The essential trace elements.

Essential trace elements are required by man in amounts ranging from 50 micrograms to 18 milligrams per day. Acting as catalytic or structural components of larger molecules, they have specific functions and are indispensable for life. Research during the past quarter of a century has identified as essential six trace elements whose functions were previously unknown. In addition to the long-known deficiencies of iron and iodine, signs of deficiency for chromium, copper, zinc, and selenium have been identified in free-living populations. Four trace elements were proved to be essential for two or more animal species during the past decade alone. Marginal or severe trace element imbalances can be considered risk factors for several diseases of public health importance, but proof of cause and effect relationships will depend on a more complete understanding of basic mechanisms of action and on better analytical procedures and functional tests to determine marginal trace element status in man.

Plasma chromium after glucose administration.

Sharp increases in the concentration of chromium in plasma were found in five subjects with normal glucose utilization after administration of glucose by mouth. This rise was not observed in two diabetics when glucose tolerance was impaired; however, it appeared when glucose tolerance was improved and when trace amounts of trivalent chromium were given as a dietary supple-ment. The source of chromium which became elevated was most likely an internal pool. Possibly there is a relation between chromium and insulin function.

Sources of variation in energy intake by men and women as determined from one year's daily dietary records.

Data from a year-long study conducted by the US Department of Agriculture's Beltsville Human Nutrition Research Center were used to identify sources of variation in daily energy intakes. A specific hypothesis was that an inverse relationship exists between past body weight and future energy intake whereas a direct relationship exists between past energy intake and future weight. Daily energy intakes of 29 male (n = 13) and female (n = 16) adult subjects were related through linear-regression analysis to sex (+ for males), age (-), height (+), weight (- for past and present measurements, + for future measurement), data collection method (- for duplicate plate), day of week (+ for Friday and Saturday), and month (+ for May, July, August, December, and January). These relationships were statistically significant (p less than 0.05). The results confirmed the hypothesis and were in general agreement with previously published studies that used larger samples but fewer days of data.

Effects of sugars on indices of glucose tolerance in humans.

Ten men and nine women were studied to determine whether replacement of utilizable complex carbohydrate by sugars (mono- and disaccharides) in a high-fiber, low-saturated fat diet would affect indices of glucose tolerance. Diets differed in that the 50% of calories derived from carbohydrate was either 35% complex and 15% sugars (low-sugar) on 15% complex and 35% sugars (high-sugar). Summation of glucose responses 30-180 min following an oral glucose tolerance test was significantly higher in men, but not women, after they consumed the high-sugar diet. Corresponding insulin responses were significantly higher in men consuming the high-sugar compared to the low-sugar diet. Insulin binding was significantly lower during the base line period and after the high-sugar diet compared to the low-sugar diet. Results indicate that sugars adversely affect indices of glucose tolerance when they replace complex carbohydrates even in a high-fiber, low-saturated fat diet.

Sodium and potassium intake and balance in adults consuming self-selected diets.

Twenty eight adults, 12 men and 16 women, participated in a 1-yr study designed to assess daily nutrient intake accurately. All subjects lived at home, consumed self-chosen diets, and maintained a detailed daily dietary record throughout the year. During four 7-day balance studies, one in each season of the year, meals, beverages, urine, and feces were analyzed for sodium and potassium content by atomic absorption spectrometry. Total intakes averaged 3.4 g/day for sodium and 2.8 g/day for potassium. The Na:K ratio for all diets analyzed averaged 1.3. Nutrient densities of sodium and potassium were 1.8 and 1.5 g/1000 kcal, respectively. Apparent absorptions of sodium and potassium were 98 and 85%, respectively, and did not change significantly over the wide range of intakes. Average urinary excretions of sodium and potassium were 86 and 77% of total intake, respectively. Mean metabolic balances were positive for sodium, +0.47 g/day, and potassium, +0.28 g/day. The data of this study provide useful information concerning the dietary intakes, excretions, and balances of sodium and potassium for adults based on analytic determination.

Evaluation of long-term dietary intakes of adults consuming self-selected diets.

Mean daily intakes of calories and 19 nutrients were calculated for 13 males and 16 females, ages 20 to 53 yr, who kept daily diet records for 1 yr. Mean daily caloric and 19 selected nutrient intakes of the subjects met or exceeded the 1980 recommended dietary allowances except for iron and calcium for females. Males had higher intakes than females for all nutrients studied except crude fiber, vitamin A, and vitamin C. However, nutrient density values were comparable for both sexes, except that the females had higher nutrient density values for vitamin A than did the males. The younger subjects had higher intakes of calories and saturated fat than the older ones. The younger males had higher intakes of total fat, saturated fat, and oleic acid than the older males. The consistency of reporting food intakes examined by applying a systematic sampling method designed for this study did not vary considerably when diet records kept over a long period of time were evaluated by four methods.

Effect of making duplicate food collections on nutrient intakes calculated from diet records.

In a 1-yr study in which food intakes were recorded daily, subjects were asked to make duplicate food collections for 1 wk during each of the four seasons. Mean calculated energy intake of the 29 subjects was 12.9% less during the food collection periods than the mean for the entire year (which included collection periods). There were also significant reductions in the reported intake of all nutrients during the collection periods. Protein, vitamin A, saturated fat, and cholesterol intakes were decreased to the greatest extent. The actual decrease in energy intake was greater for the males than for the females, but the percentage was the same (12.9%). The younger group of subjects (less than or equal to 35) decreased energy intake 16.8% and the older group (greater than 35) 8.8%. Comparison of intakes during collection periods with intakes the week before and the week after showed that 28 of the 29 subjects decreased their energy intake from 1.1 to 32.3%. These data suggest that intakes of subjects during food collection periods do not represent their habitual levels of intake reported throughout the year.

Estimation of available dietary iron.

Dietary iron requirements are dependent on the amount and availability of food iron ingested. On the basis of recent studies of food iron absorption employing extrinsic tag techniques, the availability of heme iron has been defined and estimates of the availability of nonheme iron based on the amounts of enhancing substances appear possible. A model has been developed whereby the availability of iron in a given meal may be estimated. Calculations are made on a meal basis of 1) the amount of heme iron and its availability, and 2) the amount of nonheme iron and its availability as influenced by the meal's content of enhancing factors. Examples of these calculations are provided.

What are people really eating? The relation between energy intake derived from estimated diet records and intake determined to maintain body weight.

Two hundred sixty-six free-living human volunteers, 21-64 y old, were trained by dietitians to record daily their food intake for at least 7 d. Subsequently, they were fed diets of conventional foods adjusted in amounts to maintain their body weight for greater than or equal to 45 d. Comparing their estimated energy intake with the intake determined to maintain weight yielded mean differences of 2365 and 1792 kJ (565 and 428 kcal) in men and women, respectively, representing an underreporting of 18%. Twenty-two individuals (8%) overestimated and 29 (11%) were accurate to within 419 kJ (100 kcal) of their maintenance requirement. The remaining 215 individuals (81%) reported their habitual intake at 2930 +/- 1586 kJ (700 +/- 379 kcal) below that subsequently determined as their maintenance requirement. These findings suggest caution in the interpretation of food-consumption data.

Indices of copper status in humans consuming a typical American diet containing either fructose or starch.

Twenty-four male subjects originally participated in a study to determine the effects of feeding diets comparatively low in copper (1.03 mg/day/2850 kcal) and containing either 20% fructose or starch on indices of copper status. During the course of feeding the diets for 11 wk, four of the subjects exhibited heart-related abnormalities and were removed from the study. Fructose ingestion had no effect on serum ceruloplasmin activity or serum copper concentration but did significantly reduce cuprozinc superoxide dismutase (SOD) activity of erythrocytes as compared to starch. Repletion of the subjects with 3 mg copper/day for 3 wk significantly increased SOD levels in subjects previously fed fructose but not starch. Apparent copper balance was significantly greater when the subjects consumed the fructose as compared to the starch diet. These results suggest that the type of dietary carbohydrate fed can differentially affect indices of copper status in humans.

Modification of the United States' diet to effect changes in blood lipids and lipoprotein distribution.

Twenty men, 19 premenopausal and 14 postmenopausal women consumed a diet for 13 weeks that supplied 35% of the calories from fat, 50% from carbohydrate, and 15% from protein. The diet was low in cholesterol, saturated fat, and salt, and high in complex carbohydrate and fiber. The 7-day menu was composed of common well-accepted foods prepared in a simple attractive manner. Plasma total cholesterol, LDL cholesterol, and VLDL cholesterol were reduced, but triglyceride levels were not different than after self-selected diets. When 20% of the complex carbohydrate was replaced by simple carbohydrate and other diet components remained optimal, triglyceride and VLDL cholesterol levels increased in men and premenopausal women and total cholesterol increased in premenopausal women. These results suggest that beneficial effects on the blood lipids and lipoprotein distribution of men and women may be obtained by minimal modification of a typical U.S. diet.

Three decades of dietary recommendations.

The scope of Recommended Dietary Allowances (RDAs) has markedly expanded since their first edition in 1941. There were changes from simple goals to complex, health-related objectives and a nearly threefold increase of nutrients with recommended intakes. These changes reflect the development of scientific knowledge as well as increasing public awareness of the relation of nutrition to health. This review discusses the development of the RDAs, especially during the past 30 years, and examines the changes of definitions, goals, and paradigms.

Food fortification in the United States.

Formulas for the fortification of nutrients have remained essentially unchanged for the half-century in which the U.S. government has had a fortification policy in place. During that period, the classical micronutrient deficiencies have disappeared, but changes in the U.S. food supply have occurred and concerns about adequate intakes of other micronutrients have emerged. In 1974 the Food and Nutrition Board published its "Proposed Fortification Policy for Cereal Grain Products." Of the six fortification endorsement conditions outlined in the policy statement, three do not meet the stated criteria or today's needs. New approaches to address this situation are proposed.

Risk assessment of essential trace elements: new approaches to setting recommended dietary allowances and safety limits.

By definition, every essential trace element must have a range of intakes safe from toxicity but adequate enough to meet nutrition requirements. That range is part of the total dose-response curve and its lower and upper limits are delineated on the basis of nutrition and toxicology data, respectively. Close coordination of activities to set these limits is necessary to avoid recommendations that are either impractical (narrow zones of safe and adequate intakes) or contradictory (overlapping limits, i.e., no zones of safe and adequate intakes).

Essential trace metals: new definitions based on new paradigms.

This article will concentrate on the nutritional and physiological aspects of modern trace metal research. It will try to establish meaningful relations among the research activities of the past 50 years, and to summarize the present state of knowledge as a basis for future endeavors. The discussion will address the gradual emergence during the past decades of three paradigms that can be expected to determine the directions of future research.

Chromium supplementation of human subjects: effects on glucose, insulin, and lipid variables.

Seventy-six normal, free-living subjects were given supplements of 200 micrograms chromium (Cr) in the form of chromic chloride or a placebo in a double-blind crossover study with 3-month experimental periods. Twenty of the 76 subjects had serum glucose concentrations greater than or equal to 100 mg/dL 90 minutes after a glucose challenge (1 g glucose per kilogram of body weight). Chromium supplementation significantly decreased (P less than 0.05) the 90-minute glucose concentration of these subjects from 135 +/- 9 to 116 +/- 11 mg/dL; fasting glucose concentrations also decreased significantly. The 90-minute serum glucose levels of the 35 subjects with glucose concentrations less than the fasting serum glucose level were increased significantly by Cr supplementation, from 71 +/- 1 to 81 +/- 4 mg/dL. Fasting and 90-minute serum glucose concentrations of the remaining subjects who displayed 90-minute glucose concentrations greater than fasting levels but less than 100 mg/dL were not affected by Cr supplementation. In this study, immunoreactive serum insulin concentration, body weight, lipids, and other selected clinical variables did not change significantly during Cr supplementation. These data demonstrate that Cr supplementation decreases the serum glucose levels of subjects with 90-minute glucose concentrations greater than or equal to 100 mg/dL following a glucose challenge, increases serum glucose levels of subjects with 90-minute glucose concentrations less than fasting levels, and has no effect on the serum glucose levels of subjects with 90-minute glucose values similar to but greater than fasting levels.

Mineral elements: new perspectives.

Research during the 1970s brought out the importance of interrelationships among trace elements and better definition of human mineral requirements. These have practical implications which are pointed up in this paper. For example, iron absorption (important in meeting requirements of women of child-bearing age) can be improved by co-ingestion of ascorbic acid and/or meat, poultry, or fish products. The interplay between calcium and protein metabolism is also summarized. To accommodate as yet incomplete knowledge, the 1980 revision of the Recommended Dietary Allowances has incorporated the concept of "ranges of safe and adequate intakes" for two minerals and six trace elements. Copper and chromium appear to be of special importance, and their adequacy in the diet cannot be taken for granted. The nutrient density of these two elements per 1,000 kcal can be used in assessing intake in broad terms of "poor," "marginal," or "adequate," although this is by no means a quantitative type of judgment.

Zinc and copper in self-selected diets.

Levels of zinc and copper in the self-selected diets of twenty-two men and women were determined by atomic absorption spectrophotometry. Sixty-eight per cent of the subjects consumed less than two-thirds of the recommended allowance for zinc (15 mg). Eighty-one per cent consumed less than two-thirds of the suggested level of copper (2.0 mg). Average daily intake of protein exceeded the recommended allowance. However, the mean zinc:calorie ratio for those subjects was only 4.19 mg. per 1,000 kcal. Using the recommended allowances for zinc and for energy, the zinc:calorie ratio would be 6.5 mg. per 1,000 kcal. For copper, the suggested nutrient density is 0.85 mg. per 1,000 kcal vs. the 0.50 mg. per 1,000 kcal observed in this study. These metallo:calorie ratios indicate that the nutrient density of these two trace elements in the diet is low and that diets supplying adequate amounts of energy and protein do not guarantee adequate levels of zinc and copper.

Acceptability of a 7-day higher-carbohydrate, lower-fat menu: the Beltsville Diet study.

For 13 weeks, 20 men (aged 23 to 56), 19 premenopausal (aged 21 to 48), and 14 postmenopausal women (aged 49 to 65) consumed a 7-day rotation menu conforming to dietary recommendations of several research and health organizations. The diets were designed to make minimal changes in the standard American diet by the use of well-accepted normal foods. The average daily composition of the diet was 50% carbohydrate (complex 35%, simple 15%), 35% fat (P:S 0.7), and 15% protein; it contained 100 mg cholesterol, 1 gm sodium, and 14.5 gm neutral detergent fiber per 1,000 kcal. The acceptability of the menus was examined through questionnaires administered after the experimental diet period. Subjects rated the menus and individual foods and made recommendations for improvement of the menus. Most subjects (33 of 41 responding) rated the menu better than or almost as good as their usual diet. Few (9) were ever hungry during the 13-week period. During the study, a number of biochemical parameters were measured; the measurements indicated beneficial results. Blood pressure, cholesterol levels, and glucose responses were all improved after consumption of the menu. The results indicate that with minimal changes in the normal U.S. diet, acceptable menus that have beneficial effects on risk factors for heart disease and diabetes can be developed.

The newer trace elements.

The application of the concept of a "controlled environment" led to the identification of eight trace elements with a proven or postulated biological function during this decade. Rigorous reduction of metallic contamination from air, drinking water, and diet is necessary to reduce exposure to the element under investigation below requirement levels. An essential function for a trace element is suggested when deficiency is produced, and indepently confirmed, in two or more animal species, and also when the signs of deficiency are prevented or cured by supplements. As yet, a direct role for the "new trace elements" in the human organism has not been demonstrated.