Mother’s genetics may play an important role in influencing her child's weight

A mother's genetics may play a bigger role in determining whether a child becomes overweight than a father's, as a result of a concept known as genetic nurture, finds a new study led by UCL researchers.

Published in PLOS Genetics, the study analysed genetic and health data from 2,621 UK families in the Millennium Cohort Study, a UK birth cohort study of individuals born in 2001/02. 

Researchers investigated how parents' body mass index (BMI) and related genes influence their children's weight and diet from birth to age 17.

To do this, the team examined the association between parental BMI and child birthweight, BMI, and diet at six key points during childhood and adolescence, ages 3, 5, 7, 11, 14, and 17. Children's diets were assessed through self-reported records of how often and how much they consumed different food groups, including fruit, vegetables, fast food, and sugary drinks.

By measuring both children's and their parents' genes, the researchers were able to separate the direct effects of inherited genes from the indirect effect of genes that were not inherited. Non-inherited genes can still influence children's outcomes by influencing the development environment - such as conditions in the womb and parenting practices – as these are shaped by parents' genetics.

Researchers found that while both parents' BMI was linked to their child's BMI, father's influence could be explained almost entirely by direct genetic inheritance. In contrast, the mother's BMI continued to affect the child's weight even after direct genetic inheritance.

This suggests, the researchers say, that genetic nurture - where a parent's genes shape the environment they create for their child - may be at play. For example, a mother's genes might influence her own weight, eating habits, or behaviours during pregnancy, which in turn affect her child's development and long-term health.

Mothers' genetics appear to play an important role in influencing her child's weight over and above the child's genetics. 

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." 

Dr. Liam Wright, study's lead author, UCL Social Research Institute

The researchers acknowledged that BMI is an imperfect measure of body fat accumulation, particularly among children, and so supplemented their analysis with several other adiposity-related measures, including fat mass. 

Dr. Wright added: "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."

Childhood obesity is a continuing problem in the UK and across many other countries, with NHS data showing 27% of children aged 2-15 years-old were considered obese or overweight in 2024¹.

The study was funded by the Medical Research Council, the Economic and Social Research Council, and the Norwegian Research Council.