You guessed it exercise. Aerobic exercise boosts your metabolism and helps you burn fat. If it's weight-bearing exercise, such as walking, jogging and dancing, it will also strengthen your bones and counteract bone loss, which helps prevent osteoporosis. Including strength training exercises will increase muscle mass, raise metabolism and strengthen bones. Maybe yes, maybe no.
Studies are inconclusive.
One study found that women on HRT gained more weight than those not on HRT, although the difference was not statistically significant. Another study found that HRT did appear to prevent the increase in abdominal fat. Yet another study showed that women on HRT gained less weight than other women. This was interpreted to mean that HRT doesn't cause weight gain, but also doesn't prevent it. There are many good reasons to consider HRT during menopause, such as protection against osteoporosis and cardiovascular disease.