To help understand this complex relationships how fit you are is more accurately measured by body composition readings than BMI. Specifically knowing your relative skeletal muscle mass can determine if you have an appropriate amount of strength for your gender and age. Knowing your body fat, and the differential between your visceral fat and your overall fat percentage can help determine your overall leanness. It is important to be lean for thermoregulation. Once it was thought that heavier women would have fewer hot flashes because of overall higher estrogen levels. Then the prevalent theories were that body fat functions as a natural 'sweater layer, and it was postulated that women with increased Body Fat Percentages had more hot flashes.
In a new study published in Nature in May of 2017 Mone Zaidi and colleagues tested the theory of FSH, a brain hormone that is involved in the regulation of ovulation in younger females, can be involved in how the body begins to accumulate more deep fat deposits as a person ages. The researcher gave an antibody to bind and thus lower the the pituitary hormone FSH (follicle-stimulating hormone) and showed that with this treatement increases bone mass and reduces adiposity in mice that have had their ovaries removed and much lower estrogen levels. The antibody treatment also reduced adiposity in premenopausal mice fed a high-fat diet, in part due to increased metabolism and oxygen consumption. It is thought this can both help explain some of the complex relationships between fat and the cascade of brain hormones that are responsible for our body composisiton.
The thought is that in our fat, our largest endocrine organ, some hormones are converted to estrogens. The theories have always had a few problems. The amount of hormone produced by the fat is small, and the hormones produced are weak as well. Some studies indicate that a woman's weight and BMI may not be as directly related but it is the amount of fat. We notice that the relationship between hot flashes and weight and BMI seems to change as women get older, and with careful body composition we now see that the amount of fat in a woman's body also changes as women age, and this body fat percentage is probably the key factor, not the absolute weight.Now we can explain this more accurately by understanding the relationship between the elevation in FSH in menopause and the weight issues, as well as bone loss, that occurs at this time.