A study of more than 86,000 children found that the link between parents' and children's BMI is largely explained by shared genetics.
Researchers found little evidence that a mother's BMI during pregnancy has a major effect on a child's risk of obesity later in childhood beyond inherited genes.
The findings don't mean childhood obesity is inevitable, as environment and lifestyle still influence how genetic risk is expressed.
If obesity tends to run in families, is it because children inherit their parents' habits, or because they inherit their parents' genes? A new international study suggests genetics account for much of the connection between parents' body weight and their children's weight during early childhood.
Researchers say higher body mass index (BMI) in parents has long been linked with higher BMI in their children, but it's been difficult to determine whether that relationship is driven by pregnancy-related biological effects, family environment, or inherited genetics. Understanding the answer could help shape future approaches to preventing childhood obesity.
The researchers note that maintaining a healthy weight remains important for many reasons, particularly during pregnancy. However, their findings suggest that reducing a parent's BMI before conception alone may not substantially lower a child's likelihood of developing obesity later in childhood.
“Obesity runs in families, but it is difficult to work out why this is,” researcher Dr. Tom Bond said in a news release.
“Our results suggest that the link between a mother's or father's body mass index and their children's BMI up to age 8 is mostly due to inherited genes. Expectant parents should be encouraged to maintain a healthy weight, but this may not be enough to ensure that their children also have a healthy weight.”
Looking at more than 86,000 families
For the study, researchers analyzed data from the Norwegian Mother, Father and Child Cohort Study, a large, long-running project that followed children born between 1999 and 2009.
The analysis included approximately 86,000 children. Researchers examined information on parents' BMI, children's birth weight, and children's BMI from 6 months through 8 years of age. They also looked at appetite-related eating behaviors when the children were 8 years old, including food responsiveness and emotional overeating.
Rather than simply comparing parents and children, the research team used statistical modeling to estimate how much of the relationship between parental BMI and childhood BMI could be attributed to shared genetics versus other possible influences, such as conditions during pregnancy.
They also explored whether maternal BMI during pregnancy affected birth weight and later childhood obesity risk.
What the researchers found
The results suggest that inherited genetics explained an estimated 79% of the statistical association between mothers' BMI and their children's BMI at age 8, and about 94% of the association between fathers' BMI and their children's BMI.
The researchers also found that higher parental BMI was associated with obesity-related eating behaviors in children, although they said they could not determine exactly how much of those behaviors were influenced by genetics.
Maternal BMI during pregnancy did appear to affect babies' birth weight, but researchers found little evidence that it had a large impact on a child's risk of obesity later in childhood beyond the genes passed from parent to child.
The researchers emphasize that these findings should not be interpreted to mean a child's future weight is predetermined. They note that children who inherit a genetic tendency toward a higher BMI may still experience different outcomes depending on their environment and lifestyle. They also stress that maternal obesity remains an important health concern because it is associated with other pregnancy and birth complications for both mothers and babies.