Many first-time fathers gain weight in early fatherhood, study of an interdisciplinary group of Northwestern University (NU) researchers showed.

The researchers followed 10,000 American men from adolescence to young adulthood, and found that the average man living with his child gained 4.4 pounds after becoming a first-time father. That's a 2.6 percent increase in body mass index (BMI) for a six-foot frame. In contrast, the average six-footer who was not a father lost 1.4 pounds over the same time period, according to a report released Monday on the NU research website.

New fathers' weight gain may be due to changes in lifestyle or eating habits.

"Children are constantly watching parents and will mimic their choices," says Craig Garfield, pediatrics and an Institute for Policy Research (IPR) associate.

The study, one of the first to examine how fatherhood affects BMI, also found an association between the transition to fatherhood and an increase in depressive symptoms.

The study shows that symptoms of depression increased on average by 68 percent over the first five years of fatherhood for men who were around 25 years old when they became fathers and who lived in the same home as their children.

New research published in August by investigators at the University of Bath concluded that men - but not women - gain weight in the first few years after becoming a parent, according to the NU report.

"The health of a family is interdependent. Family members affect each other, impacting each other's emotions, and each other's biology and health," says Emma Adam, an expert on human development and social policy. "Attention to the well-being of all members of the family is needed to optimize the health of the whole family. Supporting the well-being of dads should not only improve fathers' health but the health of the whole family."