Men who become fathers for the first time gain several pounds, a new study finds, whether or not they live with their children.
Researchers at Northwestern University in the US tracked the weight of more than 10,000 men from adolescence into young adulthood and found that the typical six-foot-tall man gained 4.4 pounds (2 kg) after becoming a first-time father, resulting in a 2.6 percent rise in body mass index (BMI), provided he lived with his child.
A man of the same height who does not live with his newborn gains about 3.3 pounds (1.5 kg), for a 2 percent rise in BMI.
Participants had their BMI measured at four times -- early adolescence, later adolescence, in the mid-20s and in their early 30s -- and were categorized each time as a non-father, a resident father or a non-resident father.
In the time it took fathers to put on those few pounds, non-fathers actually lost about 1.4 pounds.
Researchers suggest the lifestyle changes involved in prioritizing a baby, plus a possible change in eating habits as the house fills with snack food, might be behind the "fatherhood effect."
The study is published Tuesday in the American Journal of Men's Health.