Fad diets that cut out carbs while upping fat consumption may increase the risk of diabetes, research suggests.
Ketogenic diets low in carbohydrate and high in fat date back to the 1920s but have soared in popularity in the last few years.
They aim to force the body to burn fat as fuel, leading to rapid weight loss. Part of their attraction is that they allow the dieter to eat large quantities of fat-rich food such as meat, butter and cheese.
As well as aiding slimming, ketogenic diets are also supposed to keep blood sugar levels stable.
But new research suggests this claim at least could be misconceived.
Tests on mice put on ketogenic diets showed evidence of insulin resistance in the liver – a condition that prevents the body responding properly to the hormone insulin and is a stepping stone to Type 2 diabetes.
Lead researcher Professor Christian Wolfrum, from ETH Zurich University in Switzerland, 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.”
The findings are reported in the Journal of Physiology.
The ketogenic diet was first developed in the 1920s as a treatment for epilepsy.
Doctors discovered that a low-carb diet appeared to help reduce seizures, possibly by altering the supply of energy to the brain.
Normally the body relies on carbohydrates as its primary source of glucose, which provides fuel for cells.
A ketogenic diet mimics what happens when the body is starved of carbs. The liver is forced to use fat for fuel, converting it to “ketone bodies”, molecules that provide an emergency glucose substitute based on acetone.
Most ketogenic diets provide 70% or more calories from fat, 15-20% from protein, and 10% or less from carbohydrates.
Dr Alison Tedstone, chief nutritionist at Public Health England, said: “Cutting out whole food groups risks damaging long-term health.
“A healthy balanced diet, based on the Eatwell Guide, should include higher fibre starchy carbohydrates – this can help minimise the risk of serious illnesses such as Type 2 diabetes, heart disease and some cancers.”