Forget Good and Bad Fats:
To Lose Weight, Cut Calories

Never before have calories been so confusing.

Last week, my column¹ about the hidden calories in so-called healthy fast foods triggered a storm of letters from readers who took issue with my calorie counting.

Several readers argued that carbohydrates and fat content matter far more than calories. Others complained that the article failed to distinguish between healthy fats and unhealthy fats.

For answers, I shared my reader mail with some of the nation's top nutritionists and weight-loss experts at Tufts University School of Nutrition, the Cleveland Clinic, New York University and University of Pennsylvania School of Medicine.

Calories vs. Carbs. Several readers argued that carbohydrates matter far more than calories. "Calories have nothing to do with anything," wrote one reader. "If Americans just forgot about calories and started counting carbs, they wouldn't be so fat."

That isn't true. The fact is, weight loss boils down to basic science. To lose a pound, a dieter must eliminate 3,500 calories, either through diet or exercise. So a dieter whose body needs 2,000 calories a day to maintain basic function, would need to create a 500-calorie deficit each day to lose one pound in a week.

From purely a weight-loss standpoint, it doesn't matter if the calories come from protein, fat, sugar or carbohydrates. "A calorie is a calorie in terms of weight loss -- 1,500 kcal from different diets will very closely give the same weight loss and fat loss," says Susan Roberts, chief of the energy metabolism laboratory at Tufts University.

So the truth is, if you are counting carbs, you are still counting calories -- you just may not know it.

Foods high in carbs, such as french fries and muffins, are loaded with calories, so eliminating those foods helps people lose weight. One study put one group of dieters on a 10% carbohydrate diet and the other on a 35% carbohydrate diet. The weight loss was the same. Dietitians say that even the famous low-carb Atkins diet, when followed as directed, in reality is a low-calorie diet.

"You can't violate the laws of thermodynamics," says Marion Nestle, chairwoman of the department of nutrition and food studies at New York University. "Everybody wants to talk about fat or carbohydrates or good carbs, bad carbs, but nobody wants to talk about calories."

It's worth noting that a person on a no-carb diet likely will lose more weight the first week or two because they will lose more water, which sticks to carbohydrates.

In terms of weight, does the fat content of a food count at all? Here's where it gets tricky. If you are dieting, then it doesn't matter if you consume fat calories or carbohydrate calories or protein calories, as long as you are in caloric deficit. "You could lose weight on 1,000 calories of butter," notes Thomas Wadden, director of the weight and eating disorders program at University of Pennsylvania School of Medicine, although he obviously doesn't advise it.

However, if you are overeating, you will gain more weight on a high-fat diet than on a high-carb diet. That's because it takes more energy for the body to convert carbohydrates to body fat than it takes to convert fat to body fat. So for every 100 excess calories of carbohydrates, 77 will end up on the body as extra fat. But if you eat 100 excess fat calories, 93 of them will be converted to body fat.