This study explored whether switching from a high-carb diet to a ketogenic diet, without altering calorie intake, affects energy expenditure and body composition (Hall KD, et.al., 2016).
Seventeen overweight men first followed a high-carb diet for four weeks, then switched to a ketogenic diet which is a high fat diet.
The participants stayed in metabolic chambers, so the research was well designed. The researchers tracked changes in energy burned at rest and during sleep. Body composition was monitored using X-ray scans.
Body fat loss slowed during the ketogenic diet and coincided with increased protein utilization and loss of fat-free mass. This means they lost muscle mass. That is not what you want when you lose weight.
When the participants were on the high carbohydrate diet, they did not lose muscle mass.
The research suggests that while ketogenic diets may alter how the body burns energy, they don't lead to greater fat loss compared to high-carb diets.
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Hall KD, Chen KY, Guo J, Lam YY, Leibel RL, Mayer LE, Reitman ML, Rosenbaum M, Smith SR, Walsh BT, Ravussin E. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr. 2016 Aug;104(2):324-33.