At Mayo Clinic in Rochester, gastroenterologist Purna Kashyap has a straightforward but often misunderstood message about fiber: eat it in variety, add it slowly, and your gut will thank you in ways that go far beyond keeping you regular.
Most people think of fiber as digestive plumbing—roughage that moves things along. But fiber's real superpower lies in what happens when it reaches your colon. Your body can't actually digest fiber, so it passes through your digestive system largely intact, becoming fuel for the trillions of microbes living in your gut. Those microbes then break down certain types of fiber into compounds that support not just digestion, but heart health, immune function, metabolic health, and blood sugar control.
The evidence is compelling. Research shows that adequate fiber intake lowers cholesterol and blood pressure, improves blood sugar control to help prevent type 2 diabetes, decreases the risk of colorectal cancer and stroke, helps manage weight, and maintains the diverse gut microbiome that underpins overall health. Yet most people aren't getting nearly enough.
Dr. Kashyap explains the distinction that matters most: fermentable versus nonfermentable fiber. Fermentable fiber—the kind broken down by gut bacteria—produces beneficial short-chain fatty acids. Nonfermentable fiber mainly adds bulk to support regular bowel movements. The best approach is eating both types, which happens naturally when you choose a variety of whole foods rather than relying on supplements.
The ideal fiber sources are fruits like berries, pears and apples; vegetables including broccoli, Brussels sprouts and leafy greens; legumes such as lentils, chickpeas and beans; nuts and seeds like almonds, chia seeds and flax seeds; and whole grains including whole-wheat bread, oats and wheat bran. "The more different types of fiber-rich foods you eat, the more different types of fiber you'll get, which is optimal for your health," Dr. Kashyap says. Small swaps—whole-grain bread instead of white, nuts or fruit instead of chips—add up over time.
Most healthy adults should aim for 30 to 40 grams of fiber daily, though individual needs vary by age and health status. The catch is that jumping to that target too quickly causes bloating, gas, and abdominal discomfort. Instead, Dr. Kashyap recommends increasing fiber by about 3 grams per week—achievable through something as simple as adding half a cup of peas, squash or cauliflower, or a cup of carrots or brown rice. Hold that level for seven to ten days before increasing again. Drinking plenty of water, aiming for 80 ounces daily, smooths the transition.
"Slowly increasing your fiber intake allows your digestive system and gut microbes time to adapt, and any symptoms will improve after a short while," Dr. Kashyap explains. This gradual approach transforms what could feel like a health mandate into a sustainable habit—one that your gut microbes will adapt to, and one that supports not just digestion but your entire body's long-term health. The goal isn't perfection; it's consistency and variety, building toward changes that stick.