If you’ve ever tried to lose weight, you may have wondered whether it’s better to cut back on fat or limit your intake of carbohydrates and sugars.

After all, with food labels promoting low-fat or low-carb content, trying to figure out which is really best for your body can be downright confusing.

Scientists at the Pennington Biomedical Research Center have studied this issue in one of the largest and longest studies to measure the effect of macronutrient composition of diets on weight loss. What they learned may surprise you.

“When it comes to weight loss, cutting total calories probably matters more than what sources those calories come from,” said Dr. Catherine Champagne, a professor and chief of epidemiology at the Pennington.

That study, conducted jointly with Harvard University, involved more than 800 overweight adult participants, each of whom was randomly assigned to one of four different diets: low-fat, average-protein; low-fat, high protein; high-fat, average protein; or high-fat, high-protein. After two years, all had lost roughly the same amount of weight, about 7 pounds.

In a way, the results were surprising since several of the investigators thought that the higher protein diet would be more satiating and lead to better weight loss in the long run, Champagne said. But that was not the case.? Protein content really didn’t matter.

“This has been called a landmark study by some,” Champagne said. “That’s because it emphasizes the point that most dietetic professionals preach: ?Calories count.’ “

While the protein, fat or carbohydrate content of the diets did not predict who would lose the most weight, commitment did. Dieters who attended more group counseling sessions with Pennington dietitians saw better results. Those who stuck more closely to their assigned diets also got better results.? They were provided with meal plans to better enable them to closely adhere to the fat, protein and carbohydrate goals.

So if you’re trying to determine which diet works best, choose one that best fits into your lifestyle and enables you to stick to it, Champagne said. It’s also important to make sure that whatever the components of the diet you choose that it’s nutritionally well balanced and heart healthy, which rules out the Twinkie diet, for example.

“The most important thing is to cut back on calories,” Champagne said. “Calories count.”