Mother’s genes may hold the key to childhood obesity

A mother’s genes may influence a child’s weight more strongly than a father’s genes. This is the conclusion of a major study led by researchers at University College London.

The analysis combines deep genetic data with insights from the Millennium Cohort Study, which tracked children in the UK from birth to age 17.

The researchers examined how parental BMI and genetics affected children’s weight, diet, and birthweight. They analyzed data at six stages: ages 3, 5, 7, 11, 14, and 17.

Moms affect kids beyond just genes

The researchers used Mendelian Randomization (MR) with polygenic scores to untangle direct inheritance from indirect effects. These indirect effects are called “genetic nurture.”

A parent’s genes may shape a child’s weight not through inheritance, but by creating a certain environment – through eating habits, health during pregnancy, or household norms.

“Mothers’ genetics appear to play an important role in influencing her child’s weight over and above the child’s genetics,” explained Dr. Liam Wright from the University College London.

“In addition to the genes mums directly pass on, our findings suggest that maternal genetics are instrumental in shaping the environment in which the child develops, therefore indirectly influencing the child’s BMI too.”

Dads mostly pass down genes only

Both parents’ BMI were initially linked to higher BMI in children. But when adjusted for genetic transmission, only the mother’s BMI remained consistently associated.

The father’s BMI, in contrast, showed little to no effect once inherited genes were taken into account.

This suggests that prior studies linking fathers’ weight to children’s weight may have overestimated the impact. Those links likely came from shared genes rather than parenting behaviors.

Pregnancy and child’s future weight

The study supports the “developmental overnutrition hypothesis.” This theory says that high maternal BMI can affect the fetus by exposing it to higher levels of glucose, fatty acids, and inflammatory signals. This may permanently alter appetite control and fat storage.

Birthweight data backs this up. Children of mothers with higher BMI had higher birthweights, regardless of genetics. The link was not observed for fathers.

This connection could reflect how the prenatal environment contributes to long-term weight trends, noted the researchers.

Mom’s weight linked to child’s diet

Mother’s BMI was linked to poorer child diets, especially during adolescence. Children of mothers with higher BMI reported eating more fast food and sugary drinks and less fruit. These effects were subtle but present even after accounting for direct inheritance.

Interestingly, father’s BMI showed almost no consistent link to children’s diets. Even where slight effects appeared – like at age 14 – they were weaker than the maternal patterns.

How big is the genetic nurture effect?

The indirect effects of maternal genetics were found to be between 20 and 50 percent the size of direct inherited effects. That is a significant influence. For diet, the effect of the mother’s genes sometimes exceeded that of the child’s own.

These patterns reinforce the idea that maternal influence is not just about passing on DNA. It includes how mothers eat, behave, and care for themselves and their children – during pregnancy and beyond.

“This isn’t about blaming mothers, rather, supporting families to make a meaningful difference to children’s long-term health. Targeted interventions to reduce maternal BMI, particularly during pregnancy, could reduce the intergenerational impacts of obesity,” said Dr. Wright.

Why this matters for policy and families

This research shows that helping mothers achieve healthier weights could benefit their children – now and decades later.

The results of the study highlight the need for maternal-focused health programs during and before pregnancy. These programs can reduce long-term risks for the next generation.

At the same time, the research challenges assumptions about how fathers influence their children’s health. The findings emphasize the importance of using genetically informed methods when exploring these questions.

As childhood obesity continues to rise, understanding these hidden influences becomes essential. This study brings new clarity – and new directions for preventing obesity from one generation to the next.

The study is published in the journal PLOS Genetics.

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