If you’re reading this, you’re either on your way to one or are navigating your way around one as you look for potato chips on the bottom shelf of your cupboard: the “Dad Bod.” We aren’t here to shame you and certainly not the authority on what is or is not beautiful, but like with many things, we have become curious. Why has this trend occurred for generations? Is it simply stress, sweets and being more sedentary? You may be surprised to learn that the Dad Bod goes far beyond just increased calorie consumption and may have roots in evolutionary biology.

One thing I think we can all agree on, is the beauty and complexity of all things involved with starting a family. Let’s discuss the obvious change that occurs in many men when they are expecting

Women and men have all the same sex hormones, just at different concentrations.

For decades, we have centered the hormonal conversation around females. Females normally transition through 3 major hormonal phases: puberty, pregnancy, and menopause. When it comes to male patients, hormones are discussed in the context of puberty and erectile dysfunction. That is all. Modern medicine doesn’t even recognize all the varied hormones, usually just concentrating only on testosterone. It is important to note, women and men have all the same sex hormones, just at different concentrations. Our understanding of these hormones and what they can do for the body is imperative for a healthy, productive, and pain-free life.

Men and Pregnancy – The Emergence of the Dad Bod

Now, here is where things get interesting. Psychological and physiological changes of the female during pregnancy are to be expected, and are largely understood and researched. We can predict when certain hormones will increase and the body changes they will experience. Heck, your doctor can even tell you your due date (roughly) 9 months in advance! But what about men? 

We observe many changes in men that are expectant fathers, as well. Could it be the nerves of being a new parent? Or is it the worry about the financial effects of a growing family? Or maybe it is something else, entirely!

Like many things, the changes in men who are expecting are multifactorial; however, there is something of a hormonal synchrony that men experience with their pregnant partners. Some would say, “home comes the baby and out goes testosterone.” But, long before the sleepless nights and social media posts of your new miracle, the male body begins to change. 

Let’s dive into the research and shine some light on the shifts that may explain the emergence of the Dad Bod. One study looked at over a hundred men with varied relationship status as well as those who did and did not have kids. They concluded that married fathers had significantly lower testosterone levels than those who were married non-fathers and unmarried. The difference was significant, finding a variation of over 30% change in testosterone levels! This particular study was done with adjustments for age and body mass index (BMI) – both of these independently affect testosterone levels, so they wanted to be sure this didn’t alter the results.

In another study of 27 couples (54 individuals) who were expecting their first child, the salivary testosterone of both parents was measured multiple times across the pregnancy. Around 3.5 months postpartum, participants rated their investment, commitment, and satisfaction with their partner in the relationship. Fathers with declining testosterone across the pregnancy, and who matched mothers’ testosterone levels, reported that they felt like they had a higher postpartum investment, commitment, and satisfaction. Mothers also reported more postpartum investment and satisfaction when fathers showed greater prenatal declines in testosterone. In this study, there appeared to be a biological preference when expecting fathers have lower testosterone levels.

“It takes a village,” or so they say. It is tough to argue against the importance of both parents being present, not just for the child, but for each other. Long term bonding is a key social aspect that is not unique to humans, but seen replicated throughout many species in nature. Research finds that many women who wish to have children are biologically more attracted to men that have lower testosterone levels. In these studies, there are no defining physical features of the men with lower testosterone, it’s something on a different ‘level’ that science is still struggling to explain. For now, we call it an energy

One explanation for the lower testosterone preference could be that higher testosterone levels in men are associated with mating effort and could be interpreted as a “flight risk.” On the flip side, lower testosterone levels are associated with partner bonding and paternal care.

As testosterone declines, we begin to see greater muscle loss, which leads to lower metabolic function and a higher propensity for increased fat mass. 

Testosterone is not the only hormone, but one of the major ones that drives lean muscle mass. As testosterone declines, we begin to see greater muscle loss, which leads to lower metabolic function and a higher propensity for increased fat mass. 

Testosterone also improves muscle output; more power equals more strength gains – thus, higher levels of motivation and greater reward from workouts. Testosterone deficiency may lead directly to lower mood but also lack of desire to exercise due to diminishing returns. As you might guess, this could be the perfect recipe for the ‘Dad Bod’.

It is important we recognize, both as patients and clinicians, the signs of testosterone deficiency.

Beyond what the TV ads say are obvious signs of low testosterone, here are some other symptoms to look out for:

  • Low motivation
  • Lower metabolism
  • Lower reward-seeking
  • Depression
  • Achiness upon waking
  • Poor recovery from exercise and more prone to injuries

Up until now, we have just blamed the ‘dad transition’ on sugar, stress, and sleeplessness. Men experience significant changes in hormones throughout a couple’s pregnancy, just as women do. And just as women go through the obvious physical changes, hormones may also explain some of the physical shifts we see in some fathers. Hopefully, now we can appreciate the wonders and capabilities of the human body – female and male – during pregnancy. 

Thankfully, there are many options for testing and treatment for testosterone deficiency. A capable doctor may suggest looking at other hormones, such as thyroid, insulin, vitamin D, DHEA, estrogen, and progesterone, as well. Although we concentrated on testosterone, taking a global look at endocrine function is important to get the whole story. If you are planning to start a family or are in the process, start evaluating your current health status now. De-motivation can be a slippery slope and once that little one shows up, it may be harder to build those self-care habits. Make sure your doctor is staying up on your lab work and if they haven’t yet, at the very least ask them for a testosterone test to get the ball rolling. 

Gray, P. B., Jeffrey Yang, C.-F., & Pope Jr, H. G. (2005). Fathers have lower salivary testosterone levels than unmarried men and married non-fathers in Beijing, China. Proc. R. Soc. B Biol. Sci., 273(1584), 333–339.

Steroids. 2016 Nov;115:62-66.

J. Personal. Soc. Psychol

Horm. Behav. 2003;44:119–122.

Hum. Nat. 2004a;15:119–131.

Evol. Hum. Behav. 2002;23:193–201.