Negative calorie foods: An empirical examination of what is fact or fiction

Abstract

A proposed weight loss strategy is to include in ones diet foods that are deemed \"negative calorie\". In theory, negative-calorie foods are foods for which more energy is expended in their digestion and assimilation than is consumed, thereby resulting in an energy deficit. Commonly listed negative calorie foods are characterized by a high water and fiber content and little fat. Although the existence of negative calorie foods has been largely argued against, no empirical study has fully addressed the validity of foods being negative calorie. We conducted such a study using the omnivorous lizard the bearded dragon (Pogona vitticeps) and celery as the tested food. Celery tops many lists of negative calorie foods due to its high fiber and low caloric content. Following their consumption of celery meals equaling in mass to 5% of their body mass, we measured from each lizard their postprandial metabolic rates to calculate specific dynamic action (SDA). Feces and urate were collected after meals to determine the energy lost to excretion. The specific energy of the celery meals, feces, and urate was determined by bomb calorimetry. Lizards lost on average 29% and 14% of meal energy to feces and urate, respectively, and an additional 33% to SDA, leaving a net gain of 24% of the meals energy. When considering that only a portion of fecal energy stems from the celery meal, the net gain is expectedly higher. Although this study debunks the validity of celery and other proposed foods as negative calorie, these foods will contribute to generating a negative energy budget and thus the loss of body weight.\n\nSummaryThis empirical study refutes the existence of negative-calorie foods; however such foods will contribute to a negative energy balance, and thus the loss of body mass.