Negative Calorie Foods

You may have heard of celery, grapefruit, or some other fruits and vegetables referred to as "negative calorie foods" meaning, essentially, more calories are used to digest these foods than are provided by eating them. Such items have been praised as diet super-foods because, after all, who doesn't like the idea of getting something for nothing? (especially when it comes to calories!) With all the buzz out there about these energy burning snacks I was surprised to find that there is virtually no validated research to back the claim that some foods require more energy to be broken down in the body than they provide.

http://en.wikipedia.org/wiki/File:Celery_cross_section.jpg

However, I did find that low-calorie whole foods do in fact require more energy to be digested than other highly processed calorie-dense foods.

The calories used to break down a food item is known as it's "Thermic Effect", i.e. "the amount of energy used by your body to digest, absorb, and dispose of the food you ingest."(1) The thermic effect of foods can vary anywhere from 3% of total calories for fats to about 20% for many vegetables and 30% for most proteins.(2) That is, eating 200 calories from fat only takes 6 calories to digest while digesting 200 calories from protein would require 60 calories. In this way some foods do have lower net calories once they are processed by your body. By making foods like fibrous fruits and vegetables as well as lean protein a part of your diet it's certainly possible to stay satisfied while reducing your overall caloric intake (an essential aspect of  successful dieting).

Image Source: http://www.easyvectors.com/browse/other/computer-user-outline-clip-art

So while it is possible that some foods burn more energy in digestion than they provide themselves, relying on such quick diet fixes is hardly ever the key to healthy living. As Monica Reinagel puts it in her book How to Win at Losing, 10 Diet Myth that Keep You from Succeeding: "digesting negative- calorie foods does not constitute an exercise program" as "a half hour spent on the treadmill or bike is going to burn a lot more calories than a half hour spent digesting celery."


Sources:

1. http://www.livestrong.com 
2. http://worldfitnessnetwork.com
3. http://theoatmeal.com/comics/ie
4. Reinagel, Monica. How to Win at Losing: 10 Diet Myths That Keep You from Succeeding. New York: St.Martin's Griffin, n.d. Print.