Dad's diet can predispose unborn children to obesity

One thing we do know about what is driving the obesity crisis is that it’s incredibly complicated. Research even suggests that biological changes in the womb can predispose a child to obesity before they’re born, putting them at risk of health problems related to weight such as type 2 diabetes, high blood pressure, sleep apnoea and heart disease.

Yes, weight has much to do with what we eat and how much exercise we get, but this is rarely simply a ‘lifestyle choice’. It’s often informed by lack of choice: the cost of food, the cost of healthy food compared with the cost of junk food, whether we live near somewhere where we can safely exercise, the work we do (sedentary job or not), our level of education and so on.

Yet some children begin with a higher risk than others.

Children born underweight are known to face a higher risk of obesity, diabetes and heart disease later in life, for instance. So too are babies born overweight, and children exposed in the womb to conditions such as maternal diabetes or obesity.

This isn’t surprising. Before we’re born, we are constantly receiving signals from our mother about the world we’re about to enter. A developing foetus is exposed to nutrients, hormones and other biological cues that help shape how its body will function for years to come. These early signals can influence everything from appetite to how effectively the body regulates blood sugar, uses energy or stores fat.

Scientists are still piecing together exactly how this happens, but one explanation lies in the way genes are switched on and off. We inherit the genes that determine how our bodies work from our parents, but the environment we experience in the womb can influence how active some of those genes become. One mechanism, known as DNA methylation, acts like a series of little dimmer switches attached to the gene, turning its activity up or down.

These subtle biological changes may help explain why experiences before birth can have consequences that last a lifetime, affecting a person’s risk of obesity and other metabolic diseases decades later.

Though mothers are obviously important, fathers who provide half the genes of the child have received much less attention. We are now learning that aspects of Dad’s health, including his weight, influence the offspring’s risk of developing obesity. In our recent animal research, we found the effect of a Western junk-food diet that caused obesity in the father to have greater effects on the offspring than the same diet given to the mother. In these animal studies, we know that the father effect was transmitted with his sperm.

Tackling obesity requires treatment and prevention. People already living with obesity or metabolic disease deserve access to effective treatments, including newer medicines such as Wegovy and Mounjaro, as well as bariatric surgery.

But we also need to prevent these problems developing in the first place. That means creating healthier environments, ensuring families can afford nutritious food. In a healthy society, a bucket of KFC should never be the cheapest way to feed a family.

As obesity becomes more common, more children are born with a higher risk of developing it themselves. Our research suggests that some of the most important opportunities for prevention occur before a baby is even conceived, particularly for fathers and probably mothers as well. Acting during these windows could help break the intergenerational cycle of obesity.