A calorie is a unit of energy. All foods have calories, so the existence of negative calorie foods is, on one hand, easy to answer. It's not possible. On the other hand, proponents of negative calorie foods take the position that some foods use up more of our energy in the eating and digesting process than the calories in the foods themselves.
Theory
According to the MayoClinic.com, broccoli and celery are two often-cited examples of so-called negative calorie foods If it takes 80 calories to chew and digest a 25-calorie piece of broccoli -- as some advocates of the negative foods theory claim -- the result would be a net loss of 55 calories, which would be derived from fat in the body, thereby helping you lose weight. The foods themselves are not negative fat, which would be an impossibility. But, in theory, they use up more fat in your body than they deposit, thereby helping you lose weight.
Negative Calorie Foods
A long list of potential negative calorie foods can be found at the Fat Free Kitchen website. Negative calorie vegetables run the gamut from asparagus to carrots to celery to green beans to spinach to zucchini. Negative calorie fruits include apples, cantaloupe, honeydew melons, oranges, various berries and watermelon.
The Reality
An article in the "New York Times" posited that there could be a slight calorie deficit with celery, since a celery stalk with 8 to 10 calories requires an energy expenditure of perhaps 6 calories an hour to chew it and around 5 calories to digest it. But the article concluded that any potential net "negative" calorie effect would be minuscule.
Benefits
There may be no such thing as actual negative fat or calorie foods. But the foods that are touted as negative calorie foods are good for you. The fruits and vegetables on the list of negative calorie foods can go a long way to providing you with necessary nutrients while keeping your caloric intake low.
Conclusion
As Dr. Donald Hensrud, a preventive medicine specialist at the Mayo Clinic, states, so-called negative foods can help you lose weight as part of an overall diet plan. But they are not "a magic bullet" for weight loss. Hensrud warns against going on any diet that relies on only a few foods, since it may leave you shy of necessary nutrients. "The key to successful weight loss is adopting a healthy lifestyle that includes a balanced diet and regular exercise," says Hensrud.
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