Islamabad: A regular 6-foot-tall man living with his child gained an average of 4.4 pounds, after being a father for the first time, the study says

For "nonresident" dads, who lived in a different house than their child, the average weight gain was 3.3 pounds

Change in BMI for nonfathers was attributed solely to age, says the study

When John Kinnear's wife became pregnant, her boss warned the soon-to-be father that he gained 10 pounds for every child he'd had.

"I shook it off at the time, and now here I am two kids and 25 pounds later," Kinnear said. It's a good thing we're done having kids!"

Kinnear, who writes the "Ask Your Dad" blog, may have been personally surprised by his path to extra pounds, but a study shows he's not the only dad with such an experience.

A new study released in the American Journal of Men's Health analyzed the BMI of more than 10,000 men from adolescence into their mid-30s through data collected from the National Longitudinal Study of Adolescent Health. By comparing three groups -- nonfathers, resident fathers (who live with their children) and nonresident fathers — researchers from Northwestern Medicine discovered the dad groups showed an increase in BMI between adolescence and fatherhood.

In fact, a regular 6-foot-tall man living with his child gained an average of 4.4 pounds after becoming a dad for the first time, according to the study. There was only a slight difference for the nonresident dads. Those fathers gained, on average, 3.3 pounds.

Meanwhile, nonfathers lost 1.4 pounds over the same period.

The results were surprising to the study's lead author, Dr. Craig F. Garfield, especially given his earlier research that fatherhood motivated men to improve their health habits.

"Regardless of what kind of father you were," Garfield said, "Your weight actually increased. So all fathers ended up increasing their weight as they go through fatherhood." Garfield serves as associate professor of pediatrics and of medical social sciences at Northwestern University Feinberg School of Medicine and attending pediatrician at Ann & Robert H. Lurie Children's Hospital of Chicago.

The study accounted for factors such as race, education, income and screen time as well as marriage status, which has been shown to affect weight. Though all the young men's BMI showed an increase over time due to age, additional weight gain was shown to be contingent on fatherhood status, according to the study.

"It certainly echoes my own experience," Anderson added, and said there was much less time for eating healthy once he became a dad. He himself has had to work off the 30 pounds he gained since fatherhood.

That connection — and the fact that obesity is on the rise -- calls for a greater conversation around young men's health, according to Garfield, who said this group tends not to regularly see a primary care physician.

As a result, pediatricians are in a good position to counsel dads about taking care of their health, according to Garfield.

"The transition of fatherhood is a magical moment," said Garfield. "We need to find a way to engage men for their improved health," he added, including having doctors and the health care system be there in such a transitional period of their lives.

"It's a two for one," according to Garfield, who explained the importance of fathers setting the precedents for healthy behaviors. "By helping a father take care of himself, he ends up role-modeling for his children."