Your Grandkids Are Making Each Other Fat

A new study finds that siblings are more influential than parents when it comes to body weight.

By Andrea Atkins

If you have one overweight grandchild, and he or she has a sibling, the chances are high that his or her brother or sister will be fat as well, according to a new study.

The new report in the American Journal of Preventive Medicine, notes that the risk for obesity is twice as great in kids who have overweight siblings as it is for those with overweight parents. 

The results surprised even the study’s corresponding author, Mark C. Pachucki, Ph.D., a faculty member in the Division of General Academic Pediatrics at Massachusetts General Hospital.

“Parents have a relatively large amount of control over what their children eat, how much physical activity they get, who they spend time with, and how they learn about health,” he said, noting that parents choose the foods they buy, what restaurants they frequent and also how to eat healthfully and get enough exercise. They model how to take care of their bodies. “A 10-year-old isn’t doing the grocery shopping for the six-year-old, and so we were surprised to see that the sibling obesity association was stronger than the parent-child obesity association.”

Why Is This So?

Younger children look up to their older siblings and seek their approval, Pachucki says. They are likely to spend more time with each other than they do even with their parents. They tend to influence one another’s behavior a great deal, especially if they are of the same sex.

The study found that if siblings were of the same gender, the likelihood for the obesity to be shared was even greater. For girls, for example, it was 8.6 times more likely that they would be overweight if their sisters were overweight. For boys, it shot up to 11.4 percent greater. (Pachucki says the difference may be because girls are socialized to be more body conscious than boys.)

“There can be a pretty strong bond between same-gender siblings, and more informal mentoring that happens between an older girl and her little sister (or between an older boy and his little brother.) This may translate to a higher risk of passing along unhealthy behaviors that lead to obesity,” Pachucki said. 

Of course older brothers influence younger sisters as well as older sisters influencing little brothers. “But if they don’t identify with one another as closely, this may inhibit the younger child’s adoption of health behaviors,” he added. 

In a study that received a lot of attention a few years ago, Nicholas Christakis, M.D., Ph.D., director of the Human Nature Lab at Yale University, showed that people are greatly influenced by their friends when it comes to eating. It’s harder to be thin, he found, if you are surrounded by overweight people. Pachucki says his research is looking at this phenomenon earlier in the course of life but suspects that the influences are the same. It will fall to future studies, he says, to determine at what point siblings take a back seat to friends or other people in your life.

The One Antidote

Siblings influence each other in one important positive way—a way that can combat their bad eating habits: Exercise. “If both siblings are more physically active,” Pachucki says, “it gives those siblings the greatest chance to keep obesity at bay…when two people are active, there can be a social reinforcement effect.” The same is true for adults; it’s easier to go for a walk or a jog if you know you have someone to do it with.  

How You Can Help

You can decide what kind of grandparent you want to be: the one who always slips their grandchild cookies and other sugary treats or the one who treats them to an active day in the park or beach. Tired of the same neighborhood options? Try one of our 10 fun ideas for what to do with kids when you're out of ideas.

“I think that grandparents can and should treat their grandchildren when they are together,” Pachucki says. “But it doesn’t have to be with sugary sweets on every visit. It can also be a treat to go for a walk together in a new park. And of course, it’s fine to have the occasional sweet treat—in moderation. But it doesn’t have to be part of the routine.” 



There are also lots of great tasting, low sugar treats in the health food store.

Ernie Rosenberg on 2014-08-22 13:58:27

I suspect genes are also at work. In all fairness to parents that needs to be noted. on 2014-08-21 09:31:20

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