Could Alzheimer’s disease be more accurately described as “type 3 diabetes”? The surprising connection between blood sugar and brain health.

If you doubt that food can affect your mood, consider this: When your blood sugar drops too low, you get hungry and irritable. And when your blood sugar rises too high, you become tired and mentally fuzzy.

Now comes the blockbuster: Growing evidence suggests that blood sugar problems in the brain might just set the stage for “type 3 diabetes,” better known as Alzheimer’s disease.

The relationship between blood sugar problems and Alzheimer’s disease isn’t entirely surprising. Numerous studies have shown that type 2 diabetes and obesity (the prime risk factor for diabetes) significantly increase the risk of mild cognitive impairment and Alzheimer’s disease. In the most recent study along these lines, Yonas E. Geda, MD, of the Mayo Clinic in Scottsdale, Ariz., reported that seniors eating diets high in sugars and other refined carbohydrates—which can mess with blood sugar—were almost four times more likely to develop mild cognitive impairment, a common prelude to Alzheimer’s.

Insulin Gone Haywire

The problem isn’t so much blood sugar, but insulin—although the two are usually intertwined. Eating a lot of refined sugars and carbohydrates creates a spike in blood sugar. In response, the pancreas secretes insulin, which lowers blood sugar and moves it into cells to be stored as fat or burned for energy. Eventually, cells stop responding to the repeated insulin surges, leading to the higher levels of blood sugar and insulin characteristic of type 2 diabetes.

A parallel process occurs in the brain, according to recent studies. The term "type 3 diabetes" was coined by Suzanne de la Monte, MD, PhD, a neuropathologist at the Brown Medical School, in Providence, RI. The reason is that Alzheimer’s disease has characteristics that resemble both type 1 and type 2 diabetes. Specifically, insulin levels become low (a trait of type 1 diabetes) and insulin resistance increases (a trait of type 2 diabetes) in the brain. Insulin resistance in the brain creates the equivalent of an insulin deficiency.

Insulin has long been known as one of the hormones that regulate blood sugar, but it does far more. It’s also made in the brain, where it helps neurons absorb blood sugar for energy. Insulin regulates some neurotransmitters, such as acetylcholine, which play important roles in learning and remembering. The hormone supports “plasticity,” or adaptability in brain cells, enhancing their ability to make and strengthen connections.

Neurons transmit information to each other via synapses, which contain receptors—docking ports—for insulin molecules. Researchers now understand that the docking of insulin to synapses is essential for forming memories. Without insulin, new memories can’t form. The loss of memory is one of the key traits of Alzheimer’s disease, and the latest research indicates that the catastrophic loss of memory is related to problems with insulin.

For years, researchers have believed that clumps of beta amyloid protein in the brain are the cause of memory loss in Alzheimer’s disease, and there’s no doubt that they play a major role. However, William Klein, PhD, of Northwestern University, Chicago, recently discovered that diabetes in laboratory animals creates Alzheimer’s-like brain changes, including an increase in beta amyloid protein. Beta amyloid protein helps make brain cells insulin resistant, and it also leaves a trail of free radical damage.

There’s still more evidence from Brown University’s de la Monte. She and her colleagues analyzed brain tissue from 45 patients who had died from Alzheimer’s. They found that people who had more advanced Alzheimer’s disease had the least insulin activity.

None of this new knowledge means you can reverse Alzheimer’s, though some scientists speculate that better eating habits might slow the disease’s progression, according to a recent article in New Scientist. However, by getting your blood sugar under control, you improve your odds of avoiding this catastrophic disease.

Eating to Keep Blood Sugar in Check

Bijal Trivedi, MA, MS, writing in New Scientist observed that “we might be unwittingly poisoning our brains every time we chow down” on junk food. So if Alzheimer’s disease is a type of diabetes, or is at least related to blood sugar problems in general, what steps can you take to lower your risk?

The simplest approach is to avoid complicated diet programs that count calories or carbs or organize foods by their glycemic index rankings. Most people quickly tire of following such plans. Instead, focus on eating freshly prepared foods and avoiding the majority of foods sold in a box, can, jar, bottle, tub, or bag. Packaging often indicates some degree of processing, which tends to increase the glycemic index of foods. Whole, natural foods almost always are low carb and low glycemic.

Using fresh ingredients means either cooking most of your foods from scratch or eating in restaurants that use mostly fresh and wholesome ingredients. It’s easier than you might think. If you usually eat lunch in a restaurant, order a chicken Caesar salad sans the croutons. At home, it doesn’t take a lot of time to prepare a simple meal, such as pan frying a salmon filet in olive oil, with steamed vegetables and spaghetti squash on the side.

Protein. Opt for quality protein sources, such as fish, chicken, or grass-fed beef. Protein helps maintain normal blood sugar levels, which will, in turn, aid normal insulin function. Protein prompts the liver’s release of glucagon, a hormone that counteracts insulin and therefore reduces the risk of insulin resistance. Legumes contain a substantial amount of carbohydrate, but a 2012 study in the Archives of Internal Medicine found that they improved blood sugar levels.

High-Fiber Vegetables. Like protein, fiber also improves blood sugar and insulin levels, and studies have found that high-veggie eating habits—like the traditional Mediterranean diet—lead to a lower risk of Alzheimer’s disease. Just about all veggies are fine, with the exception of potatoes, which spike blood sugar levels. High-fiber, low-sugar fruits include raspberries, blueberries, kiwi, and melons.

Heathy Carbs. For most people, veggies provide plenty of complex carbohydrates for energy. If you exercise strenuously, you may need to add sweet potatoes, yams, and legumes to your diet. Large amounts of grain-based carbs, such as wheat and corn, can be problematic because they tend to be highly processed and contain a high ratio of carbohydrate to vitamins, minerals, and protein.

Keep in mind that many factors influence a person’s risk of Alzheimer’s disease. They include inflammation; obesity, which increases the risk of type 2 diabetes by 80 times; and free radical damage to brain cells. All of these other factors are intertwined to one extent or another, along with poor glucose tolerance and decreases in insulin function.