Impact of estrogens on resting energy expenditure: A systematic review

Context

Despite the manifold positive aspects of hormonal contraception (HC) and/or menopausal hormone therapy (MHT) the fear of unwanted weight gain is one of the main reasons for women not to initiate or to early discontinue these therapies. For clinicians, easing women’s anxiety is difficult regarding the currently limited understanding of the effects of sex hormones on body weight regulation. Resting energy expenditure (REE) is by far the largest component and the most important determinant of total energy expenditure. Given that low REE is a confirmed predictive factor for weight gain and consecutively for the development of obesity, research into the influence of sex steroids on REE is a particularly exciting area.

Objective

The objective of this systematic review was to evaluate the effects of medication with natural and synthetic estrogens on REE in healthy normal weight and overweight women.

Methods

Through complex systematic literature searches, a total of 10 studies were identified that investigated the effects of medication with estrogens on REE.

Results

Our results demonstrate that estrogen administration increases REE by up to +208 kcal per day in the context of HC and by up to +222 kcal per day in the context of MHT, suggesting a preventive effect of circulating estrogen levels and estrogen administration on weight gain and obesity development.

Discussion and Conclusion

It should be pointed out that the weight gain associated with perimenopause and postmenopause is rather a consequence of the age-related tendency to reduced physical activity, the associated loss of muscle mass, and the overall reduced energy requirement. Contrary to mainstream belief, MHT actually counteracts this age-related tendency to gain weight, with one of the mechanisms being an increase in REE. Finally, it should be emphasized that estrogens have an anorexigenic effect and thus prevent increased energy intake from compensating for increased REE. Together with this fact, our results suggest that the energy balance changes in a negative direction under the influence of estrogens. Thus, the widespread fear of weight gain solely as a result of taking HC or MHT is unsubstantiated. Our work is intended to help clinicians educate women accordingly and alleviate their fears in this regard.