Hypothyroidism, where your thyroid is underactive and doesn't make enough thyroid hormones, is associated with weight gain, colder body temperature, fatigue, and dry skin. These symptoms sound familiar? Go see an endocrinologist or your primary care doctor to get tested.
Your other hormones are out of whack
What makes men and women so different, besides every cliche that's been exploited on sitcoms and bad stand-up routines, are the differences in sex hormones. Men produce more testosterone, which is responsible for sperm production, sex drive, muscle size, and fat distribution. Women produce more estrogen, which is responsible for regulating menstrual cycles, cholesterol, and your mood, among other functions.
An imbalance of either is tied to weight gain; if women have too much estrogen, they can become insulin-resistant and store more fat. To make matters worse, extra fat tissue creates more estrogen, so it becomes an annoying cycle that can be hard to break. Men, on the other hand, can experience weight gain with too-low testosterone, since the hormone affects metabolism and muscle mass. Although hormones can be regulated with certain lifestyle changes, Dr. Splaver says people may need to take supplements to bring their hormone levels back to normal, which may help with weight loss.