7 Types of Fiber, Explained
You’re probably already familiar with the importance of eating enough fiber—doing so might help reduce the risk of developing heart disease, diabetes, and colon cancer, among other benefits. But did you know that there are actually several different types of fiber that each offer their own set of health perks? (You know, besides keeping the number two train on schedule.)
“Fiber, often categorized as ‘soluble’ (absorbs water during digestion) or ‘insoluble’ (remains unchanged), is actually much more complex,” says Connecticut-based registered dietitian Alyssa Lavy, R.D. “There are different types of fiber under these umbrellas that have various physiological effects, and ultimately, potential health effects.”
While water solubility is one of the better known properties of fiber, other properties, such as water holding capacity, ability to bind to other materials, and the ability of our gut bacteria to ferment fiber effectively, are important as well. For example, some people may be able to tolerate certain types of fiber better than others, and learning which ones agree with you best can ensure you get the most bang for your bran.
It’s best to eat a variety of foods, as able, in order to consume the many types of fiber and reap the health benefits. Ahead, a look at seven types of fiber and the foods where you can find them.
This insoluble fiber is a primary component of plant cell walls, and many vegetables—such as broccoli, cabbage, kale, and cauliflower—are rich sources of cellulose. “When eaten, cellulose passes through the gastrointestinal tract relatively intact, binding to other food components you’ve eaten and helping to move things along,” says Florida-based registered dietitian Carol Aguirre, R.D. It also keeps the digestive system healthy by aiding the growth of beneficial gut bacteria (this healthy gut flora is crucial in preventing bad bacteria from staging a coup and causing illness). Other cellulose-packed foods to add to your roster include legumes, nuts, and bran.
Soluble fibers, like inulin, leave you feeling fuller for longer by slowing digestion. This also means that it takes longer for your body to absorb sugar from the foods that you eat, helping to prevent blood sugar spikes (and the pesky junk food cravings that can strike because of them). Inulin isn’t digested or absorbed in the stomach—it actually sets up shop in the bowels, promoting the growth of beneficial flora associated with improving gastrointestinal (GI) and general health, says Aguirre. (However, it’s also a fructan, which is very fermentable by our gut bacteria, says Lavy, so some people might may experience GI distress.) Inulin is derived from chicory root, and naturally found in fruits and veggies such as bananas, garlic, onions, and asparagus, as well as in wheat (like barley and rye).
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Pectins are a type of soluble fiber that help reduce the glycemic response of foods by stalling glucose absorption (good bye, blood sugar spikes!). They’re well metabolized by our gut bacteria, and like other soluble fibers, may help to lower cholesterol by flushing fatty acids out of the body, says Lavy. Pectins can be found in relatively large amounts in foods like apples, strawberries, citrus fruits, carrots, and potatoes, and in smaller amounts in legumes and nuts.
4. Beta Glucans
Beta glucan is a gel-forming type of soluble fiber that’s fermentable by our gut bacteria. It’s considered a prebiotic, providing “food” for good gut bacteria, says Edwina Clark, R.D., head of nutrition and editorial content at Raised Real. It may be helpful in increasing satiety and managing blood sugar levels, thanks to properties that delay the rate at which food leaves the stomach and slow transit time within the intestines, says Lavy. If you want to amp up your beta glucan intake, it can be found in oats, barley, shiitake mushrooms, and reishi mushrooms, says Clark.
As a soluble fiber, psyllium helps relieve constipation by softening poop to help it pass. It also forms a handy gel that binds to sugars and helps to prevent reabsorption of cholesterol in the digestive tract, says Lauren Harris-Pincus, R.D.N., author of The Protein-Packed Breakfast Club. (The fact that it’s also a prebiotic that feeds the friendly bacteria in the gut is just an added bonus.) Because psyllium is the food source itself—the fiber comes from the outer husk of the psyllium plant’s seeds, says Harris-Pincus—you’ll only find this type of fiber as a supplement or an ingredient added to other foods, such as high-fiber cereals.
Like cellulose, lignin is an insoluble fiber that’s part of the cell wall structure in plants. Not only does it do your poop a solid (literally), but some research also suggests that insoluble fibers may help to reduce the risk of developing colon cancer, says Lavy. While the exact mechanism is currently unknown, one theory is that it hurries things along in the digestive tract, limiting the amount of time carcinogens can interact with tissue. Food sources of lignin include whole grain foods (wheat and corn bran), legumes (beans and peas), vegetables (green beans, cauliflower, zucchini), fruits (avocado, unripe bananas), and nuts and seeds (flaxseed).
7. Resistant Starch
“Resistant starch functions similarly to soluble, fermentable fiber, helping feed the friendly bacteria in the gut,” says Aguirre. This means that it passes into your large intestine, and together with your immune system and microflora, help to guard against any pathogenic bacteria that attempts to mess with your GI tract. It can also help with weight loss by taming appetite and blood sugar spikes, heart health by lowering cholesterol, and digestive health by keeping things regular. Legumes and beans are excellent sources of resistant starch, says Aguirre, as are oatmeal flakes and bananas, which have the maximum amount of resistant starch when they’re unripe.