Intakes of minerals and factors that might affect their bioavailability were estimated for 255 toddlers aged 18-30 mo living in villages in Egypt, Kenya, and Mexico. Mean intakes over 1 y were compared with international-requirement estimates by using a probability approach. The prevalence of iron intakes likely to be inadequate to prevent anemia was estimated as 35% in Egypt, 13% in Kenya, and 43% in Mexico. The prevalence of zinc intakes likely to be inadequate to meet basal requirements was estimated as 57% and 25% in Kenya and Mexico, respectively, but only 10% in Egypt, where the use of yeast-leavened breads was judged to have improved zinc availability. There was no suggestion that estimated copper or magnesium intakes were inadequate, but calcium intakes in Kenya and Egypt were well below recommended amounts. Studies of factors affecting mineral bioavailability in the diets of these countries' populations could suggest dietary changes that might improve effective mineral intake with minimal cost.

Basal metabolic rate, resting metabolic rate (RMR), and energy cost of selected activities were measured in six healthy young women who were participating in a study of protein requirements. The women were confined to a metabolic unit for 92 days during which they consumed a defined formula diet. The basal metabolic rate of the women was 20.7 +/- 2.6 kcal/kg body weight/day and the caloric requirement for maintenance of weight was 38.7 kcal/kg body weight/day. Basal metabolic rate varied significantly with the menstrual cycle. Basal metabolic rate decreased at menstruation and fell to its lowest point approximately 1 wk before ovulation subsequently rising until the beginning of the next menstrual period. RMR was 0.99 +/- 0.16 kcal/kg/h. The energy expenditure while sitting was 1.06 times RMR, while walking it was 2.81 times RMR, and while performing treadmill exercise it was 3.47 times RMR.

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The relationship of food intake and the human menstrual cycle has not been well quantified. In this study, voluntary energy and sucrose intake of seven women, aged 24-43 y, were evaluated by the weighed-intake method over one entire menstrual cycle. Portable tape recorders facilitated the recording of food intake. Although daily fluctuations of energy intake were large, analysis of variance showed intake during the luteal phase to be significantly greater than during the periovulatory and follicular phases (p less than 0.05). From 95% simultaneous (Bonferoni) confidence intervals, the estimate of difference was 283 kcal greater during the luteal phase than the periovulatory phase; the estimate of difference was 214 kcal greater during the luteal phase than during the follicular phase. No significant differences in energy intake were found among the menstrual, follicular, and periovulatory phases. No significant relationship was found between sucrose intake and the menstrual cycle.

Two studies were conducted to investigate the effects of mild exercise on nitrogen balance in men given diets supplying adequate or slightly limiting energy. In experiment A the diet supplied 91 mg N/kg body weight (0.57 g protein/kg, the FAO/WHO safe level of intake) as egg white; in experiment B the same source was used to provide the 1980 NRC-RDA for adult males, 128 mg N/kg body weight (0.8 g protein/kg). By adjusting energy intake and activity, periods of energy equilibrium and negative energy balance (-15%) were achieved at three levels of activity (X for exercise): no programmed work (0.85X), 1 hour of treadmill walking (1.0X) and 1 hour each of treadmill and cycle ergometry (1.15X). "True" nitrogen balance (TNbal) was more positive or less negative during periods of energy equilibrium as compared to those of energy deficit. This effect of energy balance on TNbal increased with physical activity. At the lower protein intake the mean difference in TNbal between the period of energy equilibrium and that of energy deficit at 1.0X was 0.19 g N/day (nonsignificant difference) and 0.54 g N/day at 1.15X. When protein intake was increased, the difference in TNbal between periods of equilibrium and deficit was significant at all levels of activity: 0.65 g N/day at 0.85X, 0.93 g N/day at 1.0X and 1.09 g N/day at 1.15X. Physical activity was anabolic when energy balance was maintained. In experiment A the addition of 1 hour of exercise (1.0X to 1.15X) spared 2.5 mg N/kg body weight; reducing activity by 1 hour (1.0X to 0.85X) cost 1.4 mg N/kg body weight. In experiment B, TNbal was more positive with increased activity (by 5.9 mg N/kg body weight) and more negative (by 11.5 mg N/kg body weight) when the men were sedentary. During periods of energy deficit, the anabolic effect of activity was also present, although less markedly. When activity increased from 1 to 2 hours in experiment A, TNbal improved by 2.1 mg N/kg body weight and in experiment B, by 3.5 mg N/kg body weight. Thus, circumstances of negative energy balance with adequate protein intake are better tolerated when the energy deficit is generated by physical activity than when it derives from reduced intake; the picture when protein intake is marginal requires further investigation.

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1. Protein utilization in young men under circumstances of one or two periods of work and both adequate and surfeit energy intake was determined by nitrogen balance; protein intake was constant at the FAO/ WHO (1973) safe level (0.57 g/kg body-weight).2. Physical activity affected protein utilization negatively by increasing sweat and faecal N losses, and positively by supporting increased energy intake.3. Efficiency with which surfeit energy improved N utilization (mg N retained/added kJ) was greater under circumstances of increased activity.4. Changes in body composition as determined by total body potassium and hydrostatic weighing supported the N retention values.After a century of quiescence, the issue of a relationship between physical activity or work and protein requirement has resurfaced. This resurgence of interest is a consequence of two major lines of evidence : discovery of significant metabolism of the branched-chain amino acids in resting and working muscle, and reports of protein-related responses to chronic exercise in man. The latter line includes reports of increased N retention with increased protein intake by active men (Consolazio et al. 1975), diminished haemoglobin levels in men during training (Yoshimura, 1961), and inadequacy of the FAO/WHO (1973) safe level of protein intake for men doing isometric exercises (Torun et al. 1977).In principle the first consideration, amino acid participation in work metabolism, would be relevant to the question of protein requirements if a net catabolism of protein could be demonstrated in the physically active individual. To date no such net catabolism has been demonstrated. The second line of evidence, while appearing conclusive, is actually derived from experiments made difficult to interpret by their design. In some studies, the work assigned involved training which might impose a short-term protein demand for the construction of muscle tissue and, perhaps, increased blood volume. In some, sweat losses were not measured and, with the increased sweating that would accompany increased physical activity, spuriously positive N balances would be expected. Finally, most studies are confounded by differences in energy intake leading to a variety of energy balances accompanying the work. These potential imbalances may have occurred as a result of increased voluntary intake, experimentally imposed constancy of intake in the face of increased need, or inappropriate augmentation of intake in association with work.To illuminate these relationships and to determine if physical activity does influence protein utilization, we measured N retention in men assigned two different amounts of exercise of equivalent load, such that any training effect would be minimized. Energy intake was either sufficient to maintain body-weight or in excess under both conditions of activity. The findings to be reported here show that both activity and excess energy intake favour N retention.available at https://www.cambridge.org/core/terms. https://doi

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