Postmenopausal weight gain is a common problem for many women. Most suspect it has something to do with declining or changing hormones, but the mechanisms have remained unclear. Fat, researchers are learning, is not merely the inert blob we thought it was, but a complex endocrine organ capable of initiating and maintaining its own growth. Not good news for those of us who carry an over abundance of this cushy substance.
In a recent study measuring the mechanisms of subcutaneous thigh fat storage it was learned that the enzymes that direct whether we store or burn fat are re-regulated post menopause, presumably by hormone changes. Called adipocyte fatty acid storage factors, these proteins determine whether and how much fat is burned or stored. For post menopausal women, not only are there more post meal fatty acids but more fat is stored. What was interesting was the mechanism. There were no differences between the pre- and post- menopausal enzymes that broke down the fats (lipoprotein lipase), meaning the capacity to burn it remained unchanged. What changed was the capacity to store it.
The researchers found the two enzymes that determine fat storage rates (adipocyte acyl-CoA synthase and dicylglycerol acyltransferase) were significantly upregulated in postmenopausal women. Why they were upregulated was not clear. The standard presumption was made that declining ‘estrogen’ concentrations must somehow regulate the fat storage enzymes, but none of the estrogens were measured.
In a similar study looking at the role androgens and fat storage in men (diagnosed hypogonadal – low testosterone and eugonadal – ‘normal’ testosterone men), researchers found the hypogonadal men exhibited upregulated fat storage factors in the femoral area (butt and thigh). The pattern was consistent to that observed in postmenopausal women. Since neither testosterone, the other androgens or estradiol and other estrogens or even progesterone hormones were measured in either study, it is unclear which hormones or hormone patterns impact these fatty acid storage factors. What is clear, however, is that aging, whether chronological or endocrine, seems to increase fat storage.