If you’ve ever been expecting a baby (or are currently expecting), you know how difficult the process can be. You worry about every single thing until the child arrives, and whether you’re adopting, using a surrogate or you or your partner are pregnant, it’s a nerve-wracking time when it seems like every little thing could affect the baby’s health.

One question that’s often brought up is whether a person’s diet can affect the baby they are carrying. We know that bacteria can have an ill effect on a fetus, and we also know that certain foods are bad for babies. For example, pregnant people are advised to avoid eating certain kinds of fish that contain mercury. But more broadly, can what a person eats, whether before or during pregnancy, affect a baby’s genetics? To understand what can alter a baby’s DNA, we need to look closely at a key question: what is epigenetics?

How Biological Parents Pass Down Their Genes

To answer the question of whether diet can affect a baby’s genes, we first have to look at exactly how genetics work in a fetus. At conception, the egg and sperm combine, and these two contain all the genetic material necessary to create a human. As these cells replicate and divide, the genetic information is copied to each new cell.

Genes are sections of DNA that determine traits such as eye color and body type. DNA comes in pairs of 23 chromosomes, with one half of every pair coming from each biological parent. While there are exceptions to this rule (such as genome-wide uniparental disomy or diploidy (GWUPD), where all genes are inherited from one parent), they are extremely rare.

Diet’s Genetic Role Starts Early

There’s often burdensome pressure placed on pregnant people to think only of the fetus inside them, and not of themselves, when they’re making choices. Individuals should consult with their doctor about which are the right choices for them. It turns out that there is a direct connection between what a pregnant person eats and their baby’s genes, and that link starts before conception.

According to a study published in Nature Communications, what a person eats before getting pregnant can have a significant impact on a child’s DNA. The team behind this study looked at pregnant people in an area of the Gambia where food availability was dependent on climate. More nutrient-rich food was eaten during the rainy season than the dry season, so the researchers looked at 84 people who had conceived in the peak of rainy season and 83 who had done so in the peak of dry season.

They found that nutritional well-being at the time of conception can affect a baby’s genetics. Diet doesn’t alter the genes themselves, but what it can do is affect which genes are and are not expressed (turned on or off), in the earliest stages of development. This is called epigenetics.

What is epigenetics? Epigenetic changes, which are caused by a person’s behaviors or environment, can play a key role in whether a person will inherit a metabolic condition, such as diabetes or insulin resistance. And it’s not just the parents that can influence this; scientists have found that the diet of grandparents and even great-grandparents can cause epigenetic changes as well. It’s not clear exactly how our genes retain these memories as they’re passed down, but there’s increasing evidence that this does occur.

Diet and Exercise Can Alter Your DNA

We know that diet and exercise can alter your DNA as an adult, so it’s not surprising that similar effects can be seen in the genes of a developing fetus. In fact, exercise can lower the risk of a child inheriting heightened risk for diabetes and other harmful medical conditions.

A 2021 study in the Journal of Applied Physiology shows that, in rodents, exercise during pregnancy can mitigate negative effects that a poor diet might have on offspring — so much so that if the parent carrying the child stays active during pregnancy, the risks of passing on a metabolic problem such as insulin resistance to a baby nears zero.

It’s increasingly clear that living a healthy lifestyle full of exercise and eating healthy foods is important before conception even occurs. But everything is in moderation, and there’s no reason to worry whether having an indulgent meal or skipping a morning run will cause harm to a fetus.

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