This article originally appeared in the Winter 2019 issue of Tufts Nutrition Medicine.
With a variety of fiber types to consider— and health claims on food labels to vet—it can be awfully difficult to separate what’s real from what’s hype. Fortunately, Nicola M. McKeown is here to help. A nutritional epidemiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, and an associate professor at the Friedman School, McKeown offers her quick guide to fiber, including how to better incorporate different kinds of it into your diet.
1 Most People Don’t Get Enough
“Dietary fiber” refers to a variety of complex carbohydrates and is found in the edible parts of plants that cannot be entirely digested. Experts recommend adults get between twenty-one and thirty-eight grams daily, but Americans, on average, consume only about sixteen grams. Getting a range of fiber types in your diet is important, so McKeown recommends eating “a variety of fruit, vegetables, legumes, and whole grains daily to meet your dietary fiber goal.”
2 Underconsumption Will Affect Your Health
The FDA considers dietary fiber a “nutrient of public health concern” because low consumption is associated with an array of potential health problems. One is constipation, the most reported gastrointestinal complaint in the United States. But research shows too little fiber can also lead to increased risk of developing Type 2 diabetes and cardiovascular disease. McKeown’s research has shown that consumption of whole grains, in particular, lowers prevalence of metabolic disorders and reduces visceral fat.
3 Soluble Fiber Can Help . . .
Soluble fibers—found in beans, lentils, apples, and other sources—absorb water from partially digested food and slow digestion, making you feel fuller longer and regulating blood sugar. By adding soluble fiber to your diet, you can lower your LDL (“bad”) cholesterol and glucose levels. Psyllium and beta-glucan (found in oats and barley) have FDA-approved health claims for reducing cardiovascular disease by lowering cholesterol.
4. . . And So Can Insoluble Fiber
Insoluble fibers, found in foods such as whole wheat bran and some whole grains, nuts, and legumes, don’t absorb water. By “bulking-up” the stool, they help food move more efficiently through the body and promote regularity—an important aspect of feeling well.
5 Track Dietary Fiber in Your Diet
Good sources of dietary fiber include fruits and vegetables, nuts and beans, and whole grains. But it’s easy to assume you’re getting more than you really are, so keep an eye on the composition of your diet. For reference, one cup of black beans yields eight grams of dietary fiber; one cup of barley will give you six. Oatmeal is a great fiber source, but if you choose a different ready-to-eat breakfast cereal, make sure whole grain is the first ingredient and be sure to check the amount of dietary fiber per serving.
6 Don’t Forget About Prebiotics
Only a subset of dietary fibers can be classified as “prebiotic.” These are fibers that get fermented in the gut and act as food for the bacteria in your microbiome, improving overall health. Food sources considered to have prebiotic effects include some whole grains, bananas, greens, onions, garlic, soybeans, and artichokes. Bottom line: Eating a variety of plant-based foods will help keep your gut healthy.
7 Take Note of Added Fiber
To increase the fiber content of processed foods, manufacturers often add isolated or synthetic fibers extracted from starchy foods or otherwise made from starches or sugars. These dietary fibers are listed on the ingredients label. If you see names like “polydextrose” and “soluble fiber dextrin” in processed foods such as cereals, soups, and baked goods, those are added fibers. “Eating processed foods with added fibers may help boost your fiber intake but will most likely be high in sugar or sodium,” McKeown warned, “so read the Nutrition Facts panel to take stock of what is in the product.”
8 The FDA is Examining Health Benefits
In the future, the FDA will ensure that the dietary fiber listed on the Nutrition Facts label delivers a health benefit, such as lowering blood glucose, cholesterol, and blood pressure levels, or increasing mineral absorption in the G.I. tract. The FDA is currently taking a closer look at the fibers being added to foods and has already approved several added fibers—including beta-glucan soluble fiber (aka oat bran fiber), psyllium husk, and pectin—and has provisionally approved others (such as inulin and resistant maltodextrin/dextrin) for inclusion on the nutrition label.
9 Different Added Fibers Do Different Work
Not all added fibers offer the same health benefits—beta-glucan, for example, may lower cholesterol when what you really want is regularity to alleviate constipation (if that’s the goal, choose wheat-bran). Talk with a registered dietitian nutritionist to help you identify fiber-rich foods or supplements that will help improve your health.
10 Whole Foods Are the First Line of Defense
Fruits, vegetables, beans, and whole grains have a mix of naturally occurring fiber types to cover the range of health benefits. They are also rich in nutrients and phytochemicals and naturally lower in sugar and sodium. Move toward eating a varied diet, with lots of plants, and you’ll be on the right track to increase your dietary fiber intake.