Wondering if you'd do better to cut carbs or fats to lose weight? A DNA test using a cheek swab may reveal which approach would work best for you, new research suggests.
Researchers from Stanford University used data on a study from 2007 in which 138 overweight or obese women were assigned to one of four popular diets for a year. The diets included: the Atkins diet (very low carbohydrate), the Zone diet (low carbohydrate), the Ornish diet (very low fat) or a health professional's diet (a low-fat diet that generally follows the US Agriculture Department's Food Pyramid). The women also had the inside of their cheeks swabbed to collect a DNA sample.
Researchers used the genetic information to assign women to a "genotype-appropriate" diet, an eating plan that would seem to be the most effective for them given their particular genetic makeup.
Women assigned to the correct diet based on their genotype lost two to three times more weight at 12 months than those who were assigned to a diet that was inappropriate. When the researchers looked at only the most extreme diets (Atkins versus Ornish), the results were even more stark. Women assigned to their correct diet for their genotype lost five times as much weight as those on the incorrect diet, the study found.
The women on the correct diets also showed improvements in their "good" (HDL) cholesterol and decreases in harmful triglycerides.
"The weight loss differences between the various diets were not that dramatic, but the weight loss difference within a particular diet was," said lead study author Mindy Dopler Nelson, a Stanford postdoctoral research fellow. "On each diet, there were a lot who lost weight, there were a lot who didn't lose weight and there were even some that gained weight. By looking at the genetics we were able to see it was less the particular diet than the individual's response to the diet."
The study was presented at the American Heart Association's Nutrition, Physical Activity and Metabolism Conference 2010, in San Francisco, US.
How you metabolise food
The DNA test, made by Interleukin Genetics in Waltham, Mass., sells for $149. It works by honing in on certain genes that play a role in the way people metabolise food, said Lew Bender, CEO of Interleukin Genetics.
From among hundreds of genes believed to be involved with obesity, researchers from Interleukin Genetics identified three genes that had been implicated in multiple clinical studies to play a role in weight management. The genes include fatty acid binding protein 2, peroxisome proliferator- activated receptor gamma, and beta 2 adrenergic receptor, Bender said.
"We went through a rigorous scientific process to find those that were the most validated and the most functional, and these were the three," he said.
In those genes, a so-called single nucleotide polymorphism - or a variation of a DNA sequence within a gene fragment - causes the gene to produce a form of protein that changes the way it functions. In the case of fatty acid binding protein 2, for example, the polymorphism leads to the production of a protein that can cause a greater absorption of fat, Bender said.
"If you look at someone who has a polymorphism that causes them to absorb more fat, combined with another polymorphism that causes them to not burn fat well, they would be more prone to obesity from diets that are high in fat," he said. "In those cases, we would recommend they go on a low-fat diet."
Dr Robert Eckel, past president of the American Heart Association and a professor of medicine at University of Colorado School of Medicine, said the study results were very preliminary and had to be confirmed by larger studies before he would recommend that anyone have their diet genotyped.
"The three genes they have identified are all genes that could affect energy balance, and the idea that polymorphisms in these genes could affect energy balance is of interest scientifically," Eckel said. "This could explain small differences in the way people respond to diet. But right now the most important predictor of successful dieting is compliance."
Stanford's Nelson, a nutritional scientist, said she was encouraged by the findings but not surprised. During her career, she's seen wide variations in weight loss among people assigned to identical diets. Some results could be explained by how well people adhered to the diet, but not all, she said.
"You do need to be on a reduced-calorie diet. You still need to eat healthy. But there is a difference in how people process calories," Nelson said. "Knowing your genotype is just one more tool to help the weight-loss process."
Interleukin Genetics has applied for a patent on the DNA test, Bender said. - (Jennifer Thomas/HealthDay News, March 2010)