Dietary fiber is a component of plant-derived food that cannot be completely digested by the body. Fiber rich foods include legumes, whole grains and cereals, vegetables in general, fruits, nuts and seeds. A high intake of dietary fiber brings health benefits and lowers the risk of several diseases.
The content of this article is based on the research presented by The Nutrition Source of Harvard T.H. Chan School of Public Health and the work of the Italian nutritionist Stefano Vendrame.
In this short article you will learn that including fiber rich foods into our regular eating habits brings at least 5 amazing health benefits:
- Soluble fermentable fiber has a prebiotic effect
- Fiber regulates the intestinal transit and reduces constipation
- Fiber makes you feel full and helps with weight control
- Fiber reduces the risk of type 2 diabetes, heart disease, and cancer
- Fiber has a cholesterol-lowering effect
Types of dietary fiber
Dietary fiber is a type of carbohydrate that the body can’t digest. Typically fiber is classified into two main categories:
- Soluble fiber, which dissolves in water
- Insoluble fiber, which does not dissolve in water
Soluble fiber rich foods
- Soluble fiber can lower glucose and blood cholesterol levels
- Examples of soluble rich fiber foods include: oatmeal, chia seeds, nuts, beans, lentils, apples, and blueberries
Insoluble fiber rich foods
- Insoluble fiber can help promoting intestinal regularity and preventing constipation by speeding up food transit through the digestive system
- Examples of insoluble rich fiber include: whole wheat products, quinoa, brown rice, legumes, leafy greens like kale, almonds, walnuts, seeds, and fruits with edible skins like pears and apples
Viscous and fermentable fiber
Fiber can also be classified as:
- Viscous, which has a gel-like consistency
- Fermentable, which act as a nourishment for our gut bacteria that break down and ferment it
Good sources of fiber
The following table summarizes the types of fiber that are naturally present in plants.
|Fiber type||Category||Presence in foods||Health benefits|
|Cellulose, hemicellulose||Insoluble||• Cereal grains|
• Many fruits and vegetables
|• Absorbs water and adds bulk to stool|
• Can have a laxative effect
|Lignins||Insoluble||• Wheat and corn bran|
• Unripe bananas
• Vegetables in general
|• Stimulates mucus secretion in the colon|
• Adds bulk to stools
• Has laxative effect
|Beta-glucans||Soluble, highly fermentable||• Oats|
|• Fermented in the small intestine, acts as a prebiotic|
• Can add bulk to stool but does not have a laxative effect
• May help to normalize blood glucose and cholesterol levels
|Guar gum||Soluble, fermentable||• Seeds||• Metabolized and fermented in the small intestine|
• Does not have a laxative effect
• May help to normalize blood sugar and cholesterol levels
|Inulin, oligofructose, oligosaccharides, fructooligosaccharides||Soluble, fermentable||• Onions|
• Chicory root
• Jerusalem artichokes
|• May help to bulk stool with a laxative effect|
• Normalizes blood glucose
• Acts as a prebiotic
|Pectins||Soluble, highly fermentable||• Apples|
• Other fruits
|• Has minimal bulking or laxative effect|
• May slow down digestion and help normalize blood sugar and cholesterol levels
|Resistant starch||Soluble, fermentable||• Legumes|
• Unripe bananas
• Cooked and cooled pasta
|• Adds bulk to stools but has minimal laxative effect|
• May help to normalize blood sugar and cholesterol levels
Health benefits of fiber rich foods
Eating sufficient fiber rich foods brings great benefits to our health, here are the most important ones.
1. Soluble fermentable fiber has a prebiotic effect
First of all, fiber has a prebiotic effect. It is food for the healthy bacteria that populate our guts. In particular, soluble fiber helps our intestine to naturally select a healthier intestinal microflora composed of more lactobacilli, bifid bacteria and streptococci. When fiber consumption is insufficient, the microflora in our colon carries a putrefactive metabolism on the nitrogenous compounds that are typical of high-protein diets based on meat, which generates toxic substances such as ammonia and favors the growth of more harmful bacterial species that increase the risk of constipation and intestinal tumors.
2. Fiber regulates the intestinal transit and reduces constipation
Insoluble fiber prevents constipation by accelerating the transit of its content in the digestive tract. This reduces the time available for water to be reabsorbed, preventing the formation of dry, hard stools that are more difficult to pass.
Soluble fiber, on the other hand, contributes to increasing volume and retains water, resulting in softer stools that pass more easily. The combined effect of these two types of fiber therefore prevents the risk of diverticulosis, which is often the consequence of chronic constipation and excessive straining during defecation.
3. Fiber makes you feel full and helps with weight control
All fiber helps filling the stomach with its volume. Soluble fiber is particularly effective at doing this as it retains water, forming a bulky, viscous gel that swells in the stomach and gives a sense of satiety. This can help us control our weight, because if we eat enough fiber we feel fuller with less calories.
4. Fiber reduces the risk of type 2 diabetes, heart disease, and cancer
Fiber slows down the absorption of nutrients during digestion, consequently it lowers down the glycemic index of meals. In particular, by slowing down the absorption of glucose, fiber reduces the glycemic peaks that occur after a meal, and in turn this reduces peaks in the insulin which is released by the pancreas. This is why regularly eating fiber rich foods reduces the risk of type II diabetes and helps people who are already affected by this disease.
Large studies found that high-fiber whole grains are most strongly associated with lower diabetes risk, whilst fibers from fruits and vegetables did not show such a strong association. These studies also found that higher intakes of whole grain cereal fibers are associated with a lower risk of heart disease and heart attacks.
Regular consumption of fiber also plays a role in colorectal cancer prevention. By increasing volume and retaining water, fiber reduces the concentration of toxic substances by diluting them and accelerates their transit through the intestine. In addition to reducing the exposure time of toxic substances in the intestine, fiber can directly glue with some potentially carcinogenic, toxic or radioactive substances, therefore preventing that they get in contact with the walls of the colon. This protects not only the digestive tract, but the entire organism, as it reduces the absorption of these dangerous substances. The prebiotic effect of fiber has a preventive action as well, by promoting the formation of a protective microflora that nourishes the intestinal walls and maintains them healthy. Furthermore, the short-chain fatty acids produced by the fermentation of the fiber modulate the activity of various detoxifying enzymes. On the other hand, that putrefactive microflora that originates with low-fiber diets generates toxic compounds that are directly harmful to the colonic mucosa, such as ammonia.
Large cohort studies also found that fiber rich diets reduce the risk of breast cancer.
5. Fiber has a cholesterol-lowering effect
Fiber plays a role in lowering blood cholesterol levels by interfering with bile acid production. In fact, cholesterol is used to make bile acids in the liver. Soluble fiber binds to bile acids in the gut and excretes them from the body. Because of this reduced level of available bile acids, the liver pulls cholesterol from the blood to make new bile acids. By doing so, it lowers blood cholesterol. In addition, the butyrate produced by the intestinal fermentation of soluble fiber inhibits the enzyme that promotes the endogenous synthesis of cholesterol in the liver. Finally, by lowering insulin spikes, fiber further reduces cholesterol synthesis in the liver, which is promoted by insulin itself.
Recommended fiber daily intake
According to the Harvard Nutrition Source, children and adults need at least 25 to 35 grams of fiber per day for good health, but most people get much less than that. If you are currently eating a low-fiber diet, it is recommended to increase fiber intake gradually and drink more fluids, so that the body can adapt to the higher fiber intake and take full benefit of it. If the fiber intake is increased suddenly, then you may experience bloating and cramping.
High fiber vegetables and fruits
Whole grains are typically high in fiber, it’s always a good idea to look at the ingredients and nutritional labels of your favourite bread, pasta, rice, etc. to see how much fiber they contain.
In the table below you can find a selection of healthy high-fiber whole foods that you could add to your eating routine. If you would like to find more information on the fiber content of specific foods, you could search directly in the FoodData Central database of the U.S. Department of Agricolture.
|Food||Amount of fiber in grams in 100g of food|
|Dark chocolate (70-85% cacao)||10,9|
|Black beans (cooked)||8,7|
|Split peas (cooked)||8,3|
|Kidney beans (cooked)||7,4|
|Lima beans (cooked)||7|
Simple tips to eat more fiber
- Minimize refined and highly processed foods and maximize the amount of whole foods you eat (fruits, vegetables and whole grains)
- A great quick win is to replace refined grains with whole grains. This means normally eating whole grains bread instead of white bread, whole grains pasta instead of white pasta, whole brown rice instead of white rice, etc.
- Include different whole grains in your eating routine like oats, barley, and quinoa. For more ideas, see my article with a must-read list of whole grains examples for great health.
- Make sure you include legumes a few times per week in your regular eating routine
- When vegetables and fruits have an edible peel, eat them with their peel
- Add fiber-rich foods to your usual meals. For example ground chia seeds, flaxseeds, pumpkin seeds, walnuts, almonds, and shell fruits & seeds in general, blueberries, etc.
- Make it an habit to read the ingredients and nutrition labels of every packaged foods you purchase to become aware of the amount of fiber these foods contain
- Take advantage of my free weekly meal planner for healthy eating to help you embed fiber rich foods in your eating routine