Our brains use sugar (glucose) as energy. People with cognitive impairment and Alzheimer’s disease have problems processing sugar. As a result, scientists are studying whether using fat as energy—instead of sugar—could fix these issues. 

The ketogenic diet has gained popularity among health and fitness influencers online, some of which promote the idea that this diet can actually treat or prevent dementia. 

This low-carb, high-fat diet forces the body to use fats—which are broken down into ketones—as a source of energy. But to force the body to make the switch, 75 percent of your daily calories need to come from fat, making the diet restrictive and difficult to keep up. People on a keto diet will typically eat a lot of butter, cheese, eggs, meat, and oils while avoiding most fruits, vegetables, grains, potatoes, and junk food. 

There is some evidence that the keto diet can help people with treatment-resistant epilepsy in children. It is also promoted as a way to lose weight or manage diabetes, though the research supporting these uses is still limited. 

Could cutting down on carbs with a keto diet help older adults protect their brain as well? 

Because it is so difficult to cut down on carbs, most people who try the ketogenic diet might not actually reach ketosis—where the body switches to using ketones as fuel. As well, if people eat too much protein on the diet, then the body will break down those proteins into glucose instead of breaking down fat into ketones.   

Are keto diets safe?

One of the problems with the keto diet that experts point to with the ketogenic diet is the reliance on fat. 

Many people who switch to this diet might eat a lot of unhealthy saturated fats which may increase blood pressure and cholesterol. The high-fat and high-protein content of the diet can also lead to kidney or liver problems. People on a keto diet also eat less fruits and fibrous vegetables, which can cause nutritional deficiencies and constipation.

Since most keto diet studies are short in duration, and the diet is notoriously hard to keep up, scientists aren’t sure about its long-term impact. One recent study however, found that older adults who are on high fat, low carb diets—like keto—had double the risk of developing heart problems over the course of 12 years. 

Speak with your doctor if you’re thinking about switching to a keto diet. They can guide you toward foods with healthy levels of fat, monitor your heart health, and spot any hazardous side effects early. 

Can keto diets protect against cognitive decline and Alzheimer’s?

There are only a handful of research studies that have rigorously tested the benefits of a keto diet for cognitive decline or Alzheimer’s disease. The studies don’t have a lot of participants, and only two studies have looked at the effects of a ketogenic diet over the course of six months, making it hard to tell whether this diet is effective.

Researchers are also trying to isolate the effects of ketone bodies. This might be a safer way to get the brain to use fats as fuel. As a result, researchers are running clinical trials on a ketone called tricaprilin to see whether these fatty fuel sources can treat cognitive symptoms in mild-to-moderate Alzheimer’s disease. A Phase 3 study for this ketone is in the works, and is set to start in 2025.