It's just calories...and cost.

CNN reports on a study of diets. The study examined high carb, high fat, low-fat and high protein diets. The researchers found that any will work, as long as the diet is nutritious, and as long as calories are reduced. You can get the press release from Havard here.

"The key really is that it's calories. It's not the content of fat or carbohydrates, it's just calories," said study co-author Dr. Frank Sacks.

So if one as good as another, let's think about cost, too. My own research showed that low carb diets are very expensive. To prove that, I used linear programming models. Requiring less and less carbohydrate makes a diet cost more and more. And if you want to constrain fat, too, the diet will be very expensive, and also much harder on the environment.