Effect of reduced dietary intake on energy expenditure, protein turnover, and glucose cycling in man.

The effect of a 50% reduction in food intake on energy expenditure, protein metabolism, glucose cycling, and body composition was investigated in eight moderately overweight men. The prestudy mean calorie and protein intake was determined for eight subjects. They were then maintained on this diet for 6 weeks (mean +/- SEM, 3,269 +/- 75 kcal/d, 20.0 +/- 0.5 g N/d, period I), after which the diet was reduced uniformly in the major foodstuffs by 50% for the next 4 weeks (1,555 +/- 38 kcal/d, 9.6 +/- 5 g N/d, period II). At the end of each period we measured (1) body fat and fat free mass by underwater weighing, (2) 24-hour energy expenditure by indirect calorimetry in a calorimeter, (3) whole body protein synthesis and breakdown rates with 15N glycine, and (4) glucose cycling between glucose and glucose-6-phosphate and fructose cycling between fructose-6-phosphate and fructose-1,6 bisphosphate with 6,6-D2- and 2-D1-labeled glucose. The results were subjects lost 4.0 +/- 0.1 kg fat (by underwater weighing) during the 4 weeks on the reduced-energy regimen. Protein turnover and glucose cycling were reduced by 20% and 15%, respectively. Twenty-four-hour energy expenditure was 2,553 +/- 166 kcal/d for period I and 2,369 +/- 69 kcal/d for period II, giving a difference of 184 +/- 34 kcal/d between the two periods. In conclusion, (1) although energy intake was reduced by 50%, the decrease in energy expenditure was small due to the buffering effect of body fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy-intake restriction and diet-composition effects on energy expenditure in men.

Eight men were fed at maintenance for 2 wk, followed by 4 wk at 50% of maintenance, then 1 wk at maintenance. The diets were formulated to contain either 40% or 20% of energy from fat. Daily energy expenditure (24-h EE) was determined by indirect calorimetry at the end of the 2-wk maintenance period; on days 1, 7, and 28 of reduced energy intake; and on days 1 and 7 of refeeding. During the reduced-energy period, body weight decreased from 96.6 to 91.5 kg and body fat decreased from 30.4% to 27.7%. There were no significant differences in 24-h EE or energy requirements per unit body weight due to diet composition or weight loss. Maintenance metabolizable-energy (ME) requirement averaged 31.0 kcal/kg body wt. Overall, the efficiency of ME use relative to body stores was 0.87 and was greater for high-fat than for low-fat diets. There was some evidence of an increase in the efficiency of energy use of body stores after weight loss. Substrate use reflected diet composition and energy-balance status independent of changes in body composition.

Sensitivity of methods for calculating energy expenditure by use of doubly labeled water.

Attempts to estimate human energy expenditure by use of doubly labeled water have produced three methods currently used for calculating carbon dioxide production from isotope disappearance data: 1) the two-point method, 2) the regression method, and 3) the integration method. An ideal data set was used to determine the error produced in the calculated energy expenditure for each method when specific variables were perturbed. The analysis indicates that some of the calculation methods are more susceptible to perturbations in certain variables than others. Results from an experiment on one adult human subject are used to illustrate the potential for error in actual data. Samples of second void urine, 24-h urine, and breath collected every other day for 21 days are used to calculate the average daily energy expenditure by three calculation methods. The difference between calculated energy expenditure and metabolizable energy on a weight-maintenance diet is used to estimate the error associated with the doubly labeled water method.

Bioavailability of lysine in selected foods by rat growth assay.

Lysine bioavailabilities in reference protein and 16 test protein diets were estimated using 10 day rat growth assays. A standard growth curve was obtained by feeding 5 diets containing casein, zein and synthetic amino acids ranging in total lysine concentration from 0.3 to 0.7%. Experimental foods were added to the basal diet at the expense of zein and/or synthetic amino acids to provide 2 specific lysine concentrations, i.e., 0.4 and 0.6%. Availabilities were established by comparing growth responses from the test food diets to the regression line of the standard growth data. Availabilities were over 88% for 13 of 16 products. Utilization was poor in pinto beans (73%), rice-wheat gluten cereal (70%), and skim milk powder heated to 100 degrees C for 12 h (66%). Addition of excess lysine (700 mg/100 g diet) to the pinto bean diet did not improve growth response; thus poor digestibility or some unidentified growth inhibitor is indicated.

The use of Streptococcus zymogenes for estimating tryptophan and methionine bioavailability in 17 foods.

As part of a cooperative study assessing amino acid bioavailability and/or protein quality, the provisional method of Boyne et al. (Brit J Nutr 21: 181-206) was used to assay 17 protein sources for methionine and tryptophan availability with S. zymogenes. Pronase was used as the predigesting enzyme. Product composition was found to affect reproducibility. The microbial assay results correlated positively with results from rat growth studies on the same foods (p = 0.05), and were generally accurate in identifying products of lower protein quality. Defatting four high-fat products increased microbial values in the methionine assay, but only the chicken franks and the sausage values in the tryptophan assay. Heating non-fat milk increased methionine values slightly. Low values for rolled oats were further reduced by finer grinding.

A collaborative study of methods of protein evaluation: introductory paper.

The USDA's collaborative study of methods of protein quality evaluation is introduced. It was intended primarily to provide a basis for the evaluation of possibly improved procedures for the labelling of foods as a source of dietary protein. In general, the usefulness of in vitro digestibility procedures has been confirmed, but problems remained for the in vitro evaluation of heat-damaged materials and of some types of pinto beans.

Rat bioassays for methionine availability in 16 food sources.

Methionine availabilities of 16 test proteins were assessed by comparing ten day rat growth response to the test diets and reference (casein) diets. In a preliminary study, various concentrations of methionine and cystine were fed to determine methionine requirements and effect of excess cystine. Results indicated a methionine requirement of about 550 mg per 100 g diet. Cystine had a sparing affect of 50-55%, i.e., about 300 mg could be used to meet methionine requirements. Further additions of cystine (up to 2.6 times methionine) did not affect rat growth. Methionine availabilities were excellent (88-100%) for 15 of the 16 test foods; only pinto beans (58%) were low, but prior evidence indicates that the poor growth response was due to some factor other than availability.

Bioavailability of tryptophan in selected foods by rat growth assay.

Tryptophan bioavailabilities were estimated in 16 protein sources using 10 day rat growth assays with casein as the reference protein. Growth responses of rats fed test food diets were compared to growth responses of rats fed basal diets with graded levels of tryptophan ranging from 50 to 100 mg of tryptophan/100 g diet. Estimates of tryptophan availabilities were 85-100% for all products except whole wheat cereal (73%) and pinto beans (59%). Results of a previous study on lysine availability indicated that poor response to pinto beans was due either to poor digestibility or to the presence of some unidentified growth inhibitor.

Whole-body leucine and energy metabolism in adult women.

Whole-body leucine and energy metabolism were studied in seven women, in order to examine the relationship between changes in energy expenditure and rates of protein synthesis when moving from the fasted to the fed state. The diets provided 1.1 g protein/kg/d and calories (joules) to maintain body weight. Each subject received primed, continuous intravenous infusions of L-[1-13C]-leucine for a total of 9 h, and were studied fasted for the first 4 h. Small isotopically neutral meals were fed every half hour for the last 5 h. Energy expenditure by indirect calorimetry was simultaneously measured. Leucine flux, oxidation, utilization of leucine for protein synthesis, and energy expenditure increased with feeding. There were no statistically significant correlations between rates of protein synthesis calculated from leucine flux and energy expenditure in the fasted or the fed state. Significant correlations were mainly due to sex and feeding differences. These results agree with earlier published results. A maximal cost of protein synthesis, of 5.08 kcal (21.15 kJ)/g, was determined from changes in protein synthetic rates and energy expenditure in response to feeding.

Caloric and selected nutrient intakes and estimated energy expenditures for adult women: identification of non-sedentary women with lower energy intakes.

Dietary intakes and energy expenditures of healthy adult women were studied. Phase I (no. = 98): 37 women (38% of Phase one subjects) reported 3-day intakes of less than 1,600 kcal/day; low nutrient intakes were associated with less than 1,600 kcal/day for women who did not take supplements. Phase II (no. = 18): group mean energy expenditures assessed by activity diaries matched 7-day intake records for 8 women who had consumed greater than 1,800 kcal/day during Phase I but not for 10 women who had consumed less than 1,600 kcal/day during Phase I. Phase III: duplicate food composites and records supported previous intake records. The data from this study suggest that some non-sedentary women maintain consistently low energy/nutrient intakes and that calculation of energy expenditure from standard tables is not appropriate for those women.

Modification of sweet acidophilus milk to improve utilization by lactose-intolerant persons.

Enhanced digestion of yogurt by lactose-intolerant individuals is believed to be due to inherent beta-galactosidase (lactase) in the culture organisms that aids in the hydrolysis of ingested lactose. However, sweet acidophilus milk, which contains lactase-rich organisms, does not enhance lactose digestion. Using breath-hydrogen measurements to indicate malabsorption in 14 human subjects, we compared utilization of: milk, yogurt, heated yogurt, yogurt plus lactose, heated yogurt plus lactase, sweet acidophilus milk (SAM), and SAM made with sonicated cells. Results indicate that both the reduction of lactose during fermentation and the presence of indigenous bacterial lactase are responsible for the increased ability to tolerate lactose in yogurt. Improved utilization of SAM by sonication suggests that intracellular lactase is not available during digestion and that sonication releases the lactase activity from the cells.

Long-term consumption of beef extended with soy protein by men, women and children: II. Effects on iron status.

The iron status of men, women and children consuming beef extended with soy protein was evaluated by measuring serum ferritin and clinical parameters of iron status during a six-month study. Fifty-two families (245 participants) were randomly assigned to consume, for 180 days, 1 of 7 beef products: all beef, beef extended with either soy isolate, soy concentrate or soy flour (20% reconstituted soy product, 80% beef), or beef extended with each of the three soy products fortified with 60 mg Fe and 25 mg Zn/100 g protein. The beef product was consumed by the subjects as their principal source of protein for 1 meal a day (children 1-18 yr) or 1-2 meals a day (11 per week; adult men and women). A control group consumed their usual self-selected diets. No evidence was found that consumption of beef extended with soy protein deleteriously affected the iron status of men, women or children. Consumption of beef extended with soy protein, at the levels used in this study, by military men and women and by school lunch participants would not appear to impose a risk in these population groups.

Long-term consumption of beef extended with soy protein by men, women and children: I. Study design, nutrient intakes, and serum zinc levels.

The effect of long-term consumption, under practical conditions, of beef extended with soy protein on serum zinc levels of men, women and children was studied. Fifty-two families were randomly assigned to consume for 180 days 1 of 7 beef products: all beef, beef extended with either soy isolate, soy concentrate or soy flour (20% reconstituted soy product, 80% beef), or beef extended with each of the 3 soy products fortified with 60 mg Fe and 25 mg Zn/100 g protein. The beef product was consumed by the subjects as their principal source of protein for 1 meal a day (children 1-8 yrs) or 1-2 meals a day (11 per week) for adult men and women. A control group consumed their usual self-selected diet. Diet records (4-day) of all foods and beverages consumed by the subjects were obtained pre-study and 63 +/- 7 and 126 +/- 7 days for calculation of nutrient intakes. No deleterious effects were found on the serum zinc levels when subjects consumed beef extended with soy protein for 180 days.

Long-term consumption of beef extended with soy protein by children, women and men: III. Iron absorption by adult men.

Forty-nine ostensibly healthy men consumed either patties of all-beef or beef extended with soy-isolate, -concentrate or -flour as the principal protein source in 1 to 2 meals daily for 180 days. Iron status was monitored by absorption of radioiron from a reference dose of ferrous ascorbate and by serum ferritin concentration. In addition, nonheme iron absorption from a test meal of the respective beef pattie consumed for the 180 days was estimated by the extrinsic tag procedure. There was no detrimental effect on iron stores as indexed by reference ferrous ascorbate absorption or serum ferritin concentration. Absorption of nonheme iron from the test meals was low except for individuals having indices of low iron stores. When adjusted for the effect of level of iron stores the relative absorption of nonheme iron from soy-isolate and -flour containing meals was greater than from the all-beef meal, indicating marked differences in the effect on iron absorption by different soy products. Consumption of soy-extended beef should have no detrimental effect on iron status of adult men if consumed in mixed diets at the level used in this study.

Metabolizable energy of human mixed diets.

Nine subjects (four women and five men) consumed the energy required to maintain body weight for 3 weeks (control) and 1000 kcal per day less than the energy required to maintain body weight for 6 weeks (undereating). Ordinary foods were used to provide a mixed diet which was standardized as to composition and analysed by bomb calorimetry and by proximate analysis. During the third week of the control period and the third and sixth weeks of the undereating period, food, faecal and urine samples were collected for calculations of the metabolizable energy of the diets. The mean coefficients of availability of the three energy nutrients were lower than predicted by the Atwater method, between 83.8 and 88.3 for protein, between 91.6 and 93.2 for fat and between 92.5 and 94.7 for carbohydrates. The calorie to nitrogen ratio of the urine of these subjects during the balance periods varied from 4.96 to 19.05. The metabolizable energy of these mixed diets was 12 to 24 per cent less than the energy calculated from US food tables. Formulas proposed to calculate the metabolizable energy of diets differed from our analysed metabolizable energies by 6.4 per cent (Miller & Payne, 1959), 6.8 per cent (Southgate, 1975) and 0.7 per cent (Miller & Judd, 1984).

Effect of food supplementation (WIC) during pregnancy on birth weight.

Of 824 women screened, 410 were enrolled at midpregnancy in a prospective, randomized, controlled nutrition intervention study. Of these, 226 were predicted as likely to have small or large babies, 184 to have average-sized babies. Two hundred thirty eight mothers received USDA Women, Infants and Children (WIC) Food Supplementation vouchers from midpregnancy, 172 did not. Leukocyte protein synthesis (as a cell model) was significantly higher (p = 0.009) by 36 weeks gestation in supplemented mothers. Mean birth weight of their babies was greater, 3254 vs 3163 g, (+91 g) p = 0.039, adjusted for sex, gestational age, prenatal visits, pregnancy interval, smoking, and previous low birth weight infants. Controlling for entry weight obviated the significance of the difference, except for WIC supplemented smokers (greater than 10 cigarettes/day) whose babies were significantly heavier by +168 g (p = 0.017) than those of unsupplemented smokers. WIC partially protects fetal growth in smokers.

PIP: Low birth weight and small for gestational age (SGA) babies demonstrate a greater incidence of cogenital malformation, perinatal death or morbidity, imparied postnatal growth, and neurologic disabilities. Consequently, studies have been designed to increase birth weight. These studies indicate that supplementation during both the 2nd period of most rapid fetal growth and 3rd trimesters have the greatest effect in increasing birth weight. Subjects were 824 women attending the prenatal clinics at the Oklahoma Memorial Hospital (OMH). Of the 824 women screened, 410 were enrolled at midpregnancy in a prosepctive, randomized, controlled nutrition intervention study. Of these, 226 were predicted as likely to have small or large babies, 184 to have average-sized babies. 238 mothers received USDA Women, Infants and Children (WIC) Food Supplementation vouchers from midpregnancy; 172 did not. WIC vouchers were for supplements of milk, eggs, and cheese and were intended to provide 40-50 g of protein and 900-1000 kcal daily. These were intended to augment the NRC Recommended Dietary Allowances for pregnancy and add to the regular diet of 1.1 g protein/kg/d and 28 kcal/kg/d. Leukocyte protein synthesis (as a cell model) was significantly higher (p=0.009) by 36 weeks gestation in supplemented mothers. By this time, a reduction in plasma alanine and B-globulin levels became evident. Mean birth weight of their babies was greater, 3254 vs 3163 g, (+91g) p=0.039, adjusted for sex, gestational age, prenatal visits, pregnancy interval, smoking, and previous low birth weight infants. Controlling for entry weight obviated the significance of the difference, except for WIC supplemented smokers (10 cigarettes/day) whose babies were significantly heavier by +168 g (p=0.017) than those of unsupplemented smokers. WIC partially protects fetal growth in smokers.

A new approach for the estimation of body composition: infrared interactance.

A new method for the estimation of body composition in humans, called infrared interactance, is discussed. Infrared interactance is based on the principles of light absorption, reflection, and near-infrared spectroscopy. Body composition (percentage fat) was estimated in 53 adults (23 to 65 yr of age) by infrared interactance and compared to results from deuterium oxide dilution (r = 0.94), skinfold (r = 0.90), and ultrasound (r = 0.89) measurements. The method is safe, noninvasive, rapid, easy to use, and may prove useful to predict percentage body fat, especially in the obese.

Calorie and protein intake and balance of men and women consuming self-selected diets.

The calorie and protein intakes of 16 women and 13 men consuming self-selected diets over a 1-yr period were determined. During four 7-day balance periods, corresponding to the four seasons of the year, duplicates of diets consumed and urine and feces excreted were collected for analysis and calculations of available energy and nitrogen balance. During the four balance periods, the food intakes and thus the calorie and protein intake of the subjects decreased as documented by 7-day food records immediately before and after the balance periods. This unexpected decrease in food consumption made the nitrogen (N) balance results difficult to interpret. The energy digestibility of these diets ranged from 87 to 98% (mean +/- SD, 93.7 +/- 2.3). The nitrogen digestibility of the diets ranged from 80 to 96% (mean +/- SD, 88.6 +/- 3.4). The analyzed calorie values (heats of combustion) of the diet composites were approximately the same as calorie values of these diets calculated from diet records using food tables. This is surprising since calorie values in food tables are available energies which have been corrected by a coefficient of availability.