Ketogenic diets, which involve eating very low levels of carbohydrates and high levels of fat, could cause an increased risk of Type 2 diabetes according to new research.
A study published in the Journal of Physiology raises questions about whether ketogenic diets could be dangerous for those following them.
Type 2 diabetes is an increasingly common challenge in modern societies, and its cause is still not fully understood.
Ketogenic diets are named because they intend to put the body into a metabolic state where it is fuelled by metabolising fat rather than through glycolysis-the process of extracting energy from glucose.
A side-effect of ketogenic diets discovered by the researchers is that it hampers the process for controlling blood sugar levels, and creates insulin resistance.
When the liver is unable to respond to normal levels of insulin to control blood sugar, this could prompt an increased risk of Type 2 diabetes.
Researchers at ETH Zurich and the University Children's Hospital Zurich discovered the side-effects by feeding mice two different kinds of diet.
Christian Wolfrum, one of the corresponding authors on the paper said: "Diabetes is one of the biggest health issues we face.
"Although ketogenic diets are known to be healthy, our findings indicate that there may be an increased risk of insulin resistance with this type of diet that may lead to Type 2 diabetes.
"The next step is to try to identify the mechanism for this effect and to address whether this is a physiological adaptation.
"Our hypothesis is that when fatty acids are metabolised, their products might have important signalling roles to play in the brain."
Tim Spector, professor of genetic epidemiology at Kings College London, told Sky News: "This study is a reminder that any extreme restriction diet can cause unforeseen problems."
Professor Spector noted though that it was based on a study in mice: "Humans are omnivores and benefit from a wide variety of foods, and restricting any one group will usually cause us problems longterm.
"Many people are on carb restricted diets which limits our plant and fibre intakes, with bad effects on our gut health."
"Ketogenic diets are proving to be an amazing treatment for childhood epilepsy for reasons we don't fully understand, and is being tried in other brain disorders, and many people with Type 2 diabetes have come off their medications by cutting out most carbohydrates with the help of their doctor.