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The bacteria in your gut can affect your blood sugar and overall health. Here's how to build a flourishing gut biome.

Karen Ansel, M.S., RDN
February 24, 2021
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cinnamon roll overnight oats shot overhead in mason jars with raspberries and pecans on top

For more than 100 years, scientists have been studying how the gut, or gastrointestinal tract, impacts our overall health. But research has skyrocketed in the past decade, and we now know that the gut is home to some 100 trillion microbes, most of which live in your colon. (Collectively, experts call these your gut microbiota.) Some of these bacteria are healthful. Others, not so much. "Given the staggering number of these bacteria, it's not much of a stretch to imagine that what lives in the gut affects much of our health and well-being," says Jill Weisenberger, M.S., RDN, CDCES. In fact, the types of bugs you harbor may favorably or unfavorably influence your body weight, blood sugar, cholesterol, immune system, emotional well-being and more. (Here are 3 surprising reasons your gut health is so important.)

How did those critters get there in the first place? Some were passed on by your mother in utero and during childbirth. But the bulk of these microbes came from the breast milk, formula and food you consumed during infancy. Over the years, the numbers and types of these bugs may have been impacted by a range of factors including what you ate, the environment you were exposed to and how often you took antibiotics.

The good news is, it's possible to improve your gut bacteria through some of these same factors. Here's how to ensure your gut microbiome is flourishing.

1. Eat More Plants

"A diet rich in plant foods is one of the strongest predictors and influencers of gut microbiome diversity and abundance that we know of," says Tamara Duker Freuman, M.S., RD, a New York City-based nutritionist specializing in digestive disorders and author of The Bloated Belly Whisperer. Here's why: Plants contain fiber, which is essentially the food that good bacteria use to grow. However, some types of fiber are more advantageous than others. One particular kind of roughage, called fermentable fiber, nurtures the growth of helpful gut microbes while simultaneously reducing unfavorable bacteria. You can find these unique fibers in foods like oats, beans, cashews, cauliflower and yams. Fermentable fiber is also added to certain foods like some cereals and snack bars in the form of inulin. Need help getting started? Try this plant-based meal plan for beginners, check out our favorite fiber-rich foods for gut health or dive into our Cinnamon Roll Overnight Oats (pictured above).

2. Focus on Unsaturated Fat

Replacing saturated fat with unsaturated fat isn't just good for your heart. It may also protect against unhealthful gut microbes that contribute to insulin resistance. How so? When you eat a big steak or a juicy burger, its saturated fat promotes the absorption of a compound called endotoxin from the gut. In the bloodstream, endotoxin interacts with cells to create inflammation that can damage insulin receptors, ultimately increasing insulin resistance. For people with diabetes, this can be especially problematic. "For many people, gut bacteria that produce endotoxin are low enough in number that they're not an issue," says Liping Zhao, Ph.D., Eveleigh-Fenton Chair of Applied Microbiology at Rutgers University. "But in [people with] type 2 diabetes, endotoxin producers can overgrow and can even become the most predominant bacteria in the gut."

When possible, trade foods high in saturated fat—like beef, lamb, pork, coconut oil, cheese, butter, and cream—for foods rich in unsaturated fats. This can help keep endotoxin sequestered in the gut and out of the bloodstream. Some of our favorite unsaturated fat sources are nuts, seeds, nut butter, avocados, olives, tahini and vegetable oils.

3. Get Moving

A growing body of research reports that exercise may help breed more favorable gut bugs. According to a 2019 review of 11 studies, professional athletes tend to have a more diverse microbiota and lower levels of certain gut endotoxins than sedentary folks. Researchers aren't sure exactly why exercise is so powerful, but they suspect several mechanisms are at play. On the most basic level, just as physical activity trains your other muscles, it also gives the gut muscles a workout. That makes your gut stronger and better equipped to speed up digestion and remove harmful microbes from your system. Staying active is also believed to reduce body-wide inflammation that may contribute to insulin resistance. And you don't have to be a professional athlete to benefit. Consistently exercising for at least three hours a week at a moderate intensity has been linked to greater numbers of healthy gut bacteria. If you need a jolt of inspiration to get moving, try one of our at-home workouts for any fitness level.

4. Eat More Nuts

For a happier, healthier colon, snack on some nuts. Nuts aren't just loaded with good-for-you unsaturated fat and fiber; they also contain potent disease-preventing substances called polyphenols. Because polyphenols are difficult to digest, the majority of them travel intact to the large intestine. When they get there, beneficial gut bacteria may pounce on them and gobble them up for food. One 2018 study found that when participants ate 1½ ounces of walnuts a day (about ⅓ cup) for eight weeks, the number of bacteria in their gut that produce healthful byproducts increased. And that's promising news: one of these byproducts, butyrate, nourishes the cells of the large intestine, making it better equipped to fight off disease. Butyrate is so powerful it's even believed to protect against colon cancer. If you're not a nut lover, not to worry. You can also find polyphenols in fruit, vegetables, seeds (like flaxseeds), whole grains, tea, coffee, and cocoa products like dark chocolate. Our roundup of healthy nut and seed recipes has plenty of creative ways to work nuts into your meals and snacks.

5. Don't Rely on Probiotics

If you love yogurt, kefir, or probiotic tea, dig in. Just know that probiotics (the live bacteria in some foods and supplements) might not live up to their hype. Why? "The gut is like an Amazon jungle," says Zhao. "And the bacteria from probiotics are like outside invaders trying to move in and find a place to grow." Problem is, all the good real estate is already inhabited by your existing gut bacteria. So there's little space for the newcomers to set up camp. That means they can stay for a while, but they can't settle there permanently. Even if they could, there are other considerations. "Unlike the live bacteria that live full time in your gut, probiotics from foods and supplements only survive in the digestive tract for a few days, so you have to consume them regularly to reap their benefits," says Weisenberger.

A better strategy, she says, is to plant-slant your diet by filling your plate with plenty of fiber-rich fruits, vegetables, nuts, seeds, legumes and whole grains to help your existing gut bacteria thrive. And consider probiotic foods to be the icing on the cake.