Counting calories is an essential routine for people trying to either lose or gain weight.
A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. Calories in food provide energy in the form of heat so that our bodies can function. Our bodies store and “burn” calories as fuel. Many dieters count calories and try to decrease caloric intake to lose weight.
Typical recommendations for weight loss focus on eating fewer calories or using more of your stored calories through physical activity.
Some foods have become popular in weight loss diets because they’re supposedly “negative-calorie,” meaning that you lose calories by eating them.
This article tells you what you need to know about negative-calorie foods, including whether they can help you lose weight.
What are Negative Calorie Foods?
A negative-calorie food is food that supposedly requires more food energy to be digested than the food provides. Its thermic effect or specific dynamic action—the caloric “cost” of digesting the food—would be greater than its food energy content.
Despite its recurring popularity in dieting guides, there is no scientific evidence supporting the idea that any food is calorically negative.
There is no scientific evidence to show that any of these foods have a negative calorific impact.
Foods claimed to be negative in calories are mostly low-calorie fruits and vegetables such as celery, grapefruit, lemon, lime, apple, lettuce, broccoli, and cabbage.
However, celery has a thermic effect of around 8%, much less than the 100% or more required for a food to have “negative calories”.
Diets based on negative-calorie food do not work as advertised but can lead to weight loss because they satisfy hunger by filling the stomach with food that is not calorically dense.
A 2005 study based on a low-fat plant-based diet found that the average participant lost 13 pounds (5.9 kg) over fourteen weeks, and attributed the weight loss to the reduced energy density of the foods resulting from their low fat content and high fiber content, and the increased thermic effect.
Nevertheless, these diets are not “negative-calorie” since they bear energy. Another study demonstrated that negative-calorie diets (NCDs) have the same efficacy to low-calorie diets (LCDs) in inducing weight loss when both of these diets are combined with exercise.
Chewing gum was once speculated as “negative-calorie food.” However a study on chewing gum reported mastication burns roughly 11 kcal (46 kJ) per hour. Therefore, one stick of gum which contains around 10 kcal would require being chewed for one or more hours to reach “negative-calorie”.
Examples of Alleged Negative Calory Foods
Foods promoted as negative-calorie are typically fruits and vegetables with high water content.
Some specific examples include:
- Celery: 14 calories per cup (100 grams), 95% water
- Carrots: 52 calories per cup (130 grams), 88% water
- Lettuce: 5 calories per cup (35 grams), 95% water
- Broccoli: 31 calories per cup (90 grams), 89% water
- Grapefruit: 69 calories per cup (230 grams), 92% water
- Tomatoes: 32 calories per cup (180 grams), 94% water
- Cucumbers: 8 calories per cup (50 grams), 95% water
- Watermelon: 46 calories per cup (150 grams), 91% water
- Apples: 53 calories per cup (110 grams), 86% water
Other similar fruits and vegetables, such as lemons, cabbages, berries or zucchini, are commonly included in these lists as well.
Since each of these foods contains calories, the question is whether or not your body uses more calories to process these foods than the foods contain.
Is Kiwi a Negative Calorie Food?
Kiwi is a fantastic fruit that although strange looking, provides an amazing amount of vitamins as well as tastes great. Kiwi is also an alleged negative calorie food, remaining so popular among people on and off of the negative calorie foods diet.
The Kiwi is an edible fruit, and all of it is edible, including the skin and many seeds. The kiwi is a berry, and yes, it is one of the rare fruits that even has protein.
It has a massive amount of vitamin C, as well as a lot of vitamins A and E. In addition to that, kiwi also has almost as much potassium as the banana.
Kiwi skin also has a lot of anti-oxidants, as well as great fiber.
Long before the negative calorie foods diet came along, kiwi fruit has been widely praised in many nations for its effects in reducing the risk of blood clots and lowering fat in the blood stream. This makes kiwi one of the healthiest fruits out there.
Do Negative Calorie Foods Exist?
Though it’s true that foods such as Kiwi fruit are nutritious, it’s unlikely that any of them are negative-calorie.
Each of them contains calories, and there is no evidence to support the notion that they require more energy to eat, digest and process than they provide.
Some people wonder if the energy expended during chewing could help contribute to a food being negative-calorie.
A limited amount of research has shown that chewing gum increases the energy your body uses by about 11 calories per hour.
Therefore, the amount of energy you use during a few minutes of chewing celery or other foods is probably very small and relatively unimportant.
While it’s true that your body uses calories to process foods, the number of calories used is less than the calories foods provide.
In fact, the amount of energy your body uses to process foods is usually described as a percentage of the calories you eat and is estimated separately for carbs, fats and proteins.
For example, the energy used to process foods is about 5–10% of the calories the food contains for carbs, 0–5% for fat and 20–30% for protein.
Most alleged negative-calorie foods are composed primarily of water and carbs, with very little fat or protein.
It’s unlikely that the energy used to digest these foods is dramatically higher than for other carb-based foods, though this has not been studied specifically.