Deep Dive: Do Low-Carb Diets Stoke the Metabolic Fire?

Weight loss is one of the most effective tools for lowering the risk of chronic diseases like diabetes and cardiovascular disease. Weight loss requires a calorie deficit over an extended period of time, which can occur via reduced calorie intake, increased energy expenditure, or both. It’s been hypothesized that the macronutrient distribution of a diet affects total energy expenditure, in that low-carbohydrate diets are successful partly due to their ability to increase the thermic effect of food and basal metabolic rate.

There have been several studies that have examined the effects of low-carbohydrate diets on total energy expenditure (TEE), as compared to high-carbohydrate diets. For example, one randomized controlled trial^[1] found that a low-carbohydrate diet containing 20% calories coming from carbs increased total energy expenditure by about 100–200 kcal per day. However, another randomized controlled trial^[2] found that a very high-carbohydrate diet led to an approximate 350 kcal per day increase in total energy expenditure, compared to a very low-carbohydrate diet. Furthermore, a previous 2017 meta-analysis^[3] of 28 studies found that a lower-carbohydrate diet reduced total energy expenditure by about 25 kcals per day. However, the trials in that meta-analysis had a median duration of about four days. Some have argued that there is a metabolic adaptation period to low-carbohydrate diets that takes several weeks, and the proposed increase in TEE only occurs after that adaptation period is complete.

To test this hypothesis, the authors of the present study conducted a meta-analysis to compare the effects of diets differing in carbohydrate content on TEE over shorter and longer periods of time.

Total energy expenditure is one of the primary components that determines weight loss. There has been speculation that differing macronutrient profiles may have meaningful effects on total energy expenditure, making some diets more effective for weight loss. Randomized trials have led to conflicting results on whether lower-carbohydrate or higher-carbohydrate diets are more effective for fat loss. Potential interactions with diet duration have not been considered in previous meta-analyses. The authors of the present study used a meta-analysis to compare the effects of diets differing in carbohydrate content on TEE over shorter and longer periods of time.