AARP Eye Center
It may be time to promote fat from sworn enemy to aging ally.
Fat can be a potent fuel for the brain, researchers are discovering, stepping up as aging neurons lose their ability to burn glucose for energy. The newest science suggests that a ketogenic diet — heavy on fat and very light on carbohydrates — could improve thinking in people with Alzheimer's disease, and that it may even help reduce the risk of the deadly brain disorder in the first place.
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What's a ketogenic diet?
At first glance, a ketogenic diet seems the polar opposite of eating plans that experts have linked to brain and heart health. For example, the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet — which has been shown to lower high blood pressure, a risk factor for Alzheimer's disease — is 33 percent fat, 38 percent carbohydrates and 26 percent protein.
A typical ketogenic diet, though, is 70 to 80 percent fat, 10 to 20 percent protein and 5 to 10 percent carbohydrate. For a 2,000-calorie daily intake, this translates to about 165 grams of fat, 40 grams of carbohydrate and 75 grams of protein. It eliminates most fruits and virtually all starchy vegetables (potatoes, corn, peas, etc.), plus beans and grains. Avocados, eggs, nuts, cruciferous vegetables, and most meats and cheeses, however, are OK.
A ketogenic diet typically produces weight loss as the body metabolizes stored fat. But it also offers other benefits. For example, the diet is very effective in treating some kinds of drug-resistant epilepsy. It's also being investigated in diabetes, cancer and a number of neurodegenerative diseases, including Alzheimer's.
Dual fuel: Fat supplements the brain's diet
So what does a ketogenic diet have to do with the brain? It provides another form of fuel.
The brain's normal diet is simple: glucose. This form of sugar comes from the carbohydrates we eat, and the cells’ “power plants,” called mitochondria, convert it into the energy that drives every life process. But when dietary carbohydrates are limited, or even absent, the brain can switch to its secondary fuel source, ketones. As glucose is a by-product of carbohydrate digestion, ketones are a by-product of fat digestion.
"The body can store fat for later use, or it can burn fat for energy,” explains Russell Swerdlow, M.D., a professor of medicine and director of the University of Kansas Alzheimer's Disease Center. “Some tissues can directly burn fat, but others, including neurons in the brain, can't. So the liver breaks stored fat down into ketone bodies. They enter the bloodstream and are transported to the brain, which uses them for energy."
To turn on this process, the body needs to enter a metabolic state called ketosis. This typically switches on when daily carbohydrate intake is less than 50 grams. (The typical American diet contains upwards of 200 grams of carbohydrates per day.) There are a few ways to induce ketosis: fasting, eating a ketogenic diet, and taking a medium-chain triglyceride (MCT) oil supplement, which, in essence, is a liquid form of easily digestible fats (more on this later).