According to a recent study, men who are fathers are about four pounds heavier than those without children. This isn't a shock in itself — "dad bods" are common enough. What is surprising is that the extra weight comes from chemical shifts rather than dads getting less sleep and eating more fast food. "The changes are hormonal," says Louann Brizendine, author of The Male Brain and a psychiatry professor at the University of California, San Francisco. "They stimulate a father to stay both physically and emotionally close to his offspring." Here's a look at what goes on after a dad — yes, dad — has a child.
Testosterone Levels Drop
Studies show that men who live with their pregnant partner can experience a 20 to 30 percent drop in testosterone until six months after the baby is born. The temporary drop in testosterone can spur Couvade Syndrome in males, known as "sympathetic pregnancy." Couvade's can affect one to two-thirds of men, and the most common symptom is an increased appetite to match their pregnant partner.
Researchers are still trying to understand why this happens, but cohabitation is likely part of it. "The hypothesis is that there is some type of pheromone put off by the pregnant body of the female partner," says Brizendine. The idea is that the pheromone’s job of decreasing your testosterone will keep males close to the nest, supplying the female with more food and driving down desire to go out and find a new female. The male stays close to the cave and helps prepare for the new infant’s arrival, ensuring that his DNA will be passed to the next generation.
Oxytocin is released whenever we give a hug or kiss, or engage in physical forms of affection — helping us attach emotionally to other people. Research shows that new fathers experience elevated levels of the hormone after rewarding interactions with their baby — teaching them how to sit up straight, tossing the baby in the air or trying to make them laugh. The hormone's release stimulates bonding and enhances a father’s defensive behaviors with strangers to better protect his infant.
The Brain Adjusts
"The 'Daddy Brain' is a real phenomenon," says Brizendine. "Once you take a male and they have an infant, their brains are able to hear babies' cries much more quickly than males who have not had a baby." In one study, fathers were able to recognize their child's cry just as well as mothers. And MRI scans show more activity in a new father’s brain for up to six months after the baby arrives in regions connected to behavior and emotion. But shifts in brain circuits like hearing and behavior only happened for fathers in close and frequent contact with the child — meaning paternal leave from work is as important for fathers to bond as it is for mothers. "It's a healthy thing," says Brizendine. "It's all in the service of helping his DNA into the next generation — helping his offspring survive."