A negative-calorie food is one that supposedly requires you to burn more calories by chewing and digesting it than the food actually has. This has become somewhat of a fad because in theory, it would allow you to lose weight through eating, eliminating calories before they have a chance to turn into fat.
Types
The fruits and vegetables that carry the negative-calorie badge are typically water-heavy, fibrous items such as celery, grapefruit, radishes, cucumbers and zucchini. Celery is generally held up as a prime example because of how low-calorie it is compared to how much effort goes into chewing it. A stalk of celery has around six calories, which leaves the impression that it wouldn't take much to burn that off.
Proof
What makes the idea of negative calories so frustrating is that there's no real proof either way. Yes, some foods such as celery are extremely low in calories, and you do burn off energy when you chew and digest the food. However, as Columbia University says, the amount you burn is so "miniscule" that it really wouldn't have an effect that you'd notice, and it's not a substitute for exercise at all. Ohio State University Extension also notes you burn -- maybe -- only 5 percent to 10 percent of the calories you eat through digestion. Despite that estimate, it's almost impossible to determine specifically how many calories you burn off when you digest something.
Perception
The idea that certain foods have "negative calories" might influence how much you eat in a meal, especially if the other foods aren't that healthy. Not-yet-published research out of Northwestern University's Kellogg School of Management found that weight-conscious people tended to estimate lower calorie counts for meals containing unhealthy foods if those foods were paired with something healthy. Subjects estimated calories for foods such as cheeseburgers. Those who saw the cheeseburger with a healthy food like celery guessed that the meal had more than 40 calories fewer than what those who saw just the cheeseburger guessed. The danger in that this might lead you to eat more than you realize.
Advantages
Even if eating celery and cucumbers doesn't burn the same number of calories they contain, these are valuable foods anyway. Fruits and vegetables provide fiber and vitamins, and they can double as substitutes for sweet foods. Grapefruit has vitamin C, of course; broccoli, another negative-calorie darling, has fiber. Zucchini can work its way into dessert dishes, as can most fruits.
Cautions
As many benefits as there are to eating an appreciable amount of these fruits and vegetables, don't go overboard. Ohio State University advises that making these the main foods of your everyday diet will make you miss out on a lot of nutrients and could result in malnutrition. Formulate a healthy diet plan or a regular eating plan with a registered dietician.
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