Neal D. Barnard, MD

Alzheimer's disease affects about 50 percent of all people older than 85, and about 5 million people in the U.S. have some form of dementia. No one knows for sure exactly what causes Alzheimer's, but some suspected causes include hyperinsulinemia, elevated glucose levels and cerebrovascular disease.

That means people with diabetes may be at higher risk than others of developing Alzheimer's disease, according to Neal D. Barnard, MD, adjunct associate professor of medicine at the George Washington University School of Medicine, Washington, D.C., who spoke Aug. 4 on "Diabetes and Alzheimer's Disease: Evidence-Based Interventions for Prevention."

Dr. Barnard and colleagues conducted a study of the effect of a low-fat, plant-based vegan diet on glycemic control among people with type 2 diabetes compared with a diet following the American Diabetes Association (ADA) guidelines. They found that both diets improved glycemic and lipid control, but people with diabetes who stuck to the low-fat vegan diet had greater improvements than those on the ADA diet.

A low-fat vegan diet can also help reduce weight. Almost every study shows that when people make a qualitative shift to a plant-based, low-fat diet, their weight control is four times better than it is by trying to force the weight off by going voluntarily hungry every day for life, he said.

The vegan diet consists primarily of fruits, vegetables, grains, and legumes. Dairy products — butter, milk, eggs — are not included because, Dr. Barnard said, they are the No. 1 source of saturated fat in American diets. "Plant-based diets improve diabetes management. They reduce the risk of cardiovascular complications," he said.

They also can help reduce the risk of dementia and Alzheimer's disease. "Saturated fats and transfats can lead to artery blockage in the heart. But the carotid arteries to the brain and the vertebral arteries to the brain can get blockages too," Dr. Barnard said.

He cited a study showing that people with lower levels of cholesterol have lower levels of Alzheimer's. "It could just be that what's good for the heart is good for the brain as well," he said.

Dr. Barnard also pointed to a study showing that elevated levels of homocysteine in the blood in people older than 70 are a risk factor for brain atrophy, cognitive impairment and dementia. B vitamins and folic acid obtained from foods can lower blood levels of homocysteine and slow brain atrophy, the study suggested.

Studies have also shown that physical activity and intellectual activity can improve memory and reduce the risk of Alzheimer's disease. Getting enough sleep can also improve memory, Dr. Barnard said.

A number of medications can have a negative effect on memory, including sleep medications, cholesterol-lowering drugs, antidepressants, and blood pressure medications.

To help reduce the risk of Alzheimer's disease, Dr. Barnard recommended that diabetes educators encourage patients with diabetes to try a plant-based diet for about three weeks. "During that time, they will find they are feeling better and their numbers are getting better," he said. "Blood sugars start to go down, their blood pressure gets better, their energy gets better, and they start to lose a few pounds."