Dad Brain: How Becoming a Father Changes Your Brain, Hormones, and Body

Brian Page
6 hours ago
8 min read

When I became a father, my mind immediately went into provider mode. I wanted to make sure my children were financially secure and had every opportunity possible. As they grew older, I became focused on outcomes: reading, math, achievement, and preparing them for success.

Now that I’m an empty nester, one of my biggest regrets is that I didn’t spend more time simply enjoying the process of being a dad. I was so focused on what I thought I needed to provide that I didn’t fully appreciate how much fatherhood was changing me.

That’s one reason I found Dad Brain by Dr. Darby Saxbe so fascinating. Saxbe is a professor of psychology at the University of Southern California who has spent roughly 15 years studying the transition to parenthood. Her lab has scanned men’s brains while they were expecting a child and then again when their babies were six months old. Researchers have also tracked fathers’ hormones, relationships, moods, and overall well-being.

When Dr. Saxbe joined us on the Modern Husbands Podcast, she explained something I wish more men understood before having children: becoming a father doesn’t simply change your schedule and responsibilities. Fatherhood can change your brain, hormones, body, behavior, relationships, and even your sense of identity.

Book Review Summary

In Dad Brain: The New Science of Fatherhood and How It Shapes Men’s Lives, Dr. Darby Saxbe makes a compelling case that becoming a father doesn’t simply change a man’s responsibilities—it can change his brain, hormones, body, and sense of identity. Drawing on years of research into fathers and families, Saxbe explains how involved fatherhood is associated with changes in brain structure and testosterone, greater emotional attunement, and a stronger orientation toward caregiving. In doing so, she challenges the stubborn stereotype that men are somehow biologically less equipped than women to nurture children.

What makes Dad Brain especially valuable is that Saxbe doesn’t treat biology as destiny. Parenting is a skill you can learn. And she points out that fatherhood is something men grow into through involvement: caring for a child can help shape the very biological and psychological changes that make a man a more responsive parent.

That message has implications well beyond individual dads. If we want fathers to become more engaged caregivers, families, workplaces, and public policy need to give men the time and opportunity to actually do the work of caregiving.

Dad Brain is accessible, thought-provoking, and ultimately hopeful. It gives fathers a science-backed reason to view caregiving not as something they are merely helping with, but as a role that can transform who they become. For couples trying to build more equal partnerships—and for anyone interested in how fatherhood is evolving—Saxbe’s book is an important and worthwhile read.

Modern Husbands Podcast Episode 1 of 2 with Dr. Saxbe

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🔔 Click here to listen and subscribe to the Modern Husbands Podcast on Spotify.

Click here to purchase Dad Brain.

What Is Dad Brain?

“Dad brain” might sound like a joke about what happens when sleep deprivation makes a new father forget where he put his keys. The science Saxbe described is much more interesting.

Her lab has found that men’s brains actually shrink during the transition to fatherhood. Christian does a great job in the episode sharing an activity he used when he taught middle school science that helps us understand that brain shrinkage is actually better because it is more efficient and processes information faster.

So yes, becoming a father may actually remodel the brain for the demands of parenting. That makes sense when you consider how dramatically a new parent’s attention changes.

How Fatherhood Changes Testosterone and Other Hormones

The brain isn’t the only thing that changes when men become fathers. Saxbe explained that researchers also see changes in hormones, including testosterone, oxytocin, and prolactin.

I gulped when I read this because the hoopla around testosterone in the manosphere has gone overboard. Yes, it is appropriate for older men; I just started taking it. As Saxbe explained, higher testosterone can be useful when a man is competing for a mate, but once a child arrives, his reproductive priorities have changed.

Testosterone levels can later rise again, and their ability to fluctuate in response to different circumstances is part of healthy hormonal functioning.

I think this is particularly important in a culture where men are often bombarded with messages suggesting that maximizing testosterone is synonymous with maximizing masculinity. Fatherhood offers a different picture.

Is Dad Bod Real?

Then there’s the infamous dad bod. According to Saxbe, there is actually research behind it. Men tend to gain weight during the transition to parenthood, and similar changes have been observed in other species.

That obviously doesn’t mean becoming a dad makes healthy eating and exercise unimportant. It does provide some useful context for the physical changes many new fathers experience. A new baby often changes sleep, stress, exercise routines, eating patterns, work schedules, and opportunities for leisure almost overnight. Hormones are changing at the same time.

The dad bod, in other words, may not simply be the result of a guy “letting himself go.” The transition to fatherhood is affecting both his environment and his biology.

How Dads Bond With Their Babies

One of the most important lessons from my conversation with Saxbe was also one of the simplest: dads become better caregivers by caregiving.

There is a persistent cultural assumption that mothers are naturally wired to understand babies while fathers are destined to stand nearby looking confused. Saxbe’s research challenges that idea. Toward the end of our conversation, she summarized the point beautifully: “Parenting is a skill, not a trait.” She explained that great parents are made through investment, motivation, experience, observation, and attunement to their own children.

Saxbe explained that fathers build competence and confidence by putting in the time. The more opportunities dads have to care for their babies, the more they can develop the sensitivity and responsiveness that help them understand their children.

That idea matches closely with what I wrote in The Great Fatherhood Shift: Why Modern Dads Are Doing More at Home. Modern fatherhood is increasingly moving beyond the idea that a good dad primarily proves his commitment through his paycheck. More fathers are taking active roles in caregiving, household responsibilities, emotional labor, and the day-to-day work of family life.

Why Dads Shouldn’t Wait to Be Told What to Do

A new dad can easily fall into the role of parenting assistant. Mom knows when the baby needs to eat, what goes into the diaper bag, which diapers to buy, when the next pediatrician appointment is, and how the bedtime routine works. Dad waits for instructions and completes whatever task is assigned. As discussed in the previous Modern Husbands Podcast episode, Overcoming Maternal Gatekeeping for Stronger Partnerships, that habit leads to maternal gatekeeping.

Her suggestion for dads is to capitalize on the micro-moments they can take the lead in parenting. Even when time is limited, a dad can take initiative by taking the baby for a walk, owning bath time, planning an activity, or taking responsibility for another piece of caregiving.

Why Paternity Leave Matters for Fathers and Families

Telling dads to spend more time caregiving only goes so far when their workplaces make that difficult. Saxbe pointed out that the United States does not have a federal paid parental leave policy, making it an outlier compared with many other countries, as shown in the image above.

Even when fathers have access to paternity leave through their employers, some are reluctant to use it because they fear being viewed as less committed to their jobs. That puts fathers in the difficult position of trying to succeed simultaneously as providers and involved caregivers.

I’ve seen this problem in my own work with couples. I have worked with high-income dual-career couples preparing for a baby, where the wife is the higher earner and has paid parental leave while her husband has little or none. In some cases, he would actually prefer to spend more time at home with the baby while she returns to work, but the financial consequences make that arrangement extremely difficult. I discussed that exact dynamic with Saxbe during our podcast conversation.

That corresponds with a point I made in the Modern Husbands article, What Can Men Do With Six Months of Paternity Leave? Everything That Matters. Paternity leave isn’t simply time away from work. It provides fathers with concentrated time to learn how to soothe, swaddle, support, adapt, and become competent caregivers through experience.

Early involvement can create a positive cycle. Dad spends time caregiving, so he becomes more confident. Confidence makes him more willing to take responsibility. As he takes more responsibility, Mom is less likely to become the automatic manager of parenting.

The 1950s Dad Wasn’t the Historical Norm

Some men still feel tension between being a provider and being an active caregiver because the breadwinner father is often presented as the traditional family model. Saxbe argues that our historical perspective is much too narrow.

She explained that the familiar image of a 1950s family—with Dad leaving for work while Mom stays home with the children—was actually unusual when viewed across human history. In hunter-gatherer societies, she noted examples of men being deeply involved in everyday childcare. In agricultural societies before the Industrial Revolution, work and family life were often happening in the same place, which meant fathers were around their children far more than the modern office worker might be.

This matters because men sometimes interpret hands-on caregiving as a rejection of a traditional masculine role. The wider historical picture suggests something different. There have been many ways to be a father, and the distant breadwinner model represents only one version.

That idea also connects to a theme running through Modern Husbands: providing for your family can mean more than earning money. Sharing domestic responsibilities, carrying part of the mental load, supporting your spouse’s career, and being an engaged parent are all meaningful ways to provide.

Dads May Play Differently, and That Can Be Good for Kids

Being an equal parent doesn’t mean mothers and fathers have to interact with their children in identical ways. Saxbe discussed research showing that fathers often engage in what researchers call proprioceptive play. That includes physical activities such as lifting children into the air, moving them through space, tickling them, and chasing them. She explained that children enjoy and benefit from this kind of play.

This is another reason dads need space to develop their own relationships with their children. A father doesn’t need to become a copy of his partner to be a capable parent. He needs experience, responsibility, and the opportunity to learn what works between him and his child.

Related Podcast Episode with Dr. Volling

🔔 Click here to listen and subscribe to the Modern Husbands Podcast on Apple.

🔔 Click here to listen and subscribe to the Modern Husbands Podcast on Spotify.

Great Dads Are Made, Not Born

If you’re a new dad and don’t feel like you know what you’re doing, Saxbe’s research offers an important message. You aren’t supposed to arrive at fatherhood already knowing everything.

The belief that Mom possesses an automatic parenting instinct while Dad is biologically clueless can become a self-fulfilling prophecy. If Mom gets all the experience because everyone assumes she knows what to do, she becomes more skilled. If Dad hangs back because everyone assumes he doesn’t know what to do, he gets less experience and remains less confident.

What happens next is partly shaped by opportunity. The more fathers are able and willing to show up, the more chances they have to learn caregiving skills and build their own relationships with their children.

I wish I had understood that when my children were babies. I spent a lot of energy trying to become the provider I thought they needed. Looking back, I better understand that providing is only one part of fatherhood. Sometimes what your child needs most is much simpler: your time, your attention, and the opportunity for both of you to grow together.

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