Among the many changes kids can bring? New lifestyle and diet habits.

By Liz Steelman
Updated July 21, 2015
H. Armstrong Roberts / ClassicStock

Confirming all of those suspicions about “Dad Bod,” first-time fathers do, indeed, gain weight—whether or not they live with their child, according to a new study from Northwestern University’s Feinberg School of Medicine.

Researchers used data from the National Longitudinal Study of Adolescent Health that followed 10,253 men over the 20-year transition from adolescence to adulthood. They tracked all participants’ BMIs in correlation to their fatherhood status in four different life-stage waves.

Though all of the men experienced age-related weight and body mass index fluctuations, overall the fathers gained weight, while their typical 6-foot-tall childfree counterparts actually reported losing 1.4 pounds in the same period. On average, the men who lived with their children gained about 4.4 pounds, while the dads who didn’t put on about 3.3 pounds. The findings will be published in the American Journal of Men’s Health.

"You have new responsibilities when you have your kids and may not have time to take care of yourself the way you once did in terms of exercise," Dr. Craig Garfield, lead study author and associate professor of pediatrics and of medical social sciences at Feinberg, said in a statement. "Your family becomes the priority."

The analysis also showed that those who self-reported high general health-levels, high mother’s education attainment, and high participation in daily activities had lower BMIs than their peers. And those who earned a higher income, were married, and spent more time looking at screens had higher BMIs.

"The more weight the fathers gain and the higher their BMI, the greater risk they have for developing heart disease as well as diabetes and cancer," Garfield said in the statement. “We now realize the transition to fatherhood is an important developmental life stage for men's health. It's a magical moment where so many things change in a man's life. Now the medical field needs to think about how can we help these men of child-rearing age who often don't come to the doctor's office for themselves.”