There has been a lot of back and forth on whether negative calorie foods exist, or whether it's all snake oil and wives' tales. One thing I've noticed while doing extensive research is that often times the people who are most adamant that "negative calorie foods" is a stupid concept seem to miss what the actual negative foods concept is about.
Negative calories foods are not foods that don't have calorie. All food has calories of some kind unless it's water. Negative calorie foods are foods belonging to a diet that empahsizes foods that are low in calories, but which the body takes more energy to burn than it receives. The theory is that the normal calorie burn from digesting the food and living a normal life will wipe out the calories eaten from these foods.
For example, if a slice of carrot had 10 calories, but took 12 to burn, that food would have -2 calorie effect on your body. That doesn't mean the carrots are -2 calories, but that the end result of this process is to lose weight. The idea with negative calorie foods, which are always certain types of fruits and veggies and are usually very high in fiber, and have a low number of calories to begin with.
These foods are excellent choices for a diet, since they keep you full, but don't add any calories whatsoever.
I repeat this because it's important: no foods have negative calories. The lowest you can possibly get is zero, which is water. But ice water requires the body to work to warm it up for use, meaning that although the calorie amounts burned are paltry (an estimated 50 calories for the recommended 8 glasses of ice water a day), that still creates a negative calorie effect since your body burned 50 calories to process ice water, which gave back 0 calories.
This is what is meant by "negative calorie foods." A more accurate description might be "Foods low in calories that produce a negative calorie effect because of how much energy it takes to burn them," but that doesn't sound very catchy. Meanwhile the term "negative calorie foods" gets the same idea across.
So as for the argument over whether these technically exist or not, negative calorie foods do what they are supposed to for a negative calorie foods diet: they make you lose weight. That's the entire point, isn't it?
The idea of negative calorie foods works for several reasons, and most of these foods have a few things in common that make this possible:
1) All of these foods are extremely high in fiber. This makes it much easier for your body to digest quickly, and use every nutrient while passing the rest straight on through quickly enough that it can't stick around to become fat.
2) All of these foods are either fruits or veggies. There is no other type of food on this list that falls into another food group. These food groups are commonly the healthiest types of food for you anyway, and almost never have any fat, though there are exceptions (like coconuts, which definitely do NOT make the negative foods list).
3) Most all of these foods will have a high water content. This makes sense since no matter how strong a metabolic effect a food has, the higher in calories it is the harder it will be to burn all of them off. Water has no calories, so fruits and veggies that are particularly high in water will have less calories and thus there is less to burn off while digesting.
This is just the beginning of many posts giving more details on the negative calorie foods diet, so keep tuned in for more updates.