Calcium and phosphorus intakes, balances, and blood levels of adults consuming self-selected diets.

Metabolic calcium and phosphorus balances, blood calcium and phosphorus levels, and alkaline phosphatase activity of 34 men and women, 20 to 53 yr of age, were determined each season during 1 yr while consuming customary diets. Dietary records were maintained 365 days. Analysis of variance indicated that serum Ca, P, and alkaline phosphatase levels were affected by season (p less than 0.0001), whereas calcium or phosphorus intakes were not. Calcium and phosphorus intakes of the men (1075 and 1533 mg, respectively) were higher (p less than 0.01) than of the women (695 and 1095 mg, respectively), but balances were not statistically different between them. Daily calcium balances for the men and women for the year were -81 and -85 mg, respectively; daily phosphorus balances were -239 and -130 mg, respectively. Stepwise regression analysis indicated that dietary calcium and protein were significantly associated with calcium and phosphorus balances, but in opposite directions, and only in women over 35 yr of age.

Magnesium intakes, balances, and blood levels of adults consuming self-selected diets.

Magnesium balances and plasma and blood cell concentrations were determined in 34 men and women, 20 to 53 yr of age, during each season for 1 yr while they were consuming their customary diets. Dietary records were maintained 365 days. Analysis of variance indicated no seasonal variation in intake or balance. Blood cell magnesium correlated with magnesium intake (r2 = 0.203; p less than 0.04). Daily magnesium intakes of the men (323 mg) were significantly higher (p less than 0.01) than of the women (234 mg), and reflected greater calorie consumption for their greater body weights. Daily magnesium balances for the men and women were -32 and -25 mg, respectively. Multiple regression analysis showed that magnesium balance was associated not only with magnesium intake but also with the intake of other nutrients such as fiber, protein, calcium, and phosphorus. Moreover, the effect of these nutrients on magnesium balance varied with age and sex.

Plasma and urinary amino acids and selected sulfur metabolites in young men fed a diet devoid of methionine and cystine.

A preliminary investigation was conducted to explore the use of plasma methionine and cystine for determining human sulfur amino acid requirements. Measurements of urinary methionine, cystine, taurine, and inorganic sulfate were included. After a 3-day control period, three young men were fed for 8 days a diet containing a purified -l-amino acid mixture, patterned after egg protein but devoid of methionine and cystine. Fasting plasma methionine and cystine levels showed little decrease during the 8-day period. Urinary cystine and taurine responses were inconsistent among the subjects. Urinary methionine and inorganic sulfate levels decreased markedly within a few days after feeding of the experimental diet, and may be useful criteria for determining human sulfur amino acid requirements.

Estimation of body fat in rats by whole-body counting.

A method for determining body fat in vivo in rats by whole-body counting of 40K is described. The technique utilizes a Nuclear Chicago Corporation TOBOR system with 5-in thallium-activated sodium iodide crystals. To test the method a regression equation was developed using the 40K counts and body weight of young adult rats weighing 333-788 g; the results were compared with those obtained from the gravimetric determination of fat in the carcass. The correlation coefficient between the two methods was 0.945.