The Internet abounds with lists of purported negative-calorie foods — foods that supposedly take more energy to digest than they provide in calories. Many of these foods are vegetables and fruits, which can be part of an overall healthy diet plan. But they're probably not negative-calorie.
The theory is that you can lose weight by eating lots of these negative-calorie foods. Celery is a commonly cited example because it's mainly water and fiber. Proponents claim that you will burn more calories digesting celery than it contains, for a net loss.
Here's the reality. Throughout the day, about 5 to 10 percent of your total energy expenditure goes to digest and store the nutrients in the food you eat. Foods that contain few calories, such as celery and other nonstarchy vegetables, provide a small number of calories but still require energy to digest. That means it is theoretically possible to have a negative-calorie food, but there are no reputable scientific studies to prove that certain foods have this effect.
The bottom line: Following extreme diets that promote eating only a few foods can cause you to miss out on important nutrients. The key to successful weight loss is adopting a healthy lifestyle that includes a balanced diet and regular exercise.