Effects of Estrogen on Metabolism and Body Composition

Dare I say you need estrogen! But wait haven’t we been told estrogen makes you watery and fat? Common practice amongst bodybuilders is to suppress estrogen far below the normal range. This is more common during contest preparation with bodybuilders utilizing aromatase inhibitors (AI) and selective estrogen receptor modulators to obtain a “dry” look. However, estrogen has many positive effects on skeletal muscle and metabolism, even being considered an anabolic hormone.

Estrogen and Insulin
Anastrozole, a common AI used in medical community for its ability to reduce serum estrogen is used recreationally by bodybuilders for this reason. We can look to literature to gain perspective on the role of estrogen in skeletal muscle and formulate a more evidence-based approach. Gibb et al, took 17 health males and provided them with 1mg of anastrozole for 6 weeks, followed by a 2 week wash out period, and then 6 weeks of a placebo(1). The gold standard for measuring insulin sensitivity (hyperinsulinemic euglycemic clamp) was used to measure glucose disposal and rates of lipolysis. Anastrozole decreased estrogen by ~50% and resulted in reduced insulin sensitivity of peripheral tissues (skeletal muscle). Researchers stating estrogen has an important role in insulin sensitivity in skeletal muscle. Now, if recall we all want insulin sensitivity in skeletal muscle for anabolism, estrogen has a main role within this.

Estrogen, Body Composition, and Reproductive Function
How might this effect someone over the long term? Finkelstein et al, took 198 men and split them into two groups. Group 1 received placebo, 1.2g, 2.5g, 5g, or 10g of testosterone gel, while Group 2 received the same treatment with the exception that anastrozole was added to the gel(2). After 16 weeks the group receiving the test gel with anastrozole had larger increases in body fat percentage than the group without anastrozole. Estrogen suppression was associated with increases in body fat gain and decreases in sexual desire and erectile dysfunction. Not only to body fat increase, but sexual function decreased with suppressing estrogen. This study demonstrates the role estrogen has a regulating metabolic and sexual function in males.

Takeaway:
Estrogen has a role in glucose and lipid metabolism, body fat regulation, and sexual function. If you are bodybuilding and suppressing estrogen, this may result in less optimal physique outcomes. A balance of androgens and estrogens should be in place for optimal performance.

John Jewett, MS, RD IFBB Pro

1.         Fraser W. Gibb, Natalie Z. M. Homer, Abdullah M. M. Faqehi, Rita Upreti, Dawn E. Livingstone, Kerry J. McInnes, Ruth Andrew, Brian R. Walker, Aromatase Inhibition Reduces Insulin Sensitivity in Healthy Men, The Journal of Clinical Endocrinology & Metabolism, Volume 101, Issue 5, 1 May 2016, Pages 2040–2046, https://doi.org/10.1210/jc.2015-4146

2.         Finkelstein JS, Lee H, Burnett-Bowie SA, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013;369(11):1011‐1022. doi:10.1056/NEJMoa1206168