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The American Diet Fact and Fallacy

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The American Diet Fact and Fallacy
Page 1132
copper deficiency have been identified in the general public. It is not known whether there exist widespread marginal copper deficiencies, or whether the copper balance studies are inaccurate. Recognizable symptoms of copper deficiency are usually seen only as a result of excess zinc intake and in Menkes' syndrome, a relatively rare X­linked hereditary disease associated with a defect in copper transport. Wilson's disease, an autosomal recessive disease, is associated with abnormal accumulation of copper in various tissues and can be treated with the naturally occurring copper chelating agent penicillamine.
Chromium Is a Component of Glucose Tolerance Factor
Chromium probably functions primarily as a component of glucose tolerance factor (GTF), a naturally occurring coordination complex between chromium, nicotinic acid, and the amino acids glycine, glutamate, cysteine, or glutathione. GTF potentiates the effects of insulin, presumably by facilitating its binding to cell receptor sites. The chief symptom of chromium deficiency is impaired glucose tolerance, a result of the decreased insulin effectiveness. The frequency of chromium deficiency is unknown. The RDA for chromium has been set at 50–200 g for a normal adult. The best current estimate is that the average consumption of chromium is around 30 g day–1 in the United States. Unfortunately, the range of intakes is very wide (5–100 g) even for individuals otherwise consuming balanced diets. Those most likely to have marginal or low intakes of chromium are individuals on low­caloric intakes or consuming large amounts of processed foods. Some concern has been voiced that many Americans may be marginally deficient in chromium.
Selenium Is a Scavenger of Peroxides
Selenium functions primarily in the metalloenzyme glutathione peroxidase, which destroys peroxides in the cytosol. Since the effect of vitamin E on peroxide formation is limited primarily to the membrane, both selenium and vitamin E appear to be necessary for efficient scavenging of peroxides. Selenium is one of the few nutrients not removed by the milling of flour and is usually thought to be present in adequate amounts in the diet. The selenium levels are very low in the soil in certain parts of the country, however, and foods raised in these regions will be low in selenium. Fortunately, this effect is minimized by the current food distribution system, which assures that the foods marketed in any one area are derived from a number of different geographical regions.
Manganese, Molybdenum, Fluoride, and Boron Are Other Trace Elements
Manganese is a component of pyruvate carboxylase and probably other metalloenzymes as well. Molybdenum is a component of xanthine oxidase. Fluoride is known to strengthen bones and teeth and is usually added to drinking water. Boron may also play an important role in bone formation.
28.11— The American Diet:
Fact and Fallacy
Much has been said about the supposed deterioration of the American diet. How serious a problem is this? Clearly Americans are eating much more processed food than their ancestors. These foods differ from simpler foods in that they have a higher caloric density and a lower nutrient density than the foods they replace. However, these foods are almost uniformly enriched with iron, thiamine, riboflavin, and niacin. In many cases they are even fortified (usually as much for sales promotion as for nutritional reasons) with as many as 11–15 vitamins and minerals. Unfortunately, it is simply not practical to replace all of
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