The ketogenic diet is all about eating the right foods in the right proportions. When you do it right, your body will start burning stored fat.

The ketogenic diet is in the news because celebrities like Kim Kardashian West and LeBron James have touted it as a successful diet for weight loss. But what is it exactly? Does it have scientific support?

The ketogenic diet emphasizes high-fat foods and severely restricts carbohydrates. In fact, 60 percent to 80 percent of calories should come from fat, according to Jason Ewoldt, RDN, LD, a wellness dietitian in the Mayo Clinic Program for Healthy Living. He notes that a true ketogenic diet also includes only moderate amounts of protein and less than 50 grams of carbohydrates per day.

Interestingly, this diet has been around for a long time. Ewoldt says that doctors began using it in the 1920s to treat children with epilepsy, and it’s still sometimes used for that. Today, however, it is gaining relevance for weight loss or extreme endurance in sports like marathons and triathlons.

How does the ketogenic diet work?
As Ewoldt explains, the typical American diet consists of 50% or more carbohydrates, which are converted to glucose in the body. Your cells burn that glucose for fuel. But when you switch to a very high-fat, low-carb diet, your body, by necessity, turns away from glucose and instead uses fatty acids and ketone bodies for energy. This process is called ketosis, hence the name of the diet.

What foods can you eat?
Ewoldt says that nuts, seeds, cheese and other high-fat dairy products, plain Greek yogurt, non-starchy and fibrous vegetables, oils, along with smaller amounts of meats, eggs and fish, are the mainstays of the ketogenic diet.

You’ll need to severely limit carbohydrates, including bread and baked goods, sweets, noodles, breakfast cereals, starchy vegetables like potatoes, sweet potatoes, corn and peas, beans, fruit, and beer .

You’re thirsty? Find a bottle of water or enjoy some sparkling water. Unsweetened coffee and tea are also allowed. Minimize alcohol consumption; if you drink, choose low-carb options (vodka, tequila) and sparkling water for mixing.

Does it really work for weight loss?
Yes, but the answer comes with a qualification. It takes two to three weeks for the dieter to start burning fat (ketosis) in the body. So don’t expect instant results. Some studies have shown that low- or very-low-carb ketogenic diets help with weight loss. However, in the long term, there is little difference between a ketogenic diet and a diet with higher levels of carbohydrates.

Ewoldt adds a note of caution: “This is a very restrictive diet that is difficult to follow. The average person is not going to stay on it long-term. Also, because the saturated fat content is high, along with limited amounts of fruits, vegetables and whole grains, is not optimal for health.

Why do some athletes follow a ketogenic diet?
Ewoldt explains it this way: “If a trained athlete eats a balanced diet that includes carbohydrates, he can store about 2,500 calories from glucose, the preferred energy source. But this same athlete has about 40,000 calories available from fat.”

The idea is that by switching to a high-fat diet, the body will adapt and instead of using carbohydrates for energy, it will use fat. Because there is so much more fat, athletes such as marathon or triathlon runners would theoretically have greater endurance. However, they need a certain level of carbohydrates to be used along with fat for energy. Ewoldt adds that the adaptation process for the body to start burning fat instead of glucose can take several weeks or months.