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When I am old, which isn’t too far down the road, I see myself sharing stories of bygone days with my good friend, Carol, and chatting about constipation as she and I rock away our final days on the large wraparound porch of our retirement home, situated in the woods of upstate New York. I’ll pick up the warm afghan that slips off her legs, and she’ll reward me with a crisp pink lady apple and a happy aphorism: “An apple a day keeps the doctor away.” She’s lost her mind, of course.
Nevertheless, Carol is sort of right; apples are a great source of fiber, and fiber has the reputation, among other magical powers, of preventing constipation and lowering blood cholesterol. Everybody knows that keeping your blood cholesterol low is a good way to live healthier and longer. The fact that I’m aware of the benefits of fiber now, while I’m still young-ish, might keep me around long enough to spend my twilight years with my good friend on a wraparound porch in upstate New York.
What is fiber? Simply put, both soluble and insoluble fiber are carbohydrates the body does not digest. Most carbs transform to sugar (aka glucose) molecules and are carried to the cells for immediate or stored energy, but fiber passes through the small intestine and into the large intestine undigested. Its function is not to deliver energy to the cells but to (a) push waste out of the colon; and (b) bind with cholesterol and bile acids in the small intestine and flush them out of the body.1
You may have heard dietary fiber referred to as roughage, a fitting term since fiber is coarse and, well, rough. Those rougher parts of plants that our bodies don’t digest include:2
- Non-starch polysaccharides like cellulose, hemicellulose, gums, and pectins.3 Much of our dietary fiber comes from pectins—found mainly in fruits like apples and citrus—which are stabilizers in semi-solid foods like yogurt, jelly, jam, and gelatin.4 Most vegetables and cereals are good sources of cellulose, and hemicellulose is found in rich supply in whole-grain cereals and bran.5
- Oligosaccharides6 like inulin, lignin, and miscellaneous plant parts like waxes and suberin. Inulin is a soluble fiber derived from the roots of certain plants, like chicory root and artichoke. It’s used as an additive in some foods, and a sugar and gluten substitute in others.7 Lignins give plants their woody characteristics and are highest in foods with edible seeds like strawberries or in mature root vegetables like carrots.8
- Resistant starches, meaning those that resist digestion, are found in pulses (lentils, chickpeas, and beans), partly-milled seeds and grains, and various breakfast cereals.
Fiber comes wholly from plant sources, but its exact composition depends on the type and age of the plant as well as the plant tissue the fiber comes from. For instance, high quantities of cellulose and lignin can be found in cell walls, and noncellulosic polysaccharides (starches), waxes, and proteins appear in smaller amounts in mature plants than in immature plants. Storage, ripening, and food-processing may also affect a particular fiber’s makeup.9
Some of those rougher components in plants are soluble and others are insoluble. Now you’re wondering what I mean by soluble and insoluble, so let’s take a minute to define terms.
The Two Faces of Fiber
Soluble fiber attracts water and turns to gelatin during digestion. That’s one way to tell if a food is made of soluble fiber—it thickens in water and turns sort of sticky or gummy.10 Soluble fiber also has some impressive health benefits. Besides helping to lower blood cholesterol levels, thereby staving off cardiovascular disease,11 it helps to keep your blood sugar balanced by slowing the rate at which food is digested in the stomach, absorbed in the small intestine, and then released into your bloodstream. According to the Dietary Guidelines for Americans, 2010, naturally occurring soluble fiber—the kind you find in food—may reduce the risk of type 2 diabetes because of the unique power it has to slow down food digestion and absorption.12
Legend has it that increasing your intake of fiber—both kinds—may reduce your risk of contracting colon cancer as well; however, recent studies are conflicting on that score. A high-fiber diet appears to have little effect on preventing colorectal cancer and is not a sure protection against a relapse of the disease.13 Stay tuned, though—the jury is still out on fiber versus colon cancer.
One point is certain: you feel more full after eating foods high in soluble fiber, and if you’re full you eat less.14 That means you may lose weight by eating more fiber... IF you don’t follow every apple with a dozen chocolate chip cookies and a long nap.
The good news is that you’ll find soluble fiber in lots of tasty whole grains, fruits, vegetables, legumes, and nuts. The best sources are oats and barley (soluble fiber is found in only small or trace amounts in most whole grains); dried beans, lentils, and dried peas; fruits like citrus, apples, pears, strawberries, and prunes (good for both types of fiber);15 vegetables like avocados, Brussels sprouts, edamame, broccoli, carrots, and sweet potatoes; seeds like psyllium and flax; and nuts like almonds, walnuts, pistachios, and peanuts. Nuts typically have more insoluble fiber
ONE CAUTION: Fiber added to packaged food may not have the same health benefits as the naturally occurring kind, so your best bet is to eat a balanced diet and a variety of whole, fiber-rich foods.17
Insoluble Fiber also attracts water to the intestines, though it doesn’t turn into a goopy mass of gelatin. Water bulks up the fiber mass; the bulkier fiber softens compact stools or solidifies runny stools, stimulates the large intestine to contract, and in general promotes regularity, thereby helping to prevent constipation.18 Insoluble fiber speeds the passage of toxic waste through the intestines and helps to reduce the risk of intestinal problems like IBS and diverticular disease.19 It also regulates your appetite by giving you that “I’m full” feeling20—always a plus if you’re looking for a way to manage your calories the healthy way.
Insoluble fiber is the more common of the two types of fiber, and you’ll find it in abundant supply in the skins of vegetables and fruit and the bran portion of whole grains.21 The best sources are 100% whole-grain foods and legumes like split peas, kidney beans, lentils, pinto beans, and chickpeas; vegetables like collard greens, string beans, carrots, broccoli, and cauliflower; fruits like prunes, dates, oranges, apples, pears, raspberries, and blackberries; and whole grains like whole-grain couscous, whole-grain flour, corn grits, and brown rice.
Want some insider information? Beans offer the highest source of insoluble fiber per serving and most are high in soluble fiber as well, so see if you can work in a couple of bean-heavy meals a week. Whole grains are the next highest source of insoluble fiber, but remember—package claims can be misleading, so study the nutrition facts label and discover how whole the grains you read about on the package really are. In general, to be a whole grain the label has to say, for instance, 100% percent whole wheat, and whole wheat should be the first ingredient on the list. Quick Tip: The higher up an ingredient appears on the list, the more of it you’ll find in the food.22
Not Just for the Young at Heart
Fiber isn’t only for the old to the very old among us; everybody needs fiber, even though the spokespeople for fiber supplement ads are often over 60. Picture me shaking my head at the blatant misrepresentation inherent in that casting choice.
According to the Dietary Guidelines for Americans, 2010—notice the word Americans not old Americans—“the AI (Adequate Intake) for fiber is 14 g per 1,000 calories, or 25 g per day for women and 38 g per day for men.”23 If you’re eating 15 grams a day you’re ahead of the game—most Americans get only about 10-15 grams on average.24
Our fiber-poor diet begins for most of us around two years old, a time when most Americans’ daily dose of vegetables drops below healthy recommended amounts. Vegetables, as you now know, are a major source of fiber; so are fruits. But by the time we’re four years old, our whole-fruit intake drops as well. We get almost 50% of our RDA of fruit by drinking juice, which would be great except that juice is high in calories and lacks dietary fiber.25
Choosing whole foods—whole grains and flours rather than refined, and whole fruits and vegetables rather than juice—will make a huge difference in the grams of fiber you can amass in a day. For instance, white rice has 0.5 grams of fiber per cup while brown rice gives you 3.5 grams of fiber for the same amount.
Increasing your daily dose of fiber is easier than you might think, so if you’re shaving bark into your oatmeal right now, put the stick down. Below are 20+ tips for squeezing that 25 to 38 grams of daily fiber into your diet, without giving up all the good food you love. Enjoy!
20+ Ways to Sneak More Fiber into Your Diet
A Little Advice: Add fiber to your diet slowly if you’re used to a low-fiber diet, and be sure to drink lots of water (6-8 glasses a day). See the table and fiber worksheet on University of Washington’s Rehabilitation Medicine website for a long list of common foods and their fiber content (http://sci.washington.edu/info/forums/reports/FiberFacts.pdf).
- Substitute whole fruits and vegetables for juice. Shoot for five or more servings of fruits and vegetables a day.
- Eat the skin of fruits and vegetables when appropriate.
- Replace white rice, bread, and pasta with whole grains—brown rice, whole-wheat bread and pasta. Your goal should be to eat at least three servings of whole grains a day.
- Serve whole grains like quinoa, wild rice, whole grain barley, or bulgur as side dishes rather than white rice or pasta.
- Choose packaged breakfast cereals with a whole grain listed as the first ingredient—and the second, too, of you can swing that.26 Five popular whole-grain cereals highest in nutrition and lowest in sugar are Post Bran Flakes, Kashi GOLEAN, General Mills Fiber One, Kellogg's Frosted Mini-Wheats Little Bites, and Whole Foods 365 Organic Raisin Bran.27
- Choose high-fiber and nutrient-rich cereals for snacks. In a recent Consumer Reports test, four cereals out of twenty-six won top honors for taste and nutrition (based on calories, fat, sodium, sugars, iron, calcium, and fiber): Kellogg’s All-Bran Original, Post Grape-Nuts The Original, Post Shredded Wheat Original Spoon Size, and Post Shredded Wheat Wheat ’n Bran Spoon Size.28
- Substitute nuts—pistachios, cashews, peanuts, almonds—for meat in stir fry.
- Snack on raw vegetables instead of chips, crackers, or chocolate bars.
- Roast or grill high-fiber vegetables like Brussels sprouts, carrots, artichokes, and red potatoes. Leave the skins on, brush with extra virgin olive oil and spices—basil, oregano, chives, garlic, and salt and pepper—for a Mediterranean flavor.
- Replace low-fiber cracker snacks with higher fiber ones. According to Consumer Reports, May 2013, three crackers made the “Very Good” rating based on taste and nutrition: Nabisco Triscuit Reduced Fat (three grams of fiber for seven crackers), Wasa Whole Grain Crispbread (two grams of fiber for one slice), and Kashi Original 7 Grain Sea Salt Pita Crisps (two grams of fiber for eleven crackers).29
- Make a combo berry smoothie using some of the highest fiber fruits around: raspberries, strawberries, blueberries, and blackberries. Add nuts or a tablespoon of ground flaxseed for added fiber PLUS a boost of omega-3 fatty acids.
- Substitute beans or legumes for meat two to three times per week. Soups and chilis take beans instead of meat without skipping a beat.
- Add a teaspoon of ground flaxseed to mayonnaise or mustard and spread your new high-fiber spread on a sandwich. Or add whole chia seeds to an eight-ounce carton of yogurt.
- Substitute whole-grain foods (breads, baked goods, cereals) for the staple foods in your diet, and choose those with at least three grams of fiber per serving. For example, switch your regular morning oatmeal for steel-cut oats. Steel-cut oats have twice the fiber per serving as old fashioned or quick rolled oats. Buy ten-grain pancake mix or choose whole-grain bread with three to five grams of fiber per slice. BUT read the ingredient list to make sure you’re getting whole-grain rather than added fiber.
- Substitute whole-grain foods (breads, baked goods, cereals) for the staple foods in your diet, and choose those with at least three grams of fiber per serving. For example, switch your regular morning oatmeal for steel-cut oats. Steel-cut oats have twice the fiber per serving as old fashioned or quick rolled oats. Buy ten-grain pancake mix or choose whole-grain bread with three to five grams of fiber per slice. BUT read the ingredient list to make sure you’re getting actual whole-grain rather than added fiber.
- To be sure you’re consuming both soluble and insoluble fiber in your diet, integrate a variety of fiber-rich foods into your meals and snacks rather than focusing on just one.
- Reach first for the fruits, vegetables, and nuts with the highest fiber content on those hurry hurry days when eating well is a challenge. Foods high in both soluble and insoluble fiber are apples, pears, oranges, raw apricots, prunes, nectarines, avocados, Brussels sprouts, broccoli, sweet potatoes, edamame, walnuts, almonds, peanuts, and pistachios.
- Create an eating routine that includes insoluble and soluble fiber. For instance, MWF and Sunday eat oatmeal with apples and cinnamon for breakfast, and a fruit and veggie salad sprinkled with seeds and nuts for lunch. TTh and Saturday eat whole-grain waffles with berries for breakfast and roasted vegetables and chicken over whole-grain couscous for lunch.
- Salads are a great way to get more fiber into your diet. The tastiest ones incorporate both soluble and insoluble fiber. To make a really healthy salad, start with dark, leafy greens. Then add legumes and/or beans, chopped vegetables, berries or chopped apples or pears, and a sprinkle of nuts or seeds. Top your salad with a low-fat dressing to keep the calories down.
- Choose fruit cobbler, fruit pies, or whole-wheat bran or fruit muffins in place of low- or zero-fiber desserts.
- Use bean dips such as black bean, hummus, and low-fat refried beans with whole-grain crackers or vegetables instead of sour cream.
- Add bran cereal or oatmeal to replace bread crumbs in meatloaf.
- Use 100% whole-wheat for half or more of the flour when baking. TIP: Baking with 100% whole-wheat instead of refined flour will change the way your bread turns out, so do your homework before diving in.
- “Fiber,” The Nutrition Source, Harvard T.H. Chan School of Public Health.
- “Dietary fibre—what’s its role in a healthy diet?” European Food Information Council (EUFC).
- Three important polysaccharides (long chains of monosaccharides) are made of glucose: starch, glycogen, and cellulose. “Cellulose is the main component of plant cell walls and so is the most abundant organic molecule on earth. Wood, paper, and cotton are the most common forms of cellulose.” “Polysaccharides,” ChemPages, University of Wisconsin.
- Denis M. Medeiros et al., Advanced Human Nutrition, 3rd ed., (Burlington, MA: Jones & Bartlett Learning, 2015), 94.
- Susan Sungsoo Cho, ed., Handbook of Dietary Fiber, (New York: Marcell Dekker, Inc., 2001), 2.
- A carbohydrate made of up of a chain of three to nine monosaccharides (simple sugars/glucose).
- Tamara Duker Freuman, “What is Inulin (Chicory Root Fiber)? U.S. News & World Report.
- Denis M. Medeiros et al., Advanced Human Nutrition, 3rd ed.
- Susan Sungsoo Cho, ed., Handbook of Dietary Fiber.
- “Food Sources of Soluble Fiber,” Dietitians of Canada, updated 2013.
- Part 101—Food Labeling, §101.77(a)(3), “Health claims: fruits, vegetables, and grain products that contain fiber, particularly soluble fiber, and risk of coronary heart disease,” FDA, Code of Federal Regulations, updated December 7, 2015.
- U.S. Department of Agriculture and U.S. Department of Health and Human Services, Dietary Guidelines for Americans, 2010. 7th Edition, (Washington, DC: U.S. Government Printing Office, December 2010), 40-41.
- “Psylluim,” University of Maryland Medical Center’s Medical Reference Guide, updated October 19, 2015.; “Fiber,” The Nutrition Source, Harvard T.H. Chan School of Public Health.
- “Soluble Fiber: Another Way to Fight High Cholesterol,” by Jeanne Cullen, MS, RD, CD, CDE.
- Sandy Keefe, “Are Prunes a Good Source of Fiber?” December 18, 2013.
- “Food Sources of Soluble Fiber,” Dietitians of Canada.”; “Soluble Fiber: Another Way to Fight High Cholesterol,” by Jeanne Cullen, MS, RD, CD.
- Dietary Guidelines for Americans, 2010, 40-41.
- “Fiber,” The Nutrition Source, Harvard T.H. Chan School of Public Health; "High Fiber Diet," University of Michigan Health System, updated June 2011.
- “Soluble and Insoluble Fiber,” Webline Plus, U.S. National Library of Medicine, National Institutes of Health (NIH), updated September 2, 2012.
- “Fiber,” The Nutrition Source, Harvard T.H. Chan School of Public Health.
- “Food Sources of Soluble Fiber,” Dietitians of Canada; “Soluble Fiber: Another Way to Fight High Cholesterol,” by Jeanne Cullen, MS, RD, CD.
- Dietary Guidelines for Americans, 2010, 37.
- Dietary Guidelines for Americans, 2010, 41.
- Dietary Guidelines for Americans, 2010, 41.
- Dietary Guidelines for Americans, 2010, 36.
- “Whole-grain foods help keep your heart healthy and are good for digestion and a healthy weight. Choose foods that boast 100% whole grains on the label. Or check the ingredient list to see if the word whole comes before the first ingredient listed (for example, whole wheat flour). If it does, the food is whole-grain.” USDA Food and Nutrition Service.
- Based on the Center for Science in the Public Interest “Best Bites” rating system. Read the full article: Alexandra Sifferlin, “How to choose a healthy breakfast cereal,” Time.com, updated Fri July 6, 2012.
- “Best high fiber cereal, healthful and tasty: Plenty of fiber-rich cereals can satisfy your taste buds,” Consumer Reports, August 2013.
- “Cracker taste-off: We compared 30 kinds of crackers,” Consumer Reports, May 2013.