Diabetes of the brain? It’s not so far-fetched.1 When Brown University neuropathologist Suzanne de la Monte, MD, first called Alzheimer’s disease “Type 3 Diabetes”2 a decade ago, dementia experts rushed in to criticize the theory. But a growing stack of research suggests that insulin resistance in the brain helps fuel the plaques, tangles and signal breakdowns of this progressive disease—even in people who do not have diabetes.
Your brain needs plenty of blood sugar—glucose—for everything from balancing your checkbook to remembering your new neighbor’s name to running thousands of body functions, 24/7. But when brain cells stop obeying insulin’s commands to absorb blood sugar in a normal way, there’s trouble—especially, research shows, in areas most vulnerable to Alzheimer’s disease. In a recent Iowa State study of 150 middle-aged people with a family history of Alzheimer’s, those with insulin resistance used less glucose in the hippocampus, a key area for learning and memory storage.3 It was an early warning. The study volunteers didn’t have serious memory problems. But the researchers saw changes in an area typically hit hard in later life by the brain disease.
"Brain insulin resistance is very much like regular diabetes, just happening in a different part of the body," de la Monte says. “There’s a growing consensus that insulin’s very important here, for many reasons.”
Insulin, she says, “is a gate-keeper in the brain. It sends glucose into cells. But it’s also involved with the production of neurotransmitters – chemicals that send messages between brain cells. It keeps cells and the cables that carry information around in the brain – the white matter – alive. When glucose can’t get into cells, there’s stress. Cells weaken and die.”
Insulin resistance seems to be involved in the formation of tangles inside nerve cells, formed by a protein called tau. And insulin resistance increases inflammation in the brain, driving the formation of clumps of protein clumps between nerve cells, too. “This amyloid accumulation makes insulin resistance worse, so it’s a loop,” de la Monte says.
Giving the brain more insulin might help – but it’s still experimental. Earlier this year, researchers from Wake Forest Baptist Medical Center in Winston-Salem, NC, tested inhaled insulin in people with mild memory and thinking problems or early Alzheimer’s. Those who had a gene that increases Alzheimer’s risk saw memory improve – and those with the most insulin resistance got the biggest benefits.4
While drug companies are studying medications that may combat memory and thinking problems by increasing insulin sensitivity,5 de la Monte says lifestyle steps can help, too:
1. Move more, weigh less. “We know that losing even small amounts of weight, like five to seven percent [about 8 to 12 pounds if you weigh 175], increases insulin sensitivity. So does regular exercise. We don’t know yet whether the improvement is the same in the brain as it is in the rest of the body,” de la Monte says. “But we do know that exercise protects against dementia and that people at healthier weights are at lower risk, too.”
2. Cut way back on processed meats. “Most, if not all, preserved and processed meats contain nitrosamines,” de la Monte explains. “And unfortunately, the ones with highest ratings for taste can have the most. In our lab research, nitrosamines combined with a high-fat diet interfered with insulin signaling. We started to see signs of type 2 diabetes, fat accumulation in the liver and neurodegeneration that looks like Alzheimer’s disease.” 6Processed meats include meats that have been cured, salted, canned or dried. Think hot dogs, ham, bacon and salami.
3. Reign in saturated fat and refined carbohydrates, too. University of Washington researchers have found that people who munched a high-fat diet loaded with foods that make blood sugar soar – like sugary drinks, candy, desserts and white-flour breads and crackers – for four weeks had changes in the fluid that surrounds the brain that looked like very early Alzheimer’s.7 In contrast, a lower-fat diet that included carbs that raise blood sugar more slowly (such as fiber-rich whole grains, beans, vegetables and fruit), was beneficial – and even improved memory. High blood sugar leads to bigger insulin spikes after a meal; the researchers suspect that even before insulin resistance begins, higher insulin levels may kick-start the development of Alzheimer’s brain plaques.8
4. Sip some polyphenols. Have a cup of green tea or a glass of red wine. De la Monte notes that rates of dementia and Alzheimer’s disease are lower in groups of people who enjoy these polyphenol-rich beverages regularly. These plant compounds help protect brain cells and blood vessels from damage.9
5. Take signs of insulin resistance seriously. Even if you don’t have type 2 diabetes, you’ve got insulin resistance if you have prediabetes. You’re also insulin-resistant if you have metabolic syndrome—any three or more of these five warning signs: 1. a wide waistline (35 inches or larger for women, 40 for men); 2. high triglycerides (150 or higher); 3. low HDL cholesterol (under 40 for men, 50 for women); 4. blood pressure higher than 135/85; and 5. fasting blood sugar over 100 mg/dL. “If you have this kind of peripheral insulin resistance, you likely have insulin resistance in the brain as well,” she says. But don’t wait to make healthy changes. De la Monte and other researchers have found signs of insulin resistance in the brain tissue of people with Alzheimer’s who did not have diabetes.