It appears that women are not the only ones who experience the postpartum weight; men gain weight too as they become fathers and sport the trendy "dad bod," which science has an explanation to.

A new large-scale study performed by researchers from Feinberg School of Medicine at Northwestern University involved following 10,2543 men from their preteens to their mid 30's for 20 years.

The researchers found that those who entered fatherhood had an increased body mass index (BMI) over the course of the study.

The study, published on Tuesday in the American Journal of Men's Health, found that a four-pound increase is seen in a man measuring six feet tall, while a childless man of the same size had a lower BMI, a 1.4-pound loss, a report from Quartz stated.

It didn't matter if the fathers live together with their kids or not — becoming a father is linked to an increase in BMI.

However, fathers who live with their kids, also called "resident dads," were the most prone to develop dad bods.

First-time dads who live with their children had an increase in BMI by 2.6 percent over the 20-year study period, as opposed to the two percent BMI increase in non-resident dads.

According to study lead author Craig Garfield, while marriage has known effects on the health of men, it appears that fatherhood can also produce health effects.

The lead author believes that BMI increase in fatherhood is most likely due to lifestyle changes. He said that fatherhood brings in new responsibilities, which means that dads would have less time to take care of themselves or hit the gym for toning up.

"Your family becomes the priority," Garfield said, according to a report from Askmen.com.

The dad bod became a trend when Mackenzie Pearson, a student of Clemson University, wrote a viral essay describing how the dad bod appeals to women, TIME reported.

Pearson described dad bod as a "nice balance between a beer gut and working out," noting that having a dad bod makes men look "more human, natural and attractive."

While dad bod has become a trend, the findings from researchers suggest the need to come up with preventive strategies for new fathers, especially since their weight also has an impact on their kids' health outcomes.