Fiber Is An Inflammation-Fighting Unicorn—Here’s Why

Fiber is an important part of a healthy, well-balanced diet—this we know. It’s long been touted for lowering cholesterol, helping control blood sugar levels, and promoting bowel health, among other things—but as it turns out, fiber may be even more of a dietary unicorn than we originally thought. In fact, recent research suggests it’s key for warding off the “I” word: inflammation.

Here’s how it went down: Researchers at Georgia State University put mice on a low-fiber diet and found that the lack of soluble fiber (the type that attracts water to form a gel and help slow down digestion and promote satiety), specifically, significantly affected their gut microbiomes. In just days, the populations of common healthy bacteria in the mice’s microbiomes plummeted, harmful bacteria became more prevalent, and their intestines developed signs of inflammation. (Their blood sugar levels also spiked, and they gained fat.)

Once the mice were put back on a fiber-filled diet, though, production of interleukin-22 immune cells increased, inflammation subsided, microbiome bacteria normalized, and fat gain slowed.

Yes, this study may have been done on little critters, but it has legit implications for us humans, too. “70 percent of our immune system resides in our gut, in close proximity to our gut microbiome, and recent science clearly shows that you cannot separate the gut microbiome from the immune system,” says Will Bulsiewicz, M.D., M.S.C.I., a board-certified gastroenterologist who was not affiliated with this particular study. “When you damage the gut, you also harm the immune system and can cause inflammation.”

Inflammation, the immune system’s response to anything that could be harmful to the body (whether an external wound or an internal issue), is meant to be a temporary corrective process. When the immune system is confused or repeatedly stimulated, though, inflammation becomes chronic and can do a lot of harm.

In fact, chronic inflammation can lead to a number of health issues, including weight gain, cognitive decline, depression, arthritis, GI diseases (like Crohn’s and ulcerative colitis), cancer, heart disease, and more, says Adena Neglia, the senior dietitian for Mount Sinai’s outpatient clinics in New York City.

That’s where the fiber comes in: “Certain types of fiber—which we call ‘prebiotic fiber’—act as fuel for our gut microbes,” says Bulsiewicz. As they nourish those good bacteria, they’re turned into short-chain fatty acids, which have been shown to have an anti-inflammatory effect.

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Reaping the gut- and immune-loving benefits of fiber starts with eating enough of the stuff—25 grams a day for women and 38 grams a day for men, minimum. Fill as much of your diet as possible with whole plant foods and pay special attention to prebiotic fibers (which include inulin, oligofructose, lactulose, and resistant starch) found in garlic, onions, sunchokes, and asparagus, says Neglia. The next time that recipe you’re following calls for two cloves of garlic, take a walk on the wild side and add four. Your gut and immune system will appreciate the extra love.

Related: 5 Prebiotic Foods That Help Probiotics Do Their Jobs