This month, DNA testing company 23andMe launched a first-of-its-kind genome-wide association study (GWAS) that seeks to identify genetic, lifestyle, and other factors that could influence individual response to specific weight-loss plans.
The 12-week study will involve 100,000 23andMe customers, who will be randomly assigned to one of three weight-loss programs: a low-carbohydrate diet, a high-fiber diet, or an increased exercise program. Researchers will then try to identify genetic variants, lifestyle factors, or other commonalities among those who show similar outcomes on each of the plans. The results could help provide weight-loss advice and predict how customers might fare on a given plan when they order a genetic report in the future, company scientists hope.
Other GWAS studies have uncovered obesity genes, such as the FTO gene, in the past but “the variants associated with intentional, behavioral weight loss may be different,” says Liana Del Gobbo, lead investigator on the trial. “Research in this field to date is in early stages. We are hoping this study will lead us one step closer to [providing] personalized health recommendations.”
Skeptics, however, warn that science is still a long way from developing genome-based weight-loss advice. “Genetics is jus one piece of the puzzle,” says Yann Klimentidis, assistant professor of epidemiology and biostatistics at the University of Arizona Zuckerman College of Public Health. “We don’t know how big a piece of the puzzle it is.”
But 23andMe researchers have access to more than 3 million customers to find some answers. For the new weight-loss study, investigators recruited volunteers from current customers who had already consented to participate in research. About 85 percent of the company’s customers have consented. Those participating in the new trial are overweight or obese adults between the ages of 18 and 70, who are otherwise healthy and willing to follow the designated weight-loss plan, Del Gobbo says.
Before the trial began, researchers gathered demographic information, weight, and waist and hip circumferences from each participant, she says. They also collected information about sleep quality, mood, diet, food preferences, cravings, physical activity, as well as participants’ motivation and feelings about the study. Now, 23andMe will provide the dieters with tips and advice via email every week. After 12 weeks, researchers will ask participants about their adherence to the diet plans and report some of what they learn. They’ll follow up again at six months and then twelve months.
“Previous studies attempting to link DNA to dieting outcomes haven’t had enough participants to zero in on genetic factors,” Del Gobbo says. “23andMe’s new project will involve ten to 100 times as many participants as previous work.”
However, despite the study’s large size, the genetic predispositions that it may uncover are likely to have small effects, critics say. As with other complex diseases associated with lifestyle, such as diabetes and heart disease, the ability to lose weight is likely the result of many factors. Some of those may be genetic, while other factors may be socioeconomic, psychosocial, or even circumstantial, “like which grocery stores are in your neighborhood,” says Klimentidis.
“Based on what we know about genetics,” he adds, “there’s probably hundreds or thousands of genetic factors that determine your success at dieting.”
Whether a person has a single genetic variant from an already complex composite of risk factors is unlikely to tip the scales one way or the other. “Those one or two genes probably explain only a small proportion of your overall response to the diet,” Klimentidis says.
Even if researchers see stronger effects of certain genes, the study results might not be that helpful for dieters themselves. Knowing your genetic predisposition towards success on one diet over another doesn’t necessarily increase your ability to stick to it, says Cecile Janssens, professor of epidemiology at Emory University Rollins School of Public Health. “When you are tested for a major mutation that increases your risk for a certain complication to almost a hundred percent, then you might respond,” she says. “But anything less, we don’t change our behaviors.”
While the 23andMe study is unlikely to offer an immediate take-home lesson for individual dieters, it takes large studies like this one to begin to chip away at the scores of genetic variants that might impede weight loss, says Klimentidis. 23andMe has the sample sizes and resources to perform such massive studies. “It’s what every researcher would like to be able to do,” Klimentidis says.
His advice for dieters enrolled in the program? “Be skeptical that it’s going to make a difference for you, but be optimistic that it’s going to advance the science.”