For years, there have been not only claims, but entire diets based around the philosophy that certain foods such as: celery, cucumber, lettuce, citrus fruits, etc. result in a negative energy balance when consumed. The theory, is that eating enough of these foods will help one to “burn-fat”, because the amount of calories required to chew, digest and assimilate them, is greater than the amount they contain. Is this true? Can foods really have “negative” calories?
The Thermic Effect of Food
Eating food, does cause an acute increase in metabolic rate, because it requires energy (measured in calories), to digest and process the foods we eat. This is what is known, as the thermic effect of food. The thermic effect of food (TEF) is not a static number, it changes based upon a number of things, including: the macro-nutrient profile of a meal, the total amount of calories a meal contains, our habitual dietary intake, insulin resistance and age. The two most important of these factors responsible for determining the dietary induced thermogenesis of a meal (the total number of calories it takes to process that meal), are its macro-nutrient composition and total calorie content.
The larger the meal (in terms of calories), the more energy that is required by the body, to digest and process that meal (i.e. the body “burns” more calories to digest a larger meal).
So… What’s the Answer?
The answer lies in the following statements: As mentioned above, the thermogenic effect of a food is largely dependent upon the meal’s composition. Each of the macro-nutrients have a different thermogenic effect:
Fat = ~3%
Carbohydrates = 5 – 10%
Protein = 20 – 30%
Alcohol = 10 – 30%
Meaning, that the amount of energy required to assimilate and metabolize some nutrients (protein and alcohol), is higher than others (carbs and fat).
So, even if a food is composed entirely of protein, the amount of calories “burned” to process that meal, would only be up to 30% of the total calories contained in that meal.
30% is not 100% (duh Steve), therefore the additional percentage of calories left over (in our scenario 70%), would NOT be used in the digestion of that meal).
So no, a food can not have negative calories.
(There may be compounds present in certain foods which increase metabolic rate themselves, however that is far beyond the scope of this article)
Practical Application
Although a food cannot have negative calories itself, many of the commonly claimed “negative calorie foods” are very low in calories anyway, due to their high-water content. From a practical standpoint, eating these lower calorie foods may help to increase satiety when dieting, by increasing the overall size of a meal, without contributing a significant amount of calories.
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References
Westerterp, Klaas R. “Diet Induced Thermogenesis.” Nutrition & Metabolism 1 (2004): 5. PMC. Web. 1 Feb. 2017.
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