The ketogenic diet, often called the keto diet, is one that is very high in fat, very low in carbohydrates, and low to moderate in protein. It typically supplies 75 to 90 percent of calories from fat, versus a more usual intake of 20 to 35 percent. It is intended to force the body to burn fat for energy, rather than glucose, to accelerate weight loss and curb appetite.
Although ketogenic diets have been enjoying a wave of popularity in recent years, primarily for weight reduction, they have been in use therapeutically for a century, under carefully controlled conditions, to treat epileptic seizures in children.
It’s not clear how a ketogenic diet reduces the hyperexcitability of nerve cells that leads to seizures. But there is mounting evidence that ketogenic diets, used judiciously for short periods of time, benefit several systems of the body, especially the brain.
The diet gets its name from ketone bodies, which are metabolites of fat produced in the liver as it breaks down stored body fat for fuel use by the rest of the body. A distinguishing feature of ketone utilization is that insulin is not required to escort ketones into cells, as it is with glucose.
Forcing the body to burn fat as fuel gives insulin time off. That restores the body’s sensitivity to insulin, resulting in lowered levels of both insulin and glucose in the blood. That has distinct metabolic benefits for the body—not just lowering weight but also cutting the risk of diabetes and other metabolic disorders. It boosts function of the brain, too.
Consuming a high-fat diet is not the only way to put the body in a state of ketosis. Fasting can do it too, as can carbohydrate restriction. Bouts of extreme exercise and excess alcohol intake can also result in ketosis.