The human body is remarkably efficient: your digestive tract can derive nutrition from almost all plant-based foods. Because of this, there are very few foods that require more calories for digestion than the foods themselves actually provide. While negative-calorie foods are few and far between, they can be extremely valuable in very low calorie diets (VLCD), especially for morbidly obese people.
Negative-calorie foods are particularly useful for serious dieters with a history of binge-eating or excessive snacking. Dr. A.N. Howard, who authored a 1981 review published in the International Journal of Obesity, notes that clinically obese patients experience weight loss of about two kilograms per week-- a rate "comparable to that seen in complete starvation"--while consuming a diet of very low-calorie or negative-calorie foods. However, some experts are skeptical: Dr. Sari Fine Shippard, an expert in eating disorders, notes that there is little scientific evidence to support the notion that any food truly offers "negative calories." Dr. Nancy Snyderman of Time magazine similarly states, "[Chewing] burns about the same amount of calories as watching grass grow." Still, this amount totals roughly 10 calories over the course of five minutes--possibly enough, or so claim the supporters of the "negative-calorie theory," to counteract the minimal calorie load associated with very low calorie foods. Combined with enzymatic action and laxative effect, these catabolic foods burn fat rather than building it.
Celery
Perhaps the most famous of negative-calorie foods, celery is loaded with fiber and requires a significant amount of energy to digest. Additionally, celery's stringy texture tends to occupy hungry mouths longer than most vegetables--a useful trait for those with a compulsive urge to overeat.
Grapefruit
This tangy fruit is loaded with catabolic enzymes, which may enhance the metabolism and inhibit the absorption of fats from other foods. Grapefruit also has a low glycemic index and provides a significant amount of calorie-cutting pectin fiber.
Vegetable Broth
Thin broths can be made by boiling carrots, tomatoes, onions, garlic, celery or greens. After the solid vegetables are removed, the remaining broth is flavorful but essentially calorie-free. Piping hot foods use more of energy than room-temperature foods, since the stomach must cool them to body-temperature.
Cucumbers
Cucumbers and pickles are composed largely of water, so they contain very few calories by volume. These calories are quickly burned off during the digestion process, because the body most break down the fibrous matter and warm it to body-temperature.
Leafy Greens
Raw, leafy greens like spinach, lettuce, turnip greens and kale are delicious negative-calorie treats. They provide sufficient enzymes and fiber to "cancel" their minimal caloric impact, as well as calcium and iron--two critical nutrients that are often lost during very low-calorie diets.
Seasonings
Low-calorie and negative-calorie diets are not always bland and boring; many seasonings are actually calorie-free or negative-calorie. White vinegar, salt, herbs, spices and lemon juice can all be used in salads, soups and prepared vegetables to add zest without calories.
References
- Howard, A.N. Int J Obes. 1981;5(3):195-208.
- Shepphird, S.F. (2009). 100 Questions & Answers About Anorexia Nervosa. Jones & Bartlett
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