Estrogen and Exercise Promote Leanness in Similar Ways

A common hormone has been found to help the body use fat and glucose as energy in the same way that exercise does. Agricultural Research Service-funded scientists will report the findings—based on animal studies—in next week’s issue of the Journal of Biological Chemistry.

The study, led by physician Andrew Greenberg and colleagues, actually reveals a number of novel mechanisms by which estrogen promotes a reduction in fat cell size and fat tissue mass. Greenberg is director of the Obesity and Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, Mass.

Estrogen is an important hormone in both women and men. It activates pathways that regulate metabolism and also directly regulates the expression of certain genes. The results shown were based on providing half of a group of laboratory mice that had no ovaries with a placebo pellet and the other half an estrogen pellet for 40 days. The mice were fed equal amounts of chow.

In the mice, estrogen replacement was found to reduce lipids, or fats, by promoting the use of fat as fuel. The three mechanisms for the observed action include: inhibiting fat storage in liver, muscle and fat tissue; activating the pathways that promote burning the fat in muscles; and breaking down stored fats used for energy reserves in fat cells.

When estrogen was present in muscle, liver and fat cells, the expression of genes that control manufacturing and storing fat was reduced, and the expression of genes that promote burning fat in muscle cells was increased.

Scientists long have known that fading estrogen levels lead postmenopausal women to accumulate more fat and sometimes develop insulin resistance or diabetes. The study demonstrates that estrogen may reduce body fat in animals and may explain some of the reasons behind the association of menopause with increased risk of insulin resistance and diabetes, according to Greenberg.

ARS is the U.S. Department of Agriculture’s chief in-house scientific research agency.