Brainfood

Brainfood

Given what we now know about the positive effects of plant components such as polyphenols and fiber in our diet and the harmful effects of animal foods and junk-food ingredients such as salt and saturated fats, it is not surprising what a systematic review with meta-analysis of studies on diet quality and dementia found: Healthier eating is associated with a significantly lower risk of dementia and Alzheimer’s. Generally, healthier eating means more fruits, vegetables, legumes, and whole grains, and less meat. In a 16-year cohort study in which more than 5000 adults with an average age of 51 years were followed, a small 4-percent minority ate healthfully and presumably therefore aged “ideally,” meaning without chronic diseases and with peak physical, mental, and cognitive performance. (Some criteria for ideal aging were easier to achieve than others. The first criterion on the list was “being alive.”)

To reduce the risk of cognitive decline and dementia, the World Health Organization guidelines recommend a diet primarily of “fruits, vegetables, legumes (e.g., lentils, beans), nuts and whole grains” while limiting added sugars, salt, saturated fats, and trans fats, which are found in processed foods and, of course, in meat and dairy products. Certain plant foods appear to be particularly important.

Using the largest twin registry in the world, researchers concluded that “higher fruit and vegetable consumption can reduce the risk of dementia and Alzheimer’s.” Studying twins is so informative because we gain special insights into environmental and dietary influences when one develops Alzheimer’s and the other does not, since twins are so genetically similar. A meta-analysis of all such observational studies found that each additional serving (100 g) of fruit or vegetables per day lowers the likelihood of cognitive impairment and dementia by 13 percent. Half a dozen cohort studies that followed tens of thousands of people for up to 30 years showed that those with the highest fruit and vegetable intake had a 43 percent lower risk of disease than those who ate the least fruits and vegetables.

Are there particular types? In a recent review on Alzheimer’s prevention, the directors of the program at Loma Linda name seven core points:

Note the emphasis on berries and leafy greens—the brainfoods among fruits and vegetables. Strawberries and spinach mitigate age-related cognitive decline in rats. And in humans?

Blueberries

There are 8000 different types of polyphenols that are ubiquitous in plant foods, but berries are packed with them. A subgroup of polyphenols are anthocyanins, natural red, blue, and purple pigments that can cross the blood–brain barrier and take up residence in brain regions involved with learning and memory. In light of their strong antioxidant and anti-inflammatory properties, aging researchers began feeding berries to rodents.

In older rats that ate blueberries or strawberries, age-related cognitive decline could be reversed. The first trials in older people were not published until 2010, starting with a small pilot study. Older men and women who suffered from memory problems were given either a juice every day for twelve weeks that corresponded to the legendary amount of four to six cups of wild blueberries, or a placebo drink. The apparent cognitive improvements after the three months justified a methodologically stricter study with a more modest daily ration. Healthy men and women between the ages of 60 and 75 were randomized to receive daily either one cup of cultivated blueberries (as freeze-dried powder) or a placebo (a blueberry-flavored and -colored powder with the same number of calories but without berries). In the berry group, greater improvements were recorded on certain cognitive measures than in the placebo group. The researchers concluded: “These results show that an easily achievable amount of blueberries in the diet of older people can improve some aspects of cognition.”

The participants in the follow-up study were not impaired in their memory performance. Is it possible that one cup of cultivated blueberries is enough to improve the cognitive abilities of healthy people, whereas impaired people need five cups of wild blueberries? A study in which mildly cognitively impaired subjects were given one cup of cultivated blueberries was not published until 2020. The randomized, placebo-controlled, double-blind study found a significant cognitive improvement compared to placebo after a few months.

But even a single meal can do that. Several randomized controlled trials have shown that in the hours immediately after consuming about one and a half cups of wild blueberries, children performed significantly better than a placebo group on tests of behavioral regulation and memory performance (but not reading). A similarly large benefit within a few hours after consuming a single dose of wild blueberries (approx. 240 ml) has also been demonstrated in adults, especially on more demanding tasks and with mental fatigue.

Milk blocks berries

In the only study that showed no clearly positive effects of blueberries, the berries were mixed with milk. We have known for 15 years that milk in black tea can completely cancel out its positive effects on arterial function. Researchers blamed casein—a milk protein that binds polyphenols and prevents their absorption. With the only plant milk tested (soy milk), the irreversible binding did not occur. But when consuming milk or dark chocolate, a glass of milk blocks the absorption of about half of the cocoa polyphenols. Accordingly, milk in coffee results in less than half of the most important polyphenols getting into the body. The same applies to cream on the berries.

If you mix strawberries with water, the level of anthocyanins in the blood rises sharply over the next three hours; if the strawberries are mixed with milk, the increase is only half as high. The same applies to blueberries, as shown by the study “The antioxidant effect of blueberries is impaired when combined with milk.” It was found that the overall antioxidant capacity of our bloodstream shoots up within an hour after consuming 1.5 cups of blueberries with water and is still elevated five hours later. With milk, you would expect a smaller increase, but the study participants actually fared even worse afterward. After they had eaten a whole bowl, their bodies had lower antioxidant power—because they had eaten the berries with milk. That could explain the lack of a clear cognitive benefit in the berry-with-milk study as well as the heterogeneity of studies on blood-pressure lowering by blueberries. The studies that used water showed a significant benefit; those with milk or yogurt did not.

Aside from the milk study, 14 of 15 randomized controlled trials on blueberries and mental performance observed a significant improvement in at least one cognitive domain. Four out of five intervention studies to improve arterial function also found a benefit from blueberries. This could explain some of the cognitive effects, as functional MRI scans found that blueberries increase blood flow to critical brain regions.