Gut health means a thriving microbiome
Credit: Illustration by Neil Web

The New Science of Your Gut: The Promise of Probiotics

Prebiotics are the dietary fiber – fruits, veggies, and whole grains – that feed the bacteria we've already got in our gut. Probiotics, on the other hand, are infusions of new bacteria that enter our system onboard the food we eat. They may come from the soil the plants are grown in, or from fermented foods, which contain bugs that are actively feeding on it, breaking it down into acidic compounds like lactic acid and vinegar – this is what gives yogurt and sauerkraut their tang.

Fermented foods are everywhere, even if you don't realize it. Go to the refrigerated section in Whole Foods and the sauerkraut, kimchi (a fermented Korean cabbage), and pickled beets sit next to kombucha (an effervescent fermented tea) and kefir (fermented milk made with grain). Even some soy sauce is fermented and full of good bacteria. The best products are unpasteurized, since pasteurization kills off most of the valuable bacteria. Your everyday sandwich pickles, though, aren't fermented; they're just steeped in vinegar, which gives the taste but not the live bacterial cultures to do God's work in your colon.

Yogurt, of course, is the most advertised probiotic in the supermarket. While certain brands, like Dannon's Activia, promise a boost of good bacteria, all yogurts contain a fair amount of microbes. But that doesn't mean that a yogurt a day will satisfy all your probiotic needs. The gut is host to thousands of different strains of bacteria (yogurt typically contains three), and while quantity is important, diversity is also key. This is why the jury is still out on supplements like Culturelle and Align – pills that pack billions of bacteria but primarily represent just a handful of strains. Lipman recommends them to his patients but admits that figuring out the right dosage and bacterial strains is a "crapshoot." O'Keefe is even more skeptical that we have the know-how to deliver what an individual gut wants or needs. "There are thousands of species of bacteria in the colon, and they're more like an orchestra," he says. "They play together to come up with a final sound." Still, when a patient is in gastrointestinal distress, typically after a course of antibiotics, O'Keefe will prescribe probiotics.

Some experts in the field predict that probiotics will evolve from an all-purpose supplement to a pharmaceutical therapy targeted to specific diseases and conditions. For now, this is a new science that has doctors, researchers, and proactive patients redrafting the terms of engagement with microbes in and around us. The old scorched-earth policy is out, replaced with the idea that our gut flora is a garden that must be carefully tended. Whether it turns out, as Michael Pollan speculates in his recent book, 'Cooked: A Natural History of Transformation,' that these bacteria are the key to a "grand unified theory of diet and chronic disease," we know enough now to say, when you're good to the microbiome, the microbiome is good to you.