Can having a sibling help protect against being overweight?

An interesting new study published in the April 2016 edition of Pediatrics shows that the birth of a younger sibling is associated with a dramatic decrease in the risk of obesity. I don’t think this ought to sway people towards having more children, but it might offer some insight into other ways to help children keep a healthy weight.

The study recruited families from 1991-1998 (yes, it’s old data. I’m not sure why it took so long to get this written and published.) About 700 children ended up participating. Through in-person visits and phone interviews, the study children were followed from birth through about first grade, tracking who ended up having younger siblings born. The authors then compared children who had younger siblings versus those who remained the only child in the household.

The numbers look strong. Having a younger sibling born between ages 2 to 4 (and especially between 2 to 3 years of age) led to a robust decrease in the upwards trajectory of a child’s BMI. In fact, children who didn’t have a younger child born while they were in preschool had three times the risk of obesity.

Crazy, huh? Three times the risk? Statistically speaking, that’s a big change. This study was unable to show why the birth of a younger sibling helped children keep a more-healthy weight. The authors suggest two possible mechanisms, or ways that having a younger sibling could be protective. Perhaps it changes the way parents feed their children. Other research has shown that ‘restrictive’ feeding practices, like limiting portions or different kinds of foods, are associated with an increased risk of obesity – and maybe having a younger child to look after leaves parents unable to monitor feedings as closely. Allowing young children more control over their food choices does lead to healthier eating and healthier weight gain.

Another idea: children who get younger siblings may themselves become more active, by playing with their little brothers and sisters. They might also become “food leaders”, trying to show their siblings how to eat healthy.

There may be other mechanisms at work here. I’m certainly not convinced I know why the study worked out this way. I do know that healthy weights aren’t about counting calories, only eating “healthy foods”, or buying organic. Hopefully further insights along these lines of this study can help with counseling even single-child families about mealtime and lifestyle routines that can best keep families healthy.

This blog was originally posted on The Pediatric Insider.

©2016 Roy Benaroch, MD