If you’ve spent any time looking into diets that promote weight loss, you’ve likely heard of “negative calorie foods.” These are foods that supposedly require more energy to digest than they provide in calories. A common example is celery — a crunchy vegetable filled with fiber and water that provides just six calories per stalk, according to the U.S. Department of Agriculture’s searchable database.
But is it really possible to have foods with negative calories?
Negative Calorie Food Candidates
Most of the so-called “negative calorie foods” are vegetables and fruits with high water and fiber content. The lowest calorie foods are vegetables, which typically have less sugar than fruits. Listed below are the number of calories in 100 grams of some common vegetables and fruits, and some meat and dairy items. The foods are listed from fewest to most calories, with the water content included in parentheses.
- Celery: 14 calories (95% water)
- Zucchini: 17 calories (95% water)
- Tomatoes: 18 calories (94% water)
- Green peppers: 20 calories (94% water)
- Romaine lettuce: 20 calories (95% water)
- Spinach: 23 calories (91% water)
- Watermelon: 30 calories (91% water)
- Strawberries: 32 calories (91% water)
- Broccoli: 34 calories (89% water)
- Grapefruit: 39 calories (90% water)
- Peaches: 39 calories (89% water)
- Onions: 40 calories (89% water)
- Carrots: 41 calories (89% water)
- Blueberries: 57 calories (84% water)
- Apples: 60 calories (85% water)
- Whole milk yogurt: 78 calories (85% water)
- Roasted chicken breast: 79 calories (77% water)
- Baked potato: 93 calories (75% water)
- 85% lean ground beef: 232 calories (60% water)
- Cheddar cheese: 409 calories (36% water)
People react in different ways to different diets, and if you are interested in changing your weight, you should consult a dietician. But on a basic level, if someone is looking to maintain or lose weight, an advantage of high fiber veggies and fruits is they fill you up and take longer to digest than highly processed foods. Therefore, they don’t provide a lot of calories but prevent you from feeling hungry — which helps you eat less. Many fruits and vegetables are rich in vitamins and minerals, and are thus an essential part of a healthy diet.
However, limiting yourself to just a few low-calorie foods is inadvisable, according to the Mayo Clinic, because you can easily miss out on essential nutrients including protein and fat. The UK National Health Service generally recommends 2,000 calories a day for women and 2,500 calories a day for men. If you decided to limit yourself to foods that contain roughly 20 calories per 100 grams (~200 calories per 1 kilogram), you would need to consume about 10 kilograms (22 pounds) of those foods a day to maintain your weight. That’s about 17 heads of romaine lettuce or 61 large green peppers. So it’s certainly possible to lose weight by consuming lots of veggies and fruits, but you’d want to mix it up by including other foods with different nutrients.
All of this still doesn’t quite answer the question of whether there are foods with negative calories, or foods that require more energy to digest than they provide in calories.
Energy Required to Digest Food
Eating food and digesting food takes energy. In a study published in the New England Journal of Medicine, the act of chewing gum burns 11 calories per hour. A stalk of celery provides 6 calories, which would be offset by a half hour of chewing. Clearly, the act of chewing isn’t enough to make celery a negative calorie food.
What about the energy required to digest food, absorb the nutrients and dispose of the waste? According to a review published in the Journal of the American College of Nutrition, approximately 60% of a person’s total daily energy expenditure is used for “basal metabolism,” or the energy required to operate your various organ systems at rest. After eating, researchers have studied the “thermic effect of food,” or when your metabolism increases after eating because your body is using energy to digest the food, absorb the nutrients and dispose of the waste. This increase in energy use after eating accounts for approximately 10% of total energy expenditure. The remaining ~30% of daily energy expenditure is used for the other activities of daily life — standing, walking, reading, socializing, preparing meals, intentional exercise, remembering website passwords, etc.
For someone consuming 2,000 calories a day, 10% of total energy expenditure is 200 calories, which would be expected to go toward digesting and processing food. Assuming that nothing else changes when you decrease the number of calories consumed — which is unlikely to be true — eating a negative calorie diet would require eating less than 200 calories a day. That’s less than four medium-sized apples. Yikes!
Of course, eating and digesting would be impossible if it weren’t for the “basal metabolism” that maintains all of your organ systems — the brain, cardiovascular system, digestive system, liver, kidney, skeletal muscle, immune system and so on. So eat your fruits and veggies as part of a healthy diet, and don’t worry too much about the “negative calorie” label.
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