Ketone bodies are endogenously produced by the liver under conditions of low carbohydrate and/or high fatty acid availability, and can affect metabolism via signalling or substrate effects. Ketone esters provide the possibility to increase circulating ketone body concentrations without the need for low carbohydrate or high fatty acid availability. This may circumvent some of the challenges and risks of ketogenic diets, facilitating more practical approaches to achieving ketosis. In this presentation evidence of the effects of ketogenic diets and ketone esters on carbohydrate and lipid metabolism will be presented. This will include effects of ketogenic diets and ketone esters on energy metabolism and body composition. Effects on glycaemia under diurnal and fasting conditions will be presented, in addition to the response to a meal challenge. Furthermore, potential mechanisms by which glycaemia is affected will be covered, in addition to trade-offs with lipoprotein metabolism.