"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," Dr. Garfield emphasizes.
The study - published in the in the American Journal of Men's Health - is one of the first to examine how body mass index (BMI) is affected by fatherhood. The researchers followed 10,253 men over a 20-year period, who had their BMI measured at early adolescence, later adolescence, in their mid-20s and in their early 30s.
"Fatherhood can affect the health of young men, above the already known effect of marriage," says lead author Dr. Craig Garfield, 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.
Analyzing the data, the researchers found that a 6-ft-tall man living with his child would gain an average of 4.4 lb after first becoming a father - a BMI rise of 2.6%. Meanwhile, dads of a similar height who do not live with their children put on 3.3 lbs on average - a rise in BMI of 2%.
However, during the same study period, the average 6-ft-tall man who was not a father lost 1.4 lb.
Age, race, education, income, daily activity, screen time and marriage status are all factors that can contribute to weight gain, so these things were taken into account when the researchers calculated the study's results.
Dads are 'pediatric chaperones'
"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. Your family becomes the priority," offers Dr. Garfield, in explanation for the association between weight gain and fatherhood.
Dr. Garfield believes that as new dads enter the health care system "as a pediatric chaperone," pediatricians have an opportunity to talk to fathers about things that are important for their health as well as their child's health. On a practical level, pediatricians are in a good position to offer nutritional counseling and mental health education to fathers.
"We now realize the transition to fatherhood is an important developmental life stage for men's health," Garfield concludes. "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."
A recent study published in the journal Cancer also found that increasing BMI in men is linked with a higher rate of prostate cancer relapse, death from prostate cancer, and death from any cause among men who had received radiotherapy.