Very low-carbohydrate diets in the management of diabetes revisited

Humans can derive energy from carbohydrate, fat, or protein. The metabolism of carbohydrate requires by far the highest secretion of insulin. The central pathology of diabetes is the inability to maintain euglycaemia because of a deficiency in either the action or secretion of insulin. That is, because of either insulin resistance often accompanied by hyperinsulinaemia, or insulin deficiency caused by pancreatic beta cell failure. In individuals dependent on insulin and other hypoglycaemic medication, the difficulty of matching higher intakes of carbohydrates with the higher doses of medication required to maintain euglycaemia increases the risk of adverse events, including potentially fatal hypoglycaemic episodes. Thus, mechanistically it has always made sense to restrict carbohydrate (defined as sugar and starch, but not soluble and insoluble fibre) in the diets of people with diabetes. Randomised clinical trials have confirmed that this action based on first principles is effective. The continued recommendation of higher-carbohydrate, fat-restricted diets has been criticised by some scientists, practitioners and patients. Such protocols when compared with very low-carbohydrate diets provide inferior glycaemic control, and their introduction and subsequent increase in carbohydrate allowances has never been based on strong evidence. The trend towards highercarbohydrate diets for people with diabetes may have played a part in the modern characterisation of type 2 diabetes as a chronic condition with a progressive requirement for multiple medications. Here we will introduce some of the evidence for very low-carbohydrate diets in diabetes management and discuss some of the common objections to their use.