Habitual sleep duration and sleep duration variation are independently associated with body mass index.

BACKGROUND: Sleep plays a vital role in maintaining homeostasis and promoting health. Previous studies show that shorter sleep duration is associated with elevated body mass index (BMI) and other cardiovascular risk factors. The goal of this study was to investigate the effects of habitual sleep duration and nightly sleep duration variation based on daily device-recorded data on BMI and obesity-related biomarkers. METHODS: In all, 748 individuals (50.6% females, 85.4% European-Americans, average age: 49.7 years old) participated in a commercial lifestyle coaching program beginning in July 2015. Daily sleep data were recorded by Fitbit Charge HR wristbands. Clinical laboratory blood tests were measured up to three times over a 12-month period. Linear regression models were used for cross-sectional analyses, and generalized estimating equations for longitudinal analyses. All models were adjusted for age, sex, geographic location, season, genetic ancestry inferred from whole genome sequencing data, and BMI (if applicable). Multiple testing issues were corrected by false discovery rate. RESULTS: We calculated habitual sleep duration and nightly sleep duration variation. In general, females slept 15-min longer on average than males. A negative correlation was found between habitual sleep duration and BMI (ß=-1.12, standard error=0.25, P<0.001). Moreover, we identified a positive correlation between sleep duration variation and BMI (ß=2.97, standard error=0.79, P<0.001) while controlling for sleep duration, indicating that larger sleep duration variation is significantly and independently associated with increased BMI. CONCLUSIONS: We explored the impact of habitual sleep duration and sleep duration variation, and identified that shorter habitual sleep duration and larger duration variation were independently associated with increased BMI.

Sex differences in obesity and the regulation of energy homeostasis.

Obesity prevalence is generally higher in women than in men, and there is also a sex difference in body fat distribution. Sex differences in obesity can be explained in part by the influence of gonadal steroids on body composition and appetite; however, behavioural, socio-cultural and chromosomal factors may also play a role. This review, which evolved from the 2008 Stock Conference on sex differences in obesity, summarizes current research and recommendations related to hormonal and neuroendocrine influences on energy balance and fat distribution. A number of important gaps in the research are identified, including a need for more studies on chromosomal sex effects on energy balance, the role of socio-cultural (i.e. gender) factors in obesity and the potential deleterious effects of high-fat diets during pregnancy on the foetus. Furthermore, there is a paucity of clinical trials examining sex-specific approaches and outcomes of obesity treatment (lifestyle-based or pharmacological), and research is urgently needed to determine whether current weight loss programmes, largely developed and tested on women, are appropriate for men. Last, it is important that both animal and clinical research on obesity be designed and analysed in such a way that data can be separately examined in both men and women.

Increased visceral fat and decreased energy expenditure during the menopausal transition.

OBJECTIVE: This study assessed longitudinal changes in body composition, fat distribution and energy balance in perimenopausal women. We hypothesized that total fat and abdominal body fat would increase at menopause due to decreased energy expenditure (EE) and declining estrogen, respectively. DESIGN: Observational, longitudinal study with annual measurements for 4 years. SUBJECTS: Healthy women (103 Caucasian; 53 African-American), initially premenopausal. During follow-up, lack of menstruation for 1 year and follicle-stimulating hormone >30 mIU ml(-1) defined a subject as postmenopausal. MEASUREMENTS: Fat and lean mass (dual-energy X-ray absorptiometry), visceral (VAT) and subcutaneous abdominal fat (SAT) (computed tomography), dietary intake (4-day food record), serum sex hormones and physical activity (tri-axial accelerometry). Twenty-four hour EE was measured by whole-room calorimeter in a subset of 34 women at baseline and at year 4. RESULTS: Body fat and weight increased significantly over time only in those women who became postmenopausal by year 4 (n=51). All women gained SAT over time; however, only those who became postmenopausal had a significant increase in VAT. The postmenopausal group also exhibited a significant decrease in serum estradiol. Physical activity decreased significantly 2 years before menopause and remained low. Dietary energy, protein, carbohydrate and fiber intake were significantly higher 3-4 years before the onset of menopause compared with menopause onset. Twenty-four hour EE and sleeping EE decreased significantly with age; however, the decrease in sleeping EE was 1.5-fold greater in women who became postmenopausal compared with premenopausal controls (-7.9 vs -5.3%). Fat oxidation decreased by 32% in women who became postmenopausal (P<0.05), but did not change in those who remained premenopausal. CONCLUSION: Middle-aged women gained SAT with age, whereas menopause per se was associated with an increase in total body fat and VAT. Menopause onset is associated with decreased EE and fat oxidation that can predispose to obesity if lifestyle changes are not made.

Consumption of a controlled low-fat diet containing olestra for 9 months improves health risk factors in conjunction with weight loss in obese men: the Ole' Study.

OBJECTIVE: To compare the effects of a standard American diet, a traditional low-fat diet, and a low-fat diet containing the fat substitute olestra on risk factors for heart disease and diabetes. DESIGN: A 9-month, double-blind, randomized, parallel-arm, feeding study comparing three diets: (1). control (33% fat), (2). fat-reduced (FR; 25% fat), and (3). fat-substituted (FS) where olestra replaced 1/3 of dietary fat (33% lipid and 25% digestible fat). Subjects were allowed to adjust their total energy intake as desired, allowing weight to fluctuate. SUBJECTS: A total of 37 healthy, obese men (age 36.7+/-1.3 y; body mass index 30.8+/-0.4 kg/m(2)). MEASUREMENTS: Body weight and composition by dual-energy X-ray absorptiometry, blood pressure, serum lipids, lipoproteins, hemostatic factors, glucose, insulin, and leptin at baseline and every 3 months. RESULTS: The FS group lost 6.27 kg of body weight by 9 months vs 4.0 kg in the control and 1.79 kg in the FR groups. There was a significant diet main effect on cholesterol (P=0.002), low-density lipoprotein cholesterol (P=0.003), and triglycerides (P=0.01), all of which decreased in the FS group but not the other groups by 9 months. Apolipoprotein B (ApoB) increased in the FR and control groups but was unchanged in the FS group (diet main effect P=0.04). High-density lipoprotein (HDL) cholesterol increased in all groups over 9 months (time main effect P=0.0001). Time main effects were also observed for cholesterol, ApoA1, ApoB, Factor VII, diastolic blood pressure, and glucose. After adjustment for % fat loss at 9 months, the effects of diet on change in risk factors remained significant only for triglycerides. DISCUSSION: Consumption of a low-fat diet containing olestra for 9 months produced significant improvement in cardiovascular risk factors, an effect largely explained by weight loss. Long-term low-fat diet consumption with or without olestra does not decrease HDL cholesterol.

Effects of feeding milk replacer once versus twice daily on glucose metabolism in Holstein and Jersey calves.

Eighteen Holstein (experiment 1) and 15 Jersey (experiment 2) heifer calves were fed milk replacer once or twice daily to determine effects of feeding frequency on weight gain, starter intake, and glucose metabolism. Body weights were measured weekly from birth to 8 wk. Blood samples were collected at wk 1 through 6 from all calves before and at 30, 60, 90, 120 and 180 min after the morning feeding. Plasma was analyzed for glucose, insulin, glucagon, and nonesterified fatty acids (NEFA). Urine was collected 90 min postfeeding to measure glucose concentration. Treatment did not affect mean starter intake or body weight. In experiments 1 and 2 mean plasma glucagon, glucose, NEFA, and insulin and urinary glucose concentrations were not affected by treatment. There was an interaction of sampling time and treatment for plasma insulin concentrations but not for glucose concentrations in both experiments. Following feeding, calves fed milk replacer once daily had higher insulin concentrations than those fed twice daily. There was an interaction of sampling time and treatment for plasma NEFA concentrations in Jersey calves only. Jersey calves fed milk replacer once daily had higher plasma NEFA concentrations before the morning milk replacer feeding. At wk 3 and 6, frequently sampled intravenous glucose tolerance tests were performed to assess glucose effectiveness, insulin sensitivity, and acute insulin response. In experiments 1 and 2 glucose effectiveness and insulin sensitivity were similar regardless of milk replacer feeding frequency. In Holstein and Jersey calves fed milk replacer twice daily, acute insulin response was greater than in calves fed once daily. However, insulin sensitivity decreased with age, while acute insulin response increased with age. These data suggest that feeding calves milk replacer once daily did not deleteriously affect performance or glucose metabolism regardless of breed.

The relation of gender, race and socioeconomic status to obesity and obesity comorbidities in a sample of US adults.

OBJECTIVE: To examine the obesity-related chronic diseases in the US adult population according to gender, race and socioeconomic status. METHODS: Data from the 1994-1996 Continuing Survey of Food Intakes by Individuals (1994-1996 CSFII) conducted by the US Department of Agriculture/Agricultural Research Service (USDA/ARS) were used in the analysis. Relevant data included self-reported weight and height, self-reported physician-diagnosed diabetes mellitus, hypertension, heart disease and high serum cholesterol. Analysis was conducted according to gender, race, income level and education level. RESULTS: There was a graded increase in diabetes, hypertension and high serum cholesterol with increasing body weight in nearly all gender, racial and socioeconomic groups. Among the obese individuals, the prevalence of hypertension was higher in black subjects and the prevalence of diabetes, hypertension and heart disease was higher in individuals with lower education compared to their counterparts. The odds of having diabetes, hypertension, heart disease and high serum cholesterol increased with increasing body weight after adjusting for age, gender, race, income, education and smoking. CONCLUSION: Although cross-sectional in nature, our results suggest that the disease burden associated with obesity in the population may be substantial. This burden increases with increasing severity of obesity. Our findings support the current opinion that, although the nature of obesity-related health risks is similar in all populations, the specific level of risk associated with a given level of obesity may be different depending on gender, race and socioeconomic condition.

Ethnic differences in dietary intakes, physical activity, and energy expenditure in middle-aged, premenopausal women: the Healthy Transitions Study.

BACKGROUND: Menopause is a time of increased risk of obesity in women. The effect of menopause in African American women, in whom obesity is already highly prevalent, is unknown. OBJECTIVE: We compared dietary intakes and energy expenditure (EE) between middle-aged, premenopausal African American and white women participating in a longitudinal study of the menopausal transition. DESIGN: Dietary intakes by food record, EE by triaxial accelerometer, physical activity by self-report, and body composition by dual-energy X-ray absorptiometry were compared in 97 white and 52 African American women. Twenty-four-hour and sleeping EE were measured by whole-room indirect calorimetry in 56 women. RESULTS: Sleeping EE (adjusted for lean and fat mass) was lower in African American than in white women (5749 +/- 155 compared with 6176 +/- 75 kJ/d; P = 0.02); however, there was no significant difference in 24-h EE between groups. Reported leisure activity over the course of a week was less in African American than in white women (556 +/- 155 compared with 1079 +/- 100 kJ/d; P = 0.02), as were the daily hours spent standing and climbing stairs. Dietary intakes of protein, fiber, calcium, magnesium, and several fatty acids were significantly less in African Americans, whereas there were no observed ethnic differences in intakes of fat or carbohydrate. Body fat within the whole group was positively correlated with total, saturated, and monounsaturated fat intakes and inversely associated with fiber and calcium intakes. Fiber was the strongest single predictor of fatness. CONCLUSION: Ethnic differences in EE and the intake of certain nutrients may influence the effect of menopausal transition on obesity in African American women.

Psychosocial variables associated with binge eating in obese males and females.

OBJECTIVE: This study tested a psychosocial model of binge eating symptoms in obese men and women. Predictor variables included depression, dietary restraint, self-esteem, weight cycling, history of teasing, body dissatisfaction, and neuroticism. METHOD: Participants (N = 808) completed a packet of self-report questionnaires. RESULTS: Weight cycling, teasing about weight and shape, body dissatisfaction, negative affect, and dietary restraint comprised the best fitting models (original and cross-validation) for binge eating in women and men. These variables explained 61-72% of the variance in symptoms of binge eating in the samples of men and 70% of the variance in the samples of women. Although the male and female models were mostly similar, notable differences between them were found. DISCUSSION: The variables that comprise these etiological models should be considered in the development of prevention programs for obese binge eaters. Longitudinal studies, however, are needed to examine these etiological paths and to test for causal relationships.

Comparison of regional fat distribution and health risk factors in middle-aged white and African American women: The Healthy Transitions Study.

OBJECTIVE: Both ethnicity and menopause appear to influence intra-abdominal fat distribution. This study evaluated intra-abdominal fat distribution and obesity-related health risks in perimenopausal white and African American women. RESEARCH METHODS AND PROCEDURES: Baseline data from a longitudinal study of changes in body composition and energy balance during menopause are reported. Healthy women (55 African Americans and 103 whites) who were on no medication and had at least five menstrual cycles in the previous 6 months were recruited. Body composition was assessed by DXA, and visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were assessed by computed tomography scan. SAT was divided into deep and superficial layers demarcated by the fascia superficialis. RESULTS: African American women were slightly younger (46.7 +/- 0.2 vs. 47.7 +/- 0.2 years, p = 0.002) and fatter (42.4% +/- 1.0% vs. 39.4% +/- 0.8% body fat, p = 0.02) than white women. In unadjusted data, African Americans had significantly more total abdominal fat and total, deep, and superficial SAT than whites. After adjustment for percent body fat and age, only total and superficial SAT remained significantly higher in African Americans. VAT, although slightly less in African American women, did not differ significantly by race. In multiple regression analysis, VAT was the strongest predictor of serum lipids, glucose, and insulin in women of both races, although superficial SAT was significantly associated with fasting glucose in whites. CONCLUSIONS: Middle-aged African American women have larger SAT depots, adjusted for total body fatness, but do not differ from white women with regard to VAT. The complexity of the relationship between abdominal fat and metabolic risk is increased by ethnic differences in such associations.

Contributions of total body fat, abdominal subcutaneous adipose tissue compartments, and visceral adipose tissue to the metabolic complications of obesity.

Obesity is related to the risk for developing non-insulin-dependent diabetes mellitus (NIDDM), hypertension, and cardiovascular disease. Visceral adipose tissue (VAT) has been proposed to mediate these relationships. Abdominal subcutaneous adipose tissue (SAT) is divided into 2 layers by a fascia, the fascia superficialis. Little is known about the radiologic anatomy or metabolic correlates of these depots. The objective of this study was to relate the amounts of VAT, SAT, deep subcutaneous abdominal adipose tissue (DSAT), and superficial subcutaneous abdominal adipose tissue (SSAT) to gender and the metabolic complications of obesity after adjusting for total body fat and to discuss the implications of these findings on the measurement of adipose tissue mass and adipose tissue function. The design was a cross-sectional database study set in a nutrition research center. Subjects included 199 volunteers participating in nutrition research protocols who also had computed tomography (CT) and dual energy x-ray absorptiometry (DEXA) measurement of body fat. The amount of DSAT was sexually dimorphic, with women having 51% of the subcutaneous abdominal fat in the deep layer versus 66% for men (P <.05). Abdominal fat compartments were compared with metabolic variables before and after adjusting for body fat measured by DEXA using 2 separate methods. The unadjusted correlation coefficients between the body fat measures, R(2), were largest for fasting insulin and triglyceride and smaller for high-density lipoprotein (HDL) cholesterol and blood pressure. A large portion of the variance of fasting insulin levels in both men and women was explained by total body fat. In both men and women, the addition of VAT and subcutaneous abdominal adipose tissue depots only slightly increased the R(2). In men, when body fat compartments were considered independently, DSAT explained a greater portion of the variance (R(2) =.528) in fasting insulin than VAT (R(2) =.374) or non-VAT, non-DSAT subcutaneous adipose tissue (R(2) =.375). These data suggest that total body fat is a major contributor to the metabolic sequelae of obesity, with specific fat depots, VAT, and DSAT also making significant contributions.

Influence of dietary carnitine in growing sheep fed diets containing non-protein nitrogen.

The influence of supplemental L-carnitine was investigated in growing sheep fed rations containing non-protein nitrogen (NPN). The experiment was conducted as a randomized block design with a 2x2 factorial arrangement of treatments. Lambs (77.4kg BW, n=24) were fed a total mixed ration (12.1-13.6% CP) with two levels of L-carnitine (0 or 250ppm) and two levels of NPN (urea contributing 0 or 50% of total dietary N) for a 50-day period. Jugular blood samples were collected at 0, 1, and 3h post-feeding, and ruminal fluid samples were collected at 1h post-feeding, during days 1, 8, 29, and 50 of the experiment. Average daily gain (121 versus 214g) was lower (P<0.0001) in lambs fed the NPN diets. Lambs consuming diets containing NPN had higher (P<0.0001) ruminal fluid pH (6.6 versus 5.9), ruminal ammonia N (4.8 versus 2.8mmol/l), and plasma ammonia N (177.1 versus 49.5µmol/l) than lambs not fed NPN. Additionally, lambs fed the NPN diets had lower plasma urea N (14.5 versus 17.5mmol/l; P<0.003) and thyroxine (T(4)) concentrations (65.8 versus 78.4ng/ml; P<0.02), and lower T(4):triiodothyronine (T(3)) ratio (37.9 versus 43.9; P<0.02). Plasma glucose concentrations were higher (P<0.05) in lambs fed L-carnitine (3.83 versus 3.70mmol/l). Two oral urea load tests (OULT 1 and OULT 2) were conducted during the 50-day trial. Urea solutions (0.835g/kg(0.75) BW) were administered as oral drenches. During the OULT 1 (day 10), plasma ammonia N and glucose concentrations were highest (P<0.0001) in the lambs fed NPN with L-carnitine compared with lambs fed control, L-carnitine, and NPN diets. During the OULT 2 (day 50), plasma ammonia N was highest (P<0.0001) in the NPN and NPN with L-carnitine groups compared with the control and L-carnitine groups. Plasma glucose was lowest (P<0.04) in the NPN with L-carnitine group compared with the NPN and L-carnitine groups, but did not differ (P>0.10) from the control group. Plasma urea N levels in both OULT 1 and OULT 2 were lower (P<0.0001) in the NPN and NPN with L-carnitine groups compared with the control and L-carnitine groups. In the present experiment, production and plasma criteria were affected by NPN incorporation in the diets. Production criteria were not affected by inclusion of L-carnitine in the diet, however, L-carnitine reduced experimentally induced hyperammonemia by day 50 of the trial.

Relationship of dietary fat and serum cholesterol ester and phospholipid fatty acids to markers of insulin resistance in men and women with a range of glucose tolerance.

High-fat diets are associated with insulin resistance, however, this effect may vary depending on the type of fat consumed. The purpose of this study was to determine the relationship between intakes of specific dietary fatty acids (assessed by 3-day diet records and fatty acid composition of serum cholesterol esters [CEs] and phospholipids [PLs]) and glucose and insulin concentrations during an oral glucose tolerance test (OGTT). Nineteen men and 19 women completed the study. Nine subjects had type 2 diabetes or impaired glucose tolerance. Fasting insulin correlated with reported intakes of total fat (r = .50, P < .01), monounsaturated fat (r = .44, P < .01), and saturated fat (r = .49, P < .01), but not with trans fatty acid intake (r = .11, not significant [NS]). Fasting glucose also correlated with total (r = .39, P < .05) and monounsaturated fat intakes (r = .37, P < .05). In multivariate analysis, both total and saturated fat intake were strong single predictors of fasting insulin (R2 approximately .25), and a model combining dietary and anthropometric measures accounted for 47% of the variance in fasting insulin. Significant relationships were observed between fasting insulin and the serum CE enrichments of myristic (C14:0), palmitoleic (C16:1), and dihomo-gamma-linolenic (C20:3n-6) acids. In multivariate analysis, a model containing CE 14:0 and percent body fat explained 45% of the variance in fasting insulin, and C14:0 and age explained 30% of the variance in fasting glucose. PL C20:3n-6 explained 30% of the variance in fasting insulin, and a model including PL C18:1n-11 cis, C20:3n-6, age and body fat had an R2 of .58. In conclusion, self-reported intake of saturated and monounsaturated fats, but not trans fatty acids, are associated with markers of insulin resistance. Furthermore, enhancement of dihomo-gamma-linolenic and myristic acids in serum CE and PL, presumably markers for dietary intake, predicted insulin resistance.

Effects of dietary inclusion of chromium propionate and calcium propionate on glucose disposal and gastrointestinal development in dairy calves.

In experiment 1, 21 male Holstein calves (43.9 kg) were fed only milk replacer at 1.4% of their body weight as dry matter for 6 wk. Dietary treatments included a commercial milk replacer (22% protein, 15% fat) containing (dry basis) either 6.4% Ca propionate or 6.4% dextrose (control) and either 0 or 0.5 mg/kg of supplemental Cr as Cr propionate. Neither Cr nor Ca propionate affected body weight gain; however, Ca propionate tended to increase the growth of the entire foregut measured after slaughter at 6 wk of age. A Minimal Model glucose tolerance test indicated that insulin sensitivity was not affected by treatment. However, calves fed Cr had higher glucose disappearance indexes than controls when propionate was not fed (0.013 vs. 0.019 units) but similar clearance when propionate was included (0.018 vs. 0.018 units, Cr x P interaction). The area under the glucose response curves after propionate-loading tests was much greater for calves fed the Cr versus control replacer when propionate was not present; however, when propionate was included, the response was less dramatic. In experiment 2, 25 Holstein calves were used to study performance and metabolic responses when milk replacer, and then postweaning starter, were supplemented with 0.5 mg/kg of Cr as Cr propionate. The metabolic responses of these calves were not affected by treatment. Overall, combined data suggested that supplemental Cr may improve glucose effectiveness; however, these responses seemed to be attenuated by supplemental propionate.

Common apolipoprotein A-IV variants are associated with differences in body mass index levels and percentage body fat.

OBJECTIVE: To determine the relationship between two common apoA-IV variants (Thr347-->Ser; Gln360-->His), and body mass index (BMI) and percentage body fat. DESIGN: Cross-sectional study. SUBJECTS: Eight-hundred and forty-eight subjects screened for participation in ongoing clinical studies. MEASUREMENTS: ApoA-IV genotype, body mass index, waist-to-hip ratio and percentage body fat by bioelectric impedance. RESULTS: Participants had an average age of 41+/-12 y and an average BMI of 28.2+/-5.5 kg/m2. Individuals homozygous for the Ser347 allele had higher BMI (32.3+/-6.6 vs 28.6+/-5.3 kg/m2; P<0.01) and percentage body fat (36.9+/-7.8 vs 31.0+/-9.6%; P<0.05) compared with individuals homozygous for Thr347. In contrast, the presence of at least one copy of the His360 allele was associated with lower BMI (27.2+/-5.0 vs 28.4+/-5.6 kg/m2; P<0.05) and percentage body fat (28.6+/-8.2 vs 30.7+/-9.1%; P<0.05). The genotype effects persisted after normalization of the data for the potential confounding effects of gender, age and race. When grouped by BMI percentile, the frequency of the Ser347/Ser347 genotype increased while the frequency of the His360 allele decreased with increasing BMI. CONCLUSIONS: These data suggest a role for apoA-IV in fat storage or mobilization and that genetic variations in the apoA-IV gene may play a role in the development of obesity.

North American Society for the Study of Obesity--annual meeting. Emerging perspectives on obesity. 14-18 November 1999, Charleston, SC, USA.

This meeting focused on the latest research and clinical developments in the field of obesity. Record high attendance emphasized the recognition of obesity as an emerging and exciting area of study, both from the basic science aspects as well as from a clinical standpoint. While presentations at the meeting emphasized the importance of retaining our current public health message of low-fat diets and exercise for obesity prevention and management, several novel approaches (both behavioral and pharmaceutical) were also presented. In animal models, the presentation of data on a novel obesity-related gene, beacon, was one of the highlights.

Low-dose T(3) improves the bed rest model of simulated weightlessness in men and women.

This study tested the hypothesis that low-dose 3,5, 3'-triiodothyronine (T(3)) administration during prolonged bed rest improves the ground-based model of spaceflight. Nine men (36.4 +/- 1. 3 yr) and five women (34.2 +/- 2.1 yr) were studied. After a 5-day inpatient baseline period, subjects were placed at total bed rest with 6 degrees head-down tilt for 28 days followed by 5-day recovery. Fifty micrograms per day of T(3) (n = 8) or placebo (n = 6) were given during bed rest. Serum T(3) concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T(3)-treated subjects showed significantly greater negative nitrogen balance and lost more weight (P = 0.02) and lean mass (P < 0.0001) than placebo subjects. Protein breakdown (whole body [(13)C]leucine kinetics) increased 31% in the T(3) group but only 8% in the placebo group. T(3)-treated women experienced greater changes in leucine turnover than men, despite equivalent weight loss. Insulin sensitivity fell by 50% during bed rest in all subjects (P = 0.005), but growth hormone release and insulin release were largely unaffected. In conclusion, addition of low-dose T(3) to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.

Testosterone administration preserves protein balance but not muscle strength during 28 days of bed rest.

Decrements in muscle strength as a result of prolonged bed rest are well defined, but little is known about potential countermeasures for preventing loss of strength under this condition. The purpose of this study was to determine whether testosterone administration would preserve protein balance and muscle strength during prolonged bed rest. Ten healthy men (age, 36 +/- 2 yr; height, 177.2 +/- 3.4 cm; weight, 80.5 +/- 3.9 kg; mean +/- SE) were admitted to our in-patient metabolic unit. After a 1-week ambulatory run-in period, each subject was confined to bed for 28 days at 6 degree head-down tilt while receiving a daily oral dose of T3 (50 microg/day). During the bed rest/T3 period, six of the men were randomized to receive testosterone enanthate by i.m. injection (T; 200 mg/week) while four received placebo in a double blind fashion. Nitrogen balance was determined throughout, and whole body [13C]leucine kinetics were assessed at baseline and on day 26 of bed rest. Before bed rest and on the third day of reambulation, the muscle strength of the knee extensors and flexors and shoulder extensors and flexors was determined at 60 degrees/s on a Cybex isokinetic dynamometer. Despite improved [13C]leucine kinetics and maintenance of nitrogen balance and lean body mass in T-treated subjects, little preservation of muscle strength, particularly in the knee extensors, was noted. Muscle strength [reported as the best work repetition in foot-pounds (FtLb)] for right knee extensors declined (P = 0.011) similarly in both groups; from 165 +/- 15 to 126 +/- 18 FtLb in T-treated men and from 179 +/- 22 to 149 +/- 13 FtLb in placebo-treated men. Overall, there was less of a decline in extension and flexion strength of the shoulder compared to the knee, with no benefit from T. These results suggest that in the absence of daily ambulatory activity, T administration will not increase or, in the case of this bed rest model, preserve muscle strength.

Comparison of a radioimmunoassay with a microparticle enzyme immunoassay of insulin for use with the minimal model method of determining whole-body insulin sensitivity.

The purpose of this study was to compare minimal model results of insulin sensitivity and glucose effectiveness using insulin levels measured by a conventional radioimmunoassay (RIA) versus an automated microparticle enzyme immunoassay (MEIA). Thirty obese subjects participated in an insulin-modified frequently sampled intravenous glucose tolerance test. The MEIA exhibited lower day-to-day variability than did the RIA. The MEIA yielded lower insulin values compared to the RIA probably because of the high cross-reactivity with proinsulin in the RIA. The MEIA yielded a good correlation with the RIA for both insulin sensitivity (r = 0.97, p = 0.0001) and for glucose effectiveness (r = 0.98, p = 0.0001). The MEIA did not significantly effect the results of the MinMod analysis and the low cross-reactivity with proinsulin makes MEIA preferable when insulin sensitivity (SI) is measured in patients with diabetes or obese individuals whose insulin:proinsulin ratio is altered.