UC San Diego

Humans diverge from our close relatives (chimpanzees/ bonobos) in high survivorship to menopause and decades of postmenopausal longevity. Evolutionary perspectives see the human postmenopausal lifespan as a species-typical life history trait that has evolved by selection for maintenance of physiological systems at increasingly older ages. Maintenance of body composition and low rates of metabolic and cardiovascular disease should thus characterize the early postmenopausal period, which they do in hunter-gatherers despite little access to Western medicine. In contrast, women in industrialized society tend to increase body fat and have high rates of metabolic syndrome during the early postmenopausal period; as such, the prevailing medical view is that menopause itself increases disease risk. Physical activity relates to metabolic health, and may help explain this disparity: older hunter-gatherers tend to be highly active, while women in industrialized society tend to be increasingly sedentary with age. Within the framework of evolutionary medicine, the present study investigates the effects of physical activity on body composition and resting energy expenditure (REE) in postmenopausal women from San Diego. Low REE, low fat-free mass and high body fat are risk factors for metabolic syndrome; exercise may increase fat- free mass and REE, and lower body fat. Long-term, habitually-active women were compared to sedentary women who completed a 16-week training program. In this sample, active women tended to have less body fat, but did not have higher fat-free mass or REE. Despite strength and aerobic fitness gains, the training program failed to increase fat-free mass and REE. Comparison of this study's subjects to published results from highly-trained athletes and data on hunter-gatherers suggests that even the active women in the present sample were rather sedentary, consistent with the idea of an intensity threshold for the effects of exercise on metabolism. Additionally, the training program's lack of effect is consistent with some past studies, supporting the idea that the metabolic response to exercise is muted with age and sedentary behavior. Thus, both the intensity and timing of exercise may be important to reducing metabolic disease risk, possibilities that can be evaluated by continuing to study postmenopausal health from the perspective of evolutionary medicine