Childhood obesity is driven not only by eating habits and inherited genes, but also by non-inherited genes. Mothers in particular play a pivotal role in whether children become obese.
“It’s not just our genes that affect us, but potentially others’ genes affect us too – because their genes influence their traits and behaviors, and consequently the environments we face,” says Liam Wright at University College London.
Studies have long noted that children with obesity often have parents with obesity. However, most of this previous work relied on observational data that did not distinguish between maternal and paternal genetic effects. Furthermore, they couldn’t determine whether a parent’s influence on a child’s weight came from the genes they passed on or from parenting behaviour and household conditions.
Now, Wright and his colleagues have homed in on exactly how parents’ genetics are linked to the weight and diet of their children.
The researchers used a genetic analysis method called Mendelian randomization (MR) to separate the effects of direct genetic inheritance from indirect environmental influences. The team analysed the body mass index (BMI), a measure of body fat based on weight and height, of over 2,600 families – mothers, fathers and offspring – in the UK’s Millennium Cohort Study.
They also tracked which obesity-related genes parents passed down to their children and which they did not. This let the researchers measure the “genetic nurture effect”, the influence of a parent’s genes on the environment they create for their child.
The study found that, though an offspring inherits equal genes from both parents, only the mother’s BMI, not the father’s, contributes to the child’s birth weight. The team also revealed that the mother’s particular influence extends beyond the genes she passes on. Her BMI is crucial to offspring BMI, not only through direct genetic pathways but also via non-genetic mechanisms, such as in-utero conditions and “food parenting” behaviours – active ways parents influence what, when, and how their children eat.
Additionally, a mother’s BMI was consistently associated with her child’s BMI during adolescence, and this link appears to be driven by non-inherited obesity genes. These genes from the mother impact her child’s weight through indirect nurture effects. This suggests that a mother’s genetic makeup shapes the home environment, which in turn influences the child’s BMI.
In contrast, the father’s untransmitted genes had almost negligible impact on children’s weight. This means that the commonly observed child-father association for BMI is likely due to direct genetic inheritance.
“Mothers and their children’s BMI are correlated, not simply because we directly inherit half of our mother’s genes, but also because genes that influence our mother’s BMI also shape our environment,” says Wright.
Journal Reference: DOI: journal.pgen.1011775
