“Keto” refers to a ketogenic diet, which is a higher fat, moderately low protein, and very low-carb diet that results in putting your body into ketosis.
What’s ketosis? Ketosis is a natural metabolic process, where your body uses fat for fuel rather than glucose (carbohydrates). Once your body is depleted of its usual go-to fuel, carbohydrates, it begins to convert fat (from your food and your body) into molecules known as ketones (blood acids) in your liver, and then uses those ketones for energy. When your body is using ketones for fuel, you’re in “ketosis.” (Note: for people with type 1 diabetes, ketosis can be a sign of insulin deficiency, with ketones rising to potentially harmful levels; we do not recommend following a keto diet if you have type 1 diabetes.)
In order to enjoy the benefits of ketosis–weight loss or management, more energy, mental acuity, and, in special cases, therapeutic benefits for certain illnesses, such as cancer and type 2 diabetes–you need to stay in ketosis. We’ve got plenty of information on that, too: