The researchers found that while maternal BMI influenced birth weight, genetics accounted for most of the similarity in parent-child BMI throughout childhood, challenging the idea that obesity risk is largely programmed before birth.
Study: Parental body mass index and offspring’s childhood body size and dietary behavior: A structural equation modeling analysis in the Norwegian Mother-Child Cohort Study. Image credit: NDAB Creativity/Shutterstock.com
Recent research published in journals PLoS Medicine Our findings suggest that maternal obesity influences birth weight more strongly than childhood BMI, and that associations with parental BMI are better explained by common genetics.
Investigating the genetics of childhood obesity in a large family study
Childhood obesity and overweight remain highly prevalent across high-income countries. This is related to both biological and social factors, such as family eating habits and physical activity. It is also familial in nature, related to parental body mass index (BMI), and occurs early in life, leading to increased interest in preventive interventions aimed at parents.
The direct biological influence of parental BMI on offspring BMI can promote the progression of obesity in subsequent generations, so it is important to understand how obesity-related traits are transmitted. The interaction of genetic and environmental factors in such transmission remains unclear.
Multiple studies suggest that genetic traits have a strong influence on parent-child BMI associations, but this has not been precisely quantified. However, an alternative explanation is the developmental overnutrition hypothesis, which suggests that parental obesity influences offspring development before conception or during life in utero. Paternal obesity can affect offspring metabolism through direct or indirect genetic effects on sperm and semen.
The heritability of obesity also introduces genetic confounds into the association. Environmental perturbations can also occur due to the significant influence of shared family socio-economic status, dietary habits, and physical activity behaviors.
The current study aimed to examine whether genetic factors explain the association between high parental body mass index (BMI) at pregnancy and offspring’s birth weight, childhood BMI, and eating behavior by age 8. This study utilized the Norwegian Mother and Child Cohort Study (MoBa), which is linked to the Norwegian Medical Birth Registry. Depending on the specific analysis, up to 85,866 parent-child pairs were included.
The researchers used expanded twin children (Multiple Children of Twins and Siblings (MCoTS) structural equation modeling) to analyze associations between related family members. This model separates the exposure-outcome association into genetic confounding and residual non-genetic components that may include causal and environmental confounding. This will allow researchers to assess whether the parent-child BMI association is explained by genetic inheritance rather than in utero or periconceptional effects of parental BMI on obesity-related traits. If so, Reducing parental BMI without changing the child’s postnatal environment may not be sufficient to significantly reduce childhood obesity risk.
Maternal BMI had a unique effect on birth weight
The researchers first compared how mothers’ and fathers’ BMI related to their children’s birth weights. They found that maternal BMI showed a much stronger association than paternal BMI, and structural equation modeling showed that this difference could not be explained by shared genetics alone.
Rather, the findings support an association between maternal BMI and fetal growth, suggesting that the biological environment during pregnancy plays a role in determining birth weight.
Childhood BMI is mainly explained by genetics
My image has changed since I was born. Children of parents with high BMI were more likely to have high BMI themselves, but mothers’ and fathers’ BMI had surprisingly similar associations with child BMI from early infancy onwards. This pattern suggested that shared genetic factors, rather than pregnancy-specific effects, were driving much of the relationship.
Structural equation modeling supported this conclusion. After 6 months of age, most of the association between parent and child BMI was explained by genetic confounding, and this contribution remained consistently high throughout childhood. By age 8, shared genetic inheritance accounted for 79% of the association with maternal and child BMI and 94% of the association with paternal BMI.
Although the researchers note that some estimates may have been affected by statistical uncertainty, the overall pattern was consistent: the association between parent and child BMI strengthened as the child grew older, but the proportion explained by common genetics remained high.
Taken together, these findings suggest that much of the association between parent and child BMI reflects inherited genetic susceptibility rather than substantial developmental programming effects of maternal obesity during pregnancy, although smaller causal relationships cannot be excluded. In contrast, birth weight appears to have a different developmental origin and is directly influenced by maternal BMI.
The authors also emphasize that these findings are statistical inferences rather than conclusive evidence of causation. However, the results are in close agreement with previous studies using different analysis methods and genetic datasets, reinforcing confidence in the overall conclusions.
Parental BMI was associated with obesity-related eating behaviors
The researchers also investigated whether parents’ BMI was associated with their children’s eating behavior at age 8. We found that higher maternal and paternal BMI was associated with higher child food reactivity, leading to more emotional overeating and lower emotional undereating. Fathers with higher BMI were also more likely to have children who had a lower satiety response and ate more quickly. Additionally, children with higher BMI tended to score higher on most eating behaviors associated with obesity, with the exception of emotional overeating.
Taken together, these findings suggest that genetic genetic susceptibility may influence childhood obesity risk, in part through effects on appetite and eating behavior. However, the researchers caution that structural equation models do not have sufficient power to distinguish between genetic and environmental influences on these behaviors, meaning this potential mechanism cannot be confirmed.
Large family cohorts enhance genetic analysis
This study investigated a large prospective cohort including intergenerational non-twin siblings and up to two children per parent. This model investigated genetically explained relationships between parent and child pairs, between first cousins, and between children and parents’ siblings. This ensured a more powerful model.
This study also has some limitations. Although this model assumes the absence of a common environment, this finding is supported by previous research and further analysis in the current study. Changes in gene expression in response to the environment are not taken into account, which may lead to an overestimation of the genetic contribution. However, the authors did not expect this to be a significant factor.
The study sample included Norwegians from a high-income country with relatively high obesity rates, and the authors noted the possibility of selective recruitment and attrition, limiting generalizability. Future studies with more diverse cohorts should replicate these findings.
Much of childhood obesity risk appears to be driven by genetics.
This result suggests that maternal BMI can have a large effect on birth weight, but the effect on childhood BMI is much smaller. Patrilineal connections may be even smaller. Therefore, lowering parental BMI before pregnancy may not be sufficient to prevent childhood obesity in children through intrauterine mechanisms.
Long-term prevention strategies may also require a stress-free home environment that supports healthy dietary patterns and more physical activity, while recognizing genetic differences in obesity susceptibility among children.
However, strategies to reduce parental BMI before pregnancy may include lasting changes in the family environment that contribute to reducing childhood obesity. Reducing maternal BMI before pregnancy is associated with improved pregnancy outcomes, regardless of childhood obesity risk.
Click here to download your PDF copy.
