What is the basis of this? Is there any truth to it?
"What are Negative Food Calories?:
The negative calorie phrase refers to a small list of foods which contain so little energy that the body uses more energy to digest and absorb the nutrients. If this was the effect then it means there would be a net loss of calories from the body resulting in a negative energy balance which is required in order to lose weight.
Negative calorie foods are foods, which use more calories to digest than the calories food actually contain! Calories from these foods are much harder for the body to use. In other words, the body has to work hard in order to extract calories from these foods. Even though foods may contain equal amount of calories, much less of these calories can possibly turn into fat in fat burning foods (negative calorie foods) as fewer calories are actually available to the body. This give these foods a tremendous natural fat-burning advantage."