Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance (4 page)

Avoid foods labeled “hydrogenated or partially hydrogenated.” Be especially wary of fast foods (fried chicken, biscuits, fried fish sandwiches, french fries, and fried foods in general), most store-bought cookies and crackers, potato chips, margarine, doughnuts, and muffins. In general, foods that come from nature (unprocessed) don’t contain trans fats. That’s one of the reasons nutritionists encourage us to eat fruits of all types, vegetables, chicken, whole-grain breads, and some cereals. Fortunately, label reading has become a lot easier since 2006, when the U.S. government started requiring that trans fat be listed on food labels along with saturated fat and cholesterol. Maintain a zero tolerance for any trans fats in your diet.

After eliminating the harmful foods, how do you decide which foods will help brain function? One way of identifying brain-enhancing foods is to select foods known to slow the rate of cognitive decline in older people. Admittedly, the reasoning here isn’t perfect (“Anything that slows the brain changes associated with aging should be helpful in maintaining brain function earlier in the life span”), but that’s about as good as we can do until it is possible to directly observe the effects of different foods on brain function.

Foods thought to slow the rate of cognitive decline include vegetables, especially green leafy ones. Not only do green leafy vegetables contain more vitamin E than other vegetables, but they’re also frequently consumed with added fats (e.g., salad dressing, mayonnaise) that increase the absorption of vitamin E and other fat-soluble antioxidant nutrients.

Antioxidants are chemicals that interrupt oxidation, the process that causes things to decay. A good example of oxidation in action is when the steel beams in a building rust. Oxidation within the body results from the action of free radicals, molecular fragments that contain at least one unpaired or odd electron. Since unpaired electrons are unstable, they attempt to achieve stability by attracting mates: electrons from other atoms or molecules such as cell membranes or the structural components in the interior of the cell. In the process, they injure or destroy these structures. Eventually the free radicals attack the DNA in cells throughout the body. The ensuing chemical damage to DNA is thought to be at least partly responsible for aging. The antioxidants in fruits and vegetables protect against this damage. In the brain the effect on cognitive function is dramatic.

In one study, older persons who ate more than two vegetable servings a day performed as well on cognitive tests as people five years younger. Moreover, this slower rate of cognitive decline held up over a six-year follow-up.

Although vegetables and fruits are often grouped together as cognitively beneficial, the evidence for cognitive enhancement secondary to increased fruit consumption is less convincing. The same study that demonstrated the benefits from vegetables failed to find a similar benefit from fruits. While it’s true that vegetables contain more vitamin E than fruits, that probably isn’t the main reason vegetables are more protective than fruits. Perhaps some “unknown dietary component that is present in fruit may offset the protective effects of antioxidant nutrients,” the authors of the study from the Rush Institute for Healthy Aging concluded.

But before emptying your fridge of fruits, consider that loads of other studies have shown that fruits
are
cognitively protective, especially fruit juices. Both fruit and vegetable juices have been linked to a delayed onset of Alzheimer’s disease. It is not necessary to drink large quantities of juices to garner the benefits. Drinking fruit or vegetable juices only three times a week was sufficient in some studies to substantially reduce the risk for Alzheimer’s disease.

Why such differences among studies? you may rightfully be wondering. I directed that question to Martha Clare Morris, the principal investigator of the Rush Institute Study.

“This is a very new field and to my knowledge there’s really only been a handful of studies that have explored the effect of fruit and vegetable consumption on the human brain,” she told me.

Added to the difficulty that we’re treading in new territory here, no aspect of diet can ever be considered apart from other lifestyle factors. People who are careful about their diet are also more likely to exercise, watch their weight, not smoke, consume less alcohol, and limit their coffee and tea intake. So which of these factors, or combination of factors, are most important? Researchers on brain health and longevity, in general, can’t provide a simple answer to that question because health habits occur in clusters, making it difficult to isolate one habit from another. Nor does everyone react in the same way to a specific substance. For instance, as will be discussed on page 239, new evidence shows that caffeine can be beneficial to brain function. But not everyone can tolerate caffeine. For instance, if I drink more than four or five cups of tea a day (I don’t like the taste of coffee), I get too “jived up” to concentrate.

Genetics, too, plays a major role in determining the effects of specific foods on our brain. As a result, conclusions about the various contributions of different foods to good health responses may vary from one population to another. For instance, the vegetable and fruit juice study mentioned above was restricted to Japanese-Americans living in a single county in the state of Washington. Could that fact help explain the different conclusions between that study and the more ethnically diverse one carried out at the Rush Institute?

In order to get answers to questions like that I sought out Carl Cotman, a researcher at the University of California, Irvine, with an international reputation for his acclaimed research on brain-enhancing foods. Cotman knows so much about what we should and shouldn’t be eating that during our discussion I found myself running through my mind a scenario in which this professor plans out the menus for all the meals I’ll be eating for the rest of my life.

The first thing I liked about Cotman is that he isn’t a food ideologue: he suggests that you eat what you want, with the exception of saturated fat-fried foods, cut back on the booze (perhaps with the exception of red wine), and throw away your Davidoff cigars no matter how much you enjoy them (and forget about cigarettes altogether).

While he agrees that genetics and culture play a significant role in determining brain health, he places a lot of emphasis on diet.

“I’m convinced that we know enough to make some highly educated estimates about the foods that are most likely to be beneficial to our brain. I eat a lot more things now containing omega-3 fatty acids, as well as more fruits and vegetables. Fish is especially beneficial, especially if we eat oily fish such as tuna, salmon, herring, mackerel, sardines, sablefish, and trout, which are loaded with the long-chain omega-3 fatty acids.

“In addition, I eat a lot less cholesterol since we found in our studies on rabbits that increasing the cholesterol makes their brain amyloid-loaded. Diet is even more important as we get older, since older cells are less efficient. Until we get more information, the food pyramid is useful and not a bad strategy.”

Cotman’s fish recommendation has historical precedent. The first hint of the brain-altering properties of oily fish turned up in the 1980s, when psychiatrists noticed that people living in parts of the world such as Japan and Taiwan, where oily fish are part of the regular diet, were sixty times less likely to develop depression than people in countries such as the United States and Germany, where fish is often only a distant second or third menu choice.

In general, the greater the intake of omega-3s in the diet, the lower the incidence of depression. Omega-3s exert an antidepressant effect among not only the clinically depressed but also people who are chronically pessimistic or suffer from frequent bouts of the “blues.” Such people often have low levels of omega-3s, and when the levels are boosted as a result of eating more fish, their mood lightens.

But suppose you just don’t like fish? Wouldn’t taking a dietary supplement work just as well? Probably not. While supplements such as fish-oil pills are also rich in omega-3s, they don’t provide the other benefits of eating fish such as lean high-quality protein low in saturated fat, along with many vitamins and minerals such as selenium. In addition, fish-oil capsules don’t have to conform to the same strict FDA regulations as medications. That means that different brands of fish-oil capsules may contain varying amounts of omega-3s.

The best news is that you don’t have to eat large quantities of fish in order to reap the benefits. Two servings of fish per week are sufficient. Even if you aren’t wildly enthusiastic about fish, two servings (about three ounces per serving) shouldn’t be difficult to work into your weekly meal plan. If you have no source of wild-caught fish, you aren’t at a disadvantage; in fact, you’re ahead of the game. Farmed fish, especially salmon, have more than twice the amount of omega-3s as wild salmon. Scientists speculate that the wild variety is leaner because of the more active lifestyle swimming in the ocean, which burns off some of the fat.

In addition to its effect on mood, omega-3s improve memory and the clarity of one’s thinking. We know this from clinical trials, which showed memory benefits in patients in the very early stages of Alzheimer’s disease after a switch to a fish diet. It’s speculated that the anti-inflammatory effect of the omega-3s interferes with the early stages of the formation of amyloid, the gummy substance that accumulates in the Alzheimer’s patient’s brain and interferes with the ability of neurons to communicate with each other. But timing was important in the trials: the brain-enhancing effect of omega-3s occurred only during a critical period, two or more years before the establishment of dementia. This corresponds to the same period in which the body’s own anti-inflammatory chemicals are elevated in the brain.

Carl Cotman is especially insistent that we do away with long-held distinctions between brain health and heart health. “Whatever enhances the heart enhances the brain. Exercise, nutrition, and stress reduction apply both to brain and heart.”

In line with Cotman’s “What’s good for the heart is good for the brain,” three ounces of farmed salmon or six ounces of mackerel a week reduce the risk of death from heart disease by 36 percent. But what about contaminants such as mercury that have been found to be elevated in some oily fish, I asked Cotman.

“Anyone over about twelve years of age who isn’t pregnant needn’t worry about the sometimes elevated levels of mercury and other contaminants found in some species of oily fish. For the most part, those parts of the brain most affected by toxic contaminants have reached sufficient degrees of maturity that anyone over twelve years of age is unlikely to be harmed.” This is also the recommendation of the Institute of Medicine of the National Academy of Sciences: the health benefits of eating fish exceed any risks from contamination by toxic chemicals or heavy metals.

So what is the bottom line here? How best to combine all of these disparate findings to create the closest thing we can to a “brain diet”? To me, after talking to Cotman and others, and conducting my own review of the literature on diet and the brain, I suggest combining into one strategy the various elements that researchers have discovered to be brain enhancing. How to do that without lugging around a textbook on nutrition? By sticking pretty much to the Mediterranean diet, which was originally developed to promote a healthy heart. As Cotman and other experts point out, heart healthy equals brain healthy.

Traditionally, menus in Mediterranean countries are rich in fruits, vegetables, legumes, and cereals. Olive oil and other unsaturated fatty acids are preferred over saturated fatty acids; fish is eaten more often than poultry or meat. Dairy consumption is low to moderate. Alcohol is taken in mild to moderate amounts in the form of wine with meals.

A study of two thousand Manhattan residents averaging seventy-six years of age found that those eating a Mediterranean diet had a 68 percent lower risk of developing Alzheimer’s disease. The Mediterranean diet not only reduces the risk of Alzheimer’s disease but, according to recent research from Columbia University in New York, may help people already afflicted with the disease live longer.

The beneficial effects of the regular but moderate consumption of alcohol recommended by the Mediterranean diet came as a surprise to some researchers. Perhaps that’s because several generations after the arrival of our Puritan ancestors on these shores, many people in our society still tend to demonize alcohol. (I’m writing these words in Vineyard Haven, Massachusetts, a town on Martha’s Vineyard where the sale of alcohol is still illegal.) Certainly, the popular profile of the regular alcohol consumer was largely a negative one (increased rates of domestic violence and motor vehicle accidents) prior to the recent discovery of the health benefits of drinking moderate amounts of alcohol in the form of red wine. According to recent research, it’s now safe to say that red wine in moderate amounts enhances brain function.

At the moment, nobody has a completely satisfactory explanation of why it is that red wine but not other alcoholic beverages benefits the brain. One theory stresses the importance of resveratrol, a natural compound found in the skins of the grapes used in red wines. Since red wine is fermented with the skins intact, and white wine after the skins have been removed, only red wine contains resveratrol and only red wine exerts a protective effect on brain function—at least that is the popular explanation.

As with many of the studies linking nutrition with brain function, the experimental work on the positive effects of red wine on the brain has been carried out in species other than our own. Giulio Pasinetti, a researcher on nutrition and brain performance at Mount Sinai School of Medicine in New York, described for me one such experiment during a conversation after his lecture at a meeting of the Society for Neuroscience.