Should You Eat to Feed Your Microbiome?

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Among the prominent and recurring themes in both medical research and health reporting is the importance of the microbiome, and rightly so. Even as we continue to learn about the diverse roles our resident bacteria—which outnumber the cells of our body by some ten to one—play in our health, we already know enough to establish that a healthy microbiome is fundamental to our overall wellness. It doesn’t just take a village to raise a well-adjusted human; it takes a village within just one!

Bacteria on our body surfaces are an integral part of the immune system, keeping out potentially dangerous invaders by occupying the front lines, where our bodies confront the outside world. Disruptions in the populations of colonizing bacteria on our skin and mucous membranes have well-established consequences, such as yeast infections following a course of antibiotics. This, in some sense, is a classic case of “not knowing what we’ve got ‘til it’s gone.” We don’t take much notice of “friendly” bacteria all over us until something wipes them out—and something unfriendly moves in.

The same can occur within. One of the grave dangers of broad-spectrum antibiotic use is something called “pseudomembranous colitis,” an infection of the colon by a bacterium called Clostridium difficile. As it’s called on medical wards, “C diff” can only spread in the intestines when the bacteria that normally live there are removed to make way for it. While certain antibiotics can treat C. difficile infection, that approach sometimes fails. When it does, repopulating the intestine with friendly bacteria derived from healthy people (a so-called “fecal transplant”) can be lifesaving.

A Gut Reaction

Under normal circumstances, the bacteria in our gut play an important role in our digestion and metabolism. Some nutrients are altered by gut bacteria, and some metabolites get from our food into our bloodstreams only because of their involvement. One of the important actions of gut bacteria is to feed on the fiber that survives passage through the stomach and small intestine.

This suggests that there are important interactions between our diets and our microbiome, and that is indeed the case. People who eat animal foods routinely have different bacteria in their intestines than do vegetarians or vegans. Consumption of highly processed food and food chemicals, such as artificial sweeteners, can disrupt the normal balance in the microbiome. A study of the Hadza, a small population of modern hunter-gatherers in Tanzania, shows that seasonal variation in diet produces a corresponding change in the microbiome.

So, it is certainly true that our diets influence our microbiomes, and our microbiomes influence our health. But that truth is all too easily corrupted into gimmickry.

Yet Another Fad

There are ever more blogs, columns, books, and programs advising you on how to eat for your microbiome. The basic contention here is that we now know how important it is to feed your microbiome well, so you should design your diet for that very purpose. You can’t be well fed, so goes the claim currently in vogue, unless your microbiome is well fed. Perhaps the most flagrant example of the trend is a book called simply: The Microbiome Diet.

Think about it, however, and you will realize that the Hadza do not have advanced knowledge of their intestinal bacteria. Rather, they live closer to nature than we do and eat a diet of natural foods. Wild animals have no knowledge of their microbiome either, but eat the native diets to which they are adapted. One presumes that the food that is right for a lion, or koala, or giant panda is right for the corresponding microbiome of each as well.

As for us, we have long had tomes of information about the effects of diet on health, including the dietary patterns associated with the health outcome that matters most: the combination of longevity and vitality. If we know what dietary patterns are associated with the highest probability of abundant years in life, and robust life in years, do we need to reconsider all of that now that we know more about the microbiome?

Of course not.

What’s Good Is Good

We do need a healthy microbiome to be healthy, but the corollary to that is: if we are genuinely healthy, then so is our microbiome. In other words, everything we know about diet for our own health can be extended to what we know about diet for the health of the microbiome, too. With or without attention to the microbiome, we’ve known that vegetables, fruits, whole grains, beans, lentils, nuts, seeds, and plain water are generally good for us; toaster pastries, donuts, ​Coca-Cola, and pepperoni pizza? Not so much. That’s all still true.

My concern about the emerging “eat for your microbiome” fad is that, like every diet fad before, it will come and go and leave us all waiting for the next idea—and the one after that. The right idea, though, is that the fundamentals of a healthful diet have stood the test of time and will not change when we learn more about gut bacteria or gene expression (microbiomics, metabolomics, or genomics). These insights may help us understand just how diet affects our health, but they won’t change what we already know about what foods are clearly good for our health overall.

Here’s the reality check: Your microbiome has been there all along. If you are taking genuinely good care of yourself, you are taking good care of your microbiome, too. You need not rethink the fundamentals of eating well for the sake of your resident bacteria. Just feed yourself well, and they, too, will benefit.

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