The debate between following a low-fat, weight-loss diet and eating to lower carbohydrates and thereby lose weight appears to be settled after a large medical study. Some people, including many ketogenic and paleo dieters, believe cutting back on carbohydrates helps them lose weight. Others, including many physicians and medical centers, promote diets that cut back on saturated fats found in red meats and dairy products, as recommended by the US Department of Agriculture in its Food Pyramid.
In a 600-person, year-long study, the two eating styles helped dieters drop almost exactly the same number of pounds — and there didn’t seem to be much rhyme or reason as to who succeeded on which plan.
Going into the study, which was published today in the Journal of the American Medical Association, researchers wanted to settle the debate but they also wanted to know if blood insulin levels or genotype had an effect on weight loss.
High blood levels of insulin are a sign of insulin resistance, which often precedes Type 2 diabetes. Many believe high serum insulin promotes storing calories as fat. Researchers looked at the genetic profile of each participant and determined which ones had particular genetic traits thought to lead to weight gain. To the researchers’ surprise, neither genetic predisposition nor high insulin levels had any effect.
Results show you can lose weight with either eating plan
People studied were between 18 and 50 years old, and all overweight or obese but otherwise healthy. They attended nutrition classes taught by a health educator. There were no calorie restrictions. Everyone was directed to minimize their intake of sugars, refined flours, and trans fats. At the same time, they were encouraged to eat vegetables and nutrient-dense foods. Everyone was encouraged to adopt healthy habits like cooking at home and sitting down for structured meals with family members.
As you would expect, not everyone on the diets lost weight and some had dramatic losses. The outliers were one individual who gained 20 pounds and another who lost 60. However, the average weight loss in each group was almost identical: 11 pounds in the low-fat group, compared to 13 pounds in the low-carb group.
“It’s not so much about that food — it’s really about [changing] this crazy way that Americans eat.”
About 30% of people in the study had a genetic signature that, in theory, should have pointed to success on the low-fat diet, while 40% had a low-carb “profile”. But the data didn’t show any strong similarity between these genetic markers and weight loss on the corresponding diet. Neither did measures of insulin resistance, which the team also thought would be related to success.
The successful dieters, regardless of which group they were in, credited their achievement to a reframed relationship with food. They began eating more mindfully, cooking at home more often and focusing on whole foods instead of processed, packaged foodstuff.
According to the lead researcher, Christopher D. Gardner, Ph.D., “That was more powerful than differentiating between low-carb or low-fat. Just getting them to be a lot more mindful about what they were eating. It’s not so much about that food — it’s really about [changing] this crazy way that Americans eat.”
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