By Sonya Collins
WebMD Health News
Reviewed by Brunilda Nazario, MD
May 13, 2015 -- Healthy eating can help you stay at an ideal weight and stave off diabetes and heart disease. Now, there's more and more evidence that a heart-healthy diet is also a brain-healthy diet -- and it may even prevent or slow dementia, which includes Alzheimer's disease.
Recent studies show that people with the healthiest eating habits have lower risks for those problems and a decline in thinking skills. Some suggest that people who already have a mild decline in thinking abilities – which can be a forerunner to dementia -- might slow or stop its progress through good nutrition.
"Many researchers believe that if we had a really potent diet, we could help slow Alzheimer's down," says Nancy Emerson Lombardo, PhD, an investigator at Boston University Alzheimer's Disease Center. "In all the different things that researchers are looking at, maybe we can find the right combination."
What's in a 'Brain Diet'?
Studies show that the Mediterranean diet, DASH (dietary approaches to stop hypertension), and the MIND diet -- a hybrid of the other two -- benefit the brain.
"All these diets are high in fruits and vegetables, most of them are high in nuts and legumes, most of them recommend whole grains instead of refined grains," says Heidi Wengreen, RD, PhD, assistant professor of nutrition at Utah State University.
These diets also emphasize fish, poultry, and seeds. Most of the fat in the Mediterranean diet comes from olive oil, an unsaturated fat that doesn't raise cholesterol the way saturated fat does. A study out this week found that the Mediterranean diet with olive oil and nuts improved thinking skills in seniors.
Brain-healthy diets also include "moderate" amounts of wine. That means up to one drink per day for women and up to two for men. The Mediterranean diet is low on dairy, eggs, and red meat -- the occasional dairy is usually low-fat cheese or yogurt. DASH emphasizes low-fat or fat-free dairy and cutting back on sodium. The MIND diet pulls foods from each of these diets that were already proven to benefit the brain in other studies.
"There's convincing evidence that green leafy vegetables in particular are important for the brain, so we specified almost a daily serving of green leafy vegetables. We include one or more servings per day of other vegetables," says Martha C. Morris, ScD, who developed the MIND diet with her colleagues at Rush Medical Center in Chicago. The diet also recommends berries, rather than fruit in general, because of evidence that says berries support brain health.
These diets steer people away from added sugar and salt, and saturated fat, as well as processed foods, because those can be high in all three.
Lombardo developed the Memory Preservation Nutrition Program. It pulls foods from other diets that have proven perks like the MIND diet does.
Some researchers have called Alzheimer's disease "type 3 diabetes."
Diabetes develops when the body becomes insulin-resistant. Insulin helps sugar, specifically glucose, enter muscle, fat, and liver cells to give them energy. When the body is insulin-resistant, glucose builds up in the bloodstream rather than getting to the cells. Eventually this can lead to type 2 diabetes.
The brain needs energy from glucose, too. But type 2 diabetes may make the brain insulin-resistant as well. Tissue damage, mental decline, and early signs of Alzheimer's can develop in brains of people that have insulin resistance.
"High-sugar diets raise your risk for developing diabetes, which increases your risk for developing Alzheimer's," says Suzanne Craft, PhD, a professor at Wake Forest School of Medicine. Eating too many simple carbohydrates and simple sugars will harm your brain, she says.
How Do Brain Diets Work?
Research suggests foods in these diets can reduce things linked to Alzheimer's like inflammation and plaque buildup in the brain. No one knows for sure whether certain foods or nutrients are key to the benefits or whether a mix of many nutrients is what helps.
"Various nutrients most likely block different pathways to Alzheimer's," Lombardo says.
Inflammation is one pathway to Alzheimer's. Too much inflammation -- a response from your body's immune system -- is linked to chronic diseases. In a study that followed more than 1,200 adults over age 65, those who stuck most closely to the Mediterranean diet had the lowest levels of a protein in their blood linked to inflammation. Their risk of getting Alzheimer's during the 4-year period was 34% lower than their peers who didn't follow the diet.
"Omega-3 fatty acids in the diet -- from the fish, seeds, nuts, and olive oil -- are anti-inflammatory," Lombardo says.
The Mediterranean diet and others like it push anti-inflammatory foods and cut out inflammatory ones. The typical Western diet's lack of variety and high levels of sugar, salt, fat, and processing increase inflammation.
Oxidative stress is also a likely player in the development of Alzheimer's disease. It happens when the body is unable to stop the damaging effects of toxins. Brain-healthy diets are high in antioxidant-rich foods, such as blueberries and spinach, that can counter oxidative stress. These foods may prevent the buildup of plaque that collects in the brains of people with Alzheimer's. In lab tests on mice or cells, substances in olive oil, berries, plums, grapes, walnuts, and apricots have helped prevent this plaque buildup.
Herbs and spices may also lower inflammation and oxidative stress. DASH is high in herbs and spices, so you won't miss the salt. Turmeric could help prevent Alzheimer's, Parkinson's, and stroke due to its anti-inflammatory and antioxidant effects, research suggests. Cinnamon has reduced brain plaque found in Alzheimer's disease and helped reverse mental decline in animal studies of the disease. In one study, 30 mg of saffron per day was as effective as donepezil, a prescription drug that helps against the symptoms of Alzheimer's.
These benefits may come together to prevent the brain from shrinking as we age. In a recent study, older adults who followed a Mediterranean-style diet had a higher brain volume than their peers.
Ongoing research continues to zero in on specific foods that might help prevent dementia. Current studies are exploring coconut oil, blueberries, turmeric, tomato extract, and red wine extract, among other foods.
While some scientists search for the ideal diet, others look for the best combo of lifestyle habits. Their studies, too, have shown that a whole set of healthy choices can prevent the loss of thinking skills. In a large study of more than 1,200 people, those who completed a 2-year program involving diet, physical and mental exercise, and social activity did better than their peers on a test of thinking skills afterward. The researchers are now planning a 7-year version of the study.
Other studies are testing the effects of exercise on long-term brain function. "Maybe it's nutrition, plus increasing different types of exercise," Lombardo says, "plus making sure you get your sleep, keep your mind active, and stay socially engaged."
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