ReviewKetogenic diets for weight loss: A review of their principles, safety and efficacy
Introduction
The increasing prevalence of overweight and obesity has been widely reported. In recent years, low-carbohydrate “ketogenic” diets have received much attention as a means of rapid weight loss. However, there is no clear consensus in the literature as to what carbohydrate intake constitutes a low-carbohydrate diet, or to what degree carbohydrates must be restricted in order to cause ketosis. Furthermore, since ketogenic low-carbohydrate diets are often high in fat, there have been concerns about their potential adverse effects on cardiovascular risk.
The use of ketogenic diets in refractory paediatric epilepsy has been extensively reviewed elsewhere [1]. These diets have a different composition and aim to generate higher ketone levels than the ketogenic diets used for weight loss. This article will briefly overview ketone body metabolism and review the available evidence relating to the efficacy and safety of ketogenic low-carbohydrate diets for weight loss.
Section snippets
Ketone body metabolism
The term “ketone bodies” refers to three compounds: acetoacetate (AcAc), 3-β-hydroxybutyrate (3HB—not strictly a ketone but rather a hydroxy fatty acid) and acetone (Fig. 1). The circulating levels of ketone bodies are dependent both on their rate of production (ketogenesis) and their rate of utilisation (ketolysis). AcAc and 3HB are the two main ketone bodies generated and used for fuel under low-carbohydrate conditions. Acetone is formed by spontaneous decarboxylation of AcAc [2] and gives a
Measurement of ketone bodies
Standard tests for blood and urinary ketones are semi-quantitative, and reflect the presence of AcAc or acetone via a reaction with nitroprusside, which produces a complex detectable on a test strip. Ketone tests based on the nitroprusside reaction can give false positive results in the presence of drugs containing sulfhydryl groups (including captopril, N-acetylcysteine and penicillamine) [13], [14]. False negative results may occur if test strips have been exposed to air for an extended
How low in carbohydrates?
The English-language literature has no clear consensus about the definition of a “low-carbohydrate diet”. A 2003 systematic review of the efficacy and safety of low-carbohydrate diets for weight loss included diets with carbohydrate contents ranging from 0 to 263 g/day [17]. Commonly, low-carbohydrate diets are considered to contain <100 g/day or <30% of energy from carbohydrates [18], [19], [20]. Since a diet restricted in carbohydrates usually contains a relatively increased proportion of the
Conclusions
Ketogenic low-carbohydrate diets have increased in popularity over recent years, but the degree of carbohydrate restriction required to achieve ketosis remains unclear. In general, studies have shown greater weight loss at 3–6 months with KLC diets compared with LF diets, however this difference is no longer apparent at 12 months. The majority of studies have found that KLC diets are associated with favourable changes in triglyceride and HDL levels, but higher LDL levels than LF diets. The
Conflicts of interest
None.
Acknowledgements
She is supported by an Endocrine Society of Australia scholarship and a Royal Australasian College of Physicians Shields Research Entry scholarship.
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