This diet concept sounds so good, you really want to believe in it. The idea that there is such a thing as foods with negative calories. At the heart of the concept it is basically assumed that more energy is required to digest some foods than these provide in calories. It therefore follows that: Such foods help to lose weight.
Above all celery and also lemons have been continually added to the weight-watcher’s shopping basket in recent years. However, some have perhaps also heard spinach and cabbage or even grapefruit described as “negative calorie foods”. Celery represents a simple example.
Celery is insubstantial from a nutrition science point of view, predominantly consisting of water, a few nutrients and roughage. A large stick of celery contains a mere 10 kilocalories. Negative calorie advocates claim that the process of chewing and digestion burns more calories than the celery stick contains, negative calories as it were. Sounds like a win-win situation, right? But what actually lies behind the theory?
Unfortunately, this is nothing more than a myth that was put forward as true in the nutrition and dieting world, even though it greatly lacks scientific evidence.

Main problems of the negative calorie myth
1. The theory is far too simple: Our digestive system requires calories, yet the amount of calories that the body needs for digestion is insignificant/tiny in comparison to the amount contained in the food. The body uses only about 10% of the total energy consumption, spread over the day, to digest food and store nutrients. There is no evidence that the energy needed to digest certain foods is greater than the energy they actually contain.
2. The list of foods is ridiculous: Diverse foods were added to the “negative calorie list” which have little in common apart from a high water content and cellulose. Examples: Celery, lemons, cabbage, corn salad, apples, iceberg lettuce, asparagus, strawberries, blueberries, red berries, cauliflower, cucumbers, cress, melons, tomatoes, to name just a few.
3. Varieties of fruit cannot be “negative calorie foods”: Fruit typically contains a great deal of water and indigestible roughage, but also sometimes very high amounts of natural sugar. Of course sugar can also be present in vegetables, but fruit usually contains more. In pure and simple terms, it is complete nonsense to describe fruit as having negative calories. One portion of watermelon typically has 46 kcal, just under 12 grams of carbohydrate, of which 9 grams are nevertheless sugar. Even if watermelon contains only 46 kcal, simple biochemistry and the laws of thermogenesis contradict the negative calorie theory.

Many varieties of fruit and vegetables actually contain only a small amount of calories. However, there is no scientific evidence for the “negative calorie theory”, a fact that reveals how this is merely a myth that has become obstinately entrenched in the world of dieting forums.
However, fresh fruit and vegetables contain high levels of vitamins and minerals as well as antioxidants and secondary plant substances that are indispensable for a healthy body. Moreover, the high water (and roughage) content is very filing. A diet rich in fruit and vegetables is good and helps to maintain or lose weight.