Ever wondered why some women, but not all, have the “pear” shape considered by many to be desirable? Researchers might have found some answers to the mystery, after discovering that estrogen, one of the sex hormones, affects where fat is stored in a woman’s body.

The study, published in the American Journal of Physiology: Endocrinology and Metabolism, involved 17 premenopausal women between the ages of 18 and 44 who were overweight or obese.

Researchers from East Carolina University asked the women to provide certain information, including:

  • Weight
  • Height
  • Fat percentage
  • Lean body mass
  • VO2 max (a measure of physical fitness).

They then analyzed how estrogen affects fat accumulation in particular areas of the body.

This was done by slowly infusing estrogen into the buttocks and belly of the women overnight. The women were then given drugs that encouraged the burning of fat in the body (lipolysis). They were also asked to exercise at a level similar to a standard exercise session, both with and without the lipolysis drugs.

Fat breakdown was measured using microdialysis – a sampling technique that looks for the amount of glycerol left behind after the breakdown of fat for eventual energy production.

The researchers found that the effect of estrogen on fat deposits was dependent on the deposits’ particular location and how the fat is burned.

Results of the study revealed that estrogen halted fat breakdown in the abdomen area when the hormone was infused alongside a lipolysis drug called isoproterenol. However, it did not have the same effect in the buttocks.

The researchers add that after a second drug was infused in the abdomen along with the first, no further fat was broken down.

But when both of the fat-mobilizing drugs were infused together alongside exercise, and when the participants exercised without the drugs, fat breakdown in the abdomen increased, although less in the buttocks.

The study authors say: “Our results indicate that the influence of E2 (estrogen) is dependent on the adipose tissue (loose connecting tissue) depot of interest as well as the specific regulatory mechanism targeted.

The authors add:

“The importance of understanding estrogen action in adipose tissue is underscored by the fact that adipose tissue is an estrogen-producing organ, particularly in postmenopausal women, where adipose tissue is the major site of estrogen production.”

The scientists say their findings could potentially lead to an understanding of why post-menopausal women are more likely to accumulate fat around the abdomen area.

When it comes to pre-menopausal women, the researchers say that the relationship between estrogen and the breakdown of fat is what may help maintain a woman’s “pear” shape – more fat around the middle area of the body.

They conclude that further research is needed to determine the mechanisms as to why and how the effects of estrogen vary.