“If all this talk about mood and libido sounds familiar, it should: testosterone has an overlapping role with our old friend estrogen. You see, testosterone can be converted to estrogen; fat cells contain an enzyme, called aromatase, that converts testosterone to estradiol. The more fat you have, the more likely it is that you’ll create an excess of both androgens and estrogens. We know that excess estrogen may make it extremely difficult to lose weight, which then reinforces the cycle of more fat, estrogen, and weight.”