HRT does slow metabolism because fat is less metabolically active than muscle. As fat replaces muscle, metabolism declines.
My most-feared side effect of HRT was slower metabolism. Indeed, I loved eating so much that the fear of lower metabolism delayed my transition. I, too, ate excessively for years but did not gain much weight, and the thought of losing that ability was terrifying. However, I found that as long as I exercised sufficiently, my metabolism did not change much at first from blocking testosterone and taking a low dose of estradiol. Unfortunately, after increasing the estradiol in December, my metabolism has been in steep decline. I ate similarly but started gaining weight, and noticed I was also more tolerant of the heat and more sensitive to the cold, both of which signify a slower metabolism. Sometimes I even get 'shiver attacks' after taking my oral estradiol, signifying a metabolism in free-fall. Dieting to compensate for that only made the problem worse, and my weight reached a record high on Sunday. Ironically, the estradiol is taking away my femininity because much of the extra weight is coming on to the waist/abdomen and shoulders, making me look more masculine! I can't even touch progesterone; that stuff makes me gain pounds in days. This is my worst fear, realized.
