Do foods with negative calories truly exist?

Celery brings me joy. Its vibrant yet subtle green hue, its convenience for lunchboxes, and the satisfying crunch with every bite make it irresistible. However, there's always that moment when someone nearby mentions two words: negative calories.

I never paid much attention to the notion that eating celery could be compared to exercising, but the idea of "negative calories" is undeniably widespread. So, do foods with negative calories actually exist? The theory suggests that you expend more calories consuming and digesting the food than the food itself contains. For instance, eating 10 calories of celery while burning 20 calories in the process would supposedly put you in the negative-calorie zone [sources: Moskovitz].

In reality, every food contains calories, and consuming them activates your body's metabolic processes. Certain foods, such as celery, watercress, cucumbers, mushrooms, and sprouts, are notably low in calories. This is where the thermic effect of food becomes relevant — the boost in metabolic rate post-consumption. However, its role in weight management or loss remains understudied.

Digesting food accounts for 5 to 10 percent of the calories you burn daily. In theory, consuming only very low-calorie foods and relying on the thermic effect to burn most of the ingested calories might seem plausible, but such an extreme diet could harm your health over time [source: Hensrud]. In practice, chewing burns about 11 calories per hour, with a few more calories spent on digestion and nutrient storage. While protein and carbohydrates require more calories to digest than fats, the difference is minimal.

Recall the celery example? Imagine consuming 225 calories of celery (around 30 stalks) in an hour. Chewing for that hour burns 11 calories, and digesting the celery might use up to 20 more calories. Subtracting the calories burned from those consumed leaves you with 194 calories, far from entering the negative-calorie zone [source: Produce for Better Health Foundation].