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The ketogenic diet gets headlines because celebs like Kim Kardashian West and LeBron James have championed it for weight loss. But what exactly is it, and does the science support the hype?

The ketogenic — or keto — diet emphasizes high-fat foods and severely restricts carbohydrates. In fact, about 60% to 80% of calories should come from fat, according to Jason Ewoldt, RDN, LD, a wellness dietitian at Mayo Clinic Healthy Living Program (HLP). He notes that a true keto diet also includes only moderate amounts of protein, and less than 50 grams of carbohydrates a day.

Interestingly, the keto diet has been around for a long time. Doctors first started using it, Ewoldt says, in the 1920s to treat kids with epilepsy, and it's still sometimes used for that. But today, it is gaining traction for weight loss or to fuel extreme endurance sports like marathon running and triathlons.