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Are “obesity genes” spreading?

Genes “conducive to obesity” may be spreading across many nations thanks to better health care, the study’s authors wrote in a paper describing their findings.

In their view, better health care allows women who are naturally obese to live longer and have more children today than they could have a century ago. Thus the average weight of the women having the most children has been inching upward. The result: a growing fraction of the world’s children carry genes conducive to obesity.

Consistent with this notion, the authors found that overweight or obese women in the United States and Canada are having slightly more children each, on average, than other women. The overweight and obese women also have slightly more siblings, also supporting the theory, the authors said.

“Combined with evidence from twin and adoption studies indicating that genes make substantial contributions to obesity, this study suggests that recent increases in obesity are partially the result of overweight and obese women having more children than is true for average and underweight women,” wrote the authors. 

The study, by Lee Ellis and Dan Haman at Minot State University, North Dakota, is published in the September issue of the research journal Biosocial Science.

The authors found that overweight and obese women, on average, have roughly one-third of a child more than other women – that is, 3.5 children rather than 3.2. They also found that overweight and obese women have on average 4.8 siblings, compared to 4.3 for others. The study included more than 15,000 women.

Although proof is lacking, this evidence suggests “the average weight of the woman having the greatest number children has shifted upward,” said Ellis. “I would guess that if we could have gone back to a century ago, we would have seen that normal-weight women were reproducing at the highest rates.”

Stouter women might have begun having more children in the past half-century, the era in which effective therapies for obesity-associated illnesses such as diabetes and hypertension appeared, the authors wrote.  

The new study suggests that obesity might continue spreading around the world even if people cut back on unhealthy habits, the authors said – contrary to common belief.

No single gene has been found that makes a person obese. However, a range of genetic factors, as well as environmental ones, are believed to contribute to obesity.

A range of studies have shown major increases in obesity throughout most of the industrialized world in the past several decades. While the United States remains at the epicenter of what some researchers call an “obesity epidemic,” studies have also documented rising body weights in at least 10 other industrialized countries, plus a few relatively non-industrialized ones such as China and Brazil.  

—EJL

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