Does a man’s weight affect fertility and his children’s early health?

This study investigated the effects of a man’s weight on his fertility and child health. This study found that overweight and obese men were less fertile, impacting pregnancy outcomes and early childhood weight.

Male infertility is involved in about 40 to 50% of infertility cases. However, most fertility studies focus on women. Studies have shown that female obesity can affect fertility and pregnancy outcomes. Studies in mice suggest that male obesity may also affect pregnancy and childhood health. The effects of men’s weight on fertility and pregnancy are under investigation.

This study looked at 17 studies of male obesity and fertility. BMI (body mass index; a measure of weight compared to height) was measured in each study. BMI was also measured for patients' female partners. These women all had a normal BMI (25 or less).

The partners of obese men (BMI of 35 or higher) took 33% longer to get pregnant than the partners of men with a normal weight (BMI less than 25). Obese men (BMI of 30 to 35) were significantly more likely to have infertility (49% higher odds).

Compared to men with a normal weight, men with obesity had an 18% higher chance of infertility. Every 3-point increase in BMI increased the chances of infertility by 12%.

Male obesity also affected the weight of newborns compared to men with a normal weight. Obese men were 1.99 times more likely to father heavier babies (over 4000 grams or 8.8 pounds). Obese men were also 1.5 times more likely to father smaller babies who did not develop as quickly during pregnancy.

At three months old, the babies of obese men weighed significantly more than the babies of normal weight men. They were also gaining weight faster. The growth of babies from birth to age 3.5, measured by BMI, was significantly different between the children of obese and normal-weight fathers. By age 7.5, the BMI of children was related to the BMI of their fathers. One study found that the children of obese men (BMI > 30) were 53% more likely to be on the autism spectrum.

This study looked at the relationship of paternal BMI to fertility and early childhood outcomes. This study found that men with high BMI were more likely to be infertile and that babies of obese fathers gained weight more quickly.

The studies included here looked back in time to analyze data. This may bias the results. Also, a child's weight may also be influenced by their upbringing, such as diet and exercise.