A healthy body is key to fertility. Being under or overweight can lead to infertility in both men and women. Maintaining a healthy BMI and a balanced diet increase the chances of pregnancy. Men with a BMI of less than 20 may have limitations on sperm production, similar to underweight women who may have irregular menstruation patterns. A higher than recommended BMI can reduce male fertility as well. Men with a BMI higher than 25 have 22% reduced amount of sperm. Women with a high BMI can also have problems with menstruation patterns. 30-40% of the women in this group can have problems with their ovulation. Fat cells in the body stimulate the production of estrogen. Too high levels of estrogen on the other hand can then act like a natural birth control.