This story is a part of The Elemental Guide to Vitamins. Here are the vitamins and supplements that are covered: multivitamins, vitamin D, vitamin C, calcium, B vitamins, omega-3, vitamin E, fiber, protein, and probiotics.
Fiber is a funny thing. The human digestive system can’t absorb it — or even break it down very effectively — and the human body doesn’t put it to use building cells or doing any of the other jobs nutrients typically perform. But arguably no dietary component is linked with so many health benefits.
“Fiber has benefits throughout the digestive tract,” says Joanne Slavin, co-author of that Nutrients review and a professor in the Department of Food Science and Nutrition at the University of Minnesota. “It slows down absorption of fats and carbohydrates in the small intestine, and in the large intestine it provides food for healthy bacteria.” Fiber also acts as a kind of intestinal scrub brush, sloughing away bits of food that could otherwise accumulate and cause trouble.
Slavin says that the term “fiber” refers to a diverse group of plant carbohydrates, which can be broken up into two subcategories. Soluble fibers are ones that dissolve in water, and that can act as food for healthy gut bacteria. Insoluble fibers do not dissolve in water, and these mostly improve the passage of food through the GI tract. They also make it easier to poop. Many healthy whole foods contain both types of fiber. But nuts, seeds, and beans are especially high in soluble fiber, while whole vegetables and whole grains are insoluble fiber champs.
“High-fiber foods like fruits and vegetables contain phytonutrients that may also have anti-inflammatory effects.”
It’s important for people to get both types of fiber. When ingested together, soluble and insoluble fiber form a protective “latticework” that slows the small intestine’s uptake of sugar and other food molecules, says Robert Lustig, MD, an neuroendocrinologist and former professor of pediatrics at the University of California, San Francisco. Slowing digestion is good for several reasons. “Fewer calories will hit your liver all at once, which means the liver stays healthy,” he says. Slower digestion also means blood sugar levels don’t spike as dramatically after a meal, and more food molecules make it to the lower intestine where they can feed healthy bacteria.
Fiber has been linked to lower levels of blood cholesterol and to reduced appetite and cravings in people with obesity. But if a person only eats soluble fiber, which is often found in processed grain foods or in some popular fiber supplements, he or she may not experience these same benefits.
This is where fiber supplements come into play. Many contain soluble fiber only, says Berkeley Limketkai, MD, director of clinical research at the UCLA Center for Inflammatory Bowel Diseases. And while a 2017 review in the American Journal of Clinical Nutrition found evidence that soluble fiber supplements can help people control their appetite and blood sugar, and maybe also lose weight, a lot of the research on soluble fiber supplements is shaky, the authors of that review write.
Even if a supplement contains both types of fiber, Limketkai says food sources of fiber are healthier. “High-fiber foods like fruits and vegetables contain phytonutrients that may also have anti-inflammatory effects,” he explains. Fiber supplements likely don’t provide all these same benefits.
That’s not to say fiber supplements can’t be helpful. Especially for people who struggle to digest high-fiber foods — whether due to existing GI problems or to food-related sensitivities — supplements can help them increase their fiber intakes. These supplements tend not to contain the full complement of fibrous plant molecules found in food. But they also seem to be very safe.
The bottom line: If you can’t manage to get fiber from food, a supplement may be a good alternative. But choosing the “best” supplement is mostly educated guesswork, and experts agree that getting fiber from dietary sources is optimal. According to resources from the Mayo Clinic, legumes such as beans, lentils, and peas are all fiber powerhouses. So are fruits — especially berries, apples, and pears — and vegetables like green beans and broccoli. Nuts, seeds, and whole grains are also sources.
This story is a part of The Elemental Guide to Vitamins.