If You Can’t Lose Weight, Don’t Blame Your Genes

There are nearly 100 genes now connected to overweight and obesity, and there’s no question that genes can play an important role in how you break down calories and store fat. But to blame your DNA for the more difficult challenge of losing weight wouldn’t be right. That’s the conclusion of a study led by John Mathers at Newcastle University and published in the BMJ.

Obesity-related genes explain nearly 3% of the differences among people’s body mass index (BMI), a measure of weight and height. And among those, one stands out as having the strongest connection to weight among whites and African-Americans. First identified in 2007, a specific form of the FTO gene, which is involved in regulating how the body either burns calories for heat or turns them into fat, has been associated with being heavier.

Mathers and his team wanted to see how strongly the genetic variant affected weight by studying how the gene might hinder or help people’s ability to lose weight. Would having the obesity-related gene make it harder for people to shed pounds than people without the weight-gaining form of the gene?

Among a group of nearly 9,000 people who were enrolled in 11 studies in which they agreed to genetic analysis and were randomly assigned to a variety of weight loss methods, including diet, exercise or drug-based therapies, Mathers found the answer was a surprising no.

He found that whether or not they had the weight-inducing form of the FTO gene didn’t seem to matter when it came to how much weight the people lost. While previous studies found that people with that variant were on average six to seven pounds heavier than people with other forms of the FTO gene, when it came to losing weight, there was no effect. And there were no differences among people with and without the FTO variant and their weight loss whether they tried dieting, exercise or weight-loss drugs.

“We found no evidence at all that FTO genotype affected weight loss,” says Mathers. “It didn’t affect weight loss when we simply looked at kilograms of weight lost, or BMI or waist circumference; however we looked, the FTO genotype did not seem to matter. We think this is good news — carrying the high risk [form of the gene] makes you more likely to be a bit heavier but it shouldn’t prevent you from losing weight. That should encourage people.”

The results mirror those from previous studies of people with variants of the FTO gene, who were able to counteract the effects of their DNA and avoid excessive weight gain with exercise.

The study still doesn’t answer exactly how the FTO gene contributes to weight, but researchers suspect it has something to do with appetite and people’s ability to feel full. The fact that the researchers did not find differences in people’s waist circumference, a stand-in for the type of fat that a body holds, suggests that the gene isn’t strongly related to the build up of unhealthy visceral fat which can lead to weight gain.

That means that for now, the findings “reinforce some very straight forward public health messages,” says Mathers. “No magic genes change anything in that respect. You have to bite the bullet, and eat a bit less, or be more active [to maintain a healthy weight].”