Can our genes make us feel fat? That’s the question asked by University of Colorado Boulder researchers in a new study that examines the extent to which our “weight identity” is ingrained in our DNA. They estimate that perceived weight status is 47 percent heritable, and that genetic influences seem to be particularly strong for women.
Previous research, the study authors note, has suggested that traits like perceived well-being may be due, in large part, to genetic variation. How a person views their health in relation to genetics, however, has rarely been considered. “This study is the first to show that genes may influence how people feel about their weight,” says doctoral student and lead author Robbee Wedow.
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Wedow and his colleagues looked at data from more than 700 pairs of twins (identical and fraternal) who answered questions about their health and body image five times between 1994 and 2008. During each follow-up visit, participants had their body mass index (BMI) measured and were asked how they felt about their own weight. Their answer choices included “very underweight,” “slightly underweight,” “about the right weight,” “slightly overweight,” and “very overweight.”
Studying twins allowed the researchers to tease out the influences of genetics, as opposed to social or environmental triggers, and to see how these influences differ between brothers and sisters who share many of the same genes.
When they crunched the numbers, they determined that how a person feels about their weight has a heritability of 47 percent. (In genetics research, heritability estimates range from zero to 100 percent—zero meaning that genes don’t contribute at all to a certain trait, and 100 meaning that they are the only contributing factor.)
What’s more, perceived weight status remained about 25 percent heritable even when changes in actual BMI were taken into account. “So this is truly connected to how people feel about their weight, even outside of physical changes,” says Wedow.
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This is important, say the study authors, because previous research has shown that how people feel about their bodies has a big effect on things like physical health and longevity.
“One's own perception about his or her health is a gold standard measure—it predicts mortality better than anything else,” said co-author Jason Boardman, PhD, in a press release. “But those who are less flexible in assessing their changing health over time may be less likely than others to make significant efforts to improve and maintain their health.”
The study, published in the journal Social Science & Medicine, also found heritability to be much stronger in women than in men. “The extent to which genes influence weight identify is dependent on gender,” says Wedow. “We believe that the social environment surrounding weight norm differences between women and men likely have something to do with these heritable differences.”
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The researchers were not able to isolate specific genes that may be involved in weight identity, and cannot suggest any actionable advice as a result of their findings. But they are hopeful that their discovery helps fuel further understanding of the many complex reasons people feel the way they do about their bodies.
They also stress that “suggesting a role for genetics does not mean that identities do not and cannot change.” Even when there is a genetic connection to a particular behavior or trait, they say, a person’s upbringing, social environment, and lifestyle choices are still very important in shaping who he or she becomes.