The aim: Weight loss through fat-burning.
The claim: You’ll quickly lose weight and ultimately feel fuller with fewer cravings, while boosting your mood, mental focus and energy.
The theory: By slashing the carbs you consume and instead filling up on fats, you safely enter a state of ketosis. That’s when the body breaks down both dietary and stored body fat into substances called ketones. Your fat-burning system now relies mainly on fat – instead of sugar – for energy. While similar in some ways to familiar low-carb diets, the Keto diet’s extreme carb restrictions – about 20 net carbs a day or less, depending on the version – and the deliberate shift into ketosis are what set this increasingly popular diet apart.
The Keto diet has its roots in the decades-old therapeutic ketogenic diet. Clinically, the ketogenic diet is used in neurologic medicine, most notably to reduce hard-to-control seizures in children. Studies also suggest possible benefits in other brain conditions such as Parkinson’s and Alzheimer’s diseases.
Fairly recently, the diet was introduced as a weight-loss diet by an Italian professor of surgery, Dr. Gianfranco Cappello of Sapienza University in Rome. In his 2012 study, about 19,000 dieters received a high-fat liquid diet via a feeding tube inserted down the nose. The study showed an average weight loss of more than 20 pounds in participants, most of whom kept it off for at least a year. The researchers reported a few minor side effects, like fatigue.
Today, several versions of the Keto diet (using real food) are detailed in books, blogs and Facebook posts. The common thread is choosing high-fat foods coupled with very low daily carbs. Guidebooks include “The Complete Ketogenic Diet for Beginners” by Amy Ramos and “The Keto Diet: The Complete Guide to a High-Fat Diet” by Leanne Vogel.