There are a number of theories about healthy eating and misconceptions that have been adherents for quite some time. Among them is the theory of products with negative or negative calories.
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Adherents of the theory argue that there are products with too little calorie content, when digested, the body uses more calories than these products contain. For example, a cup of leaf lettuce contains about 30 kcal, 40-50 kcal is consumed for digestion, that is, 10-20 kcal, the body seemed to “burn” in the process of digesting food, which is undoubtedly a plus for people who are losing weight or following a sports diet. This may already seem absurd. It seems that no training is needed, products with negative calorie content will be a kind of gym or treadmill, just eat these products. A number of "negative calories" include all types of leafy salads, cabbage, tomatoes, cucumbers, some types of citrus fruits and apples, and some other plants.
Scientists are skeptical about the theory of negative calorie foods, explaining this by the existence of the so-called thermal effect of food (short for TEF). It is ETF that expresses the amount of kcal consumed by the body in digestion. The ETF coefficient can in no way exceed 100%, but ranges from 3% to 30%. Simply put, for every 100 kcal received, the body spends a maximum of 30 kcal. But even the maximum 30% of the body spends on the digestion of protein foods, that is, most often food of animal origin, which does not include salads, cucumbers and so on.
Indeed, foods with a "negative calorie content", like carbohydrate foods, spend only 5-10% on their digestion. For example, with an apple of 50 kcal, the body will receive about 40 kcal. Remote confirmation of the theory can be seen in the content of certain products of special substances that increase the body's metabolism (for example, synephrine in grapefruit), but this is not a negative calorie content.
So, products with a "negative calorie content" are actually only low-calorie foods, the advantage of which is fiber and water in the composition, which gives a saturation effect and generally has a beneficial effect on digestion. This leads to a decrease in body weight, since the volume of the food itself is reduced due to low-calorie vegetables. When calculating the daily diet, such vegetables can generally not be taken into account, since their calorie content is too low for deposition in fat. And indeed, no one has yet grown fat eating cucumbers, cabbage or salad. Conclusion: vegetables, especially green ones, should be present whenever possible at each meal because of their extreme usefulness, but not to be confused with negative calories.