Folate nutritional status was estimated by radioassay of folate levels in plasma and erythrocytes during and after aa long-term supplementation of folic acid. A 1-mg dose of folic acid per day was administered orally to 6 healthy subjects for 17 weeks. After 4 weeks of supplementation the mean folate concentration in plasma reached 11 ng/ml and remained constant thereafter, but decreased exponentially after stopping the supplementation. However, the folate concentrations in reticulocytes and erythrocytes increased linearly in all subjects during the supplementation. These results suggest that folate-rich, young erythrocytes are mixed at a constant rate with circulating ripe ones, which have a lower folate content, during folate supplementation.
The erythorbic acid (ErA) content in the tissues of guinea pigs administered ErA was compared with that of ascorbic acid (AsA). Guinea pigs were administered 1, 5, 20, and 100mg ErA/day or 1, 5, and 100mg AsA/day for 16 days and then sacrificed. The liver, adrenal glands, spleen, and kidneys were removed to determine the contents of ErA and AsA using HPLC. Only a small amount of ErA was found in four tissues of the animals administered 20mg or more of ErA/day. On the contrary, AsA was found in the tissues of all animals administered 1mg or more of AsA/day. The ErA content in the tissues was much lower than that of AsA even when the amount of ErA administered was the same as that of AsA. However, the body weight gains of animals administered ErA were similar to those of animals administered AsA. These observations suggested that the mechanism of the retention of ErA in the tissues was much different from that of AsA and that the vitamin C activity of ErA might be more than one-twentieth that of AsA.
The possible role of insulin status in the increase in liver lipogenic enzyme activities upon feeding medium-chain triglyceride (MCT) was investigated with streptozotocin-induced diabetic rats and insulin-treated diabetic rats. Rats were fed synthetic diets that contained either 2% corn oil (control), fat free, 13% MCT +2% corn oil, or 13% lard +2% corn oil, respectively. Feeding the MCT diet for 3 days increased serum ketone bodies in both the normal and diabetic rats. Insulin levels of MCT-fed rats tended to be higher than in normal animals. MCT feeding caused an enhancement of fatty acid synthetase (FAS) and malic enzyme (ME) in the liver of normal rats, whereas diabetic rats failed to register an increase in those activities due to MCT feeding. Administration of insulin to diabetic rats resulted in a recovery of the level of those enzyme activities to about the same degree as in each of the normal rat groups. It was interesting that diabetic MCT-fed rats with insulin treatment maintained higher enzyme activities in comparison to the lard and control groups. These results suggest that the increase in lipogenic enzyme activities caused by dietary MCT is presumably dependent on differences in insulin status.
Twenty-four hour (24-h) urinary creatinine excretion was measured and correlated with anthropometric measurements (height, weight, skinfold thickness, and arm muscle area (AMA)) in 119 healthy Japanese children, aged 2 to 18 years. The results indicated highly significant correlations between creatinine excretion and age (r=0.88 for boys, 0.90 for girls), height (r=0.91, 0.88), weight (r=0.96, 0.94), and AMA (r=0.91, 0.70). In the multiple regression estimation, weight alone, or weight and height, accounted for most of the variation in 24-h creatinine excretion (r2 =0.93 for boys, 0.89 for girls), and the addition of other variables did not further improve the estimation.
The alleviation mechanism of methionine toxicity by dietary glycine was investigated in weanling rats fed a high-methionine diet. When rats were fed a 10% casein diet containing 2% methionine, the activities of methionine adenosyltransferase, cystathionine β-synthase, and cystathionine y-lyase, which participate in the methionine metabolism in the transsulfuration pathway, were significantly enhanced. But the addition of 2% glycine to the high methionine diet did not cause further increase in these enzyme activities; the activities of methionine adenosyltransferase and cystathionine β-synthase were rather decreased while cystathionine γ-lyase activity was not altered. Methionine transaminase activity was essentially insensitive to the dietary addition of methionine and glycine. In rats fed a high methionine diet, the hepatic methionine level was significantly increased with a concomitant decrease in the levels of glycine, serine, and threonine. The addition of glycine to the high methionine diet effectively suppressed the enhancement of the hepatic methionine level and almost completely restored the glycine level, but it only partially restored the serine level and further decreased the threonine level. From these results, it is suggested that the alleviating effect of dietary glycine on methionine toxicity is primarily elicited by the restoration of the hepatic glycine level rather than by an increase in hepatic enzyme activity.
The effect of brown rice with low protein intake was studied in five healthy young men. Feces were weighed, the digestibility of nutrients was determined, and blood tests were made. Each subject followed a diet consisting mainly of polished rice for 14 days and one consisting mainly of brown rice for 8 days. Both diets contained 0.5 g protein per kg of body weight. The brown rice diet had 3 times as much dietary fiber as the polished rice diet. On the brown rice diet, fecal weight increased, and apparent digestibility of energy, protein, and fat decreased, as did the absorption rates of Na, K, and P. The nitrogen balance was negative on both diets, but more negative on the brown rice diet. The phosphorus balance on the brown rice diet was significantly negative, but other minerals were not affected by the diet. The levels of cholesterol and minerals in the plasma were not significantly different on the polished rice diet and the brown rice diet. Comparing these results with data on standard protein intake (Miyoshi, H. et al. (1986) J. Nutr. Sci. Vitaminol., 32, 581-589.), we concluded that brown rice reduced protein digestibility and nitrogen balance.
Department of Food and Nutrition, Faculty of the Science of Living, Osaka City University2Department of Clinical Nutrition, National Cardiovascular Center, The effect of nitrogen intake on nitrogen balance was studied in six obese patients receiving low energy diets. They were given a control diet containing 2, 000 kcal of energy and 80g of protein for the first ten days. Then they were given Diet A with 1, 100 kcal of energy and 70g of protein for the next 2 weeks, followed by Diet B with 1, 100 kcal of energy and 50 g of protein for 2 weeks. The relationship between nitrogen intake (X, mg/kg) and nitrogen balance (Y, mg/kg) during the low energy diet periods was statistically significant, with Y=0.388X-60.32 (SD=17.71, r=+0.67, n=11, p<0.05). The nitrogen and protein requirements were estimated from this equation to be 201.1 mg/kg and 1.26 g/kg, respectively. In our experiment, the nitrogen balance in obese patients was well maintained although total energy was reduced to 1, 100 kcal/day in Diet A. It is suggested that protein quantity in the diets should be taken into account when a low energy diet is used for the treatment of obesity.
The effects of low energy diets on protein metabolism in terms of the metabolic pool, active protein pool, and active and inactive protein synthesis rates were studied using [15N]glycine in five obese patients (percentage of ideal body weight, 120-190%). For 10 days, the patients were given a control diet containing 2, 000 kcal of energy and 80 g of protein. For the next 2 weeks, they were given Diet A with 1, 100 kcal of energy and 70g of protein, and for the last 2 weeks given Diet B with 1, 100 kcal of energy and 50g of protein. During the Diet A period, the active protein pool and the active and inactive protein synthesis rates were about the same as during the control diet period, although the metabolic pool tended to be slightly smaller than during the control diet period. During the Diet B period, the metabolic pool, active protein pool, and active protein synthesis rate were all significantly different from the values during the control diet period. The results suggest that protein metabolism in obese patients is not maintained with less than 70g of protein daily when energy intake was restricted to 1, 100 kcal/day.
The effect of dietary taurine on hepatic cholesterol 7α-hydroxylase activity was investigated in mice. At first, male ICR strain mice were fed a commercial non-purified diet for 4 weeks and killed at 01:00 h (midnight) or 13:00h (daytime) and the cholesterol 7α-hy-droxylase activity in the hepatic microsomal fraction was measured. The enzyme activity was 5.9-fold higher at midnight than in the daytime. Next, to investigate the effect of dietary taurine on the activity of this enzyme, male ICR strain mice were fed semi-purified diets for 5 weeks: a cholesterol-free diet (standard), a lithogenic diet containing 0.5% cholesterol and 0.25% sodium cholate (C-CA), and a lithogenic diet supplemented with 5% taurine (C-CA+5% taurine). All mice were killed at midnight and cholesterol 7α-hydroxylase activity was measured. The enzyme activity of the mice fed the lithogenic diet was about 20% that of mice fed the standard diet. Dietary taurine increased the activity by 1.9-fold. Therefore, it was concluded that the inhibitory effect of dietary taurine on cholesterol gallstone formation was related to increased bile acid synthesis as reflected by stimulation of cholesterol 7α-hydroxylase activity.
The regulation of histidine and arginine intake in rats was investigated using the self-selection feeding method. The usefulness of the self-selection feeding technique for the determination of amino acid requirements is also discussed. When weanling rats were offered a choice of two diets differing only in histidine or arginine content for 2 weeks, they chose diets to support maximal growth, with the exception of some groups that did not grow to the maximum level. Histidine and arginine intake of the self-selecting rats ranged from 0.25% to 2.22% and from 0.43% to 2.43% of the diets ingested. These results demonstrate clearly that rats have the ability to consume a minimum amount that satisfies histidine and arginine needs for maximal growth. Previous and the present results suggest that the self-selection feeding method is a useful technique for the determination of amino acid requirements in growing rats.