Friday, March 26, 2010

Negative Calorie Foods? We Wish!

Wouldn’t it be wonderful to eat foods that make you burn more calories than are in the food itself? You could eat to your heart’s content and lose weight while you’re at it. Google “negative calorie foods” and you’ll find “negative calorie diets” and lists of calorie burning foods. Usually these diets feature foods that are good for you like celery and grapefruit, so there’s no harm done if you try to outsmart your metabolism by eating them.

But do they really do what the claims promise? Possibly, but not likely. While proponents claim to have research studies that support the negative calorie premise, there isn’t any. I’ve seen some sites that claim that when you eat celery you burn up “a lot” more calories to process that celery. But the data is just not there. For most foods, it takes roughly 10% of the calories in that food to digest and absorb it. So to process that 6 calorie stalk of celery is probably costing you about 0.6 calories. Even if these foods do burn up extra calories, it would probably be an insignificant amount when it comes to actual weight loss.

Since most of the foods on “negative calorie” lists are fruits and vegetables, eating lots of them could help you lose weight. Here’s where the data is solid. Foods that weigh a lot (meaning high in water content) fill you up and so you eat less. Several research studies show that we eat about the same amount of food in weight every day. You may have seen the book Volumetrics. It’s based on this concept. Our own UAB EatRight weight loss program is based on this idea too. So if you eat heavy foods that are low in calories, you signal your body to feel full and satisfied on fewer calories.

The bottom line on negative calorie foods? This is one for The Journal of Wouldn’t It Be Nice? But Too Bad Because It Probably Isn’t.

Beth Kitchin, MS, RD
Assistant Professor
UAB Department of Nutrition Sciences

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