Fiber 101 – The Basics
About the Types of Fiber and Their Varieties
What is dietary fiber?
Dietary fiber is sometimes called “roughage” and includes parts of plant foods that the body cannot digest or absorb. Other food components, like fats, proteins, and carbohydrates are broken down in the digestive process and absorbed into the blood stream. Fiber, on the other hand, is a type of carbohydrate, but it cannot be digested by the human body. Instead, it travels through the stomach and intestinal tract providing food for our intestinal bacteria.
Researchers have found that increasing fiber intake over a mere two-week period significantly altered subjects’ gut microbiome. Specific species of bacteria that break down fiber were increased. When such bacteria digest fiber, they release short-chain fatty acids (SCFAs). SCFAs then become a source of fuel for the cells of the colon and are also used in cell signaling. Some SCFAs also have anti-inflammatory properties, and may influence insulin sensitivity and body weight.
Fiber has two general classifications: soluble and insoluble. Each type has its own health benefits in addition to providing food for the beneficial bacteria that live in the intestines. The amount and types of fiber found in foods varies, but it is only found in plant foods. Whole, intact plant foods (such as vegetables, fruits, whole grains, legumes, beans, peas, nuts and seeds) will provide dietary fiber, whereas processed plant foods (such as white flour) will provide little to none. Animal-based foods do not provide dietary fiber.
What is insoluble fiber?
Insoluble fiber remains pretty much unchanged as it moves through the digestive tract. Humans do not have the enzymes necessary to break down insoluble fiber. Since it is not broken down during digestion, insoluble fiber does not provide calories in the diet. In the intestines, it absorbs fluid and binds to other nearby materials, forming stool. This type of fiber helps to move the contents of the intestines forward, warding off constipation and promoting bowel movements. Whole grains, nuts, beans, and vegetables are good sources of insoluble fiber.
Types of Insoluble Fiber and Their Food Sources
Cellulose. Cellulose is the main fibrous component of plant cell walls. Many vegetables, such as broccoli, cabbage, kale, and cauliflower are rich in cellulose. Legumes, nuts, and bran from grains are also rich in cellulose. Cellulose passes through the gastrointestinal tract relatively intact, binding to food components moving them forward along the tract. Cellulose also helps to keep the digestive system healthy by feeding beneficial gut bacteria and supporting their colonies.
Hemicellulose. Hemicellulose is a type of dietary fiber that can be soluble or insoluble. It is a nondigestible fiber found in plant cell walls that can absorb and retain water in the gut. Despite the fact that it absorbs water, it has little effect on stool size. Hemicellulose can be digested by our gut bacteria. It is sometimes used in foods as an added fiber, thickener, emulsifier, or stabilizer. Green beans are high in hemicellulose. They are also found in cereal grains.
Lignin. Lignin is another type of insoluble fiber that is part of the plant cell wall structure. Lignin provides rigidity to plants. It is also found in some seeds. Lignin is not broken down by human enzymes, and is also poorly digested by our gut bacteria. It absorbs water in the gut, and gives bulk to stool. Lignin can be found in whole grains (such as wheat and corn bran), legumes, vegetables (like green beans, carrots, horseradish, cauliflower, peas, and zucchini), fruits (like avocado, unripe bananas, peaches, and apples), and nuts and seeds (especially flaxseed and Brazil nuts). It is also found in edible seeds, such as those found in berries and tomatoes.
What is soluble fiber?
Soluble fiber is the type of plant fiber that absorbs water and fluids in the intestinal tract, forming a gel-like substance. The gel moves through the digestive tract and is digested by bacteria in the large intestine. The remainder is excreted in feces. The bacteria release gases as they digest the gel, which is what may cause some people to experience bloating when ingesting fiber-rich foods. Good sources of soluble fiber include oats, peas, beans, apples, citrus fruits, carrots, barley, and psyllium.
Types of Soluble Fiber and Their Food Sources
Inulin. Inulin helps to keep you feeling full for longer since it slows digestion. This type of fiber also takes longer to absorb, which helps to prevent blood sugar spikes after a meal. Inulin is not digested in the stomach nor absorbed in the intestinal tract. Instead, it promotes the growth and support of beneficial bacteria in the gastrointestinal tract. Inulin is found in chicory root, grains such as wheat, barley, and rye, and fruits and vegetables such as bananas, garlic, onions, and asparagus. Inulin is readily fermented by our gut bacteria. This property may give some people GI distress when eating inulin-rich foods.
Gums and Mucilages. Gums are complex carbohydrates that are soluble in water, forming gels and mucilages. Mucilages are a type of thick, viscous gum in plant roots and seeds. The gelling characteristics of gums and mucilages allows them to be used in many food products as thickening agents, and additives for moisture retention, emulsification, and stabilization. Commonly used food sources of gums and mucilages include guar bean, locust bean (carob), tamarind, seaweed (agar and carrageenan), fenugreek, aloe vera, cactus, and flax.
Pectin. Pectin is a type of soluble fiber that helps reduce the glycemic response in the body by slowing glucose absorption after a meal. Like other soluble fibers, pectin helps to feed our gut bacteria. It also helps to keep cholesterol down by flushing fatty acids out of the body. Pectins can be found in abundance in foods like apples, strawberries, citrus fruits, carrots, and potatoes. Legumes and nuts also contain pectins, but in smaller amounts.
Beta-Glucan. Beta-glucan forms a gel in the intestinal tract that is fermentable by gut bacteria. It is considered to be a prebiotic, providing food for helpful bacteria. Beta-glucan may also be helpful in increasing satiety and managing blood sugar levels, thanks to the fact that it has a slow transit time in the stomach and intestines. Beta-glucan is plentiful in oats, barley, shiitake mushrooms, and reishi mushrooms.
Psyllium. This soluble fiber is the active ingredient in products like Metamucil. It is known for softening stool, helping it to pass out of the body. Psyllium also forms a gel that binds to cholesterol in the digestive tract, preventing its absorption into the body. Psyllium is also a prebiotic, feeding friendly bacteria in the gut. Psyllium is derived from a shrub-like herb (Plantago psyllium), grown mainly in India. It will not be found in any specific food source. However, it is often used in fiber supplements, both in powders and pills. Researchers have studied the effects of psyllium and found that it may help to reduce the risk of cancer, diabetes, heart disease, diverticulosis, high blood pressure, and obesity. It may also improve diarrhea, constipation, gas, irritable bowel syndrome, inflammatory bowel disease, and high cholesterol. However, since it is a soluble fiber, those benefits may also be obtained from ample food sources of soluble fiber in the diet.
Resistant Starch. Resistant starch is a type of carbohydrate that resists digestion in the small intestine. It travels pretty much intact until it reaches the large intestine. There, friendly bacteria feed on the undigested starch, so it is often referred to as a prebiotic, feeding the good bacteria in the gut. Resistant starch also helps to control the appetite and reduce blood sugar spikes after a meal. Since resistant starch is not broken down during digestion, it does not release glucose, so it cannot raise blood sugar levels. It can also help to increase our feeling of fullness after a meal, and be used to treat and prevent constipation. It also helps to lower cholesterol, improve digestive health, and lowers the risk of colon cancer. Resistant starch is fermented slowly in the gut, so it causes less gas than other types of fiber. Legumes, peas, beans, lentils (with white beans and lentils being especially high in resistant starch), oats, barley, plantains, and unripe bananas are excellent sources of resistant starch.
How Much Fiber Do You Need?
The Institute of Medicine provides the following recommendations for adults:
* Men age 50 or younger should get 38 grams of fiber.
* Men age 51 and above should get 30 grams of fiber.
* Women age 50 or younger should get 25 grams of fiber.
* Women age 51 and above should get 21 grams of fiber.
Health organizations recommend that both children and adults should get about 14 grams of fiber for every 1,000 calories they eat. That usually means that children ages 1 to 3 years should get about 10 grams of fiber a day. Children ages 4 to 8 years should eat about 25 grams of fiber a day.
Research has shown that the amount of fiber typically consumed in the Western diet is merely between 12 and 14 grams a day. Less than 5 percent of Americans consume the recommended amount of fiber. There is ample scientific evidence that indicates that dietary fiber affects normal physiologic function and the onset of chronic diseases and their progression. Therefore, increasing fiber intake offers a prime opportunity to improve our health and ward of serious chronic diseases.
Despite the above recommendations, there is scientific evidence that ancient man consumed as much as 100 grams of fiber a day! Of course, that was from unprocessed plant foods, primarily from fruits and vegetables. Keeping this in mind, we certainly have plenty of leeway for increasing our daily fiber intake with as many fruits, vegetables, nuts, seeds, and whole grains that we can manage to eat.
Benefits of a High Fiber Diet
To keep things easy and get the most benefit from your diet, focus on simple, whole, unprocessed plant foods. Work as many fruits, vegetables, and whole grains as you can into your day without worry about how much soluble vs insoluble fiber you’re eating. Most plant foods have a combination of both in different ratios. What’s important when trying to reap the health benefits from fiber in foods is looking at the total picture and focusing on increasing your overall fiber intake through whole, unadulterated foods. The following are some benefits from enjoying a high fiber diet.
Prevents Constipation. Dietary fiber promotes the movement of the contents of the digestive tract forward. It increases stool weight and size, so it helps prevent constipation and irregular bowel movements. If you have loose, watery stools, fiber may help to solidify the stool because it absorbs water and adds bulk to the stool.
Helps Maintain Bowel Health. A high fiber diet helps to reduce your risk of developing hemorrhoids and small pouches in the colon (diverticular disease).
Aids in Weight Management. High fiber foods tend to be more filling than low fiber foods, so you’re less likely to overeat and more likely to feel full longer. Fiber takes up space in the stomach and intestines, which helps us to feel full after a meal, which in turn helps us to manage our weight. We’re less likely to overeat when the meal has had ample fiber. Furthermore, high fiber foods tend to be lower in calories than low fiber, processed foods or animal products. So, loading up on plant foods can help us to manage weight in more ways than one!
Cancer Prevention. Increased fiber intake may help to reduce the risk of developing colon cancer. The American Institute for Cancer Research reports show that for each 10-gram increase in dietary fiber, the risk of colorectal cancer is lowered by 7 percent. There is also scientific evidence that indicates that a high-fiber diet may also be protective against breast, ovary, and endometrial, as well as gastrointestinal cancer.
Helps Prevent Heart Disease and More. Soluble fiber is especially important because it can help to reduce the risk of heart disease and stroke by reducing blood pressure, improving our blood lipid profiles, and reducing inflammation.
Soluble fiber is known to help lower blood cholesterol levels. In the digestive tract, soluble fiber binds with bile acids, carrying them out of the body in the feces. Bile acids are made in the liver from cholesterol, and exported to the gallbladder where it is stored until it is needed. When dietary fat leaves the stomach and enters the duodenum, the first section of the small intestine, the gallbladder receives the signal to release bile into the duodenum to emulsify the fat that just left the stomach. This is important because the emulsification process allows the fat to be disbursed among the watery fluids in the intestines. This improves the breakdown of foods and the absorption of nutrients. Without bile, fatty substances may tend to “float” toward the top of the watery fluids in the intestines, hindering the proper breakdown of foods and absorption of their nutrients.
When soluble fiber binds to bile acids in the digestive tract, it carries the bile out of the body through the feces. This action forces the liver to make fresh bile from cholesterol. This process helps to lower blood cholesterol, thereby reducing the risk of heart disease and atherosclerosis, while improving our blood lipid profiles and reducing inflammation.
If our diet does not contain enough soluble fiber to carry the bile out of the body, the unbound bile acids will be reabsorbed into the blood from the intestines, and carried back to the liver to be used again. When this happens, the bile becomes more concentrated with toxins, which in turn, can lead to inflammatory diseases such as gallbladder disease, intestinal inflammation, and even skin conditions like acne, eczema, and psoriasis.
Also, research suggests that increasing your dietary fiber intake is associated with a reduced risk of dying from cardiovascular disease and all cancers.
Helps Control Blood Sugar Levels. In those with diabetes, fiber (especially soluble fiber) can slow the absorption of sugar helping to improve blood sugar levels. A healthy diet with ample fiber may also reduce the risk of developing Type 2 diabetes.
Best Sources of Fiber
Categories of foods that can boost your fiber intake include:
* Beans, peas, and other legumes
* Nuts and seeds
Refined or processed foods are lower in fiber than the fresh foods they were made from. This includes canned fruits and vegetables, pulp-free juices, white breads and pastas, and cereals made with refined grains. The refining process of grains removes the bran, or outer coat, from the grain. This lowers the fiber content of the grain. Along with the removal of the bran, the germ layer is usually removed too. The germ is where many vitamins and minerals associated with the whole grain are found. When these two components are removed from grains, the inner starchy endosperm that remains is what is processed into white flour or sold as the refined grain. Many times, the refined grains are enriched where some (but not all) of the nutrients that were stripped away, are added back. However, the fiber content is not added back in the enrichment process. So, the only way to get the full nutritional value of a grain, including the fiber content, is to use only the whole grain.
Fiber Supplements. Metamucil, Citrucel, and Fibercon are examples of fiber supplements. Some people may need such supplements if they suffer from bowel issues and dietary changes aren’t enough to fix the problem. It is advisable to check with your healthcare provider before starting such supplements.
Some specialty foods have fiber added to them. Some cereals, granola bars, yogurt, and ice creams are examples. The added fiber is usually inulin or chicory root. Before adding such foods to your diet, it is important to note that some people complain of gas and bloating after eating foods with these added fibers.
Generally speaking, whole foods are a better option than fiber supplements. Whole foods naturally provide a blend of soluble and insoluble fibers, along with vitamins, minerals, antioxidants, and other phytonutrients that the fiber supplements don’t have. Consuming whole foods as nature provides, offers complementary nutrients that often have a synergistic effect on the body. In other words, their combined effect is often greater than if the individual components were taken separately. Furthermore, foods have many yet-to-be-discovered components that we will never find in isolated supplements. So, it is best to choose whole foods as nature provides, whenever possible.
Tips for Adding More Fiber to Your Diet
There are a LOT of ways to add more fiber to your diet. The following are just a few points that may help along the way. Try what works best for you for starters. Add more as you’re able to and build from there. Take it slow to allow your body (and gut microbiome) time to adjust to the new foods and added fiber intake. This approach will help you to avoid discomfort, gas and bloating, and possibly even diarrhea.
* Examine your usual breakfast. Are you eating low-fiber foods such as processed cereals, pastries, white bread, juice (pulp-free), and/or an array of no-fiber foods like animal products such as bacon, eggs, sausage, milk, cheese, and even yogurt? Try substituting some of those foods with high-fiber options, like oatmeal or a whole-grain cereal and fresh fruit instead of fruit juice.
* How about your snacks? Are you snacking on doughnuts, pastries, cake, cookies, candy, and a sugary beverage or coffee? Try replacing the calorie and fat-laden, low-fiber pastries with fresh fruit and maybe a cookie made simply from whole oats, bananas, a touch of cinnamon, and raisins. How about snacking on fresh vegetables and a small handful of nuts? Or enjoy a snack of vegetables dipped in hummus. Replace sugary beverages or coffee with a tall glass of lemon water or an herbal tea, sweetened with honey, if desired.
* Make it a routine to add a tossed green salad to either lunch or supper each day. Be mindful of what ingredients are added to the salad. Load it up with lettuce and other assorted fresh greens, and top it with assorted chopped fresh (or even lightly cooked) vegetables. Leave off the croutons, shredded cheese, and added meats. Use the simplest dressing you can tolerate. Even just a squeeze of fresh lemon, lime, or orange juice is extremely healthful, although it may take some time to get used to it if you’re accustomed to fat and/or sugar-laden dressings. Studies have shown that those who eat a salad or a small serving of vegetable soup before a meal not only increases fiber intake, but has been linked to eating fewer calories during the meal.
* Once you get used to enjoying a side salad every day, try increasing that to one meal a day consisting of a very large green salad. As detailed above, load it up with your favorite vegetables, and even fruit if you want. Add some cooked beans, peas or lentils for additional protein if you want. Top it with a simple dressing and enjoy! Work up to making this a daily routine and your health will benefit in many ways in addition to getting a nice fiber boost.
* Lean on legumes. Beans, peas, and lentils are wonderful sources of fiber and added protein. Add legumes of choice to soups or a large meal salad.
* At least once a week, choose a meal of beans, peas, or lentils served over a whole grain of your choice. Brown rice, millet, quinoa, amaranth, or even steel cut oats would all work well. Serve it with a large portion of any vegetable of choice and you’ll have a healthy, filling, fiber-filled meal.
* Try a wrap with cooked beans (pinto or black beans would be tasty), lots of fresh vegetables including leafy greens, served on a whole grain tortilla. Top your filling with salsa before rolling it up, and enjoy!
* Make it a point to load up on fruits and vegetables every day. Strive to eat at least five servings a day. As you get used to boosting your fruit and vegetable intake, try to slowly increase your servings to as many as ten servings a day. To do this, you may find that you need to cut back on other foods (the stomach can only hold so much!). Examine the foods you’re eating and identify the least healthful, most processed foods that you’re eating and strive to replace them with more healthful options. That will not only boost your fiber intake, but also will increase your vitamin, mineral, antioxidant, and other phytonutrient intake as well. Your health can only benefit from such a transition.
* Make desserts count. Instead of indulging in cheesecake, ice cream, traditional cookies, or chocolate cake for dessert, opt for a piece of fresh fruit. If you yearn for ice cream, try blending a frozen banana and making “Banana Nice Cream.” If desired, it can be flavored with a little cocoa powder, cinnamon, added fruit, vanilla extract, or even a little milk of choice for smoothness and flavor.
* Enjoy fruit as a snack. Apples, pears, and berries are examples of high-fiber fruits that make a quick and easy snack. They are easy to transport also, and can be included in a packed lunch, tucked in the car when traveling, or stashed in a backpack when hiking.
* When shopping, always opt for whole grains rather than refined or processed foods made with refined flour. When at home, you’ll be reaching in the pantry for foods to prepare. If you don’t have it, you can’t prepare it. Make it a priority to buy only foods that you know will benefit your health.
* Try adding chia seeds to overnight oats, your favorite smoothie, or pudding. Use chia seeds as an egg replacer in some dishes like quick breads, pancakes, and puddings. Combine 1 tablespoon of chia seeds with 2-1/2 to 3 tablespoons of hot water in a small bowl. Allow it to rest about 5 minutes to thicken. Chia seeds provide omega-3 fatty acids, protein, vitamins, minerals, and about 10 grams of fiber per ounce. They are packed with nutritional value, so it pays to include them in your diet any way you can.
* Flax seeds are another high fiber seed to consider. They provide about 2 grams of fiber per tablespoon. Be sure to enjoy them ground rather than whole since they are very hard to break down in the digestive process. Add ground flax seeds to oatmeal, a smoothie, pudding, granola, breading, and baked goods. Mix it into applesauce as a thickener. Use it in recipes in place of wheat bran, wheat germ, or oat bran. Soups and stews may also be thickened with ground flax seeds. Sprinkle it on nut butter. Add it to homemade crackers. Sprinkle a little ground flax on salads. Add it to sauces as a thickener. Add a little ground flax to your favorite hummus (try 1 to 2 teaspoons of ground flax seed to 1 cup of hummus). Ground flax seed can be used as an egg replacer, just like chia seeds. Follow the same directions as detailed above.
* Replace refined fruit juices with whole fruit. Whole fruit has a lot more nutritional value to offer than refined fruit juices. And, the whole fruit will also quench thirst at the same time. For example, enjoying a juicy, ripe pear can satisfy your thirst, help fill a void in the tummy, and provide plenty of vitamins, minerals, and fiber all at once.
* Avocados are very nutritious fruits, and there are many ways to add them to your day. Their creamy flesh is rich in vitamins, minerals, monounsaturated fatty acids, and fiber too. One half of an avocado delivers 5 grams of fiber. Furthermore, avocados have been linked to a reduced risk of metabolic syndrome, a condition that increases your chances of heart disease, stroke, and Type 2 diabetes.
* When possible, try to enjoy fruits and vegetables with the peel left on. There is often a lot of nutritional value and fiber associated with the peels, and most of that gets tossed in the trash when the peel is removed and not eaten.
* Try to include some type of fiber-rich food (or foods) at each meal. Whole grains, fresh fruits, vegetables (cooked or raw), cooked beans, peas, or lentils, and nuts or seeds can be included with meals and snacks throughout the day. Enjoy a variety of fiber-rich foods as often as you can until it becomes habit and you no longer have to think about it. That will help you to develop life-long habit of eating fiber-rich foods. Your body will thank you!
* Snack on fresh veggies with your favorite hummus dip for a fiber-rich snack.
* Try whole grain pasta instead of pasta made with refined flour. Also, there are some new types of pasta available that were made from legumes and no grain at all. They are naturally high in fiber and are at least worth a try to see if they work well for you.
Adjusting to Increased Fiber Intake
Suddenly switching from a low-fiber diet to one with a lot of fiber too quickly can promote intestinal gas, bloating and cramping, and maybe even diarrhea. Increase your fiber intake slowly over a few weeks or even longer. This allows you time to adjust to the change in food choices and also gives your intestinal bacteria time to adjust to the change as well. This will also give your intestinal tract time to adjust to the increased fiber, especially if you’re going from being chronically constipated to slowly establishing regular bowel movements.
Also, it is VERY important to drink plenty of water throughout the day. Fiber works best when it absorbs water in the stomach and intestines. This makes your stool softer and bulky, promoting regular bowel movements. Herbal teas and fresh vegetable juices are also excellent additions, but should not replace adequate water intake.
It’s helpful to make small, manageable changes at a time. If they work well for you, maintain those changes, then find another change you can make and add it to your regimen. Then maintain both of those changes and find yet another. Repeat the process as often as you feel it is necessary to improve your diet and achieve your goals. This process allows you to gradually change your dietary habits as your body and gut microbiome adjust. Make it a point to maintain those changes until they become second-nature. Such changes should be considered to be lifelong adjustments and not temporary for the sake of achieving a goal within some short period of time, then reverting back to prior habits. That’s a recipe for failure. It’s best to think in terms of lifelong changes that you can maintain long-term. Over time, you’ll be so accustomed to your new habits that you won’t yearn for the foods you left behind and you won’t have to give much thought to what you’re doing at the grocery store or in the kitchen.
Fiber is an important component of whole plant foods. It is critical to consume plenty of fiber-rich foods to prevent constipation and bowel issues, along with many other serious diseases and conditions. Chronic constipation (provided you have no otherwise obstructive bowel issues) is a clear sign you need more fiber in your diet. Increasing your intake of whole plant foods is a simple solution to the problem. When you’re not used to eating a lot of such foods, it is helpful to increase your intake slowly over time, especially when increasing the amounts of legumes, beans, and peas in your diet. Gradually increasing such foods will help minimize the risk of gas, bloating, or diarrhea that may occur. Give yourself time to work your way up to about ten servings a day of fruits and vegetables. Eventually, your bowel habits will stabilize and constipation will be a thing of the past. You’ll also greatly increase your intake of vitamins, minerals, and important antioxidants and other phytonutrients in the process. Your body will thank you!
Whitney, Ellis and Sharon Rady Rolfes. (2011) Understanding Nutrition. 12th Edition. Belmont, CA: Wadsworth, Cengage Learning.
Julia W. Klee (Judi) began her journey enjoying “all things food” in elementary school when she started preparing meals for her family. That love of food blossomed into a quest to learn more and more about health and wellness as related to nutrition. She went on to earn a BS Degree in Food and Nutrition, then an MS Degree in Nutrition. She has taught nutrition and related courses at the college level to pre-nursing and exercise science students. Her hunger to learn didn’t stop upon graduation from college. She continues to research on a regular basis about nutrition as it relates to health. Her hope is to help as many people as possible to enjoy foods that promote health and wellness.