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Your DNA won't determine the best diet to help you lose weight

Your DNA won't determine the best diet to help you lose weight
A new study found that a person's genetic makeup had no bearing on whether they lost weight by following a low-fat or a low-carbohydrate diet. (Jack Gallagher)

Trying to lose weight? Researchers have some good news: You can chose either a low-fat or low-carb diet. As long as you stick with it, you can slim down no matter what your genetic make-up or metabolic particulars.

And here’s an added bonus: You won’t even have to count your calories.

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The findings were published Tuesday in the Journal of the American Medical Assn.

Early research has suggested that certain clusters of gene variants might be good predictors of an individual’s response to certain diets. On a medical landscape in which DNA testing is increasingly used to tailor treatments to individual patients, the idea of such “precision medicine” for weight loss has had a powerful allure.

That research, much of it done by the same Stanford Medical School team that conducted the new JAMA study, has also proved tempting for genetic-testing labs looking to drum up business. Advertising its genomic match-making services to dieters, for instance, one lab offers customers the chance to “lose up to 3x more weight on your DNA diet.”

Whether those factors actually made a difference in how subjects responded to a low-fat or low-carb diet was the study’s central question.

The researchers from Stanford’s Prevention Research Center were motivated by a modern-day puzzle.

In clinical trials of weight-loss interventions, there’s a lot of range behind the “average weight loss” numbers reported for groups of study volunteers. After 12 months of dieting, individual subjects may lose as much as 55 pounds. Others, however, will gain 11 pounds.

“The substantial variability of weight loss response suggests some strategies may work better for some individuals than others, and that no one diet should be recommended universally,” wrote the authors, led by nutrition and obesity researcher Christopher D. Gardner.

Gardner and his colleagues recruited 632 overweight or obese adults between the ages of 18 and 50 and randomly assigned them to follow either a healthy low-fat diet or a healthy low-carbohydrate diet for a year. In all, 609 completed the study.

Before embarking on their weight-loss journeys, the subjects took a glucose tolerance test to see whether, according to previous research, they should have a particularly strong response to a low-carb diet. They also took a DNA test to place them into one of three categories: those who carried a cluster of gene variants known to make them more sensitive to dietary fats; those who are genetically more sensitive to carbohydrates; and those who have none of the diet-related genetic variations researchers tested for.

Once the dieting got underway, participants learned and practiced the fundamentals of reducing either fats or carbs in their diets. In as many as 22 small-group meetings led by coaches, they were also encouraged to avoid the unhealthy pitfalls of each diet, like bingeing on bacon on the low-carb diet or snarfing “fat-free” brownies on the low-fat diet.

Participants in each group were instructed to find the lowest level of low-fat or low-carb eating that they could sustain “indefinitely.” And those in both arms of the study were encouraged to eat foods prepared at home whenever possible, to maximize vegetable intake, and to minimize their consumption of processed foods, or those made with added sugars, refined flours and trans-fats.

Importantly, there were no instructions to keep track of their calories.

“We only told them how to cut back on carbs and fat. And we encouraged them — pushed them really — to not be hungry, to find their sweet spot,” Gardner said. “We said it up front: We want this to be long-term, to be healthy, to have fun and enjoy your food.”

After a year, the 305 subjects on the low-fat diet had lost an average of about 11.5 pounds, while the 304 subjects who completed the low-carb diet had lost an average of 13 pounds.

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None of the genomic or metabolic tests were good predictors of a subject’s success on one diet or the other, the researchers found.

“Neither of the two hypothesized predisposing factors was helpful in identifying which diet was better for whom,” they wrote.

Gardner cautioned that his latest research casts doubt only on the value of testing for the specific metabolic and genomic traits his team measured. Someday, better predictors of which diets will work for a particular individual may be found, he said.

In the meantime, Gardner said he has distilled some insights into a few factors that determine success or failure on any diet.

“We found so much psychological and emotional trauma in a subset of participants” who gained weight during the study, said Gardner. “Their issue was childhood scars, broken marriages, stress at work. Food for them was a comfort. They needed a pint of ice cream.”

At the other end of the spectrum were people on both low-carb and low-fat diets who lost 40 to 60 pounds.

“One of the things I heard most often from these participants was, ‘Thank you! You changed my relationship to food,’ ” Gardner said. For these dieters, low-carbs or low-fat appeared to take a back seat in importance to becoming more mindful — and careful — about what they ate.

The idea that you don’t need a costly precision medicine work-up to choose a successful weight-loss regimen will likely disappoint a new industry that has sprung up to provide such match-making services to would-be dieters.

And the incidental finding that counting calories isn’t necessary could upend generations of conventional wisdom about weight loss.

“The calorie tracking is only working for a subset of folks,” Gardner said. “Most people start logging and tracking and finally say, ‘This sucks! I’m not doing this anymore.’

“We really have got to find other ways” to change people’s diets, Gardner added. “We don’t need one solution … we need dozens of solutions.”

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