A negative-calorie food is a food that uses more food energy to digest than iis contained in the food. The thermic effect is the caloric usage of digesting the food. It would be more than the energy content contained in the food or beverage. This effect is scientifically called specific dynamic action.
One negative-calorie beverage is ice water. It has no calories but the body has to expend energy to raise the liquid to body temperature.
Some foods that are considered to be negative-calorie foods are the following:
hard boiled eggs
other low-calorie fruits and vegetables
Although these may not be true negative calorie foods, they are low in calories, healthy, and with roughage.