In a Perspective, John Speakman and Kevin Hall suggest that, while insulin does play a role in body fat regulation, it does so independent of dietary carbohydrates. Thus, low-carb, high-fat diets - including the popular "ketogenic" diet - may not be any more effective at keeping obesity at bay than those that balance calorie intake with energy expenditure. Although the primary cause of common human obesity remains uncertain, one explanation - the popular "carbohydrate-insulin" model (CIM) - suggests that excessive body-fat gain stems from consumption of carbohydrates, which leads to the production of after-meal insulin that promotes energy storage (as fat tissue) and the desire to eat more. The result is a vicious, diet-driven positive feedback loop that contributes to obesity. The solution to this has been to implement dietary regimes that replace carbohydrates with dietary fat, which does not stimulate postprandial insulin secretion - the "ketogenic" diet, for example. However, the theoretical basis of the CIM model of obesity has been refuted by several recent studies, suggesting that insulin plays a role in body fat regulation independent of dietary carbohydrates. Here, Speakman and Hall present an alternative model of body fat regulation. According to the authors, the mechanisms underlying the effects of insulin on weight gain are more complex than proposed by the CIM. They argue that obesity can be better understood by considering the dynamic effects that insulin has on multiple organs. Speakman and Hall suggest that the basal level insulin in response to the balance of energy intake and expenditure, rather than diet alone, is more important in regulating weight gain. "Failure of the CIM should not be taken to mean that low-carbohydrate, high-fat diets cannot be beneficial for weight loss," write Speakman and Hall. "However, direct modulation of the carbohydrate-insulin axis in adipose tissue is unlikely to be the primary mechanism underpinning body fat loss in individuals successfully engaged in such diets."