Could Alzheimer's disease be a kind of diet-induced diabetes?

Possibly, according to work by neuropathologist Suzanne M. de la Monte, MD, of Brown University and other researchers. In fact, de la Monte and her team have dubbed Alzheimer's "Type 3 diabetes."

In Type 2 diabetes, the body's cells stop taking in glucose from the bloodstream, either because the pancreas stops creating enough insulin or cells start ignoring insulin's repeated requests for them to pick up glucose — the latter a condition known as insulin resistance. With Type 3 diabetes, says de la Monte, the problem is insulin resistance in the brain.

In a paper published in Current Alzheimer Research, de la Monte reviews the growing body of evidence suggesting that Alzheimer's is fundamentally a metabolic disease in which the brain's ability to use glucose and produce energy is impaired. In one study, for example, de la Monte and her colleagues found that blocking insulin's path to the brain resulted in Alzheimer's-like neurodegeneration in rats.

Alarmingly, she adds, the drug they used to block insulin in the experiment resembles the nitrites found in many processed foods. High-fat diets exacerbate the neurodegeneration brought on by nitrites, she says.

Age-adjusted trends in Alzheimer's and Type 2 diabetes prevalence are similar, de la Monte points out. And because genetic forms of Alzheimer's represent the minority of cases, she says, the rapid rise in its prevalence suggests an "exposure model" of disease. The evidence, she writes, suggests that Alzheimer's "is a metabolic disease with virtually all of the features of diabetes mellitus, but largely confined to the brain."

The findings underscore the importance of psychologists' helping clients ditch the junk food and get off the couch, says psychologist Margaret Gatz, PhD, whose own research has found diabetes to be a significant risk factor for Alzheimer's.

"We know that if people observe good habits with respect to diet and exercise, it can make a difference in their risk of diabetes and in turn for their risk of dementia," says Gatz, a professor of psychology, gerontology and preventive medicine at the University of Southern California. "That's another reason psychologists should absolutely be encouraging good health behaviors and helping people make lifestyle changes."

While Gatz agrees with the premise of the new research, she's not 100 percent behind the name "Type 3 diabetes."

"I wouldn't want diabetes to be the only focus," says Gatz. After all, researchers are exploring many other risk and protective factors for Alzheimer's, including intellectual and social stimulation. Says Gatz, "We know that cholesterol, physical exercise and a panoply of other behavior changes could also affect the risk of dementia in later life."

—Rebecca A. Clay