Negative calorie diet

The basics
In a negative calorie diet and several versions of this diet, ostensibly, dieters are to eat and drink food products that are nutritious but are said to have a negative caloric effect; i.e., provide fewer food calories than the calories needed to digest them. The energy that the body needs to digest the food is usually given as a certain amount of calories, whilst the energy content of the food is given as kilocalories - often written "Calorie". Note that 1 kilojoule (kJ) = 1000 joules 1 kilocalorie = 1000 calories = 1 Calorie (1 Cal)  

Foods
The "negative calorie" foods allowed in this diet are mainly vegetables and fruits. Foods that have been claimed to "contain" negative calories include :

Criticisms
This diet is criticized as basing its main premise on unsound science. There is much debate about the factual existence of negative calories; there is also controversy surrounding whether it is possible for a food to contain "negative" calories. Factually, the only foods which could genuinely and without qualification fall into this category are cellulose and water, the belief being that the action of the esophagus, stomach, intestines, etc. to move these substances through the system would burn a small amount of calories. Water contains zero burnable calories and the calories in cellulose are inaccessible to humans due to the lack of a cellulase enzyme.

Aside from the factual dispute of whether negative calorie foods exist, some also criticize that such dieters use the concept of negative calories to justify eating unlimited quantities of such foods, and that doing so is not healthy. Similarly, although some of the foods mentioned are traditionally considered to have fair nutritional value, others may contain very little, or lack certain nutrients, which may lead to malnutrition.