There have been a number of studies on estrogen and weight gain and estrogen is believed not to increase weight. Many women do gain weight and believe it is due to estrogen, but the studies don't support it.Some increase in breast size and some fluid retention do happen. Having your ovaries out can also affect your thyroid hormone levels and that can cause weight gain. Ask your doctor to check your thyroid levels.here have been a number of studies on estrogen and weight gain and estrogen is believed not to increase weight. Many women do gain weight and believe it is due to estrogen, but the studies don't support it. Some increase in breast size and some fluid retention do happen.