Want to lose weight? Eat less.

A new diet study just out from the American Journal of Clinical Nutrition went to a lot of trouble to prove the obvious.  When it comes to weight loss, how much you eat matters more than the proportion of fat, carbohydrate, and protein in your foods.

Researchers at the Pennington Biomedical Research Center got volunteers to eat diets that were supposed to differ in proportions of fat (40% vs 20%), carbohydrates (35% vs. 65%), and protein (25% vs. 15%).

The results of the study are consistent with the findings from many previous studies:

• The major predictor for weight loss was adherence to the diet.
• People on all of the diets lost weight by six months, but regained some of it by two years.
• The study had a high drop-out rate (hence the importance of adherence).
• It was hard for people to stick to the diets, especially those at the extremes of one dietary component or another.

In my book with Malden Nesheim coming out on April 1, Why Calories Count: From Science to Politics, we review the previous studies of whether what you eat matters more to weight loss than how much you eat.

Some people find it easier to stick to diets that are higher in protein and fat.  I’m guessing that proponents of low-carbohydrate diets will argue that none of the diets in this particular study was really low in carbohydrate.

But studies show that people have a hard time adhering to diets that are very low in carbohydrate.  The low range in this study—35%—is at the lower end of acceptability for many people.

The bottom line: all diets work if you stick to them.