The gut-brain connection is a story that just keeps giving. The idea that gut microbes could affect your mood and cognition is startling and potentially very useful. The microbes that improve your mood are called psychobiotics. Microbes eat prebiotics, which include complex sugars like fiber. Recent studies show that substances called flavonoids are also prebiotic, and seem to stave off age-related mental decline.

Certain gut microbes can churn out important molecules like butyrate that both nourish and heal the gut lining, thus lowering inflammation. Because chronic inflammation can cause depression and anxiety, these microbes can be considered psychobiotic.

Microbes can also secrete psychoactive chemicals like dopamine, serotonin, and GABA. These are the same chemicals used by the brain to transmit signals. Like our brain cells, microbes likely use these molecules to communicate among themselves. Surprisingly, microbes may use them to communicate with us as well. In fact, your cravings may actually have roots in the desire of your microbes for specific sugary treats like donuts or candy bars.

It’s not a real excuse, but when it comes to bad food choices, you might say that your microbes made you do it. And satisfying those cravings can lead to a population explosion of these slacker microbes, leading to further mischief. If your gut microbes get unbalanced, they may go rogue and make you sick, anxious or depressed – while still craving donuts.

So how do you keep your gut microbes balanced and happy? That turns out to be as easy to describe as it is difficult to execute. The trick is to feed your good microbes and starve your bad microbes. If you think the research is telling you to swap your donuts for actual plant-based food, you are correct.

Veggies and fruit, unlike donuts, contain fiber that is coveted by your good microbes. Sadly, the standard American diet is very low in fiber. That’s because we purposefully extract it from our food, which likely plays a role in the triple epidemics of obesity, diabetes, and depression that have been accelerating over the last 50 years.

It turns out that prebiotic fiber can improve your health and your mood, and here we introduce some brand-new characters to this remarkable story.

The Positive Cognitive Effects of Flavonoids

A recent study presents compelling evidence that another set of nutrients can work in concert with fiber. They are called flavonoids. As the name implies, they give flavor to fruits and veggies. Best of all, they can be quickly identified by the color they impart. Think of red apples, purple beets, and orange oranges. These colors and flavors are all due to flavonoids. Your mother told you these were better for you than Oreos, and she was right. But then she may have poured you a glass of apple juice and missed the target. That’s because most manufacturers peel the fruit before juicing and thus toss away the nutritious flavonoids.

A new analysis by Walter Willett and his Harvard colleagues combined two large databases of female and male health professionals reaching back to the mid-1980s. They were able to look at over 75,000 people, which granted them a great deal of statistical power. They found that the consumption of flavonoids was inversely correlated with cognitive decline. Large longitudinal studies like this are remarkable for letting researchers tease out complicating factors as they follow their subjects over time. They found a clear dose-response curve, which means that the greater the amount of flavonoids, the greater the positive cognitive effect.

This study showed a significant correlation but was not designed to demonstrate causality. However, there are hints in that direction. Flavonoids are strong antioxidants, neutralizing highly reactive oxygen molecules that are a toxic byproduct of metabolism. These molecules can damage tissues if they are not mopped up quickly. Thus, flavonoids can stop tissue damage and inflammation.

Separate studies in both animals and humans have shown that flavonoids can reduce the amyloid fibrils associated with Alzheimer’s and decrease brain inflammation. In addition, flavonoids are known to have a beneficial impact on your gut microbes, favoring a less inflammatory environment. They reach the colon intact, where they discourage the growth of pathogens and increase the growth of healthy bacteria. These and other studies show the surprising impact prebiotic flavonoids have on cognition and brain function as well as overall health.

How to Get More Flavonoids Into Your Diet

If you want to keep your brain in peak condition, then this is a slam-dunk. Eat colorful fruits and veggies. Wash them with water, but don’t peel them. That’s where much of their goodness resides.

Here are some of the most potent sources of flavonoids, more or less in order of their impact on cognition:

Intriguingly, this list of cognitive-friendly flavonoids is somewhat different for men and women. Beets, for instance, are higher on the list for men than women. But in general, these colorful fruits and veggies are good for both female and male brains.

Flavonoids Versus Sugar

It’s true that some of these foods, especially the fruits and root veggies, contain sugar. However, all sugars are not alike. Many consist of indigestible chains of sugars like maltose, fructose, and mannose, most of which are prebiotics. If you are diabetic, trying to lose weight, or just find it hard to consume so many fruits and veggies, you might try a prebiotic containing flavonoid extracts.

Many of the foods on the list, like Brussels sprouts and broccoli, are high in fiber and flavonoids while still being low in sugar. Unfortunately, these exemplary foods are two of the most vilified veggies in the land, especially for kids. They are bitter and sulfurous, but to your gut microbes they are ambrosia. As adults, we ought to be less petulant and learn to deal with it. We can add a squeeze of lemon and a pat of butter and might actually come to love them.

If you don’t mind a little fruit sugar, it’s hard to argue with strawberries and oranges as treats. Yes, it’s hard to say goodbye to that morning donut – after all, you have an insistent crowd of microbial malcontents with a vested interest in sweets. But you can change your microbial balance to favor a smarter set of microbes and keep your brain in peak operating condition. After all, you’re calling the shots, and if you do it right, your microbes will find a better balance. Then they can help you stay healthy, happy and sharp for as long as possible. This is your fight to win.

References

Yeh, Tian-Shin, Changzheng Yuan, Alberto Ascherio, Bernard Rosner, Walter Willett, and Deborah Blacker. “Long-Term Dietary Flavonoid Intake and Subjective Cognitive Decline in US Men and Women.” Neurology, June 28, 2021