Sammy Nickalls
August 30, 2015 10:11 am

We all know that in order to watch our weight, we should try to eat healthy and get ourselves moving most of the time. But we also know that body types can be highly genetic: some people can eat whatever they want and not gain a pound, while others eat healthy and hit the gym all the time and still remain heavier than they would like. It turns out, though, that weight might be partially predetermined in a way you may not expect: your birth order.

According to a study conducted by University of Auckland in New Zealand and Sweden’s Uppsala University, and published in the Journal of Epidemiology & Community Health, there may be a major benefit to being born second. First-born women in Sweden were 29% more likely to be overweight. . . and 40% more likely to be obese.

The study involved an analysis of 13,406 pairs of sisters from the Swedish Birth Register. The register contains info dating back to the first newborn checkup on almost all births in Sweden since 1973, according to CBS. The researchers then measured the women’s height and weight and compiled information on current health, lifestyle, and family histories. Initially, when they were born, the older sisters were more likely to be slightly lighter, but something changed as they grew older. First-borns were more likely to have a higher weight and BMI.

As CBS notes, this is the largest study conducted of its kind on women, and the results are consistent with findings in similar past studies done on men, which have indicated that firstborn men are more likely to have high blood pressure and diabetes. But the reasoning behind this is unclear to researchers. It could have to do with a change in blood supply to the placenta between first and later pregnancies, hypothesizes lead study author Professor Wayne Cutfield from the Liggins Institute at the University of Auckland. As he explained, this change could reduce the nutrient supply so that later in life, the firstborn child is more likely to store fat.

Maria Peña, Director of the Center for Weight Management at Lenox Hill Hospital in New York City, told CBS that she believes it could be less biological and more environmental. “In many cultures, moms are more meticulous with their firstborns,” she told CBS. “With the very firstborn, everyone’s helping out and over-feeding the baby, making sure it’s at a ‘healthy weight.’ But with second children, parents know what to expect and they’re not so overprotective so maybe they feed them a little less.”

Unfortunately, this “over-feeding” could dictate the firstborn child’s eating patterns for the rest of their lives. “People that develop obesity later on in life forget to listen to the signal in their brain that tells them to stop eating,” Peña continued. “Early on in life, some kids are taught to override that signal. If a parent tells a child to keep eating even when they’re not hungry, then that’s a habit they learn.”

However, this study isn’t perfect. For a better idea of how birth order affects everyone universally, the pool of subjects should be more diverse, and different cultures should be taken into account. But this could be a groundbreaking start in how we treat obesity both in the doctor’s office and out — as well as in the parenting world.

(Image via iStock)

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