Probiotic foods and supplements are among the fastest growing sectors in the health food marketplace, thanks to an explosion of popular and scientific interest in the “microbiome.” It’s clear that the bacteria that live in and on our bodies have an enormous impact on our health—one that we are only just beginning to explore.
But commerce isn’t one to wait around for all the data to come in. Although we have a long way to go to before we understand exactly how to influence and interact with our microbiota, we’re already being bombarded with new products: probiotic powders, juices, teas, fizzy vegetables, funky soybeans, and fermented grains. Some of these are traditional foods that have been around for thousands of years, of course. But until a year or two ago, you wouldn’t have found them on your grocer’s shelf with a bar code.
All of these probiotic foods, by definition, contain beneficial bacteria. And the hope is that by eating more of them, we will end up with more of them in our intestines. Stocking the pond, as it were.
Do Beneficial Bacteria Survive Digestion?
The problem is that, in order to get from our mouths to our intestines, the bacteria have to survive the rigors of our digestive system, where they’ll be bathed in acid and then worked over by enzymes. How many and which ones survive? That is very much an open question.
Some of the bacteria in our kimchi or kombucha make it to the intestines alive but may be relatively short-lived there. Even if they don’t set up permanent housekeeping, however, these food-based bacteria can have anti-inflammatory and immune-modulating effects and can influence the health and behavior of the gut’s more permanent residents.
Other food-borne beneficial bacteria don’t survive digestion. But that doesn’t mean that they don't do anything for us. Most traditionally fermented foods are nutrient-dense foods to begin with. The fermentation process increases the levels of some nutrients and makes others—particularly minerals—more bioavailable. Probiotic foods also often contain prebiotic nutrients which serve as nourishment for the bacteria in our intestines.
Prebiotics Are Where It’s At
And that actually brings me to the punchline: If you’re looking for a more reliable way to increase the health and diversity of your gut bacteria, don’t worry so much about stocking the pond. Instead, focus on the care and feeding of the bacteria that are already in there.
Diet definitely has a significant impact on our gut bacteria. But the prebiotics you consume may be far more significant than the probiotics. Prebiotics are the indigestible carbohydrates (aka fiber) and other compounds in our food that provide a food source for those bacteria in the gut.
Your Diet Determines Their Destiny
Just like people, different bacteria have different food preferences. Some bacteria really dig cheeseburgers and fries. Other bacteria really love kale and oat bran. When you eat a steady diet of cheeseburgers and fries, those protein and fat-loving bacteria thrive and grow in number and the fiber-loving bacteria wither away. When you eat a lot of vegetables, legumes, and whole grains, the fiber-loving bacteria throw a party and the cheeseburger- loving bacteria sulk in the corner.
Just like people, different bacteria have different food preferences.
This has been dramatically demonstrated in human trials. Change the composition of your diet from one that’s high in animal fat and protein to one that’s high in plant fiber and you can change the profile of your intestinal bacteria in a couple of weeks or in as little as a day.
This is more than just a parlor trick. It turns out that the fiber-loving bacteria are the ones that are associated with all sorts of positive health benefits, while the cheeseburger-loving bacteria tend to be associated with obesity, colon cancer, ulcerative colitis, and metabolic syndrome.
And here’s an even more sinister possibility: Mouse studies have shown that the effects of diet on gut bacteria can persist for multiple generations.
Probiotic Foods Are Probably Not Enough
Feel free to explore and enjoy all the new (and old) probiotic foods out there. But if you’re looking for the health advantages associated with a healthier microbiome, what you feed your gut bacteria may be far more important.
It’s still OK to enjoy a cheeseburger from time to time. And your diet doesn’t necessarily have to be low in protein or fat; but if you want to encourage a healthy microbiome, your diet does need to contain plenty of fiber-rich foods. Eating a variety of vegetables, whole grains, nuts, and legumes on a daily basis will help to cultivate and nourish the kind of bacteria you want and starve the types you’d be better off without.
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