Few things captivate the public more than a new diet. From Atkins to Ornish to the Mediterranean diet, each new theory attracts attention and true-believer adherents and generates lots of book sales and interviews on daytime TV. People passionately argue about whether a diet low in carbohydrates or low in fat is best for weight loss. But until now no large trial has ever been done to answer the question.
This week’s New England Journal of Medicine published the largest study that directly compares different diets to measure which yields the greatest weight loss. Over 800 overweight adults were randomized to one of four different diets. (Importantly, diabetics were excluded.) They were all given diets calculated to provide 750 calories fewer than they were burning daily, but the four diets differed in the percentage of calories from fat, protein, and carbohydrates. Two of the diets were low-fat and two were high-fat. Two were average-protein and two high-protein. And the four diets provided a broad range of carbohydrate intake from low to high.
The participants were also asked to participate in periodic group counseling sessions and were instructed to do 90 minutes of moderate exercise per week. They were followed for 2 years and their compliance with group attendance, diet and exercise was tracked.
Interestingly, the four diet groups lost weight at the same rate. Six months into the study the participants lost an average of 13 lb, 7% of their body weight. After that, on average, they slowly regained weight, so that by two years the average weight loss was 9 lb, the same in all four groups.
So diet and exercise lead to weight loss, and whichever low-calorie diet you can stick to is as good as any other. So get started. You can still buy the latest diet book and swear that it’s the best because your favorite actor lost weight on it. Only you and I will know that you owe your success to the New England Journal of Medicine.
New England Journal of Medicine article: Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates
NY Times article: Study Zeroes In on Calories, Not Diet, for Loss