"Let food be thy medicine and medicine be thy food", Hippocrates. During the past twenty-five hundred years since the time of Hippocrates science has made significant progress in understanding how food exerts its beneficial effects upon health. We now have solid proof that the foods and beverages that are consumed by humans, in particular those derived from tea leaves, coffee and cocoa beans, grapes, berries, hops and other grains have clearly defined beneficial actions upon brain function. While these foods and drinks have quite different chemical compositions, they all contain compounds called flavonoids. Flavonoids are not nutritious; however, they are believed to be responsible for the beneficial effects of these foods upon the brain.
For many decades the biochemical benefits of flavonoids were attributed to their ability to confer protection from oxygen, i.e. they are anti-oxidants. While flavonoids are capable of acting in this fashion in laboratory experiments, it is unlikely that they can provide this benefit within the brain. The reason is that the flavonoids obtained from the diet do not achieve an adequate level in the brain that would allow them to act as effective anti-oxidants. So how do they benefit us?
In order to answer this question, scientists have investigated what flavonoids can do when their concentration in the brain is extremely low, i.e. the levels that might be achieved by a diet rich in these fruits. The flavonoids directly induce neurons in the brain to become more plastic, i.e. more capable of forming new memories. The flavonoids achieve this by directly interacting with specific proteins and enzymes that are critical for learning and memory. They also induce the birth of new neurons, a process that is critical for recovering from injury, exposure to toxins and the consequences of advanced age, such as increased levels of brain inflammation. Finally, some recent studies have shown that flavonoids actually enhance blood flow to active brain regions.
So how much is enough? Let's consider two of my favorites: wine and chocolate. If you consumed about 200 ml (6.7 oz) of Cabernet Sauvignon or about 50 grams (1.7 oz) of dark chocolate (71% cocoa powder) you would intake nearly identical quantities of flavonoids; which, fortunately, is now the daily wine intake recommended to produce the most health benefits in a typical adult. When young adult females were given flavonoid-rich chocolate drinks, blood flow to their brain was significantly increased within just two hours and their performance on a complex mental task was greatly improved.
No one is certain whether all flavonoids are capable of producing these benefits. However, recent investigations have suggested that it does not matter which type of food provides the flavonoids, only that they are eaten as often as possible. In addition to those edibles mentioned above, studies to date have also identified benefits from apples, blackcurrants, pears, blueberries, strawberries and grapefruits. One final caveat: no studies have yet proven a true cause-and-effect connection between the life-long consumption of flavonoid-rich diets and a reversal of age-related deterioration in learning or general mental function. Still, I think that we should all be willing to make a leap of faith that the connection is real and modify our diets accordingly.
© Gary L. Wenk, Ph.D. Author of Your Brain on Food (Oxford University Press, 2010)