Are you in a happy relationship and do you think you have been putting on weight ever since your first sexual encounter? While it might seem crazy to think that any physical activity could cause you to gain weight, this fear became popular among men and women after stories surfaced on the internet. New can sex make you gain weight shows that a certain enzyme plays a key role in midlife weight gain. Anonymous March 23, at pm. Not at all. Gay people have a life expectancy 22 to 25 years below average, whether men or women.