Coffee and Tea

In the Adventist Health Study-2, the largest prospective study of plant-based diets to date, I was surprised to see that the average polyphenol intake of nonvegetarians was higher than that of vegetarians and vegans. Why? Mainly because the nonvegetarians drank more coffee, and in the United States it is by far the leading source of polyphenols. Is coffee consumption good for the brain? That’s not easy to answer, as I lay out in detail in see.nf/coffeetea. No overall association between coffee consumption and dementia can be demonstrated, perhaps because high coffee consumption obscures the fact that low coffee consumption is healthy.

With green tea, dose and effect appear to be directly proportional, meaning that any green tea drinking is better than none, and when it comes to the risk of cognitive deficits, the rule is: the more, the better. Interventional studies have found that black tea can acutely increase attention and wakefulness, but population studies found no association with a risk of dementia or the risk of cognitive decline.

Brain-Boosting Spices

Garlic supplements and extracts have been shown to improve age-related cognitive dysfunction and reduce Alzheimer neuropathology in rodents. For a garlic trial in humans, young, healthy volunteers were randomized to take capsules twice a day for five weeks containing only one eighth of a teaspoon of garlic powder, the kind you can get at any supermarket. The control group got placebo capsules with the same color, texture, size, shape, and even the same smell. Compared to controls, participants who got the garlic powder saw significant improvements in memory and attention. As I discuss in see.nf/brainspice, ginger may help in middle age, and as little as a quarter teaspoon of ground black cumin seeds can have positive cognitive effects in both young and old people.

Hot Beans

The association between legumes and improved cognitive performance has been invoked to explain why the prevalence of dementing illnesses is lower in East Asia, where people eat 10- to 40-times more soy foods than in the West. I discuss the conflicting population data in see.nf/brainsoy. However, when it comes to the evidence from interventions, 16 randomized controlled trials with more than 1000 participants have shown that interventions with soy or soy components improve cognitive function and memory overall. For example, soybeans hidden in chili, intended to randomize participants into a more soy-rich diet, led within ten weeks to a significant improvement in short- and long-term memory.

More or Less Equol

There is a randomized placebo-controlled double-blind study of soy isoflavones in Alzheimer patients. For six months, they were given multiple servings of soy foods a day, but no cognitive benefit compared to placebo was found. However, there were indications of a benefit in people who produce the natural substance equol. Among older Japanese, equol producers also had on MRI less than half the white matter brain lesions of nonproducers. Details can be found at see.nf/equol, but in short, some people benefit more from soy than others because they have gut bacteria that convert the isoflavones in soy into an even more useful substance called equol.

About half of Japanese and Koreans can produce equol, but only about one in seven Americans can. Excessive amounts of antibiotics wipe out our good bacteria and turn an equol producer into a nonproducer, but how do we get the bacteria in the first place? In the West, there is a group of people with high equol production rates: vegetarians, perhaps because they eat more fiber or less fat or cholesterol. Whatever it is about them, they may soon be the only remaining equol producers, because Asians are increasingly aligning their diets with ours.

Whole Grains for Full Brain Power?

Based on cross-sectional studies with thousands of men and women over 50, high whole-grain consumption shows a positive effect on the Successful Aging Index, a metric that expresses not only whether someone suffers from diseases or disabilities or not, but also the extent to which cognitive function is preserved and the person engages in physical, social, and productive activities. This was found after trying to examine various other dietary and lifestyle factors, but it is impossible to account for everything. When mice were randomized to receive barley instead of white rice, they lived significantly longer, had less hair loss, developed a glossier coat, could balance better on a rod and hang upside down from it longer, and retained better long-term spatial memory. In contrast, as I document in see.nf/braingrain, the results to date in humans are not very convincing.

Nuts for a Healthy Brain

Those who frequently eat nuts tend to live longer and think better, but that does not necessarily mean that nuts have anything to do with it. In see.nf/nutbrains, I go into some factors that make population studies on nut consumption so difficult. A sub-study of PREDIMED suggests, however, that it might be worth increasing from a half handful of nuts a day to a full handful and switching from regular to extra virgin olive oil.

Fish Oil Flop

Is fish oil healthy for the brain? In a review of strategies to reduce dementia risk, a list of common characteristics was compiled of those foods that are purported to be healthy for the brain. People are urged to eat less meat including poultry, fewer fatty, sugary, and salty industrial foods, and instead to eat a predominantly plant-based diet, with lots of fruits and vegetables (especially berries and green leafy vegetables), legumes, and whole grains. But there is also a tendency to recommend fatty fish.

This recommendation to eat fish is based on observational data that found, for example, a significantly lower risk for Alzheimer (but not for dementia in the broader sense) among fish eaters, a significantly lower risk for dementia (but not directly for Alzheimer) among people who take fish oil supplements, and a larger hippocampal volume associated with higher omega-3 levels in the blood. But fish eaters also tend to consume more green vegetables and berries, smoke less, exercise more, and have a higher education level than non–fish eaters. People who take fish oil supplements also appear to eat more fruits and vegetables, smoke less, and exercise more than those who do not take these supplements. In addition, they generally have a higher socioeconomic status. To find out whether the apparent benefit of aquatic omega-3 fatty acids in population studies is real and not due to confounding circumstances, scientists have conducted dozens of randomized controlled interventional studies.

There were three randomized placebo-controlled trials, lasting six, twelve, and eighteen months, respectively, of omega-3 fatty acids in the treatment of Alzheimer’s, but unfortunately none demonstrated a cognitive benefit. Perhaps the participants’ disease was already so advanced at baseline that it was too late. The World Health Organization funded the most recent and largest investigation of long-chain omega-3 fatty acids (from algae or fish) with respect to cognitive performance. The researchers found no significant protection against cognitive impairment or dementia and only “clinically insignificant” effects on cognition overall. The authors conclude: “People who are concerned about their cognitive health should know that taking long-chain omega-3 supplements does not help them in this regard.”