A ketogenic (or "keto") diet is an eating plan that's designed to seriously minimize carbohydrates, your body's favorite fuel source, and dramatically increase fats. The idea is that as carbohydrate levels drop, the body becomes forced to burn stored fat as its primary source of fuel, which can result in often dramatic weight loss. The diet represents a total turnaround from how most people eat: While the typical American diet is about 50 percent carbohydrate, 15 percent protein, and 35 percent fat, the breakdown on most typical keto diets is 5 to 10 percent carbs, 70 to 75 percent fat, and the rest from protein.
The "keto" part refers to ketones, which are water-soluble molecules that the liver makes when metabolizing fats, particularly when carbohydrate intake is low. Ketones can be used for energy by most tissues in your body, including the brain, which can't use unrefined fats as fuel.
Your body is always using a mix of fat and glucose for energy, but in a non-keto-adapted state, it reaches for glucose first, since only low amounts of ketones are normally generated during fat metabolism and some tissues of the body—for example, the heart—prefer using ketones when they're available. The brain can't use fat, so it depends on glucose when you're in a non-keto-adapted state.
If glucose is the body's normal go-to source of energy, you may be wondering what happens when it suddenly doesn't have enough to use as its main fuel.
Read article: https://www.verywellhealth.com/what-is-keto-adaptation-2241629