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The POWER Study

Prevention of Obesity in Women via Estradiol Regulation

Power Study Results

Gaining weight after menopause is a common complaint of women. The purpose of the POWER study (Prevention of Obesity in Women via Estradiol Regulation) was to determine if the loss of the sex hormone estrogen (E) accelerates weight gain in women. Seventy healthy premenopausal women were enrolled in the study and underwent 5 months of drug treatment to decrease their estrogen to the level of a postmenopausal woman. Half of the women also received an estrogen patch to bring their estrogen level, but not other sex hormone such as progesterone, back up to normal. We measured how body composition (body weight, body fat, muscle mass, bone mass), 24-hour energy expenditure (the amount of calories burned throughout the day), and resting energy expenditure (amount of calories burned at rest) changed from before to after the 5-month intervention.

The results showed the women with decreased ovarian hormones for 5 months had:

  • Decreased bone mass
  • Decreased muscle mass
  • No change in weight or whole body fat mass
  • Increased abdominal (belly) fat
  • Decreased 24-hour and resting energy expenditure

Importantly, in the other group of women that had their estrogen replaced, these changes did not occur, except for the decline in 24-hour energy expenditure.

As a preliminary study on the influence of exercise on body composition and energy expenditure changes with the loss of estrogen, about half of the women in each hormone group completed a resistance exercise program, coming into our exercise facility to do a variety of weightlifting exercises 4 days each week. Although the numbers of women in the exercise groups were small, we found some preliminary evidence that exercise may have favorable effects on bone mass, muscle mass and abdominal fat mass, similar to that observed with the estrogen replacement. Despite having these beneficial effects on body composition, resistance exercise appeared to have little to no effect on either resting or 24 hour energy expenditure in either hormone group.

In summary, the POWER study demonstrates that suppression of ovarian hormones in premenopausal women causes an increase in abdominal fat and decreases in muscle mass, bone mineral density, and resting energy expenditure and that these changes are related to the loss of estrogen. Our preliminary data further suggest that resistance exercise may help to maintain muscle mass and bone mineral density during ovarian hormone suppression, but further research will be needed to confirm this potential benefit. It is not clear whether the findings from this study of ovarian hormone suppression in premenopausal women reflect changes that occur in response to the natural menopausal transition. Our follow up study to POWER, called FAME (Females, Aging, Metabolism, and Exercise), is now underway to help us more closely examine the role that female sex hormones play in metabolism, energy expenditure, physical activity, and chronic disease.