Myths

Negative-calorie foods: why celery cannot make you lose weight by itself

No food costs more energy to digest than it provides. Celery and cucumber are still useful for a diet, just not for the reason the myth claims.

The negative-calorie myth claims that some foods, most often celery, cucumber, lettuce or grapefruit, use up more energy during chewing and digestion than they contain, so eating them leads to a net calorie loss. It is an appealing idea, but it does not hold up. The energy used to digest food, called the thermic effect of food, is roughly 5 to 10 percent of the calories eaten for carbohydrates and 20 to 30 percent for protein. Even for watery vegetables, it is a fraction of their calories, not more than all of them.

A large stalk of celery contains roughly 6 to 10 calories. Digesting it might use around one of those calories, and chewing burns very little extra energy. A study that directly measured this found that celery still provided a small positive amount of energy. The same is true for other low-calorie vegetables: they are close to zero, but not below it. Eating plates of them will not cancel out a dessert.

The real value of these foods is their low energy density. They are mostly water and fiber, so they add volume, crunch and fullness to meals for very few calories, which makes it easier to eat less overall without feeling deprived. Filling half your plate with vegetables, starting a meal with a salad or snacking on cucumber instead of crisps are all effective habits. Just think of these foods as almost free, not as fat burners.

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