Many A-list celebrities credit the ketogenic diet, better known as "keto", for their svelte physique.
Originally developed to ease epileptic seizures in children, the diet recommends up to 90% of a follower's daily calorie intake comes from fat. The aim is to induce ketosis, when fat stored in the liver is used as fuel, leading to overall weight loss.
With little research into its safety, dietitians from the non-profit Physicians Committee for Responsible Medicine (PCRM) in Washington DC analysed the available evidence, in what they have called "the most comprehensive analysis yet".
Results, published in the journal Frontiers in Nutrition, suggest the keto diet could trigger a range of health complaints – including raised cholesterol, kidney failure and pregnancy complications.
The risks of going keto are thought to outweigh any weight-loss benefits, with one medic even calling the eating plan "a disease-promoting disaster".
"The typical keto diet is a disease-promoting disaster," said lead author Lee Crosby.
"Loading up on red meat, processed meat and saturated fat – and restricting carbohydrate-rich vegetables, fruits, legumes and whole grains – is a recipe for bad health."
Keto diets can range from a 4:1 or 3:1 fat to protein-plus-carbohydrate ratio.
As well as supposedly aiding weight loss, keto advocates have claimed the diet is beneficial for diabetes, cancer, heart disease and Alzheimer's patients.
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After analysing the available evidence, the PCRM dietitians have stressed keto diets are not a "panacea".
Restricting carbohydrates – namely fruits and vegetables – may raise a person's risk of cancer, they found.
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Pregnant women, or those who could conceive, may be particularly at risk. The dietitians have linked the keto diet to neural tube defects. These occur when the neural tube – which forms a foetus' early spine and brain – does not close properly in the womb, leading to conditions like spina bifida.
Taking folic acid, recommended to ward off these defects, may also not mitigate the risk of following a keto diet.
"In addition to the significant risks to kidney disease patients and pregnant women, keto diets are risky for others, too, as these diets can increase LDL cholesterol levels and may increase overall chronic disease risk," said Crosby.
The keto diet was found to raise levels of "bad" cholesterol in many of its followers. This is likely due to the eating plan encouraging a high saturated fat intake, with lots of lard, coconut oil and butter.
Going keto may also hasten kidney failure, when the organs suddenly stop working, in kidney disease patients. The kidneys help to break down protein and may be overloaded if dieters up their intake.
In addition, "while keto can reduce body weight short-term, this approach is not more effective than other weight-loss diets", added Crosby.
The only well supported use of a keto diet is to reduce seizure frequency in patients with drug-resistant epilepsy while under medical supervision, according to the dietitians.
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