Dietary boron supplementation enhanced the action of estrogen, but not that of parathyroid hormone, to improve trabecular bone quality in ovariectomized rats.

This study investigated whether boron would enhance the ability of 17beta-estradiol (E2) or parathyroid hormone (PTH) to improve bone quality in ovariectomized OVX rats. Adult OVX rats were treated for 5 wk with vehicle, boron (5 ppm as boric acid), E2 (30 microg/kg/d, sc), PTH (60 microg/kg/d, sc), or a combination of boron and E2 or PTH, respectively. The E2 treatment corrected many adverse effects of OVX on bone quality, increased bone Ca, P, and Mg contents, and decreased trabecular plate separation. Dietary boron supplementation had no effects on these bone parameters in OVX rats. When OVX rats were treated with boron and E2 together, trabecular bone volume (Tb.BS/TV) and plate density were increased significantly more than that caused by E2 alone. The boron and E2 combination also increased trabecular bone surface (Tb.BV/TV) and decreased trabecular plate separation in OVX rats. In contrast, whereas daily PTH injection also increased bone Ca, Mg, and P contents, Tb.BV/TV, Tb.BS/TV, trabecular plate density and thickness, and decreased trabecular plate separation in OVX rats, the combination of boron and PTH had no additional improvement in bone quality over that achieved by PTH alone. In summary, this study shows for the first time that boron enhanced the action of E2, but not that of PTH, to improve trabecular bone quality in OVX rats.

Dietary boron supplementation enhances the effects of estrogen on bone mineral balance in ovariectomized rats.

The present study investigated whether boron would enhance the action of 17beta-estradiol (E2) or parathyroid hormone (PTH) on bone mineral balance in ovariectomized (OVX) rats. Forty-three days after OVX, the rats were treated for 5 wk with vehicle, boron (5 ppm as boric acid), E2 (30 microg/kg/d, sc), PTH (60 microg/kg/d, sc), or a combination of boron and E2 or PTH. Bone mineral balance was assessed by measuring apparent absorption, excretion, and retention of calcium (Ca), phosphorus (P), and magnesium (Mg). Serum Ca, P, Mg, and osteocalcin were also measured in this experiment. Boron alone had no effects on food consumption, weight gain, bone mineral balance, and serum levels of Ca, P, Mg, and osteocalcin. E2 alone increased serum P and Mg and decreased serum osteocalcin, but it had no effect on bone mineral balance. The combination of boron and E2 markedly improved apparent absorption of Ca, P, and Mg. In addition, the combination treatment increased the apparent retention of Ca and Mg (but not P) and also increased serum Ca and Mg but not serum P. On the other hand, boron cotreatment did not prevent the E2-induced reduction in serum osteocalcin in OVX rats. PTH alone significantly increased serum Ca, P, Mg, and osteocalcin concentrations, although it had no effect on bone mineral balance. Contrary to the boron-E2 combination treatment, the combination of boron and PTH did not enhance bone mineral balance. However, inasmuch as boron-PTH cotreatment did not enhance the stimulatory action of PTH on serum Ca, P, and osteocalcin, boron completely abolished the stimulatory effect of PTH on serum Mg. In conclusion, we have demonstrated for the first time that although boron by itself has no effect on bone mineral homeostasis, it appears to have synergistic enhancing effects on the action of E2 on Ca and Mg homeostasis in OVX rats.

Maintenance requirements for dietary protein in 11- and 18-month-old male rats.

Body weight, lean body mass (total weight less body fat), carcass protein, and serum protein were examined as potential parameters by which to assess the effect of age on protein requirements for maintenance in male rats, aged 11 months and 18 months, fed diets containing 1.53, 3.41, 4.98, 6.52, or 8.05% dietary protein, casein plus methionine, for a 5-week period. Body weight change was maintained in older animals at 6.52% dietary protein and in younger animals at 4.98% dietary protein. Older animals consuming the two diets highest in protein had a greater percent body fat and less percent body protein than younger animals. Significant effects of diet and the interaction of diet and age on serum protein were also observed. As dietary protein level increased, serum protein increased gradually in younger rats, but only between 3.41 and 4.98% dietary protein in older rats. Lean body mass and total carcass protein increased as dietary protein level increased, but there were no significant differences due to age or the interaction of diet and age. Changes in body weight indicate a greater protein requirement for 18-month-old rats compared with 11-month-old rats, although complicated by greater food intake and fat deposits in older animals. Measures of body protein indicate that age has some influence on protein needs for maintenance purposes.

Diet, hormonal, and metabolic factors affecting bone mineral density in adolescent amenorrheic and eumenorrheic female runners.

Seven adolescent female runners with secondary amenorrhea and six adolescent eumenorrheic female runners received dietary supplements of 1200 mg calcium carbonate and 400 IU vitamin D/d for 12 months. Bone mineral density (BMD) of the axial skeleton was measured by dual photon densitometry at the beginning and end of the 12 month period. Plasma estradiol and ionized calcium concentration were also determined. Bone mineral density decreased in two of the amenorrheic subjects, with the lowest estradiol values concurrent with the severest training regimen and highest calcium intake. There was a significant decrease in plasma estradiol concentration in the amenorrheic runners (p less than 0.05). Plasma ionized calcium and estradiol explained 99% of the variation in BMD (r2 = 0.999). A significant inverse relationship between plasma estradiol and miles run/week was observed (r2 = -0.748). Adolescent female runners who train extensively and have low plasma estradiol levels may be adversely affecting BMD despite supplemental calcium and vitamin D intake.

Macronutrient content of a hypoenergy diet affects nitrogen retention and muscle function in weight lifters.

Weight lifters (WL) attempt to achieve a low body fat while maintaining fat free mass (FFM) and muscle function. Body composition and isometric muscular endurance were tested in 19 experienced male WL at the end of a weight maintenance and exercise routine standardization week. The subjects were assigned to either a control (C), moderate-protein (0.8 g.kg-1.d-1), high-carbohydrate hypoenergy diet (MP/HC), or high-protein (1.6 g.kg-1.d-1), moderate-carbohydrate hypoenergy diet (HP/MC). Both hypoenergy diets provided 75.3 kJ (18 kcal).kg-1.d-1. Apparent nitrogen balance (NBAL) was assessed using nitrogen in the diet, urine, and sweat. Body fat and FFM loss via hydrostatic weighing were not different between the hypoenergy groups. However, lean body mass (LBM) change as assessed by NBAL showed that the MP/HC group had an average negative NBAL of -3.19 g.d-1 while the HP/MC group had a positive NBAL of 4.13 g.d-1. Macronutrient mix did not affect biceps endurance, but quadriceps endurance declined for the HP/MC group during the experimental week. In conclusion, a hypoenergy diet providing twice the RDA for protein was more effective in retaining body protein in WL than a diet with higher carbohydrate but the RDA for protein. However, the lower carbohydrate of this diet contributed to reduced muscular endurance in these athletes.

Effect of dietary fat and cholesterol on plasma lipids and lipoprotein fractions in normolipidemic men.

In a controlled feeding situation, male subjects were assigned to one of four treatment groups: low fat (31% of total kcal)/low cholesterol (193 mg/d) (LFLC), low fat/usual cholesterol (504 mg/d) (LFUC), usual fat (46% of total kcal)/low cholesterol (UFLC) and usual fat/usual cholesterol (UFUC) intake. For the first 2 wk of the 10-wk study all subjects consumed the UFUC diet. Subjects consumed experimental diets during wk 3-7 and resumed their customary intake during wk 8-10. Plasma total, high-density-lipoprotein (HDL), low-density-lipoprotein and very-low-density-lipoprotein cholesterol and triglycerides were determined weekly. A significant effect (P less than 0.05) of dietary fat on plasma total and HDL cholesterol was observed between the end of wk 2 and 7. Low fat intake resulted in 17 +/- 2 mg/dL lower total cholesterol and 10 +/- 1 mg/dL lower HDL cholesterol than the usual fat intake. Plasma lipids were not affected either by dietary cholesterol or by any interaction of dietary fat with cholesterol.

Zinc and copper retention during pregnancy: the adequacy of prenatal diets with and without dietary supplementation.

Twenty-four pregnant women, in their second trimester, participated in two seven-day metabolic experiments to evaluate zinc and copper utilization from self-selected diets, with or without supplementation. Recommended dietary allowances for zinc or suggested intakes for copper were not met unless supplements of these nutrients were consumed. Zinc retentions in the unsupplemented group were 1.9 and 0.3 mg/day during the first and second metabolic periods, respectively. Zinc retentions in the supplemented group were 2.3 and 4.7 mg/day during the same two periods. Intakes above 8 mg/day resulted in positive retentions. Based on individual variation, however, intakes of 20 mg/day, the current RDA, would not be excessive although possibly some level between these two extremes would be adequate. Copper retentions in the unsupplemented and supplemented groups combined over the two balance periods were -0.02 and 0.89 mg/day, respectively. Adequate copper retention does not appear possible without the use of a supplement.

Yields and nutrient content of selected fresh fruits.

Proximate composition, edible yields, and selected nutrients were measured in cantaloupe, cherries, grapes, nectarines, plums, and watermelon sampled in six major U.S. markets. Yields were lowest (about 55%) for the melons, but were much higher (about 90% or above) for other fruits. Fruits were high in moisture, low in protein, fat, and energy. The estimated carbohydrate content ranged from about 8% for the melons to 17% for cherries. Vitamins A and C were present in moderate concentrations, but fruits were found to be low in vitamin B-6, folic acid, and pantothenic acid, as well as in the mineral elements.

Erythrocyte and dietary zinc in adolescent females.

Erythrocyte zinc has been suggested as an index of zinc status. This study was undertaken to investigate the possible relationships of erythrocyte zinc concentration to age, physical maturity, and zinc intake of teenage girls of two races. Dietary zinc was calculated from two 1-day food recalls, and erythrocyte zinc was determined for over three hundred 12-, 14- and 16-yr-old girls in Oklahoma and Virginia. Erythrocyte zinc concentration increased and the intake of zinc from the diet decreased after attainment of menarche. Among girls of the same menarcheal state, age was not related to zinc intake, but concentration of zinc in erythrocytes increased with each 2-yr age increment in those that were past menarche. Results did not show a direct relationship of erythrocyte zinc values to calculated intakes of zinc by adolescent females. Black and white races did not differ in either zinc intake or red cell zinc content.

Evaluating upper arm anthropometric measurements.

Jelliffe's standards for evaluating measurements of mid-upper arm circumference, triceps skinfold thickness, and mid-upper arm muscle circumference of American adults were compared with percentile distributions developed from the first Health and Nutrition Examination Survey (NHANES I). These comparisons show that the standards poorly represent the adult U.S. population. Replacement of the standards with updated sex-specific values is not recommended, as (a) no single value for each arm parameter can be considered as "normal" for men or women of all ages and (b) the expression of arm measurements as percentages of standards is an inappropriate method of evaluation. Instead, measurements should be evaluated by comparison with age- and sex-specific percentile distributions developed from the NHANES I.

Effects of short-term aerobic conditioning and high cholesterol feeding on plasma total and lipoprotein cholesterol levels in sedentary young men.

The plasma total cholesterol (TC) and lipoprotein cholesterol concentrations of sedentary young men (n = 23) were determined during 4 wk of controlled feeding and 6 wk of supervised aerobic conditioning. Subjects were assigned to dietary treatments of 400 mg cholesterol per day (M) or 1400 mg cholesterol per day (H); both diets had a P/S ratio of about 0.6. Dietary groups M and H were subdivided into exercise (MX and HX) and sedentary (MS and HS) groups. Compared to the sedentary groups, MX and HX exhibited significant (p less than 0.01) improvements in cardiorespiratory fitness. After 2 and 4 wk of high cholesterol feeding, group HS exhibited significant (p less than 0.05) elevations in TC (+30 +/- 7 and +32 +/- 9 mg/dl) with nonsignificant increases in very low-density lipoprotein cholesterol and low-density lipoprotein cholesterol. Group HX exhibited consistent weekly increases in high-density lipoprotein cholesterol (HDL-C) (from 46 +/- 3 mg/dl, the base level, to 53 +/- 4 mg/dl at wk 4) with aerobic conditioning. By combining exercise and sedentary group data at each level of dietary cholesterol it was shown that TC and HDL-C levels significantly (p less than 0.05) increased by the 4th wk of high cholesterol feeding. The TC/HDL-C ratio significantly (p less than 0.05) increased for the sedentary subjects as compared to all the exercising subjects by wk 4 of controlled feeding.

Effect of dietary zinc and protein levels on the utilization of zinc and copper by adult females.

Zinc and copper utilization were examined in twenty-three young adult females fed either a moderate protein, low zinc diet, a high protein, low zinc diet, a moderate protein, high zinc diet, or a high protein, high zinc diet during a 24-day metabolic balance study. The moderate and high protein diets contained 7.9 g and 15.2 g nitrogen per day, respectively. The low and high levels of zinc were 9.5 or 10.1 and 18.4 or 19.9 mg daily. Copper intake was constant at approximately 2.0 mg/day. Urinary zinc excretion was significantly greater (P less than 0.05) in subjects consuming the high protein diets. Fecal zinc paralleled zinc intake but was not affected by protein intake. Apparent retention of zinc was not significantly different among dietary treatments ranging from -0.29 to 1.58 mg/day. Fecal excretion and apparent retention of copper were not affected by protein intake. Mean copper retentions ranged from 0.12 to 0.30 mg/day. Dietary zinc did not affect copper excretion or retention. Dietary protein, at levels commonly consumed by a substantial portion of the American adult female population, did not affect zinc and copper utilization. Individuals were not consistently in positive balance although average retentions were generally positive.

Effect of coarse wheat bran fiber and exercise on plasma lipids and lipoproteins in moderately overweight men.

The effects of the American Association of Cereal Chemists coarse wheat bran fiber and exercise were evaluated in 20 males, aged 24 to 35 yr, and at least 10% above ideal weight. Thirteen of the subjects participated in a 4 mile walk-jog run program 3 times weekly. In a cross-over design with diets switched midway through the experiment, both the exercising and sedentary groups consumed isocaloric amounts of either white bread or white bread containing wheat bran (0.5 g/kg body weight). Plasma total and lipoprotein cholesterol and triglycerides, body weights, and percentage body fats were determined at 0, 6, and 12 wk. No consistent effects were observed as a result of the wheat bran feeding on any of the parameters measured. Exercise training tended to decrease body weights and percentage body fats, and was associated with significantly increased (p less than 0.05) plasma high-density lipoprotein cholesterol levels and high-density lipoprotein cholesterol to low-density lipoprotein cholesterol ratios. After a rise in triglycerides at wk 6, a significant decline (p less than 0.05) back to base-line values was observed at wk 12 for the exercised subjects.

Hepatic gluconeogenic enzymes, plasma insulin and glucagon response to magnesium deficiency and fasting.

Three experiments were conducted to assess the effects of magnesium deficiency on the activities of hepatic glucose-6-phosphatase (G6Pase), fructose 1,6-bisphosphatase (FDPase) and phosphoenolpyruvate carboxykinase (PEPCK). Experiment 1 was designed to determine if magnesium deficiency interfered with the gluconeogenic response to fasting. Rats were fed either a control (C) or magnesium-deficient (MD) diet for 12 days. One-half of each group of rats was fasted for 24 hours prior to death. Hepatic enzyme activities, plasma and liver magnesium, and whole blood glucose were measured. Activities of G6Pase and PEPCK were higher in fasted group C rats compared to fed group C rats. Activity of FDPase was lower. The response was similar in the MD groups. Comparison of C and MD groups indicated that magnesium deficiency was accompanied by an increase in PEPCK activity. To verify this result and to investigate the role of anorexia in producing increased PEPCK activity, experiment 2 included a pair-fed group (PF). The results indicated that anorexia was not responsible for increased PEPCK activity in MD rats. The relation of circulating insulin and glucagon concentrations to effects of magnesium deficiency was explored in experiment 3. A decreased insulin:glucagon ratio was observed in MD rats. The results of these experiments suggest that magnesium deficiency alters PEPCK activity by affecting secretion of pancreatic hormones.

Copper and zinc utilization in elderly adults.

Elderly adults were provided with 2.33 mg of copper and either 7.80 or 23.26 mg of zinc daily during a 30-day metabolic study. Excretions of both minerals were measured throughout the study. The subjects were able to maintain apparent positive balance for copper, but were in negative balance for zinc on both levels off intake. Copper retention was significantly reduced by intake of the higher amount of zinc. These results support other reports indicating antagonism between the two nutrients. The hair content of zinc and copper was higher in females than in males and was in the ranges indicative of long-term adequate intakes. Recumbent length was significantly greater than standing height and should be investigated further as a more accurate measure of body height in the elderly.

Carcass nitrogen as a predictor of protein requirement for mature female rats.

The minimal level of dietary protein required for maintenance of nitrogen equilibrium was investigated using Sprague-Dawley rats, 12 months of age. Rats were fed casein, supplemented with methionine, at levels ranging from 0.84 to 5.18% of the diet for 4, 8 or 12 weeks and were compared to a control group fed a similar diet containing 9.90% protein or to a baseline group fed a stock diet. The effect of dietary protein levels on total serum protein and on liver and carcass composition was assessed. Protein requirement levels with 95% confidence intervals were predicted by linear regression. Dietary protein levels of 2.14% or lower were not adequate to maintain body weight and serum protein levels, and animals fed these diets had elevated levels of liver lipid. Protein nutriture of rats fed 3.20% protein was generally intermediate between those fed 2.14% or less and those fed 3.62% or greater. Compared to carcass nitrogen, carcass water was not as reliable a parameter for determination of protein requirements. Using the baseline group for comparison and carcass nitrogen as the dependent variable, a dietary protein requirement was predicted for these animals of 3.91--4.19% with confidence intervals of 3.50--4.56% and 3.13--5.48%, respectively. This level is comparable to the maintenance protein requirement of 4% indicated by the National Research Council for adult rats.