What Is the Ketogenic Diet
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.
How the Brain Benefits
Glucose is the brain’s preferred source of fuel because it’s fast. But glucose is inefficient; it doesn’t burn clean. Debris accumulates in the mitochondria, the fuel furnaces of cells. And glucose generates free radicals of oxygen, which progressively damage cells.
Oxidative stress also leads to the buildup of toxic proteins that are the hallmark of Alzheimer’s disease. Over time, the processes that power brain cells lose efficiency, setting the stage for cognitive decline. The same processes may contribute to other psychiatric disorders, such as depression.
When glucose is not available and brain cells must call on fat as their back-up fuel, they get a more efficient source of energy. Oxidative damage to brain cells is curbed. Turning to ketones intermittently also resets the machinery of glucose utilization and insulin sensitivity, and it stimulates cell-renewal processes. Memory and mental processing speed are maintained.
Many experts believe that it’s possible to retain cognitive capacity into old age and the best way to do it is through periodic ketogenesis, but not by a high-fat diet. Instead, evidence supports intermittent fasting, confining food consumption to an 8- to 12-hour window during the day and restricting intake, especially of carbohydrates, for at least 12 hours overnight.
Further, the many similarities between epileptic seizures and bipolar disorder make ketogenic diets of experimental interest in treating bipolar disorder.
Ketones confer a distinctive sweet or fruity smell to breathe. While nutritional ketosis is generally healthy in the short term, excessively high levels of ketone bodies can lead to ketoacidosis, a life-threatening condition. It most often occurs in untreated or undertreated Type 1 diabetes, from a lack of insulin, but it can also result from extreme keto dieting.
Ketogenic diets tend to be high in saturated fat and are known to increase levels of “bad” (LDL) cholesterol, which is associated with cardiovascular disease. They are also deficient in micronutrients, including vitamins, and in fiber. Ketogenic diets impede gut function. And they can put a burden on the kidneys. But for short periods, they have been proved safe.