Age-related Changes In Body Composition Research Articles

Body composition in French women 75+ years of age: The EPIDOS study

Background: There are presently no published data on age-related changes in body composition in French individuals older than 65 or 80 years. This paper presents a cross-sectional study of 7518 community-residing French women older than 75 years. Methods: We examined age differences changes in body composition and anthropometry between age groups (76–80, 81–85, and 86–95 years of age). Whole body composition was estimated using a dual energy X-ray absorptiometry (DXA) scanner. Measurements of appendicular skeletal muscle (ASM) mass and sarcopenia were performed for a subsample of 1321 women. Results: Significant age differences exist in total fat mass and total bone mineral content in elderly women between 76 and 95 years of age. There was also a significant decreased in fat free soft tissue mass from 76 to 85. The decline in fat free mass may be reduced over 85 years of age. The prevalence of low muscle mass, or sarcopenia, increased with age from 8.9 in 76–80 to 10.9% in 86–95 age group, but the difference was not statistically significant. Conclusions: Interventional programs developed to prevent or reduce sarcopenia would have a better influence on population under 85 years, i.e. when the decline in ASM mass is the most severe. Others longitudinal studies could be performed to confirm our results.

Body composition of prolactin-, growth hormone, and thyrotropin-deficient Ames dwarf mice.

Ames dwarf mice have primary deficiency of prolactin (PRL), growth hormone (GH), and thyroid-stimulating hormone (TSH), and live considerably longer than normal animals from the same line. In view of the documented effects of GH, PRL, and thyroid hormones on lean and fat body mass and skeletal growth, and the suspected relationship of body size and composition to life expectancy, it was of interest to examine age-related changes in body composition of Ames dwarf mice. Lean mass, fat mass, bone area, and bone mineral content (BMC) were determined in dwarf and normal mice at the ages of 2, 4.5 6, and 18 mo using dual X-ray absorptiometry. In addition to the expected significant declines in lean mass, bone area, and BMC, dwarf mice exhibited attenuation of the age-related increase in bone mineral density and delayed or attenuated increase in percentage of body fat. Percentage of body fat was lower in adult dwarfs than in the corresponding normal controls. Patterns of age-related changes in body composition in Ames dwarf mice are consistent with the recent report of age-related changes in body composition in PRL receptor knockout mice. We suspect that reduction in relative adiposity may contribute to the previously reported increase in insulin sensitivity of Ames dwarf mice and thus may be a factor in delayed aging and increased longevity of these animals.

Body composition, leptin, and the leptin receptor and their relationship to the growth hormone (GH) axis in growing wethers treated with zeranol

Age-related changes in body composition, leptin, and hypothalamic-pituitary expression of the leptin receptor and associative relationships of these factors to constituents of the growth hormone (GH) axis were evaluated. Seventy wethers were randomly assigned at birth to one of four treatment groups: control; treatment 1 implanted with the estrogenic compound zeranol (12 mg, Ralgro ®) on days 0, 45, and 90; treatment 2 received zeranol on days 45 and 90; and treatment 3 received zeranol on day 90. Serum and tissues were collected from wethers ( n≥5) from each group on days 28, 73, 118, and 135. Percent body fat and leptin increased linearly ( P<0.01) with age, but were not influenced ( P≥0.14) by zeranol. The leptin receptor in the pituitary appeared to be differentially ( P=0.097) expressed across days 73–135, but no differences ( P≥0.43) were detected in expression of this receptor in the hypothalamus among treatments and ages. Leptin and % body fat were negatively correlated ( r≥−0.52, P<0.05) to mRNA levels of factors involved in pituitary synthesis and secretion of GH. Serum leptin increased with age as did percent body fat, but zeranol did not influence body composition, serum leptin, or expression of the leptin receptor in the hypothalamus or pituitary; however, the leptin receptor appeared to be differentially expressed among the hypothalamus and pituitary with level of body fat and leptin being inversely associated to transcriptional-factors involved in somatotrope synthesis and secretion of GH.

Body Composition and Circulating Levels of Insulin, Insulin-Like Growth Factor-Binding Protein-1 and Growth Hormone (GH)-Binding Protein Affect the Pharmacokinetics of GH in Adults Independently of Age

The aim of our study was to scrutinize the association among age, body composition, and GH status in healthy adults. Using two-step, primed constant infusions of GH during suppression of endogenous GH secretion with octreotide in a group of 26 healthy nonobese men [mean age, 37.3 yr (range, 22-55 yr); body mass index, 24.6 +/- 0.4 kg/m(-2)] we investigated the contributions of age, body composition, insulin, and binding proteins to the variability in the pharmacokinetics and acute actions of GH. All subjects were investigated twice, with the infusion rates of GH calculated according to either total body weight or intraabdominal fat mass. Body composition was determined using computed tomography and bioimpedance measurements. There was no correlation between age and body weight, yet strong positive correlations were observed between age and intraabdominal fat area (r = 0.78; P < 0.0001) and waist to hip ratio (r = 0.71; P < 0.0001) and to a lesser degree to sc fat area (r = 0.42; P < 0.03). The between-subject variability in steady state GH levels was significantly larger when GH was administered per cm(2) intraabdominal fat area than per kg BW (P < 0.001). During primed constant infusions of GH at rates of 1.5 and 3.0 microg/kg x h, the corresponding MCRs of GH were 148.8 +/- 5.4 and 89.8 +/- 2.4 ml/min x m(-2), respectively, and the MCRs were inversely related to the achieved steady state GH levels (P < 0.0001). The MCR was unrelated to age, but was negatively correlated to baseline concentrations of IGF-binding protein-1 (IGFBP-1; r = -0.53, P < 0.01) and positively correlated to basal levels of insulin (r = 0.46; P < 0.05), GH-binding protein (GHBP; r = 0.52; P < 0.01), IGFBP-3 (r = 0.47; P < 0.05), and total body fat (r = 0.44; P < 0.05). GH infusion caused significant changes in the concentrations of IGF-I, free fatty acids, GHBP, IGFBP-1, and insulin, but none of these effects was correlated to age. Based on our results we conclude that 1) the clearance of GH is concentration dependent; 2) the pharmacokinetics and acute effects of GH are not affected by age per se; and 3) basal levels of insulin, IGFBP-1, and GHBP as well as age-related changes in body composition are important predictors of GH pharmacokinetics.

Physical activity and parameters of aging: a physiological perspective.

Increasing age is associated with a decline in fat-free mass. The question is whether age-related changes in body composition can be delayed by an active life style. This analysis includes data where physical activity was assessed with doubly labeled water and body composition with hydrodensitometry or isotope dilution. Subjects were 136 women and 180 men over 20 years, who were tested in Maastricht University between 1983 and 1998. Increasing age was associated with lower activity levels and lower fat-free mass. After controlling for age there was no longer any association between physical activity and fat-free mass. A few exercise intervention studies showed that elderly subjects compensate for exercise training by a decline in spontaneous physical activity, in contrast to younger subjects. Although no effect of habitual activity level on changes in body composition are observed, training has a positive effect on muscle function. Elderly subjects with relatively high levels of physical activity are not different from those with low activity levels, as far as fat-free mass and fat mass are concerned. However, training might delay the age-induced impairment of personal mobility associated with a reduction in physical activity.

NEUROENDOCRINE AGING IN MEN: Andropause and Somatopause

Aging is accompanied by gradual but progressive reductions in the secretion of testosterone and growth hormone in men, and by alterations in body composition and functional capacity that, to some degree, undo the effects of puberty. Preventing or reversing these changes with the use of trophic factors, including androgens, growth hormone, and growth hormone secretagogues, is an appealing prospect, but documenting the effectiveness of these interventions and their benefits and risks has proven to be a difficult undertaking that is far from complete. Small-scale clinical studies have shown that it is practicable to boost growth hormone and IGF-1 levels for periods of up to 12 months, and testosterone for up to 36 months, to reverse at least some age-related changes in body composition. Information regarding the effects of these interventions on strength, exercise capacity, and the ability to perform activities of daily living is still sparse, and additional reports from recently completed or currently ongoing clinical trials will not provide sufficient data to make firm conclusions. From the limited information currently available, androgen supplementation may be of benefit in some men aged more than 65 years, particularly in men with low serum testosterone levels (< 2 ng/mL). In this group, supplemental androgen therapy would be expected to increase lean body mass, bone mass, and possibly strength. In older men with testosterone levels between 2 and 3.5 ng/mL, some benefit might result from androgen supplementation, but it is not yet clear whether the benefits outweigh the risks. For men in this category, one might consider a 6- to 12-month trial of therapy after a full discussion and explicit consent, followed by a reassessment of the value of ongoing treatment. The even more limited data on growth hormone or growth hormone secretagogue interventions in aging do not support their general clinical use in healthy older men. Growth hormone is much more expensive than testosterone and is not covered by insurance for off-label uses. Patients who persistently seek a trial of therapy should be encouraged to enroll in a study if one is locally available. All of the growth hormone studies reported to date have focused, generally for reasons of safety, on healthy and robust groups of older subjects, men in whom the need for intervention is least compelling and in whom the functional effects of treatment may be the most difficult to observe. Phase II studies of intermediate size and duration examining prefrail groups of elderly who are at greater risk for functional loss and who stand to benefit the most from either preventive or restorative interventions are underway but are limited to the intermediate outcomes of body composition, strength, and function. Trials designed to assess clinically relevant final outcomes, such as falls, fractures, and institutionalization, are of necessity large-scale, long-term, and expensive. Support for larger phase III studies of growth hormone is unlikely to be forthcoming until the phase II studies are completed and show further promise. A multicenter clinical trial of testosterone is currently being planned under the joint sponsorship of the National Institute on Aging, the Veterans Health Administration, and industry, aimed at assessing the effects of testosterone on the risk for falls and fractures. The results of this trial and other large clinical trials should help to better define the balance of benefits and risks of trophic factor intervention in normal older men.

Elderly subjects show severe impairment of dehydroepiandrosterone sulphate and reduced sensitivity of cortisol and aldosterone response to the stimulatory effect of ACTH(1-24).

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis in ageing has been reported both in humans and in animals and may be involved in age-related changes in body composition, structure functions and metabolism, as well as in brain ageing. Despite the supposed HPA hyperactivity and its refractoriness to negative glucocorticoid feedback, low levels of dehydroepiandrosterone (DHEA) and its sulphate have been clearly demonstrated in human ageing and may suggest another cause of age-related changes in structure function and metabolism. Thus, our aim was to verify the adrenal responsiveness to various ACTH doses in normal elderly subjects. We studied cortisol (F), aldosterone (A) and DHEA responses to the sequential administration of very low, low and supramaximal ACTH1-24 doses (0.06 microg or 0.5 microg followed by 250 microg ACTH1-24 i.v. at 0 and +60 minutes) in healthy elderly subjects (ES) [six females and two males, aged 63-75 years, body mass index (BMI) 22-26 kg/m2]. The results in ES were compared with those recorded in healthy young subjects (YS) (six females and six males, aged 22-34 years, BMI 20-25 kg/m2). Basal DHEA levels in ES were lower (P < 0.05) than in YS, while F and A levels were similar in both groups. DHEA, F and A responses to ACTH were dose-dependent in both groups. In ES, however, DHEA levels showed no response to the 0.06 microg dose, a modest increase after 0.5 microg and a clearer rise after 250 microg ACTH; at any dose, the DHEA response in ES was clearly lower than in YS (P < 0.04). The F responses to 0.5 microg and 250 microg ACTH in ES were similar to those in YS; whereas, in ES, 0.06 microg ACTH elicited a non significant F increase which was significantly lower than in YS (P < 0.05). Similarly, the A responses to the highest ACTH doses were similar in both groups but, in ES, 0.06 microg ACTH elicited no increase in A secretion, which was clearly lower than in YS (P < 0.03). Normal elderly subjects show severe reduction of DHEA response to a wide range of ACTH doses, in agreement with peculiar impairment of the activity of the adrenal reticularis zone in ageing. In contrast to young adults, elderly subjects also show no cortisol and aldosterone response to a very low ACTH dose. This evidence indicates a reduced sensitivity to ACTH in the fasciculata and glomerulosa zones of the adrenal gland in ageing.

Relation between body composition, fat distribution, and lung function in elderly men

Body composition changes with age, with increases in fat mass and visceral fat and declines in skeletal muscle mass; lung function also declines with age. Age-related changes in body composition and fat distribution may be associated with the pulmonary impairment observed in the elderly. Our goal was to evaluate the relations between body composition, fat distribution, and lung function in elderly men. We studied 97 men aged 67-78 y with body mass indexes (BMIs; in kg/m2) ranging from 19.8 to 37.1. Body composition was evaluated by using dual-energy X-ray absorptiometry and fat distribution was evaluated by using waist and hip circumferences, waist-to-hip ratio, and sagittal abdominal diameter (SAD). Spirometry was done in all subjects and the distance walked by each subject during a 6-min walking test was evaluated as was leg strength. A significant negative correlation was found between adiposity, fat distribution indexes, forced vital capacity (FVC), and forced expiratory volume in 1 s (FEV1). A positive correlation was found between fat-free mass and FVC. After adjustment for age, height, and weight, SAD still correlated negatively with FVC and FEV1 (r = -0.367 and -0.348, respectively; P < 0.01), whereas percentage body fat and fat mass correlated negatively and fat-free mass correlated positively with FVC (r = -0.313, -0.323, and 0.299, respectively; all P < 0.01). After the sample was subdivided by tertile of fat-free mass adjusted for age and BMI, FVC and FEV1 were significantly lower in the lowest fat-free mass tertile (P < 0.01). Stepwise multiple regression analysis performed with use of lung function variables as the dependent variables and age, height, fat mass, fat-free mass, waist circumference, and SAD as the independent variables showed that 3 variables entered the regression for predicting FVC: height, which entered the regression first; SAD, which entered second; and fat-free mass, which entered third. Only 2 variables entered the regression for predicting FEV1: height, which entered the regression first, and SAD, which entered second. Our cross-sectional data show a significant association between body composition, fat distribution, and lung function in elderly men.

Age-related decrease in resting energy expenditure in sedentary white women: effects of regional differences in lean and fat mass

Lean mass and resting energy expenditure (REE) decrease with age. However, it is unknown whether age-related changes in regional lean and fat mass are responsible for the age-related decrease in REE. Our objective was to determine how regional lean and fat mass vary with age and whether age is independently related to REE after adjustment for regional fat and lean mass. The study was a cross-sectional evaluation of 58 white women aged 23-77 y. Regional and whole-body lean and fat mass were measured by dual-energy X-ray absorptiometry, subcutaneous abdominal tissue (SAT) and intraabdominal adipose tissue (IAF) by computed tomography, and REE by ventilated-canopy indirect calorimetry. Independent of other significant correlates, age was significantly and independently associated with greater IAF (beta = 0.49) and less leg lean mass (beta = -0.35). IAF (r = -0.28) and IAF:SAT (r = -0.31) correlated negatively with REE. REE was negatively associated with greater age (beta = -0.42), independent of changes in lean and fat mass in different parts of the body. By contrast, trunk lean (beta = 0.27) and leg fat (beta = 0.27) mass were associated with greater REE independent of age and other body-composition variables. These results suggest that trunk lean mass (presumably primarily organ tissue) is relatively resistant to age-related changes in body composition, whereas muscle mass, especially leg muscle, tends to be lost. These data also suggest that the age-related decreases in REE are not fully explained by changes in body composition.

Symposium on endocrinology and aging: the 1st meeting of the European Interest Group hormones and aging.

Abstract The decline of multiple hormone systems observed with aging could contribute to the age-related morbidity and mortality. However research protocols addressing the reduction in hormonal function with advanced age and trials assessing the value of hormone replacement therapy in the aged are lacking behind the rapidly increasing number of old persons in Europe. To increase the awareness and to raise the interest for the endocrinology of aging, the recently established European Interest Group of Hormones and Aging has gathered gerontologists and endocrinologists for the inaugural International Symposium. Speakers from Austria, Germany, the United States and Switzerland presented research data as well as an overview of current topics in clinical geriatric and endocrine research, such as somatopause, adrenopause, male menopause, the relationships of age-related changes in body-composition with carbohydrate metabolism and the effects of substitution of DHEA on psychological well-being in young and old individuals. In the current report these presentations are summarized and a Consensus Statement is added.

Growth hormone and aging

The potential usefulness of growth hormone (GH) as an anti-aging therapy is of considerable current interest. Secretion of GH normally declines during aging and administration of GH can reverse age-related changes in body composition. However, mutant dwarf mice with congenital GH deficiency and GH resistant GH-R-KO mice live much longer than their normal siblings, while a pathological elevation of GH levels reduces life expectancy in both mice and men. We propose that the actions of GH on growth, development, and adult body size may serve as important determinants of aging and life span, while the age-related decline in GH levels contributes to some of the symptoms of aging.

Physiology of aging with respect to gastrointestinal, circulatory and immune system changes and their significance for energy and protein metabolism.

Age-related changes in body composition can be considered the consequence of changes in energy and protein metabolism, while also having a leverage effect on protein and energy requirements. Changes in organ and systems weights obviously affect energy balance regulation. Considered at the system level, age-related changes are numerous, but it is still debated whether they are related to aging per se or to conditions (such as poor nutrition, disease, drug treatments etc.) that prevail in elderly persons. It is likely that most changes occuring in the gastrointestinal, circulatory and immune system do not affect energy and protein requirements at rest. However, aging is associated with difficulties in adapting to new environmental conditions that lead to stress. Repeated episodes of stress might lead to accumulation of deficits that can affect energy and protein balances.

Nutrition of the elderly: Interactions with physical activity

Elderly subjects have a lower energy requirement compared to young adults as a result of lower physical activity and a lower basal metabolic rate. A lower energy intake in the elderly could lead to undesirable low intakes of essential nutrients. The reduction of the energy turnover is caused by, or a consequence of, a decrease in active cell mass. Thus, the effect of exercise training on habitual activity across age ranges, and age-related changes in body composition in relation to habitual activity level, are investigated here. The focus is on data on physical activity and body composition obtained with doubly labelled water. The results suggest that exercise training does not affect energy requirement in the elderly and the age-related decrease in fat-free mass is not delayed in subjects with a relatively high habitual activity level. Beneficial effects of exercise training in the elderly are endurance, flexibility, range of motion and balance control, all contributing to a delay in the age-induced impairment of personal mobility. Energy intake will inevitably go down as a result of a reduction of the energy requirement. Thus, the nutrition of elderly subjects needs more attention with regard to the essential nutrients than the nutrition of younger adults.

Age-related changes in body composition of 3- to 6-year-old Japanese children.

This study was undertaken to establish an approach for the investigation of age-related changes in indices of body composition during childhood in Japan. It provides current reference values for total body fat mass (TBFM) and lean body mass (LBM) as indices of body composition in an urban population of 3- to 6-year-old Japanese children. Moreover, we assessed the age-specific patterns of body fat distribution [subcutaneous fat mass (SFM) and internal fat mass (IFM)] during childhood. Measurements of body composition by bioelectrical impedance were made in 141 boys and 139 girls, all apparently healthy, aged 3-6 years. Determinations of impedance were made using a four-terminal impedance analyzer (TP-95K; Toyo Physical, Inc., Fukuoka, Japan). LBM was calculated using the equation of Kushner et al. (1992) and Goran et al. (1993). SFM was calculated using a modification of the equation derived by Skerjl et al. (1953). IFM was calculated as the difference between TBFM and SFM. From ages 3 through 6 years, the mean LBM increased with age in boys and girls, and showed significant age differences. Between the ages of 3 and 6, the average increment in LBM was 5.1 kg in boys and 4.4 kg in girls. On average, boys gained 0.5 kg of TBFM each year, whereas girls gained 0.4 kg of TBFM each year. Furthermore, both groups gained 0.3 kg of SFM each year. Percentage body fat decreased in both genders until approximately the age of 5, and increased again slightly at the age of 6. The age-specific pattern of fat accumulation during childhood was characterized by an almost linear increase in SFM in girls, but a transient decrease in IFM in boys. We conclude that further research is required, including longitudinal assessment of body composition variables, in order to unravel the dynamics of body composition change in Japanese children.

Age-related changes in body composition, hydroxyproline, and creatinine excretion in normal women.

We have made a cross-sectional study of relationships among age, whole body bone mineral content (WBBMC), and non-bone lean body mass (NBLBM) measured by dual energy X-ray absorptiometry (DXA), and daily excretion of hydroxyproline (OHP) and creatinine (Cr) in a group of normal women. WBBMC fell with age from the 6th decade, whereas NBLBM was almost constant. Creatinine excretion fell with age from the 5th decade until the 9th, to a much greater degree than NBLBM, reaching a nadir in the 8th decade. Daily excretion of hydroxyproline showed a peak in the 6th decade and fell moderately thereafter. The greater fall of creatinine compared with hydroxyproline resulted in rising OHP/Cr ratios with advancing age, in contrast to the pattern of hydroxyproline excretion. The use of creatinine as a correction for urine dilution or for lean body mass (LBM) in assays for markers of bone turnover must therefore be viewed with caution.

Does growth hormone prevent or accelerate aging?

It is very well documented that plasma growth hormone (GH) levels decline with age in the human and in experimental animals, and there is considerable evidence that age-related changes in body composition may be caused by reduced function of the GH-IGF-I system. However, excessive GH levels are associated with reduced life expectancy in acromegalic patients and with symptoms of accelerated aging in GH transgenic mice. Hereditary dwarf mice deficient in GH, prolactin, and TSH live much longer than their normal siblings. Possible mechanisms of delayed aging in dwarf mice include lower core body temperature and reduced oxidative processes. It is suggested that the controversies concerning the apparent potential of GH to both prevent and accelerate aging may be reconciled by interpreting the results in light of the negative relationship between body size and life span within a species.

AGE-RELATED CHANGES IN BODY COMPOSITION FOR 643 JAPANESE AGED 20 TO 75 YEARS.

1350 There has been few information on body composition of Asian population. The aim of this present study was to investigate age-related body composition changes in Japanese adult. 308 male and 335 female volunteers ranging from 20 to 75 years were examined. The Body composition was assessed by densitometry using an underwater weighing method. The Brožek et. al. equation was applied to calculate the percentage of body fat (%BF). Body height (BH), body weight (BW), seven skinfold thicknesses and seven body circumferences were also measured. The subjects were divided into five age groups (20-29, 30-39, 40-49, 50-59, 60+).%BF and waist hip ratio (WHR) significantly increased with age (male: r=0.469 and 0.504, female: r=0.575 and 0.450), while BH and lean body weight per BH (LBW/BH) significantly decreased with age (male: r=-0.335 and -0.382, female: r=-0.408 and -0.306). ANOVA of the different age groups revealed the most pronounced change in%BF between 20-39 years for men and above 50 years for women. And the present study found consistently smaller%BF values for the Japanese population compared to presented reports for Caucasian population. TableTable

Age-related variations in the growth hormone response to growth hormone secretagogues

Growth hormone (GH) secretagogues are synthetic peptidyl and non-peptidyl molecules which possess a strong, dose-dependent and reproducible GH-releasing effect after intravenous and even oral administration in humans. This effect is probably mediated via the activation of specific receptors, mainly present at the pituitary and hypothalamic level; a human pituitary GH secretogogue receptor has already been cloned, pointing to the existence of an endogenous GH secretagogue-like ligand. The GH-releasing effect of GH secretagogues is gender-independent but undergoes marked age-related variations. In fact, the effect is low at birth, increases markedly at puberty, persists at a similar level in adulthood and decreases thereafter, being already similar in middle age to that in elderly subjects. It is likely that the reduced activity of GH secretagogues in aging reflects the age-related changes in the neural control of somatotrope function. These could include the hypothetical impairment in the activity of the putative natural GH secretagogue-like ligand. Prolonged treatment with non-peptidyl GH secretagogues has been shown to restore spontaneous GH pulsatility and insulin-like growth factor I (IGF-I) levels in aged humans as well as in animals. The possibility that chronic treatment with GH secretagogues in aging rejuvenates the activity of the GH/IGF-I axis and counteracts the age-related changes in body composition, structure functions and metabolism seems very attractive.

Age-related changes in body composition of healthy and osteoporotic women

The study was carried out to assess age-related changes of body composition and to evaluate the influence of lean and fat mass in bone mineral density of healthy and osteoporotic women. 166 healthy women in premenopause (43.2 +/- 6.7 years), 591 healthy postmenopausal women (59.9 +/- 8.1 years) and 373 women with established involutive osteoporosis (66.2 +/- 7.8 years) were evaluated: bone mineral density (BMD) and soft tissue composition (fat mass, lean mass) were measured by a total body Lunar DPX device. no difference in lean mass was appreciated between the groups. Fat mass was significantly lower in premenopausal women (19.5 +/- 6.5 kg) and osteoporotic patients (18.8 +/- 5.2 kg) than in postmenopausal healthy women (21.8 +/- 5.7 kg). In premenopause weight, soft tissue mass and fat mass increased with age (P < 0.05). In postmenopause, lean mass decreased significantly in healthy women (P < 0.05). Fat mass was lower in the osteoporotics than in normals. Total BMD correlated significantly with fat and lean mass in all groups (P < 0.01). BMD/height ratio correlated significantly with fat mass (P < 0.01), not with lean mass. BMD is closely related to fat mass in healthy premenopausal and postmenopausal women, and in osteoporotic patients; osteoporotic patients and healthy premenopausal women are characterized by a lower fat mass than healthy postmenopausal women; fat mass may be considered one of the determinants of bone mass also in involutive osteoporosis.

PHYSICAL ACTIVITY AND BODY WEIGHT REGULATION IN DIFFERENT POPULATIONS867

This symposium will Focus on the role of fiabitual physical activity on the regulation of body weight and composition and energy metabolism in different adult populations. Dr. Hill will present an overview on what is currently known about the impact of physical activity on body weight, and the mechanisms involved. Emphasis will be on the effect of changing physical activity patterns on the prevention and treatment of obesity. Dr. Davy first will describe age-related changes in body composition and the associated increases in chronic disease risk in the general population. He will then discuss the ability of regular physical activity to minimize these age-associated changes, and the potential mechanisms by which these favorable modulatory effects may be conferred. In Dr. Melby's presentation, diet (energy and macronutrient intake), energy expenditure (both resting and physical activity-related), and macronutrient oxidation will be discussed as possible contributors to the high prevalence of overweight and obesity in specific minority populations in the United States. Dr. Horton will discuss how males and females may differ in substrate utilization during acute exercise, and the experimental challenges associated with research in this area. The concept that females utilize more total lipid fuel than men and the related implications regarding long-term maintenance of fuel stores through an interactions with food intake will be emphasized. Finally, Dr. Israel will present the results of human studies that attempt to clarify the relationship between fat mass and plasma leptin levels, and the impact of exercise training on this ob gene product. In particular, he will address the question of whether or not exercise trainingper se affects systemic leptin levels and its signaling pathways, or whether training-related changes in leptin levels are dependent on alterations in fat mass.