Metabolic advantage is a term used in nutrition to describe the ability of a diet to achieve greater weight loss (or less weight gain) than another diet of equivalent calories. It is a claimed effect of low-carbohydrate diets and was popularised by the Atkins diet, but although several mechanisms exist to make it biologically plausible, it has yet to be definitively demonstrated as a significant factor in weight control. Some studies  that have specifically measured the changes in basal metabolic rate under isocaloric very high-fat and very high-carbohydrate diets have failed to find any statistically significant differences.
The human body obtains the majority of its energy through the citric acid cycle, which can use any of the macronutrients to generate adenosine triphosphate (ATP) used to transport chemical energy within cells. The chemical processes involved use energy themselves, so variations in the efficiency of these processes will have the same effect as variations in caloric intake.
The human body requires glucose for the brain and nervous system, and a diet that has very few or no dietary carbohydrates forces it to generate this glucose from protein through gluconeogenesis, with an efficiency of approximately 57% (protein and carbohydrate are approximately equal in calorific value; each has about four kilocalories per gram, but gluconeogenesis can produce only 57g of glucose from 100g of protein). This could be a significant contributor to metabolic advantage.
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