A study of older adults in Oregon identified mixtures of nutrients that seem to protect the brain, and other food ingredients that may worsen brain shrinkage and cognitive decline.
Diets high in trans fats -- long known to harm the heart and blood vessels -- stood out as posing the most significant risk for brain shrinkage and loss of mental agility. People whose diets supplied them with an abundance of vitamins B, C, D, and E consistently scored better on tests of mental performance and showed less brain shrinkage than peers with lesser intake of those nutrients.
"Trans fats appeared the most detrimental to cognitive function and brain volume in our study," said lead author Gene Bowman, a naturopathic doctor and assistant professor of neurology at Oregon Health & Science University. "Levels of trans fat weren't that high in the blood, so it doesn't take that much."
Unlike previous studies, which have relied on questionnaires to estimate nutrient intake, the Oregon researchers directly measured levels in the blood. That makes the evidence stronger, although not as definitive as a controlled clinical trial. "We wanted to take recall ability out of the equation," Bowman said.
Researchers at OHSU and Oregon State University enlisted 104 of the women and men who have volunteered for the Oregon Brain Aging Study that began in 1989. Their average age was 87. All of them completed a battery of tests of memory and thinking skills, and 42 volunteers also had MRI scans to measure their brain volume.
Rather than focus on single nutrients, the researchers analyzed combinations of nutrients and how they related to brain health.
Measuring blood levels allowed researchers to account for important variables all at once, including differences in the way people metabolize food.
"Thus, nutrient biomarker patterns may more closely reflect what is available to brain tissues," said Christy Tangney of Rush University Medical Center and Nikolaos Scarmeas of Columbia University in a commentary on the study.
The Oregon researchers found two nutrient patterns that appeared to promote brain health: The BCDE pattern high in vitamins and antioxidants found in fruits and vegetables, and an omega-3 pattern high in the fatty acids found in fish. But the effect of omega-3 was only significant on one of the six tests of brain function after researchers took into account differences in blood pressure and depression, big risk factors for cognitive decline. The lack of a strong effect fits with a 2010 clinical trial in which fish oil supplements failed to slow the advance of Alzheimer's disease.
|The BCDE diet|
|Nutrient||Good food sources|
|Thiamin (B1)||Whole grain cereals, legumes, nuts, lean pork, yeast|
|Riboflavin (B2)||Milk, eggs, nuts, fish, chicken, broccoli, spinach|
|Folate (B9)||Green leafy vegetables, citrus fruit juices, legumes|
|Vitamin B12||Shellfish, fish, lean beef, chicken, eggs, milk|
|Vitamin C||Citrus fruits, strawberries, tomatoes, sweet peppers, broccoli|
|Vitamin D||Salmon, sardines, mackerel, eggs, milk|
|Vitamin E||Olive and other vegetable oils, nuts, whole grains, green leafy vegetables, avocados|
The negative effect of trans fats (also called "partially hydrogenated vegetable oil" or "vegetable shortening") showed the strongest link, consistent with earlier observational studies. Trans fats are abundant in processed convenience food, fast food, margarine spreads, and baked goods such as cookies, doughnuts, and pies.
Factors such as age, education and high blood pressure accounted for about half of the variation in cognitive performance among the 104 study volunteers. The influence of dietary nutrients wasn't as strong, but it accounted for 17 percent of the variation in cognitive performance. And nutrients accounted for 37 percent of the variation in brain shrinkage. The study, funded by the National Institutes of Health the Portland Veterans Affairs Medical Center, appears in the journal Neurology.
Bowman says the next step is to conduct a clinical trial. His group hopes to pin down the key nutrient combinations that could provide the most protection, and find out whether it's best to get them from whole foods or with supplements.
For now, Bowman says the evidence isn't strong enough to recommend supplements to prevent age-related dementia. To protect the brain, experts agree that it makes sense to follow the measures proven to protect the heart: quit smoking, exercise every day, maintain a healthy body weight, and keep cholesterol, blood pressure and blood sugar under control. Bowman says his study provides more evidence that people should steer clear of all foods containing trans fats, and commit to eating a diet rich in fruits, green leafy vegetables, beans and other legumes, nuts, and fish.
"They are the food medicine cabinet," he says. "They've got all the nutrients we detect with these blood tests."