Negative Calorie Foods

Experts do know that you burn between 5 and 10 percent of the calories you eat each day simply digesting food. This is called the thermic effect of food and it's one part of how your overall metabolism works. "It's very difficult to measure the energy expenditure for individual foods," Lanou says. However, she says, they can make an educated guess. For example, one stock of celery has about six calories. If you munch on three stocks of celery, you've consumed 18 calories. Digesting that celery is likely to cost more than 18 calories -- perhaps 25 -- potentially leaving you with a seven-calorie loss. While it's true that every calorie adds up, it's not going to have much of an effect overall. In fact, you'd probably burn more calories going for a walk around the block after a meal.

Another thing to consider is that eating three stalks doesn’t provide much sustenance. The generally agreed-upon list of negative calorie foods are mostly fruits and vegetables and eating these foods by themselves won't fill your caloric needs for the day. You need protein and carbohydrates too. If you try to rely on celery alone, the eventual hunger will make you more likely to reach for something unhealthy that contains a lot more than your "free" seven calories.

However, Lanou says, "if you're going to reach for a snack, it's better to reach for something that isn't going to add much to your overall calorie count. After all, celery is a better snack than potato chips. Plus, there is a strong body of research that shows that eating certain low-calorie foods such as vegetables, fruits, or broth-based soups before a meal reduces the amount you eat at mealtime.

There is also growing evidence that certain compounds have a thermogenic effect on your metabolism—meaning they help you burn more calories without even trying. Hot peppers and ginger contain capsaicin, which raises your body temperature and energy expenditure. The only caveat is that the amount of hot peppers you'd need to eat to make a real difference would leave your mouth on fire for days. But if you like spicy foods, it can't hurt to try. Coffee and green tea can also be thermogenic because they contain caffeine. There has been special interest in green tea, since it has both caffeine and catechins, thought to help you break down fat more effectively. One study showed that drinking three or more cups of green tea daily raised metabolism by 3.5 percent over 24 hours. However, caffeine isn't well tolerated by everyone: It can make some people jittery or anxious, and people with any kind of heart condition are generally advised to avoid caffeine.

The research on caffeine and green tea has led to the development of engineered negative-calorie drinks, such as the artificially-sweetened, caffeine-loaded Enviga, which has 5 calories and 100 mg of caffeine per 12-ounce can. The makers of the product claim that healthy adults who drank three cans a day (15 calories total) burned 106 calories a day. Nutritionists opinions are mixed. "It's a lot of caffeine, plus I think using beverages other than water for weight loss is a poor strategy," Lanou says. As for the claim of weight loss, the Center for Science in the Public Interest (CSPI) actually filed suit against Coca-Cola (maker of Enviga) in February of 2007 for making fraudulent claims based on insufficient evidence. Coca-Cola hasn't altered its claims so the case is going forward and is currently in deposition stage, says a spokesperson for the CSPI.

Instead of getting caught up in any questionable diet aide that may offer a tiny percentage of potential metabolism gains here and there, Lanou says the best strategy is to replace high-fat, high-sugar foods of little nutritional value with more fruits and vegetables. In simplest terms, she says, "just eat more plants."