Individual differences in physical activity are closely associated with changes in body weight in adult female rhesus monkeys (Macaca mulatta)

Abstract

eron. Individual differences in physical activity are closely associated with changes in body weight in adult female rhesus monkeys (Macaca mulatta). Am J Physiol Regul Integr Comp Physiol 291: R633-R642, 2006. First published April 13, 2006; doi:10.1152/ajpregu.00069.2006.-The increased prevalence of overweight adults has serious health consequences. Epidemiological studies suggest an association between low activity and being overweight; however, few studies have objectively measured activity during a period of weight gain, so it is unknown whether low activity is a cause or consequence of being overweight. To determine whether individual differences in adult weight gain are linked to an individual's activity level, we measured activity, via accelerometry, over a prolonged period (9 mo) in 18 adult female rhesus monkeys. Weight, food intake, metabolic rate, and activity were first monitored over a 3-mo period. During this period, there was mild but significant weight gain (5.5 Ϯ 0.88%; t ϭϪ6.3, df ϭ 17, P Ͻ 0.0001), whereas caloric intake and activity remained stable. Metabolic rate increased, as expected, with weight gain. Activity level correlated with weight gain (r ϭ Ϫ0.52, P ϭ 0.04), and the most active monkeys gained less weight than the least active monkeys (t ϭ Ϫ2.74, df ϭ 8, P ϭ 0.03). Moreover, there was an eightfold difference in activity between the most and least active monkeys, and initial activity of each monkey was highly correlated with their activity after 9 mo (r ϭ 0.85, P Ͻ 0.0001). In contrast, food intake did not correlate with weight gain, and there was no difference in weight gain between monkeys with the highest vs. lowest caloric intake, total metabolic rate, or basal metabolic rate. We conclude that physical activity is a particularly important factor contributing to weight change in adulthood and that there are large, but stable, differences in physical activity among individuals.exercise; obesity; weight gain; energy balance EPIDEMIOLOGICAL STUDIES INDICATE that body weight and body fat increase through early and middle adulthood such that by late middle age there is an increased percentage of overweight and obese individuals compared with the early adult period (33,57,63,108,115). Weight gain over the adult years has escalated over the past two decades such that 65% of adults in the United States have a body mass index (BMI) above the healthy range (Ͼ25.0 kg/m 2 ) (32). Weight gain and obesity in adulthood have been associated with overall increases in morbidity and mortality (82) and in the risk of diabetes mellitus (23, 33, 53, 115a), gall bladder disease (115a), coronary heart disease (41, 49, 53, 69, 86, 111, 115a), hypertension (53, 115a), stroke (115a), dyslipidemia (115a), osteoarthritis (115a), gout (115a), pulmonary diseases (115a), colon cancer (35), and breast cancer (118).A large body of epidemiologic data shows an association between low levels of physical activity and a higher rate of adult weight gain, and a greater increase in percent body fat, throughout adult...

Effects of hyperandrogenemia and increased adiposity on reproductive and metabolic parameters in young adult female monkeys

“…Although T-treated monkeys did not eat more calories than control animals, there was a strong trend toward the T-treated animals being less active than controls during the last 10 mo of this study. Studies in humans and animals found that individuals that are less active tend to gain more weight (17,47,82), which is consistent with the current data. Because activity levels were not assessed in our prior study (59) before T implants were placed, it is unknown if the T-treated animals had lower levels of activity at baseline or whether the decreased activity levels occurred later as a result of chronic T treatment.…”

“…The animals were fed ad libitum, and each meal was supplemented with a high-sugar, highcalorie treat (e.g., a cookie, snack cake, etc.). Previous studies have shown that monkeys eating this diet gained over 10% of their body weight within the first 5-6 mo of being on this diet (80,82).…”

“…Metabolic rate was measured over a 24-h period when the animals were 4.5 yr old (pre-WSD) and 12 mo after onset of WSD, using previously published methods (81,82). The animals were placed in a sealed Lexan and stainless steel metabolic chamber (Columbus Instruments, Columbus, OH) at ϳ1000.…”

Sex differences in the physiology of eating

“…Interestingly, the fattest, least active monkeys showed the largest activity increases and weight losses. They also previously reported that spontaneous activity levels, but not food intake levels, were inversely correlated with weight gain over a 3-mo period in intact female rhesus macaques (706). These data, together with Lovejoy et al's (443) report that spontaneous activity decreases across the menopausal transition, identify physical activity and eating as important targets for future menopause research.…”

Relevance of animal models to human eating disorders and obesity

“…The characterization and selective breeding of these two groups of rats has lead to the identification of differences in food intake, feed efficiency, and the expression level of hypothalamic food intake regulatory peptides . Nonhuman primate studies indicate that there are large differences between individuals in high-fat-diet-induced weight gain and that the individuals with the highest levels of physical activity are the least likely to gain weight (Sullivan et al 2005;Sullivan et al 2006). Many investigators are currently using animal models to identify physiological, genetic, and neural circuit influences on susceptibility to diet-induced obesity.…”