Find Out About Fiber: What It Is and Why You Need It

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Find Out About Fiber: What It Is and Why You Need It

We hear over and over again that we should be eating more fiber. Commercials tout fiber supplements and foods high in fiber all the time. We also hear that most of us don’t get enough fiber. But what does fiber really do for us? How much do we need? And, how does fiber impact diabetes?

What is dietary fiber?

Dietary fiber, sometimes called “roughage” is a type of carbohydrate found only in plants. We don’t digest fiber like we do other types of carbs, such as starches and sugars. Fiber is made up of glucose units similar to those in starches and sugars, but in fiber, the units are bonded in such a way that we can’t break them apart in the digestive tract. That’s because we lack the enzymes to do this; as a result, fiber pretty much stays intact as it travels through the gut.

However, once fiber reaches the large intestine, it’s fermented by intestinal bacteria, called probiotics. Probiotics are sometimes called “good” bacteria because they impart certain health benefits. Some fiber isn’t fermented by bacteria and simply passes right through us.

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Insoluble fiber

One type of fiber is insoluble fiber. Insoluble fiber is further broken down into:

  • Cellulose, a carbohydrate that makes up cell walls in plants and that gives plant stems, leaves, and roots their structure
  • Hemicellulose, a carbohydrate made up of sugars, such as xylose, mannose, and galactose
  • Lignans, plant chemicals that may be phytoestrogens or antioxidants

Insoluble fiber is what most of us think of when we hear the terms “bulk” or “roughage.” This fiber works like a broom in the digestive tract, helping to move food along and also give bulk to the stool.

Benefits of insoluble fiber

Benefits of insoluble fiber include:

  • Preventing constipation
  • Preventing hemorrhoids (swollen veins inside or outside the anus and rectum)
  • Preventing diverticulosis (pouches that bulge out through the large intestine)
  • Forming softer, bulkier stools, helping with “regularity”
  • Possibly helping to lower the risk of colon cancer
  • Decreasing exposure to toxins and other harmful substances in the intestines
  • Helping you feel full so that you eat less

Foods that contain insoluble fiber

Foods that contain insoluble fiber include:

  • Whole-wheat bread
  • Wheat bran
  • Brown rice
  • Quinoa
  • Nuts
  • Seeds
  • Beans
  • Vegetables (e.g., cauliflower, green beans, carrots, potatoes)
  • Fruits (e.g., strawberries, raspberries, blueberries, grapes, kiwi, pineapple)

Soluble fiber

The other type of fiber that you might be familiar with is soluble fiber (also called viscous fiber). Unlike insoluble fiber, soluble fiber dissolves in water to form a gel in the digestive tract.

Benefits of soluble fiber

Benefits of soluble fiber are:

  • Helping to lower cholesterol levels
  • Helping to lower blood glucose levels, which can help with both diabetes prevention and management
  • Lowering the risk of heart disease
  • Promoting healthy bacteria in the gut
  • Helping to manage irritable bowel syndrome (IBS)
  • Helping you feel full so that you eat less
  • Possibly reducing the risk of breast cancer

Foods that contain soluble fiber

Foods that contain soluble fiber include:

  • Oat bran and oatmeal
  • Barley
  • Beans
  • Nuts
  • Seeds
  • Vegetables (e.g., avocado, carrots, eggplant, broccoli, Brussels sprouts, artichokes)
  • Fruits (e.g., apples, pears, berries, citrus fruits)
  • Psyllium (a fiber used in fiber supplements and found in some cereals)

How much fiber do you need?

According to the Dietary Guidelines for Americans, 2020-2025, “More than 90 percent of women and 97 percent of men do not meet recommended intakes for dietary fiber.” These guidelines recommend aiming for 14 grams of fiber per every 1,000 calories each day. Here’s what that looks like:

Age 19-30 years

Women: 28 grams
Men: 34 grams

Age 31-50 years

Women: 25 grams
Men: 31 grams

Age 51 and older

Women: 22 grams
Men: 28 grams

For a list of the fiber content of various foods, visit the Dietary Guidelines for Americans website.

Your fiber needs may be different, especially if you have digestive disorders such as Crohn’s disease, ulcerative colitis, or diverticulitis (an infection or inflammation of pouches in the intestines). With these conditions, you may need to cut back on or even avoid high-fiber foods, at least temporarily. Other reasons for limiting your fiber intake include recent digestive tract surgery, diarrhea, gastroparesis, or trouble digesting food. Talk with your health care provider if you aren’t sure how much fiber you need or to discuss if you need to limit your fiber intake.

Why you may not be getting enough fiber

For reference, most Americans get, on average, between 10 and 15 grams of fiber per day. One reason is that a typical “Western diet” tends to be high in processed foods (foods that are usually “stripped” of their fiber) and low in foods that naturally contain fiber (meaning vegetables, fruits, whole grains, and legumes, for example). People who eat low-carb or keto may not get enough fiber, as well, since foods that contain fiber also contain carbohydrate. And following a gluten-free, wheat-free, or grain-free diet can also lead to a decreased intake of fiber.

Other reasons that some people don’t get enough fiber is that they may find that high-fiber foods don’t taste good, are expensive, or are difficult to prepare, according to an article published in 2017 in the American Journal of Lifestyle Medicine. Interestingly, this article also mentioned research that shows many people think they get enough fiber. For example, people who choose foods “made from whole grains” mistakenly think that these foods are high in fiber (and they may not necessarily be).

How to increase your fiber intake

When it comes to getting more fiber, the saying “start low, go slow” definitely applies. All too often, people jump on the fiber bandwagon by suddenly eating too many high-fiber foods at once. The result? Gas, bloating, cramps, diarrhea, or constipation. And since no one wants to deal with those symptoms if they don’t have to, they stop eating high-fiber foods. Here’s how to be smart about boosting your fiber intake:

  • Introduce one or two new high-fiber foods every few days or even every week. For example, add a couple more servings of vegetables or fruit into your eating plan. Or try a recipe that includes beans, such as black beans, kidney beans, or chickpeas.
  • Spread your high-fiber foods over each meal and snack, rather than eating a lot of high-fiber foods at one meal.
  • Leave the skin or the peel on your fruits and vegetables (when it makes sense to), since that’s where most of the fiber is.
  • Switch out whole-grain versions of bread, pasta, rice, and cereal. Tip: read the ingredient list. Look for whole-grain ____ (e.g., wheat, rye, oats), whole wheat, stoneground whole wheat, wheat berries, oats, oatmeal or brown rice as the first ingredient on the list. Terms like “multigrain” or “wheat” do not mean that the food is a whole grain.
  • Add vegetables to soups, stews, and sauces.
  • If you eat snacks, go for raw vegetables, whole-grain crackers, nuts, or seeds.
  • Sprinkle chia seeds or ground flaxseed into your cereal, smoothie, or yogurt.
  • Read the Nutrition Facts label on food packages. A food that contains 2.5 grams of fiber per serving is a “good” source of fiber. A food with 5 grams or more of fiber per serving is a “high fiber” food.
  • Drink plenty of water. Going full force with fiber without increasing your fluid intake can lead to constipation, gas, and bloating. Fiber needs water to help move through your digestive tract.
  • Stay active. Physical activity helps food move through your digestive tract.

Let your digestive tract be your guide. If you start to feel uncomfortable with bloating or gas or have a change in your bowel movements, don’t keep increasing your fiber intake. Let your body adapt before you add more fiber.

Also, keep tabs on your blood sugars. You may find that the more fiber you consume, the better your blood sugars. But if you start having more low blood sugars, talk with your provider about possibly adjusting your diabetes medication.

Too much fiber?

Since many people fall short on fiber, it may be hard to imagine getting too much. But it’s possible. Eating upwards of 50 to 70 grams of fiber daily can cause:

  • Bloating
  • Abdominal pain
  • Diarrhea
  • Constipation
  • Feeling too full
  • Weight gain or loss
  • Intestinal blockage

Remember, too much of a good thing isn’t good. Seek medical attention if your symptoms don’t improve, and go easy on the fiber. Also, be very cautious about using fiber supplements (e.g., Metamucil, Benefiber, FiberCon). They don’t provide other nutrients that foods do, they can interact with some medications, and you can easily exceed your fiber goals if you’re not careful. Talk with your provider or dietitian if you have questions about using fiber supplements.

Want to learn more about eating well with diabetes? Read “Strategies for Healthy Eating,” “Improving Your Recipes: One Step at a Time,” and “Top Tips for Healthier Eating.”

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES on social media

A Registered Dietitian and Certified Diabetes Educator at Good Measures, LLC, where she is a CDE manager for a virtual diabetes program. Campbell is the author of Staying Healthy with Diabetes: Nutrition & Meal Planning, a co-author of 16 Myths of a Diabetic Diet, and has written for  publications including Diabetes Self-Management, Diabetes Spectrum, Clinical Diabetes, the Diabetes Research & Wellness Foundation’s newsletter,, and

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