"With the progression of the obesity [epidemic] there has been attention that over-nutrition could also have negative consequences," says Dr. David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital.
"It is quite extraordinary when you think about it; the effects during pregnancy can potentially have a lifetime implication."
Ludwig looked at the body mass index (BMI) of 42,133 mothers at the birth of their 91,045 children and BMI data of these children until age 12. The researchers only studied mothers who had more than one child to rule out other confounding factors, such as genetics and environment. Siblings share the same genetics and generally grow up eating the same food and exercising the same. If one sibling was overweight but the other normal, researchers could rule out environment and genetics, something that has been difficult to do in other studies.
Then Ludwig compared the BMIs of each mother between her pregnancies to see if the mother's weight gain changed and if that influenced her child's weight.
"Variations in pregnancy weight gain accounted for a half unit difference in child BMI at an average of 12 years," Ludwig said. Since the 1970s when the obesity epidemic began, the change in BMI across the population increased by about two units. This effect remains small on an individual basis but could be one of the factors causing childhood obesity.
While researchers have long known that under-nutrition has a detrimental effect on children, this is the first study that shows that over-nutrition can also harm offspring.
"Excessive weight gain, above recommended levels, can also place that next generation at risk," Ludwig says.
Image: Pregnant belly, via Shutterstock