Wendy M. Kohrt, PhD

Disclosures

June 29, 2009

Question

Does exercise attenuate or prevent the weight gain that occurs during peri- and postmenopause?

Commentary from Wendy M. Kohrt, PhD

The short answer is, yes, exercise can attenuate or prevent weight gain during peri- and postmenopause. The prevention of weight gain at any age requires only that energy intake not exceed energy expenditure. Thus, it is possible to maintain body weight by modifying exercise and/or eating habits. However, although simple in theory, there are physiologic changes that make it particularly challenging for middle-aged women to maintain energy balance (ie, intake = expenditure). Because the menopause transition occurs over a number of years, it is difficult to determine whether the increased propensity for weight gain at midlife is primarily a consequence of the menopause transition or of advancing age. Both involve factors that make weight maintenance a challenge.

Menopause-related factors that promote weight gain. Studies of laboratory animals provide compelling evidence that estrogen plays an important role in the regulation of body weight. Oophorectomy has consistently been found to cause excess weight gain, and this is prevented by estrogen replacement.[1] There appear to be multiple mechanisms by which estrogen deficiency leads to weight gain in animals, including increased food intake, decreased spontaneous physical activity, and a suppression of metabolic rate. If such effects of estrogen deficiency also occur in humans, this would suggest that there is a "biological drive" around the time of menopause toward weight gain.

In fact, there is evidence that estrogen regulates body weight in women. A number of large, randomized, placebo-controlled, and open-label trials of estrogen-based hormone therapy (HT) have provided strong evidence that weight gain and, more specifically, fat gain, is attenuated in women on HT when compared to women on placebo or no HT.[2] Suppressing sex hormone levels in premenopausal women with gonadotropin-releasing hormone (GnRH) agonist therapy also causes fat gain. For example, women treated for 16 weeks with a GnRH agonist gained 1.0 kg of fat, which equates to an energy excess of about 80 kcal per day.[3] Because it is difficult to accurately measure changes in energy intake and expenditure of this magnitude in humans, it is not clear whether the suppression of sex hormones influences eating and/or exercise habits. However, short-term hormone suppression has been found to cause a decrease in resting metabolic rate of 40 to 70 kcal per day.[4] This reduction in metabolic rate would be expected to cause weight gain if not accompanied by a compensatory decrease in energy intake or increase in physical activity.

Aging-related factors that promote weight gain. Even if the menopause transition does not alter bioenergetics in a way that promotes weight gain, there are unavoidable factors related to aging that do so. Two important factors are the loss of muscle mass and the decline in maximal aerobic power. Lean body mass is an important determinant of resting metabolic rate. As lean mass declines with aging, there is a decrease in metabolic rate and, therefore, daily energy expenditure. The decline in metabolic rate will result in weight gain unless appropriate behavioral changes are adopted (ie, decrease in energy intake or increase in physical activity).

Maximal aerobic power, also referred to as aerobic capacity or VO2 max, is a direct index of the rate at which an individual can expend energy during exercise. For example, a healthy young woman with an average VO2 max for her age can easily increase her energy expenditure by 8 to 10 kcal per minute during exercise. However, there is a decline in VO2 max with aging that cannot be avoided, due in part to the inevitable decrease in maximal heart rate (ie, maximal heart rate = 220 minus age). Accordingly, with advancing age there is a decline in the rate at which energy can be expended during exercise, even in people who maintain a vigorous level of physical activity.[5] Rather than being able to increase energy expenditure by 8 to 10 kcal per minute during exercise, middle-aged women may be able to burn only 6 to 8 kcal per minute. This has an important impact on how women can use exercise to maintain body weight as they age. Because the rate at which energy can be expended decreases gradually with aging, maintaining the same level of total exercise energy expenditure may require an increase in the amount of exercise time.

Do physically active women gain less weight than sedentary women during peri- and postmenopause? Exercise can prevent weight gain in peri- and postmenopausal women, but factors related to menopause and aging make weight maintenance a challenge. Even though regular exercise does not come with a guarantee against weight gain, prospective studies of perimenopausal women indicate that the most active women gain the least weight.[6,7] Most important, women should not abandon their exercise habits if they become discouraged by what they perceive as a lack of effectiveness of exercise to prevent weight gain. Exercise has numerous health benefits that are independent of its effects on body weight regulation.[8]

From the NAMS Menopause e-Consult-newsletter released April 2009

For more, please visit http://www.menopause.org/Members/eConsulteNewsletter.aspx

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