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.
How does the keto diet work?
As Ewoldt explains, a typical American diet consists of 50% or more carbohydrates, which convert to glucose in the body. Your cells burn that glucose as fuel. But when you switch to a very high-fat, low-carb diet, your body, by necessity, shifts away from glucose and instead uses fatty acids and ketone bodies for energy. This process is called ketosis — hence the diet's name.
What foods can you eat?
Ewoldt says nuts, seeds, full-fat cheese and other dairy products, plain Greek yogurt, nonstarchy and fibrous vegetables, oils, along with smaller amounts of meats, eggs and fish, become keto diet mainstays.
You'll need to sharply limit carbohydrates, including bread and baked goods, sweets, pasta, breakfast cereals, starchy vegetables like potatoes, sweet potatoes, corn and peas, beans, fruit, and beer.
Thirsty? Reach for the water bottle, or enjoy some sparking water. Unsweetened coffee and tea also are allowed. Minimize alcohol intake; if you do drink, choose low-carb options (vodka, tequila) and soda water as a mixer.
Does it really work for weight loss?
Yes — but that answer comes with a qualifier. It takes two to three weeks on the diet to start fat burning (ketosis) in the body. So, don't expect instant results. Some studies have shown that adhering to low- or very-low-carbohydrate ketogenic diets helps people lose weight. However, long term there is little difference between a ketogenic diet and a higher carbohydrate diet.
Ewoldt adds a cautionary note: "This is a very restrictive diet that's tough to follow. The average person is not going to keep doing this long term. Also, because the saturated fat content is high, coupled with limited amounts of fruits, vegetables and whole grains, it is not optimal for health."
Why do some athletes follow a keto diet?
Ewoldt explains it like this: "Following a balanced diet that includes carbohydrates, a trained athlete can store about 2,500 calories of glucose, the preferred source of energy. But this same athlete has around 40,000 calories of fat available."
The idea is that by switching to a high-fat diet the body will adapt from using carbohydrates for energy to using fat. Because a vastly greater amount of fat is available, that would, in theory, keep endurance athletes like marathon runners or triathletes going longer. However, athletes do need some carbohydrate to use along with fat for energy. Ewoldt adds that the process of adapting your body from glucose-burning to fat-burning can take several weeks to months.