In recent years the ketogenic diet has gained legions of devotees with promises of rapid fat loss and a host of other benefits, but a new study claims that it may be a net negative in the long term.
Driven by endorsements from celebs like Halle Berry and Gwyneth Paltrow, the diet has been taken up around the world despite some well know side effects like keto breath, keto flu and... keto crotch (Google it).
Glossy photos on Instagram promise a leaner figure, glowing skin and increased energy.
But new research from Yale University has highlighted more serious issues with the diet, some of which can kick in after just one week.
What is the problem with keto?
Put simply, a ketogenic diet prescribes the consumption of large amounts of healthy fats and a tiny amount of carbohydrates.
Because of the low carbs the body goes into a "starvation state" and begins to burn fats instead of carbs, leading to weight loss.
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As this fat is burned up, the body produces chemicals called ketone bodies, which in turn produce gamma delta t-cells as they are burned.
The t-cells have tissue-protective qualities and are credited for many of the other health benefits claimed by keto.
Yale's research, published in the journal Nature Metabolism, was done using mice and showed that when mice ate a keto diet for more than a week they developed - and were more likely to develop - diabetes and obesity.
The researchers put this down to the mice consuming more fat than they could burn, thereby losing "the protective gamma delta T-cells in the fat".
"Our findings highlight the interplay between metabolism and the immune system, and how it coordinates maintenance of healthy tissue function," said one of the study's authors, Emily Goldberg.