Scientists Debunk So-Called 'Fat Gene'

Just as death and taxes are inevitable, some people assume they're also fated to be fat.

Overweight parents tend to have overweight children, but is DNA or diet the culprit? Is it nature or is it nachos?

It's true that we can't pick our parents, we can't change our genes. Most of us are not hard-wired to become obese, though, suggests a new study published today in the New England Journal of Medicine.

So, while you may be having a hard time fitting into your favorite jeans, it's unlikely that your genes are to blame.

A team of British scientists examined 300 people who became severely obese at a young age, to determine whether a faulty gene was involved. Researchers were looking specifically at the gene in charge of the leptin receptor.

Leptin is a hormone that controls appetite and can influence how much we feel like eating. It has been previously implicated in animal obesity studies.

Scientists examined the obese study participants to see whether this so-called obesity gene was disturbed in any way. They found that only 3 percent of people had an abnormal leptin gene -- indicating that leptin is probably not a factor for most obese people.

Genes Might Play a Role

The same group of scientists behind today's report were actually the first to find human subjects with a defective leptin gene, nearly 10 years ago.

In the earlier study, they identified a leptin deficiency in two obese children from the same Pakistani family. The children lost significant amounts of weight following leptin injections.

The finding, combined with the previous animal studies, seemed to set off a firestorm of "leptinomania," so to speak.

Leptin -- derived from the Greek word "leptos," meaning thin -- continues to be touted by some supplement sellers and diet-book authors as a cure for obesity. Today's report, though, suggests leptin probably won't work any magic.

Janet Helm is a registered dietitian and freelance nutrition writer in Chicago.

"Many of the pills and diets that refer to leptin do not have any scientific rationale behind them," said lead researcher Sadaf Farooqi, of the Cambridge Institute for Medical Research, in an e-mail.

Scientists Still Seek Biological Basis for Obesity

Today's finding might be a disappointment to leptinomaniacs, but scientists are actively exploring other avenues and other genetic links to weight gain, metabolism and appetite.

Beyond leptin, five other genes are known to cause weight problems, and there are likely to be many more, Farooqi said.

One "fat gene" that has received a lot of attention lately is MC4R or the melanocortin 4 receptor, which, according to Farooqi, affects at least 1 percent of all obese people.

"Finding these genes will help us to understand why some people gain weight more easily than others and to find ways to prevent and treat severe obesity," she said.

In the meantime, throwing in the towel and blaming your genes isn't the answer. Scientists have found that thin people also have some of the same genetic defects.

So, while you can't control your heredity, you can control what you eat and your activity level. And for most people, these environmental factors remain the strongest influence over body weight -- regardless of their genes.

Janet Helm is a registered dietitian and freelance nutrition writer in Chicago.

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