The Effect of Low Carbohydrate on Energy Metabolism

Objective: To investigate whether low-carbohydrate diets are efficient for reduction of body weight and through which mechanism.

Design: A couple of studies using low-carbohydrate diets in the treatment of obesity are reviewed. Mechanisms for explaining the reduced appetite are described in relation to knowledge on regulation of appetite for fat and carbohydrate.

Results: Studies with low-carbohydrate diets demonstrate a rapid weight loss, being more pronounced after 3 and 6 months compared to low-fat diets. After 12 months there is no difference between the low-carbohydrate and the conventional low-fat diet on weight loss. Both diets lead to improvements in risk factors for coronary heart disease, the low-carbohydrate diet leading to a greater decrease in serum triglycerides and increase in HDL cholesterol compared to the low-fat diet. Blood pressure, insulin sensitivity and LDL cholesterol were improved to a similar degree by the two diets. The mechanism for the rapid weight loss with the low-carbohydrate diet is a suppressed appetite, first through the high-protein content of the diet, second through the ketogenic nature of the diet with satiety signals for fat being active and third through the absence of hunger-promoting carbohydrate components like sucrose and/or fructose.

Conclusion: A rapid initial weight loss occurs with a low-carbohydrate diet due to a suppressed appetite. There is as yet no indication of an increased metabolic rate and an increased thermogenesis by the low-carbohydrate diet. The safety and efficacy of low-carbohydrate diets have to await further studies.