You may have heard that certain foods are so difficult for the body to break down that the process of digesting them uses more calories than they contain. These foods, dubbed negative-calorie foods, supposedly promote weight loss just by eating them. Some commonly cited examples are celery, cucumbers, cabbage and broccoli.
Foods with such little energy content that the simple act of eating them causes you to lose weight would be a fat loss dream come true. But while the prospect of burning extra calories as a reward for chowing down on some veggies sounds delightful, does it work? As it turns out, not exactly.
The thermic effect of food
About 10 percent of the calories that you burn in a day come from eating. This is because, when you eat, not only do you absorb calories from the food you’re eating, but you also burn calories digesting and processing the food. The burning of calories from eating is called the thermic effect of food, which is defined as the temporary increase in your metabolic rate that occurs after you’ve eaten. 
While an average mixed meal — one that consists of a blend of protein, fat and carbohydrate — has a thermic effect of around 10 percent, the thermic effect of each macronutrient in isolation varies.  Protein, for example, has a thermic effect of 20 to 30 percent, while carbohydrates have a thermic effect between 5 and 15 percent.  Fat offers very little in the way of thermic effect, clocking in somewhere between 2 and 5 percent.
For a food to be considered negative-calorie, that would mean that its thermic effect is greater than the number of calories that it contains. While it’s true that some macronutrients confer a considerably higher thermic effect than others, the fact remains that the thermic effect of any food can never exceed its total energy content.
Take celery, for example. One medium stalk of celery provides 6 calories, most of which are from carbohydrate.  Even if we assign the thermic effect of celery a high-end estimate of 15 percent, you’d still only burn about 1 calorie digesting it — leaving you with 5 net calories. So, while celery is undoubtedly a low-calorie food, it is not a negative-calorie food.
Still, eat your vegetables
While negative-calorie foods are something of a misconception, that doesn’t mean you shouldn’t eat plenty of low-calorie fruits and vegetables. While a high fruit and vegetable intake may not be absolutely needed from a body composition perspective, as calories reign supreme there, it does contribute to overall health. And it may even aid in weight loss — but not because of negative calories.
Why then may increasing your fruit and vegetable consumption assist with your fat loss goals? The primary reason is that fruits and vegetables contain a lot of water and fiber, which makes them incredibly satiating. In other words, they’ll keep you fuller longer, meaning that you may consume fewer calories overall.
But remember that calories still count, so adding a ton of fruits and veggies to an already hypercaloric diet without changing anything else isn’t a magical path to fat incineration. If fat loss is the goal, the added fruits and vegetables need to replace more calorie-dense options.
Figure 1.1 – This Is Not How It Works
For example, you could replace half of your pasta with zucchini noodles. You could make a stir-fry with lots of vegetables, but opt for a smaller portion of rice. You snack on a bowl of cantaloupe instead of a sleeve of crackers. Each of these scenarios would increase the volume of food you’re eating while also reducing your caloric intake.
The take-home message
In short, there are no negative-calorie foods. Still, no matter what your goal is, eat lots of fruits and vegetables. Because they’re awesome. And if you want to lose weight, don’t forget to also reduce the number of calories that you consume.
- Kinabo, J.L. and Durnin, J.V.G.A. “Thermic effect of food in man: effect of meal composition, and energy content.” British Journal of Nutrition. 64 (1990): 37—44.
- Westerterp, Klaas R. “Diet induced thermogenesis.” Nutrition & Metabolism. (2004): 1—5.
- Halton, Thomas L. and Hu, Frank B. “The Effects of High Protein Diets on Thermogenesis, Satiety and Weight Loss: A Critical Review.” Journal of the American College of Nutrition, Vol. 23, No. 5 (2004): 373–385.
- United States Department of Agriculture. “Basic Report: 11143, Celery, raw.” National Nutrient Database for Standard Reference Release 28. Accessed 11/04/2016.