Which type of fiber is best soluble or insoluble?

If you drink a glass of pure orange juice, for instance, that sugar gets metabolized pretty much immediately, causing your blood sugar to climb more quickly. But if you eat a whole orange, which contains soluble fiber, the rate of sugar uptake is more gradual, Linsenmeyer says. This is helpful for anyone trying to maintain steady blood sugar levels, such as those with prediabetes or type 2 diabetes, Lisa Young, R.D.N., C.D.N., Ph.D., adjunct professor in the department of nutrition and food studies at New York University and author of Finally Full, Finally Slim, tells SELF.

Soluble fiber also has a regulatory effect on the absorption of dietary fat and cholesterol. “It attaches to the cholesterol in food, so that it gets excreted from the body instead of absorbed by it,” Linsenmeyer says. (Remember, fiber doesn’t get digested the way other nutrients do.) This can help lower the level of LDL cholesterol (low-density lipoprotein, the “bad” one) in the blood, according to the FDA—and, in turn, potentially lessen the risk of heart disease, according to the U.S. National Library of Medicine. That’s why Young recommends clients at elevated risk for heart disease incorporate plenty of soluble fiber in their diets.


Insoluble Fiber

If you’re guessing insoluble means this kind of fiber does not dissolve in water, bingo! Soluble fiber’s sister is found in the highest amounts in whole grains (like whole wheat flour and wheat bran), nuts, beans, and some vegetables (like cauliflower, potatoes, and green beans), according to the Mayo Clinic.

Insoluble fiber doesn’t pull in water to form a digestion-slowing gel—its role is just the opposite, actually. This kind of fiber passes right through us looking pretty much the way it came in, hurrying along the movement of food through the digestive system and adding bulk to our stool, according to the FDA.

Yes, this is the the poop-powering kind of fiber you’ve heard so much about. Because of how it moves digestion along, insoluble fiber can help prevent and treat constipation, per the FDA. Young advises clients struggling with constipation and complications like hemorrhoids to up the insoluble fiber in their diets.

Insoluble fiber can also be beneficial for various digestive conditions associated with sluggish or irregular bowel movements. For instance, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends people with diverticulosis—a disease in which little sacs bulge out of the weak areas of your colon wall—incorporate more fiber into their diet. Of course, if you have diverticulosis or any other digestive condition, always speak with your doctor to find out what the best diet is for you.

The added volume in your stomach provided by insoluble fiber can also help enhance the feeling of fullness you get after eating, so it may help people with weight management, Linsenmeyer says. According to the FDA, both soluble and insoluble fiber can help increase feelings of fullness for longer after a meal. Larson says people who have been advised to lose weight by their doctor may find that adding more of either kind of fiber to their diets helps.

One more thing to consider when it comes to soluble vs. insoluble: Scientists are still studying the links we’ve observed between overall fiber intake and reduced risk of a number of health issues. For instance, research suggests a negative correlation between fiber intake and how likely you are to get colorectal cancer, according to the AND, but isn’t conclusive about whether soluble or insoluble fiber is to thank. It may be both.

So how can you make sure you’re getting enough of both?

The topline takeaway here is that fiber is generally great. “Both types are very healthy,” Linsenmeyer says. “One isn’t better for you than the other, and we need both in our diets” for optimal digestive and overall health. So while all of this fiber goodness is fascinating and important to know, it’s not like you need to be tallying up how much insoluble versus soluble fiber you’re getting. (Besides, that’d be pretty difficult to do, given many foods don’t list them separately.)

Dietary Fiber

What We Now Know About Food Fiber

During my years in practice, I was a firm advocate of increasing food fiber in the diet. I was aware of the work of researchers in Africa who discovered that rural Africans who consumed a largely plant-based diet with lots of fiber had 2-3 large, soft bowel movements a day. In addition, they seldom had diseases of the colon that are so common in the Western world. A high fiber diet made sense to me and many of my patients were relieved of constipation and simply felt better on such a diet. Further, some epidemiologic studies (including heart disease and cancer) began to show health benefits when fiber was significantly increased in the diet. Still, it seemed that this was the end of the fiber story. Little did I know!

There are many types of fiber that have been discovered in plants, including various types of starches, lignins, cellulose, and others. These were of interest to plant chemists, but not to physicians. Then in the 1980s, it was discovered that fiber could broadly be separated into insoluble and soluble types. No fiber is digested by the small intestine. All of it arrives into the colon unchanged. Insoluble fiber does not dissolve in water, is not fermented or broken down by colon bacteria, but does retain lots of water in the colon and so provides a larger, softer stool. Soluble fiber, on the other hand, is broken down and fermented by colon bacteria. We really didn’t know too much more about these two types of fiber until the 1990s when better measuring methods were devised. In the last 15 years, the difference between these two fibers, insoluble and soluble, has become increasingly important, especially with the discovery of prebiotic soluble fibers.

The History of Fiber

At one time before farming occurred and animals were domesticated, our ancestors wandered around, eating berries, fruits, root vegetables and any plant that promised to have some nutrition. The diet contained 50-100 grams of fiber a day, all of it from plant material. Interestingly, one of the best-studied prebiotics fibers, inulin, has been found in over 36,000 plants, so these people were eating a lot of this beneficial fiber.

Then came villages with farming, growing grains, and raising livestock. Fiber intake gradually diminished. Furthermore, in Westernized countries, fiber was removed from the grains as it was felt to be useless. We were left with white bread without fiber and many of the minerals and vitamins. The food industries also began boxing and packaging food products in ways that required further changes to basic foods. Many substances were added to prolong shelf life and enhance the taste but they did not contribute to health as far as we knew. High fructose corn syrup was found to be as sweet as sugar and replaced it in many drinks and foods, as it was much cheaper. This corn derivative and other sweeteners were used in many products and have resulted in or are associated with the epidemic of obesity we now see in our society. Food fiber was sidelined as an important factor in the diet.

What is Prebiotic Fiber?

There are two basic types of food fiber – insoluble fiber, which does not dissolve in water and is not fermented by the gut’s bacteria, and soluble fiber, which does dissolve in water and is fermented by the colon’s microorganisms or bacteria. Almost all plant food, which is where fiber comes from, will have some of each but in different proportions. For instance, wheat is about 90% insoluble fiber. Oats are 50/50 and the psyllium plant is mostly soluble fiber. All of the above have been well-known for some time. In addition, it has been long known that in societies that consume large amounts of plant foods each day, such as in many rural African societies, that the general bowel health of the population is very good, and that the incidence of many disorders of the lower GI tract are almost non-existent. These include bowel irregularity, diverticulosis, colon cancer and polyps, Crohn’s disease and ulcerative colitis. We did not know exactly how or why this was occurring although it was obvious that the plant-based diet was important.

Then in the mid-1990’s, medical researchers and nutritionists began to discover something quite remarkable about some soluble fibers. They found that certain soluble fibers such as inulin, oligofructose and FOS (fructooligosaccharide) caused some remarkable changes in the bacterial mix of the colon. They had discovered prebiotics.

Prebiotic Fibers

Prebiotic fiber comes from plants such as the Jerusalem artichoke, chicory root, onions, whole grains, bananas, and garlic. These essential soluble fibers do more than help people who ingest them in adequate amounts stay regular; multiple studies demonstrate that prebiotic fiber can favorably change the bacterial mix in the lower gut. For most of the 20th century, medical schools taught doctors that the bacteria that live in the human body were harmless; we now know that some of these bacteria actually perform important health functions. These functions include strengthening the bowel wall, improving the body’s ability to absorb essential nutrients such as calcium, producing the hormones that control appetite and anxiety, and more. The fact is that medical science is just at the beginning of a new world of exciting lower gut health discoveries.

Watch the full video on CBN News!
Unfortunately, many people won’t or can’t eat enough of these prebiotic-rich foods to gain the health benefits bacteria offer. For these people – including vegetarians, vegans and those who are gluten-intolerant – an all-natural prebiotic supplement can offer a lifeline to better overall wellness. A prebiotic supplement such as Prebiotin provides an easy, low-calorie way to get all the fiber you need – without having to eat difficult-to-find and potentially unappetizing meals.

Fiber Now

Fiber has made a comeback, however. By its very definition, fiber is not digested and broken down in the small intestine. Rather, it moves on down into the colon. In the 1970s and 80s, we learned that there were two major types of fiber – insoluble fiber and soluble fiber. Insoluble fiber is not acted on or fermented in the colon. It provides no nutrition to the bacteria there. It does, however, hold lots of water and, in so doing, helps to get a softer, more regular bowel movement. Soluble fiber, on the other hand, is used by colon bacteria as a food source.

Another major development has been an understanding of the dramatic and major role that bacteria within the colon play in maintaining good health. In short, we benefit enormously from the bacteria in our colon. The soluble fibers, called prebiotics, provide the most benefits. These are health fibers. While there are many “candidate” prebiotics fibers, just a few have been studied to the extent that researchers and physicians understand what they can do and feel confident in recommending foods and supplements that contain prebiotic fibers.

Insoluble Fibers and You

When trying to figure out how you can add more fiber to your diet, the research is coming so fast and furious that it’s hard to know what to do. The good news is that adding dietary fiber in the form of non-digestible carbohydrates is easier than ever before. Here’s what you need to know about resistant starch, inulin soluble fiber, oligofructose and why making small, manageable changes to your dietary lifestyle can reap more health benefits than you ever thought possible.

Soluble and Insoluble Fibers

Medical scientists and nutritionists categorize dietary fiber into two classifications. Soluble fiber, as the name suggests, dissolves easily in water. Plants such as beans, greens, and other complex carbohydrates contain soluble fiber; some foods, such as the potato, contain a mix of insoluble fiber (the peel) and soluble fiber (the flesh underneath). The human body breaks down these complex carbs into a gelatinous, viscous byproduct that the large intestine turns into gasses and acids that encourage the growth of beneficial bacteria in the lower gut. These bacteria positively affect several essential bodily functions and overall health.

Insoluble fiber won’t dissolve in water but is just as important to overall health and well-being as soluble fiber. We can further classify insoluble fiber into two types: fermentable and non-fermentable. Non-fermentable insoluble fiber is known primarily as a bulking agent, and consuming adequate insoluble fiber keeps people regular. Fermentable insoluble fiber — such as resistant starch —produces the same healthy gasses and acids in the large intestine that soluble fiber does. One important difference between the two types of fibers is that soluble fiber tends to slow digestion while insoluble fiber speeds it up.

Resistant Starch

Entering the dietary fiber mix is resistant starch, considered a third type of fiber that provides the benefits of both insoluble and soluble fibers. The term “resistant” refers to this starch’s ability to resist digestion. Instead, it passes to the large intestine where it produces the same effects of soluble and insoluble fibers. Although the terms are complex, you probably eat resistant starch and other fibers in your diet every day — food such as seeds, unprocessed whole grains, legumes, and potatoes all contain resistant starch. People sometimes avoid eating starches because they fear weight gain; however, eating suitable amounts positively affects health in several ways.

These resistant starch foods help people stay fuller longer because they are not as easily digested. That means people who eat resistant starches (even unknowingly) are more likely to consume fewer calories over the course of one day. Also, resistant starch helps people burn fat while avoiding fat storage, according to several studies; it also boosts metabolism. Natural resistant starch foods also help diabetics manage their condition by decreasing glycemic response and increasing insulin sensitivity. It increases the growth of healthy bacteria in the lower gut, just like its fermentable soluble and insoluble fiber cousins. Still, more research suggests that resistant starch contributes to digestive, brain, kidney and eye health.

How Much Fiber Do I Need?

The last 15 years have seen an incredible amount of research demonstrating the importance of fiber to overall health. Fiber-rich foods aren’t hard to find, either — green vegetables, whole grains, nuts, fruit, beans, and supplements all provide excellent sources of prebiotics. Unfortunately, most Americans don’t eat nearly enough fiber-rich foods, according to WebMD. On average, adults consume about 15 grams of dietary fiber every day — sound like a lot? It isn’t, considering women and men should consume between 25 and 38 grams per day, respectively. And people who have an aversion or allergy to certain foods, such as wheat, have an even more difficult time ingesting their daily requirement.

To put these numbers into perspective, consider how much fiber is contained in the average serving size of common foods such as bananas, cereal, and almonds. Eat a whole-grain bran cereal for breakfast and consume only 5 grams of fiber. Add a banana to your bowl and reap another 3 grams. Ready for a mid-morning snack of 24 almonds? You just added 3.3 grams of fiber, according to WebMD. The point is, eating enough fiber can’t be left to chance — making it a habit requires consciously eating fiber at every meal because getting to a minimum of 25 grams takes a lot of careful planning.

The Easy Alternative

There is another alternative to planning each meal with military-like consistency. Prebiotic supplements that contain fermentable insoluble fibers such as inulin and oligofructose contain enough plant fiber to make securing your daily intake much easier. Another added benefit? All-natural prebiotic supplements such as Prebiotin are low in calories, don’t impart an offensive taste or texture on foods and provide all the same benefits that whole food prebiotics do — without the planning, math and potential weight gain.

Regardless of how you choose to add non-digestible carbohydrates to your diet, get in the habit of reading every label before you make a purchase — because now more than ever before, you are what you eat.

Irritable bowel syndrome, also known as IBS or functional gastrointestinal disorder, is a combination of symptoms that include abdominal pain, constipation, and diarrhea. It’s more prevalent in women than men and affects about 10 to 15 percent of the American population. If you suffer from IBS, making simple lifestyle adjustments, especially to your diet, can make a huge difference.

Simple Tips for Controlling IBS

One of the easiest and most important steps you can take is avoiding large meals. Eating several small meals throughout the day can help with the symptoms of IBS. You should also avoid greasy, high fat foods, dairy, alcohol, sodas, and foods that can cause gas.

10 Foods That Won’t Upset IBS

Here we explore ten foods that are nutritious and won’t aggravate IBS, enjoy!

1. Lean Chicken or Turkey

If you eat meat, lean chicken and turkey are excellent choices for IBS. Poultry is a healthier protein source than red meat and it’s easier to digest when eaten with a salad or a side of organic, raw vegetables. Just make sure to choose organic, vegetarian-fed options.

2. Wild-Caught Fish

It’s important to be careful and avoid fish that is likely to contain mercury, but another food for IBS sufferers is wild caught fish. Farm-raised fish are often subject to disgusting conditions and, often, best avoided. Fish is a naturally lean source of protein and adding a side of organic vegetables and fruit will give you a solid meal that’s unlikely to upset your stomach.

3. Brown Rice

Brown rice is another food that won’t trigger IBS and is far more nutritious than white rice. Organic brown rice also offers soluble fiber and can encourage irritated bowels to function normally.

4. Organic Green Beans

Organic green beans are another source of soluble fiber and a perfect complement to organic poultry or fish.

5. Coconut Milk

Unless we’re talking about formula for infants, replacing cow’s milk with coconut milk can be a great idea. Cow’s milk is not only bad for IBS, but can also be bad for your health. Many people have trouble with the lactose and the pasteurization process alters the milk in undesirable ways. Other organic alternatives include hemp milk, sunflower milk, and rice milk.

6. Fermented Foods with Probiotics

People who have to give up dairy because of severe IBS symptoms often find relief by cultivating strong, probiotic colonies in their gut. A probiotic supplement is one way to achieve this, eating probiotic rich fermented foods is another.

7. Eggs

Eggs have a caveat; although the yolk can be undesirable for people with IBS, the egg whites are easier to digest, lower in fat, and can be well tolerated.

8. Organic Raw Honey

Although refined sugar is not good for anyone, organic raw honey is an excellent, natural sweetener that can be eaten without upsetting IBS.

9. Green Tea

Green tea is an excellent substitute for carbonated and alcoholic beverages. It is a flavorful drink that can add a boost to your day and won’t upset IBS.

10. Lemon Juice

Adding lemon juice to water can add flavor without consequence. Not to mention that lemon juice is good for cleansing and offers nutritional support to the liver.

There you have it, ten nutritious foods for IBS sufferers. Do you have other suggestions? Leave a comment below and share your thoughts!

References (9)

†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.


Resources > Archives > Soluble & Insoluble Fiber: What is the Difference?

Soluble & Insoluble Fiber: What is the Difference?

What’s the difference between soluble and insoluble fiber? Are they both good for you, and how can I include them in my diet?
Dietary fiber, the edible portions of plant cell walls that are resistant to digestion, is an extremely beneficial component of our diets. Not only does it help ward off many diseases, it has been shown to aid in weight loss by reducing food intake at meals. This is because fiber-rich foods take longer to digest and thus result in an increased feeling of fullness and satiety. In addition, the more gradual absorption slows the entrance of glucose into the blood stream, thereby preventing large blood glucose and insulin spikes.
The recommended fiber intake is 20 – 35 grams per day for adults, or 10 – 13 grams for every 1,000 calories in the diet. This recommended amount should come from a combination of soluble and insoluble fiber, since each type provides different benefits. While it’s not necessary to track, a 3:1 ratio of insoluble to soluble fiber is typical. Although neither type is absorbed by the body, they have different properties when mixed with water, hence the designation between the two. However, due to overlap in function between the two types and disparities in measurements of each depending on the method used, the National Academy of Sciences has recommended that these terms “gradually be eliminated and replaced by specific beneficial physiological effects of a fiber”. Thus you may hear less about “soluble vs. insoluble fiber” in the future.
Soluble fiber is “soluble” in water. When mixed with water it forms a gel-like substance and swells. Soluble fiber has many benefits, including moderating blood glucose levels and lowering cholesterol. The scientific names for soluble fibers include pectins, gums, mucilages, and some hemicelluloses. Good sources of soluble fiber include oats and oatmeal, legumes (peas, beans, lentils), barley, fruits and vegetables (especially oranges, apples and carrots).
Insoluble fiber does not absorb or dissolve in water. It passes through our digestive system in close to its original form. Insoluble fiber offers many benefits to intestinal health, including a reduction in the risk and occurrence of hemorrhoids and constipation. The scientific names for insoluble fibers include cellulose, lignins, and also some other hemicelluloses. Most of insoluble fibers come from the bran layers of cereal grains.
Since dietary fiber is found only in plant products (i.e., nuts, whole grains, legumes, fruits and vegetables), these are essential to a healthy diet. The average American significantly falls short of the recommended amount of fiber, consuming on average only 12 – 17 grams per day. Ways to increase dietary fiber in your diet are:

  • Choose whole fruits and vegetables (with peels when possible) instead of juices.
  • Choose whole grain bread, cereals and pasta in place of their overly processed, refined counterparts.
  • Replace white flour (or at least a portion of it) with whole wheat flour in baked goods.
  • Replace white rice with brown rice.
  • Replace meat with beans or other legumes in meals. Lentils are perfect for this!

Try experimenting with the above tips. Slowly modify recipes until you attain a balance that is appetizing and tasteful to your taste buds. If you are not accustomed to a high-fiber diet, increasing fiber intake slowly will minimize any gas or bloating.

Our expert, Dr. Sharon E. Griffin, holds a B.S., M.S., and Ph.D. in the areas of exercise science/physiology. She also holds a second M.S. degree in Nutrition and is a licensed nutritionist and an ACSM certified health and fitness instructor.

Fiber is defined as “dietary material containing substances such as cellulose, lignin and pectin that are resistant to the action of digestive enzymes.” In other words, fiber is the substance found in plant foods (carbohydrates) that is not metabolized in the stomach and intestines, but rather passes through the gastrointestinal tract and makes up a part of stools.

The Dietary Guidelines for Americans states that adults should aim to get about 14 grams of total fiber each day for every 1,000 calories they eat. Unfortunately, it’s estimated that the average American consumes only about half of the recommended amount of dietary fiber on most days — due to eating lots of processed foods and refined grains, and not eating enough vegetables, fruits, legumes, and so on.

Why is it so important to to eat high-fiber foods? Insoluble fiber and soluble fiber each have unique benefits. Insoluble fiber is the type that helps to prevent constipation, cleans out the GI tract and even helps protect against serious problems like colorectal cancer.

What Is Insoluble Fiber?

There are two main types of dietary fiber:

  • Insoluble fiber, which does not dissolve in water and is left intact and undigested. Insoluble fiber can help to speed up the passage of food through the stomach and intestine. It also adds bulk to the stool and can help relieve constipation.
  • Soluble fiber, which dissolves in water, retains water, and forms a gel-like substance in the colon. It slows down digestion and nutrient absorption from the stomach and intestine.

Which foods are high in insoluble fiber? Some examples include: wheat bran, many types of vegetables, nuts and seeds, potatoes, fruit with skin, legumes and whole grains. There are actually several different types of insoluble fibers found in various foods, some of which include cellulose and lignin fibers.

4 Insoluble Fiber Benefits

1. Helps Prevent and Treat Constipation

One of insoluble fiber’s main jobs is to provide bulk in the intestines and to form stool, which leads to regular bowel movements and less constipation. Insoluble fiber does not dissolve in water like soluble fiber does, so it helps move material through the colon by increasing the bulk of stools.

2. Slows Down Absorption of Carbohydrates/Sugar

While fiber is found in carbohydrate foods, it doesn’t raise blood sugar levels; in fact it helps to slow down absorption of sugar from carbs, which is beneficial for stabilizing blood sugar.

A diet high in both types of fiber has other metabolic and health benefits too, such as protecting against obesity, cardiovascular disease, diabetes and metabolic syndrome.

3. Can Help With Appetite Control and Weight Management

Insoluble fiber found in high-fiber foods can help to make you feel full and keep you satisfied between meals. Insoluble fiber is also not technically a source of calories since it’s undigested and remains intact once eaten.

4. May Help Prevent GI Issues Like Diverticulosis and Hemorrhoids

Insoluble fiber helps to speed up the movement and processing of waste in the digestive system, which is why it’s useful for producing regular bowel movements. It may also help to prevent gastrointestinal blockages and straining that accompanies constipation, which can lead to problems like hemorrhoids.

Additionally, insoluble fiber helps to absorb and sweep out byproducts and carcinogens from the gut, lowering the chances of developing problems like SIBO, diverticulosis, etc.

4. May Help The Risk for Developing Colorectal Cancer

Studies have found that a higher total dietary fiber intake is associated with a significantly reduced risk of developing colorectal cancer. Two food groups that are high in insoluble fiber, whole cereal grains and whole pieces of fruit, have been shown to be especially protective against colon cancer formation.

Researchers believe that increased fiber intake may have cancer-fighting effects because it leads to a reduction in fecal carcinogens, reduced transit time and bacterial fermentation of fiber to short-chain fatty acids that have anticarcinogenic properties.

Is insoluble fiber good for IBS? This depends on the type of IBS someone has, their food personal “triggers” and a person’s specific symptoms, such as whether they tend to struggle with diarrhea or constipation more often.

Insoluble Fiber vs. Soluble Fiber

What is the difference between soluble and insoluble fiber? And do you need soluble or insoluble fiber, or both?

Many foods contain both soluble and insoluble fiber, and both types of fiber are important parts of a healthy diet, since both have been shown to help with appetite control, weight management, digestion, bowel movements, cholesterol balance, and so on.

The job of soluble fiber is to create a gel in the digestive system. It helps to bind with fatty acids, which is beneficial for maintaining healthy cholesterol levels and heart health. Soluble fiber also prolongs stomach emptying, which improves absorption of nutrients, provides satiety after eating and controls hunger. Soluble fiber can also regulate blood sugar levels, helping to prevent spikes in blood sugar and risk for problems like insulin resistance or diabetes.

Soluble fiber is found in foods like beans, legumes, oats, barley, berries and some vegetables — many of which also provide insoluble fiber.

Which is better for constipation, soluble or insoluble fiber?

Insoluble fiber is usually better for preventing constipation, although both types of fiber can be helpful for staying regular and free from digestive issues.

Insoluble fiber won’t ferment in the gut, but soluble fiber does ferment in the stomach, which can lead to some bloating and gas. Soluble fiber is digested by bacteria in the large intestine, which wind up releasing gas, sometimes which causes lots of flatulence when following a high-fiber diet. On the other hand, insoluble fiber remains intact while traveling through the GI tract, which helps with constipation and also tends to produces less gas.

This is why a very high-fiber diet may sometimes make IBS symptoms worse, although it depends on the person. Because each person reacts to various fiber-containing foods differently, it’s important to increase these foods in the diet gradually and also to drink plenty of water.

Maybe you’re wondering which type of fiber some of your favorite foods provide? Let’s take a look at a few examples:

  • Soluble fiber is found in foods such as oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables.
  • Are bananas soluble or insoluble fiber? A bananas has about 2–3 grams of fiber, most of which is insoluble fiber, although it contains both types.
  • Is rice soluble or insoluble fiber? A cup of brown rice has about 3–4 grams of fiber, almost all of which is insoluble.
  • Is spinach and lettuce soluble or insoluble fiber? Dark leafy greens are a great source of insoluble fiber. One cup of cooked spinach has about 6 grams of fiber, about 5 of which is insoluble fiber.

Top 25 Insoluble Fiber Foods

Below are some of the top insoluble fiber foods:

  1. Wheat bran and wheat germ
  2. Oat bran
  3. Beans, lentils and legumes of all kinds (kidney, black, garbanzo, edamame, split peas, lima, navy, white, etc.)
  4. Berries, including blackberries, blueberries, raspberries, strawberries, etc.
  5. Whole grains, especially barley, quinoa, sorghum, millet, amaranth, oatmeal and rye
  6. Turnips
  7. Green peas
  8. Okra
  9. Spinach
  10. Radishes
  11. Rutabaga
  12. Coconut (grated flakes or flour)
  13. Cocoa
  14. Apples with skin
  15. Pears with skin
  16. Flax seeds
  17. Avocado (Florida avocados have more than California avocados)
  18. Sunflower seeds
  19. Potatoes and sweet potatoes
  20. Dried apricots, prunes, raisins, dates and figs
  21. Almonds
  22. Walnuts
  23. 100% whole grain pasta and breads
  24. Passionfruit
  25. Popcorn

Insoluble Fiber Supplement Options and Dosage

How much insoluble fiber should you get each day? There isn’t currently a recommended daily intake of strictly insoluble fiber, but rather total fiber. The recommended intake for total fiber (soluble and insoluble combined) for adults 50 years and younger is 38 grams per day for men and 25 grams per day for women.

Adults over 50 may struggle with indigestion if they consume too much fiber, so around 30 grams for men and 20 to 25 grams for women per day is recommended, although eating more is not a bad thing if it doesn’t cause any issues.

Food labels usually show the total grams of fiber per serving, not just grams of insoluble fiber. This can make it difficult to know exactly how much of each type of fiber you’re consuming — however, the real goal should be to eat a variety of high-fiber foods, rather than focusing too much on the numbers.

While it’s ideal to get fiber from whole foods, fiber supplements are an option for people who can benefit from getting even more insoluble fiber, such as to help prevent constipation. In supplement form, fiber is extracted from natural sources, such as psyllium husk, in order to form a concentrated dose. Each fiber product has a different strength, so always follow directions carefully, starting with a lower dose and increasing if needed, while also drinking plenty of water.

If you’re experiencing diarrhea, keep in mind that you are better off with a soluble fiber supplement than one that contains insoluble fiber.


Is insoluble fiber ever bad for you? If you’re prone to diarrhea or loose stools, perhaps because you suffer from inflammatory bowel disease or IBS, then eating lots of insoluble fiber may potentially cause you discomfort and worsen symptoms. Use caution when increasing insoluble fiber intake if you have celiac disease or are gluten intolerant.

If you change your diet to include more foods high in insoluble fiber, and then notice loose stools or other GI issues, it’s a good idea to cut back on the amount of fiber you’re consuming and also mention this to your doctor in order to get their advice. You may also want to follow an elimination diet to pinpoint which types of high-fiber or FODMAP foods are problematic for you.

You also want to be sure to drink plenty of water when eating a high-fiber diet, since water helps fiber do its job properly.

Read Next: The Best Keto Fiber Foods and Why You Need Them

Ask the doctor: What are the differences between soluble and insoluble fiber?

Published: June, 2011

Q. I enjoyed your article on diverticular disease and the fiber content of various foods. However, could you make some distinctions between soluble and insoluble fiber? Some fiber makes me feel very bloated.

A. Dietary fiber, sometimes referred to as roughage, consists of the indigestible parts of plant foods. As you note, there are two kinds. Soluble fiber dissolves in water; insoluble does not. Both are important for healthy digestion; both can help prevent not only diverticulitis and constipation but also heart disease, obesity, and diabetes.

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Soluble and insoluble fiber: What is the difference?

The health benefits of dietary fiber are plentiful. Some of the main ones are listed here.

Soluble fiber

  • Lowering fat absorption and helping weight management: As a thick, spread-out gel, soluble fiber blocks fats that would otherwise be digested and absorbed.
  • Lowering cholesterol: Soluble fiber prevents some dietary cholesterol from being broken down and digested. Over time, soluble fiber can help lower cholesterol levels or the amount of free cholesterol in the blood.
  • Stabilizing blood sugar (glucose) levels: Just as it prevents fats from being absorbed, soluble fiber slows down the digestion rate of other nutrients, including carbohydrates. This means meals containing soluble fiber are less likely to cause sharp spikes in blood sugar levels and may prevent them.
  • Reducing the risk of cardiovascular disease: By lowering cholesterol levels, stabilizing blood sugars, and decreasing fat absorption, regularly eating soluble fiber may reduce the risk of heart disease and circulatory conditions.
  • Feeding healthy gut bacteria: Some soluble fiber-rich foods feed gut bacteria, as it is fermentable in the colon, and so it helps the bacteria thrive longer.

Insoluble fiber

  • Preventing constipation: As an indigestible material, insoluble fiber sits in the gastrointestinal tract, absorbing fluid and sticking to other byproducts of digestion that are ready to be formed into the stool. Its presence speeds up the movement and processing of waste, helping prevent gastrointestinal blockage and constipation or reduced bowel movements.
  • Lowering the risk of diverticular disease: By preventing constipation and intestinal blockages, insoluble fiber helps reduce the risk of developing small folds and hemorrhoids in the colon. It may also reduce the risk of colorectal cancer.

Soluble and insoluble fiber

  • Feeling satiated or full longer after meals: Soluble fiber slows down how quickly foods are digested, meaning most people feel full longer after fiber-rich meals. Insoluble fiber physically fills up space in the stomach and intestines, furthering the sensation of being full. These properties can help people manage their weight.
  • Helping lower disease risk: Due to fiber’s many health benefits, a high-fiber diet is associated with a lower risk of many diseases, including obesity, cardiovascular disease, diabetes, metabolic syndrome and others.

Good sources of fiber

Share on PinterestRegularly consuming good sources of fiber may help to stabilize cholesterol, blood sugar, and fat levels.

The nutrition label on food packaging lists the amount of dietary fiber found in each serving of the product.

If a product is marketed as being high in fiber or having associated health benefits, the amount of soluble and insoluble fiber in grams (g) per serving must be listed under the dietary fiber heading. Some manufacturers may also voluntarily give the soluble and insoluble content of the fiber element of the product.

According to the FDA, foods that are considered high in fiber contain at least 20 percent of the recommended daily value (DV) of dietary fiber per serving. Foods that have 5 percent or less are considered poor sources of dietary fiber.

Beans, peas, and whole grains are high in fiber. Some fruits and vegetables are also relatively high in fiber. Common foods that are good sources of fiber include:

A healthful diet contains a mix of both soluble and insoluble fiber. Soluble fibers are more common in foods, such as beans, peas, oats, barley, apples and citrus fruits. Good sources of insoluble fiber include beans, whole wheat or bran products, green beans, potatoes, cauliflowers, and nuts.

While many fiber supplements exist, most do not contain the additional vitamins and minerals, including vitamin B and iron, found in fiber-rich foods. Supplements may also not be, as easily or fully absorbed by the body.

August 2016 Issue

Fiber & Irritable Bowel Syndrome — Strategies
for Counseling Patients
By Judith C. Thalheimer, RD, LDN
Today’s Dietitian
Vol. 18 No. 8 P. 34

Fiber often triggers symptoms in IBS patients, but it’s also a commonly recommended treatment. Here’s how patients can eat a fiber-rich diet without worsening GI distress.

Between 25 and 45 million people in the United States suffer with irritable bowel syndrome (IBS).1 “IBS is a symptom-based condition defined by the presence of abdominal pain and altered bowel habits,” says William Chey, MD, a professor of gastroenterology at the University of Michigan. “Patients may have constipation, diarrhea, or both,” Chey says. The cause of this condition, which affects all age groups, is unknown, but symptoms may be a result of a disturbance in the way the gut, brain, and nervous system interact.1
“IBS is impacted by many factors,” says Torey Armul, MS, RDN, CSSD, a national spokesperson for the Academy of Nutrition and Dietetics, “including genetics, the gut microbiome, the immune system, gut-brain interaction, and diet.” Diet doesn’t cause IBS, but eating may aggravate symptoms as the gut overresponds to the stimulus of food.1

There are no diagnostic tests for IBS, and there’s no universal treatment.1 While a variety of medications are available that target specific symptoms like diarrhea or constipation, dietary changes are a common way to approach managing this condition. “Treatment for IBS is very individualized,” says Emily Haller, RDN, who counsels IBS patients at the University of Michigan Health System’s division of gastroenterology. According to the International Foundation for Functional Gastrointestinal Disorders (IFFGD), there’s no generalized dietary advice for treating IBS. Methods such as food diaries and elimination diets typically are used to identify trigger foods, and it’s recommended that patients avoid known gas-producing foods and attempt to address diarrhea and constipation through diet.1 Since constipation is a very common symptom in IBS, increasing fiber intake seems like a reasonable dietary recommendation. The IFFGD reports that adding fiber may help improve bowel function, especially in IBS with constipation (IBS-C).1

What Kind of Fiber Is Best?
“Fiber tolerance in IBS is very variable,” Haller says. “We know fiber is essential for good health, but as with anything, too much of a good thing can be bad.”
While people have different food triggers, Armul says that fibrous foods are one of the most common. “Fiber can certainly be a trigger for some clients,” Armul says, “but it can also be a great help to others. It varies from person to person.” The trick is that not all fibers are created equal. Some fibers are soluble, some insoluble; some fibers are fermentable, some aren’t. Understanding the difference is key to helping IBS patients find a diet that eases their symptoms.

Soluble vs Insoluble
Soluble fibers are dispersible in water; insoluble fibers are not.2 A review of 17 randomized controlled trials of fiber supplements in IBS patients found that supplementation with insoluble fiber, such as corn or wheat bran, didn’t improve IBS symptoms, but supplementation with soluble fiber, such as psyllium, ispaghula, or calcium polycarbophil, significantly improved symptoms.3 “Fiber creates bulk, but not all fibers are the same,” Chey says. “Insoluble fiber works for constipation by increasing biomass in the stool, and it may even create mechanical stimulation in the bowel, triggering motility. This can help ease constipation, but in people with underlying abnormalities in motor function and overly sensitive gut sensations characteristic of IBS, insoluble fiber can make symptoms worse.” But soluble fiber doesn’t have the same effect, Chey says. “Soluble fiber increases biomass, but not in the same purely mechanical way. It increases the water-holding capacity of the stool, softening it and making passage easier.” So, from a purely mechanical standpoint, insoluble fiber may be more likely to trigger IBS symptoms, while soluble fiber may actually bring some relief, particularly in IBS-C.
” different studies have shown that soluble fiber benefits constipation and overall symptoms in IBS patients,” Chey says.
Much of this research has looked at the fiber supplement psyllium. “This special kind of soluble fiber has a lot of good research around it,” Armul says. A three-month randomized, placebo-controlled trial of 275 patients with IBS found that supplementation with 10 g psyllium per day improved symptoms of abdominal pain or discomfort in the first two months of supplementation and also improved symptom severity after three months’ supplementation.4
However, getting enough soluble fiber without supplementation can be challenging. “Clients don’t typically understand the difference between the two types of fiber,” Armul says, “and most fibrous foods have both soluble and insoluble.” The soluble fibers (β-glucans, gums, mucilages, and some pectins and hemicelluloses) are commonly found in oats, barley, legumes, fruits (particularly berries), and seeds. The insoluble fiber cellulose is found in all plants, since cellulose is a component of plant cell walls.2 So while legumes and seeds, for example, are good sources of soluble fiber, they also top the list for insoluble cellulose (along with root vegetables, brans, and plants in the cabbage family).1,2 Therefore, increasing dietary soluble fiber also may increase intake of insoluble fiber, which, although it helps with constipation, could mechanically trigger IBS symptoms. And there’s another concern with increasing soluble fiber intake: Soluble fibers are more readily fermented than insoluble fibers, and fermentation in the colon has emerged as a key trigger in IBS.
Fermentable vs Nonfermentable
“Fermentability is a big piece in the IBS puzzle,” Chey says. “When the bacteria in the colon break down fermentable fiber, they produce hydrogen, methane, and carbon dioxide. These gases cause luminal distention, stretching the intestines and colon. This can be uncomfortable for anyone, but particularly so for people with IBS whose bowels can be overly sensitive to a variety of stimuli such as food or stress.” But increased gassiness isn’t the only problem with fermentable fiber in IBS sufferers. “When the bacteria break down the fermentable fiber, they don’t just produce gas; they also create short-chain fatty acids. These acids lower the pH of the colonic environment,” Chey says. “The gut microbiome is highly influenced by pH, so that could play a role, but bile acids are also highly dependent on pH. Emerging research is showing that bile acids may play an important role in IBS. People with IBS with diarrhea have higher levels of primary bile acids in their colon, and people with IBS with constipation have lower levels. The presence of bile acids seems to affect how quickly or slowly things move through the colon.” Soluble fibers like pectins, β-glucans, and guar gum (found in oats, barley, and many fruits and vegetables) are readily fermented; insoluble cellulose, and the insoluble lignins from woody plants and seeds, are not.2

The fact that fermentation by gut microbiota is related to IBS symptoms has lead to the emergence of a diet low in fermentable foods as an IBS treatment. “The traditional approach to treating IBS was to recommend more frequent smaller meals, and less insoluble fiber, fat, caffeine, and gas-producing foods,” Armul says. “A newer approach is a diet low in FODMAPs.” FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, all of which are short-chain carbohydrates fermented by gut bacteria. Numerous observational and randomized-controlled studies support the efficacy of the low-FODMAP diet in patients with IBS.5

Fiber on a Low-FODMAP Diet
Many fiber-rich foods must be omitted on a low-FODMAP diet, since fiber often is fermentable. “Getting enough fiber on a low-FODMAP diet can be hard because good fiber sources like whole-grain breads and most legumes are excluded,” Haller says. “If other low-FODMAP, high-fiber foods are not incorporated, we can see fiber intake plummet on this diet, which is not good.”
One key to incorporating fiber into a low-FODMAP diet is to control portion sizes. Smaller amounts of trigger foods may not elicit symptoms. “We use a bucket analogy,” Haller says. “The bucket represents a person’s unique capacity to tolerate FODMAPs. Since FODMAPs can have a gradual and cumulative effect, a person’s bucket can ‘fill up’ with high-FODMAP foods. If a person with FODMAP sensitivities exceeds their limit and ‘fills their bucket,’ they will experience symptoms. Sometimes just one type of FODMAP contributes to filling the bucket (just lactose, or just fructose, for example). Sometimes it’s a cumulative effect: too many short-chain fermentable carbohydrates from a variety of sources, and your bucket overflows.”

Fortunately, there are high-fiber foods that aren’t high in FODMAPs. “Quinoa is a high-fiber, low-FODMAP source,” Haller says. “So are oats. One-half cup of oatmeal or two tablespoons of oat bran per sitting are considered low FODMAP.” While beans and legumes are generally high FODMAP, Haller says that one-half cup of lentils and one-quarter cup of chickpeas may be tolerated. The galacto-oligosaccharides in these pulses are water soluble, so soaking and discarding the liquid before using is essential.6 Haller recommends sticking to canned chickpeas and lentils and rinsing and draining well. “It’s thought that the FODMAPs leach into the canning liquid over time, so rinsing canned chickpeas or lentils will wash away a lot of the FODMAPs,” she says. Nuts and seeds are great low-FODMAP sources of fiber. “All nuts except cashews and pistachios are low FODMAP,” Haller says, “but we recommend small handfuls. For example, 20 almonds are on the high-FODMAP list, but you won’t get too many FODMAPs if you only eat 10 to 15. And all seeds, including sunflower, chia, and flax, are fine in appropriate quantities as well.” Haller recommends adding ground flax or chia seeds to food. “This is another great way to add soluble fiber without changing the taste or volume of the food,” she says. “If you’re working with someone who’s a picky eater or doesn’t want to make changes, tricks like that can up the fiber in their diet.” Haller recommends a website developed by the University of Michigan division of gastroenterology and hepatology (myginutrition.com) and The Monash University Low FODMAP Diet app for information on low-FODMAP foods and portion sizes.

Many fruits and vegetables are low in FODMAPs as well, and some of these also are high in soluble fiber. “Oranges and bananas are low-FODMAP foods that are high in soluble fiber, as are passion fruit and guava if those fruits are familiar to your patient population. Berries like blueberries and strawberries, melons like honeydew and cantaloupe, and grapes are also low FODMAP, and, although they aren’t considered high in soluble fiber, they do have some, and it all adds up,” Haller says. “One-eighth of an avocado at a sitting also is a moderate-FODMAP food that delivers great fiber as well as healthful fats.” As far as vegetables are concerned, Brussels sprouts, carrots, eggplant, okra, sweet and white potatoes, and turnips are all low-FODMAP foods with great soluble fiber content.7,8 Sticking to appropriate portion sizes is essential on a low-FODMAP diet. A tablespoon of ground flaxseeds or one-quarter cup butternut squash are considered low FODMAP, for example, but any more than that at one sitting delivers too much fermentable fiber.8
Putting It Into Practice
The IFFGD suggests IBS patients strive for the same 20 g to 35 g of fiber recommended for the general population. Increasing fiber can help improve bowel function and decrease symptom severity, even though certain high-fiber foods like bran may increase gas and bloating.1 Emphasizing soluble fiber may be particularly helpful. According to the Linus Pauling Institute, the results of randomized controlled trials suggest that increasing soluble fiber intake gradually to 12 g to 30 g per day may be beneficial for patients with IBS-C, although fiber supplements could exacerbate symptoms in people whose main symptom is diarrhea.2 It’s essential to increase fiber intake gradually, as adding too much fiber too quickly can make things worse.1,2 If targets can’t be reached with dietary intake, fiber supplements (especially psyllium supplements) may be helpful.1,2
However, incorporating fiber into the diet of people with IBS should be done in concert with other treatment advice, such as keeping meals small. Since fiber isn’t the only IBS symptom trigger, and because the effect of fiber varies from person to person, elimination diets and food diaries may be useful for identifying particular trigger foods. Besides FODMAPs, caffeine, alcohol, high-fat meals, and sugary foods are known to be common triggers.1 “Recording types of food, size of meals, meal frequency, and how you felt throughout the rest of the day helps find links between food and symptoms,” Armul says. “Use that information to inform an elimination diet.”

“Registered dietitian nutritionists are best suited to assess the overall diet and determine what changes need to be made,” Haller says. “I work to gradually increase patients’ fiber intake, choosing low-FODMAP grains, starches, fruits, and vegetables.” While she agrees that the balance of soluble and insoluble fiber is important, Haller doesn’t recommend pointing that out to a patient. “They have enough to worry about, especially during the FODMAP elimination phase,” Haller says. “We as nutrition professionals should be familiar with low-FODMAP, high–soluble fiber foods and work that information into our plans and suggestions for patients. Sample menus, lists, and ideas are really helpful. We’ve created meal and snack suggestions that provide a balance of nutrients, including fiber.”

Fiber can trigger IBS symptoms by setting off an overreaction to mechanical stimuli or by providing fodder for bacterial fermentation. But fiber, and especially soluble fiber, has been shown to ease overall symptoms and constipation in IBS sufferers. By slowly increasing fiber intake with appropriate portions of high-fiber (and particularly high soluble fiber) foods that also are low in fermentable carbohydrates (ie, FODMAPs), patients with IBS can find relief—along with a more healthful overall dietary pattern.
— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, a community educator, and the principal of JTRD Nutrition Education Services.

3. Bijkerk CJ, Muris JW, Knottnerus JA, Hoes AW, de Wit NJ. Systematic review: the role of different types of fibre in the treatment of irritable bowel syndrome. Aliment Pharmacol Ther. 2004;19(3):245-251.

Does Fiber Help Diarrhea or Make It Worse? – Explained


Insoluble fiber, as you can imagine, is not soluble in water. This type of fiber goes through the G.I. tract unaffected and ends up in the colon, where it then can be fermented by the healthy bacteria living there.

This type of fiber, because it does not absorb water, is the kind you would want to avoid it if you have diarrhea.

  • Speeds up bowel movement transit time
  • Helps balance pH level in the GI tract

Some sources of insoluble fiber include…

  • Cellulose – Found in grains, seeds, nuts, fruit & vegetable skins
  • Lignin – Found in grain, nuts, seeds, fruit & vegetable skins


And then there is soluble fiber, which is the type of fiber that is soluble in water. This type of fiber also goes through the G.I. tract and is fermented by bacteria, but there is a key difference… It absorbs water.

Soluble fiber absorbs water in the intestines and turns into a gelatinous substance, adding bulk and helping firm up loose stool.

  • Absorbs water and firms up stool
  • Reduces transit time of bowel movements
  • Lowers cholesterol and regulates blood sugar level

Some good sources of this type of fiber include…

  • Pectin – Commonly found in fruits
  • Resistant Starch – Found in unripe bananas and oats

Soluble Fiber Seems to Be Good All-Around, While Insoluble Fiber Isn’t Recommended for Those With Diarrhea

Fiber does not get digested and because of this can cause an osmotic effect, where the undigested particles attract more water into the colon, which is great for constipation but not so great for diarrhea.

The reason soluble fiber can help with both is because, not only does it attract water into the colon, but it also absorbs water, which leads to a healthy balance of stool overall. Whereas insoluble fiber just attracts more water and does not absorb, leading to looser and more watery stool.

In a 2015 study 87 patients who had IBS and were prone to developing diarrhea received 24 g of pectin (soluble fiber) for a 6 week treatment. The results were positive and that the patients’symptoms had reduced.

On the flip-side, a separate 2014 study conducted on 80 patients with constipation experimented by giving them 24 g of pectin per day for 4 weeks. The results here were that it also alleviates symptoms of constipation.

Pretty interesting, but it makes sense.

As far as insoluble fiber goes, it is only shown to help treat constipation, but have negative effects when it comes to diarrhea if consumed in too high amounts.

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