Whether low-carb or low-fat diet is better for weight loss

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The researchers speculated that genes involved in how carbohydrates and fat are metabolised, as well as the production of insulin (the hormone that regulates blood sugar), would impact the success of the diets.

In recent years, the big dietary villain has prominently shifted from fat to carbohydrates, with some studies suggesting high-fat, low-carb diets could be the best way to shave off those pounds and keep healthy. Frustrating anyone wanting a definitive result, the data compellingly suggests individual diet outcomes are much more subjective than many previously thought.

During the first two months, dieters in each group were told to limit carbohydrates or fats to 20 grams daily, about the amount that's in 1 1/2 slices of whole wheat bread and a handful of nuts, respectively.

Despite the similar overall averages, the researchers found huge individual variations in weight loss among the subjects and, interestingly, none of the variations correlated with either specific genotypes or a person's baseline insulin levels.

'We've all heard stories of a friend who went on one diet - it worked great - and then another friend tried the same diet, and it didn't work at all, ' said Dr Christopher Gardner, a professor at Stanford University School of Medicine. Participants on both diets who consumed the fewest processed foods, sugary drinks, unhealthy fats and ate the most vegetables lost the most weight.

Crucially, they were also taught to eat in a way that didn't make them feel hungry or deprived. Also, some people lost as much as 60 pounds and others gained 15 pounds - more evidence that genetic characteristics and diet type appeared to make no difference.

Participants who lost the most weight reported that this approach reshaped their relationship with food and made them more thoughtful about how they ate, he added.

Whether low-carb or low-fat diet is better for weight loss
Whether low-carb or low-fat diet is better for weight loss

In a face-off between a low-fat and a low-carbohydrate diet, neither reigned supreme.

Still, despite these varied results, searchers found no link between one diet and weight loss, over another. Several companies now sell DNA tests that claim to identify certain genetic markers that can reveal whether a person is better suited to a low-carb or low-fat diet.

The findings were published in the February 20 issue of the Journal of the American Medical Association. "We really need to focus on that foundational diet, which is more vegetables, more whole foods, less added sugar and less refined grains".

"I'm hoping that we can come up with signatures of sorts", he said.

The study was well-conducted but because participants were not provided with specific foods and self-reported their food choices, it wasn't rigorous enough to disprove the idea that certain genes and insulin levels may affect which types of diets lead to weight loss, said Dr. David Ludwig, a Boston Children's Hospital obesity researcher.

For many people, she said, this requires a willingness to "ascend a learning curve that includes creating new lifestyle habits, shopping, cooking and food prep techniques, trying new foods and creating strategies to help manage chaotic schedules, families and life's ups and downs".

The study was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases, the Nutrition Science Initiative, the National Heart, Lung, and Blood Institute, and the Stanford Clinical and Translational Science Award.

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