There have been several large, long-term randomized controlled clinical trials that compare the different types of diets to try find which diet works best for weight loss. Let’s quickly review the results of six large clinical trials, each of which compare at least two different diet types. Researchers randomly assigned 322 obese people to a low carbohydrate diet, a “Mediterranean” diet and a low fat diet and followed these people for 2 years. At the end of the trial, the authors concluded that the choice of which diet to follow should be based upon an individual’s preferences and on which diet you are likely to continue to follow long-term. Another comparison trial involved 160 participants who were randomly assigned to follow the Atkins diet, the Zone diet, Weight Watchers, or the Ornish diet. Researchers found that those who lost the most weight were the people who reported that they most closely followed the diet, regardless of which diet they were assigned to. A third trial in the United Kingdom randomly assigned 293 obese men and women to the Atkins diet, the Weight Watchers diet, the Slim-Fast diet and the Rosemary Conley diet, or to a control group that did not diet. The authors concluded that those who lost the most weight are the people who strictly followed the diet, regardless of which diet they were following. An editorial pointed out that, though each of these four diets produced the same amount of weight loss, they differed a large amount in how much they cost to participate in, with Slim-Fast costing the most, Weight Watchers the second most expensive, and the Atkins diet the least expensive. A fourth comparison trial randomly assigned 311 overweight or obese women to follow the Atkins diet, the Zone diet, the Ornish diet or the LEARN diet (which means: Lifestyle, Exercise, Attitude, Relationships, Nutrition). After 12 months, those who lost the most weight in any of the assigned groups were the ones who most closely followed the recommended diet, and continued following it for the longest time. A fifth trial randomly assigned 307 obese people to two years of a low carbohydrate diet or a low fat diet. The authors conclude that weight loss does not depend upon the amount of dietary fat or carbohydrate in your diet. Even with intensive counseling and support, more than one third of the people who enrolled in the trial had withdrawn by two years. The largest randomized controlled trial to compare different types of diets assigned 811 overweight men and women to one of four different diets with varied amount of fats, carbohydrates and proteins. The diets varied from 20% to 40% of calories from fats, from 15% to 25% of calories from protein, and from 35% to 65% of calories from carbohydrates. The authors concluded that none of the diets were better than another at decreasing hunger, and people were equally satisfied with each of the diets. Those who attended more groups sessions tended to lose the most weight, regardless of which diet they were following. The authors concluded that any of the diets were equally effective in promoting weight loss as long as they caused people to eat fewer calories. The specific amounts of carbohydrates, fats and proteins in the diet are less important than choosing a diet that you are likely to stick with long-term. There are at least four lessons to be learned from these trials. First, it does not really matter for weight loss if you restrict the amounts of fats, proteins or carbohydrates in your diet. Second, in every weight loss trial, the people who lost the most weight are those who followed the diet most consistently, regardless of which diet they were following. Third, the more difficult the diet is to follow, the less likely you are to follow it long term. This is especially true for diets that severely restricted how many fats or carbohydrates you can eat. And fourth, you can pay a lot of money to follow some commercial diet plans that provide the food for you, but you are not necessarily going to lose more weight that way than by following a less expensive diet plan.