There is intense debate about what diet is the most effective for weight loss — high protein, low fat or a balanced approach. In fact, there are now dozens if not hundreds of popular diets which are all based on varying amounts and percentages of carbohydrates, proteins and fat. We have seen a shift in the popular rhetoric about diets from emphasizing low fat to embracing high fat diets, with the proclamation that “fat doesn’t make you fat.” Several studies have demonstrated that low carbohydrate, high-protein diets resulted in more weight loss over the course of 3 to 6 months than low-fat diets, but other studies did not show this effect. More research with extended the follow-up to 1 year did not show that low-carbohydrate were better than low-fat diets. Other studies have found that a very-high-carbohydrate, very-low-fat vegetarian diet was better than a traditional low-fat diet. Another study has shown that a Mediterranean-style diet was better than a low-fat diet.
The novelty of the diet, attention in the press and social media, and potential bias of the researchers could affect the results of any type of diet. The more important question is whether there is any advantage to long term to diets that emphasize a specific combination of proteins, carbohydrates and fats. Dr. Frank Sacks recognized the need for a large trial designed to compare the effects of different diets. Dr. Sacks and his colleagues published the article "Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates" in the New England Journal of Medicine in 2009. 800 overweight and obese subjects were recruited for the study which lasted two years. The four diet groups were: 20% fat, 15% protein and 65% carbohydrate (low-fat, average-protein); 20% fat, 25% protein, and 55% carbohydrate (low-fat, high-protein); 40% fat, 15% protein, and 45% carbohydrate (high-fat, average-protein); and 40% fat, 25% protein, and 35% carbohydrate (high-fat, high-protein). After two years the weight loss was similar in all diet groups. Most of the weight loss occurred in the first 6 months. After this time, some participants started gaining back the weight, others were able to maintain their weight loss. Hunger, fullness and cravings as well as diet-satisfaction scores were similar among the diets. The major result of this trial was that all the diets were equally successful for weight loss and the maintenance.
The bottom line is that the type of diet or the macronutrient composition is not critical to your overall weight loss success. More important than the type of diet is the adherence to that type of diet. I tell my patients that the best diet is the one that you can follow and stick to it. Another determinant of success on the diet is attendance at a group session. The better the attendance the better the weight loss. Diets that are successful for weight loss can emphasize a range of fat, protein, and carbohydrate compositions. These diets can be individualized for personal and cultural preferences and therefore have the best chance for long-term success.