoid the problem of niacin deficiency. Corn was boiled in a solution con- taining lime (calcium carbonate, ash, etc.); this process resulted in the liberation of niacin from an undigestible complex, and also improved the food’s amino-acid bal- ances. When corn was introduced to Europe during the Columbian period, the lack of a tradition for its process- ing led to outbreaks of pellagra. A similar example is the leavening of wheat to make bread, or fermentation to make beer. Both of these processes increase the bioavail- ability of the minerals calcium, iron, and zinc. When soy- beans are processed into bean curd, as is common in East Asia, they lose their protease inhibitors, which interfere with protein digestion.

On the other hand, it is also the case that some food- processing techniques—such as heating, boiling, or dry- ing—can destroy vitamins in foods. Vitamin C degrades in the presence of heat and aridity; folic acid and thi- amine likewise are sensitive to heat. Some of the other B vitamins break down in the presence of alkaline or acidic conditions. Others, such as vitamins B6

and B12

, are quite

stable under most cooking conditions. Milling and pol- ishing rice into smooth white grains, which are valued highly in East Asian cuisine, reduce the protein and thi- amine content of rice, and contribute to the risk of the disease beriberi (thiamine deficiency). Industrial process- ing of foods often reduces their nutrient profile, but many foods, especially those that are consumed widely such as cereals, are enriched to replace lost nutrients. In addi- tion, grilling or broiling meats until they are well-charred has been associated with the production of the chemical compound Benzo(a)pyrene, which has been linked to gas- trointestinal cancers.

Nonnutritive Food Components

When diets are derived largely from plant foods, partic- ular combinations of food are known to improve the over- all dietary quality, particularly with respect to the balance of essential amino acids. Corn, for example, is low in the amino acids lysine and tryptophan, but in native Ameri- can cuisine, corn is often combined with legumes that are rich in those amino acids. Likewise, the combination of rice and legumes can provide the full array of essential amino acids. A peanut butter sandwich, a staple in the diet of many American children, contains complemen- tary amino acids from the wheat and peanuts.

However, it is not only the nutrient composition of foods that is relevant to disease. Other qualities of foods —especially plant foods—recently have been found to contain other chemicals that reduce the risk of certain diseases. Phytochemicals derived from plant foods may

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reduce the risk of some cancers, while others may pro- tect against heart disease and/or diabetes. Some poten- tially important phytochemicals include polyphenols (in red wine and green tea) and carotenoids (in orange, yel- low, and green vegetables). Many of these have been found to have antioxidant effects and may prevent cell damage from oxygen-free radicals. Widespread con- sumption of red wine has been credited by some with the “French Paradox,” the observation that, although the French tend to eat foods high in fat, their consumption of red wine may offset some of the risk of cardiovascular disease usually associated with such diets. Phytoestro- gens, a form of isoflavones found in legumes such as soy- beans, may reduce the risk of many cancers, especially breast cancer, by binding to estrogen receptors, and these also may reduce bone loss associated with osteoporosis. Proteins in soybeans also may reduce cholesterol levels and thus reduce the risk of heart disease. The organosul- fur constituents of garlic may inhibit platelet aggregation and reduce blood lipids, thereby reducing the risk of coronary heart disease. Tannins (found in tea, coffee, co- coa, red wine, and some legumes and grains) and phy- tates are hypoglycemic, and may contribute to reduced risk of diabetes.

Other plant compounds have links to infectious dis- ease, such as the protozoan disease malaria, which is a common disease (and often life-threatening) in tropical and semitropical areas. Manioc (Manihot esculenta; also called cassava or yuca), a widely cultivated root crop in the tropics, contains cyanogens, which appear to inhibit the growth of the malaria parasite in red blood cells. Like- wise, fava beans contain vicine, a potent oxidant that dis- rupts malarial reproduction in red blood cells. However, individuals who are deficient in the enzyme G-6PD (a deficiency most common in Mediterranean populations) are susceptible to the potentially fatal anemia, favism, be- cause their red blood cells are extremely vulnerable to destruction by potent oxidants such as vicine.

Many secondary compounds in plants do not have such salutary effects, or their benefits are tempered by potential negative effects on health. The cyanogens in manioc, lima beans, and other foods can interfere with thyroid function, glucose metabolism, growth and devel- opment, and other important physiological functions. Cruciferous vegetables such as cabbage contain thio- cyanate compounds that act as goitrogens, and thereby contribute to thyroid disease. Tannins, which are dis- tributed widely among plant foods, inhibit protein di- gestion and interfere with iron absorption. The ingestion of solanine, a glycoalkaloid found in commercial strains of potatoes that have been exposed to light, or in many wild varieties, can lead to serious gastrointestinal and neurological symptoms. Interestingly, traditional modes of consuming potatoes among Andean populations ap- pear to reduce the risk of solanine exposure; their pota- toes are consumed often with a clay-based slurry, which effectively detoxifies them.

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