Fiber – Everything You Need to Know

What is Fiber?

Did you know there are different types of fiber?

It can get confusing! The Institute of Medicine published the following definitions in 2005:

Dietary Fiber: “non-digestible carbohydrates and lignin that are intrinsic and intact in plants” – meaning fiber naturally found in foods like fruits, vegetables, grains, nuts/seeds, and legumes that cannot be digested.

The 2 types of Dietary Fiber are soluble fiber and insoluble fiber.

• Soluble Fiber: fiber that dissolves in water and turns into a gel consistency. Soluble fiber may add calories because most of it is fermentable, but it also helps keep you full longer!
• Insoluble Fiber: fiber that does not dissolve in water, but adds bulk to your stool and speeds up the elimination process. Most insoluble fiber is not fermentable, therefore it does not add many calories.

Functional Fiber: “isolated, non-digestible carbohydrates that have beneficial physiological effects in humans.” Functional fiber is also referred to as “Added Fiber” – fiber added to foods or supplements for example, in the forms of gums, inulin, psyllium, or ß-glucan.

Fiber Recommendations

The Dietary Reference Intakes (DRI) is a set of reference values that tell us how much of a nutrient, vitamin, or mineral we should consume per day for our health: Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake Level (UL).

Each reference value is established in a certain way, for certain reasons.

Fiber recommendations are based on the reference value, Adequate Intake (AI), because fiber cannot be measured in the body and there was not enough evidence to create more common values such as the EAR and RDA.

AI is typically based on observed intake levels of an apparently healthy group that appear to be adequate OR is based on an approximated average intake by an apparently healthy group that appears to be adequate. The reference value of fiber is specific to protecting against and lowering the risk of developing coronary heart disease but also serves a purpose in reducing the risk of developing Type 2 Diabetes.

Fiber is measured in grams(g) and total daily fiber recommendations vary by age group and gender but are based on 14g of fiber per 1,000 calories. For example, the AI for men 19-50 years old is 38g/day and for women, 19-50 years old (not pregnant or lactating) is 25g/day.

The next section will fill you in on how much fiber you get from common foods!

Fiber in Foods

Foods with dietary fiber provide both soluble and insoluble fiber.

The list below is from the North Ottawa Wellness Foundation.

Although no specific recommendations exist for how much soluble or insoluble fiber you should eat per day, the US Department of Health and Human Services promotes 5-10g of soluble fiber can reduce your bad cholesterol (LDL) by 3-5%.

You even have the potential to lower your LDL by up to 30% if you also add 2g of plant stanols/sterols per day, lower your cholesterol and saturated fat intake, and lose up to 10-pounds of weight if you are overweight.

The Health Benefits of Fiber – Whole Foods

Fiber has many other benefits in addition to keeping you regular and lowering cholesterol!

1. Bowel Health

This large review covers an enormous amount of benefits fiber has to offer.

To name a few:

• Constipation: Can lead to several issues like hemorrhoids, blockages, fecal impaction, rectal prolapse, or an anal fissure. Research supports 2 servings of high fiber fruits can promote regularity to avoid constipation-related issues.
• Irritable Bowel Syndrome (IBS): 2-3 servings of low FODMAP fruits per day OR 5-10g of fruit fiber (like pectin) may reduce your risk of developing IBS and reduce flare-ups in those already with IBS.
If you suffer from IBS, it may be helpful to consume fruits at least ~3 hours in between to avoid overwhelming your gut and ensure specific fruits work for you.
• Diverticular Disease: Meeting current fiber recommendations with adequate fruit intake may reduce your risk of developing diverticulitis and reduce flare-ups in those already diagnosed with diverticulosis.
• Promote a healthy gut: A minimum of 2 servings of whole fruit per day with more than 2.5g of fiber per serving (specifically high in soluble fiber) has been found to significantly increase the activity of healthy bacteria, reduce the number of bad bacteria, and offer more protection against bacteria-related diarrhea in both children and adults (as compared to 1 whole fruit serving per day).

2. Weight Maintenance and Weight Loss

• A large study over an 11-year time span concluded as fiber intake increased, the prevalence of inflammation, metabolic syndrome, and obesity decreased.
• Several studies like the one discussed here, support high fiber diets to promote weight loss in general. Noting high fiber diets are healthier, typically lower in calories, and provide longer bouts of satiety leading to less food consumed, as compared to low fiber diets.
• Some studies have even found high fiber diets to actually eliminate a small amount of energy from food consumed due to fiber binding to it and decreasing total calories stored.

3. Bone Density

High fiber diets may increase calcium absorption and protect against bone loss in certain areas in men and women as discussed in this recent study, but more research is needed.

4. Blood Sugar Levels and Type 2 Diabetes

This updated study in the Journal of Nutrition discusses research supporting fiber’s role in lowering blood sugar and the risk of developing Type 2 Diabetes.

• Soluble fiber: improves post-meal blood sugar levels (as opposed to them being higher after consuming low fiber carbohydrate-containing meals)
• Insoluble fiber: improves insulin resistance and research consistently associates high intakes of whole grains and insoluble cereal fiber with a lowered risk of developing Type 2 Diabetes by up to 20-30%!

5. Cardiovascular Risk

A large study over a 23-year time frame found a high fiber diet to be associated with much lower rates of cardiovascular disease and coronary heart disease.

6. Cancer

This large prospective study concluded high fiber diets were associated with lower risks of colon and rectal benign tumors and cancer.

Added Fiber

There is conflicting evidence regarding the effectiveness of added fiber in supplements due to the type of fiber used. Although fiber supplements are a great option to increase fiber intake without having to make dietary changes, some fiber supplements may not provide the same benefits as fiber does from whole foods.

This study found fiber supplements made from psyllium or ß-glucan to still be able to lower cholesterol and blood sugar levels unlike those containing inulin, wheat dextrin, or wheat bran.

Word of Caution

It is possible to consume too much fiber too quickly as well as too much fiber in general. Gas, bloating, nausea, diarrhea, cramping, and even constipation are common symptoms of too much fiber.

If you are looking to increase your fiber intake, do it slowly – even as slow as 2g a day.

Slowly increasing your fiber intake will help ease your gastrointestinal tract into a higher fiber diet and avoid upset.

Bottom Line

There are numerous benefits to consuming a high fiber diet. Adding the best type of fiber supplement to your daily intake may be able to improve some aspects of your health, but a regular intake of high fiber foods appears to be more promising and has the potential to increase your life span.

Jaime Buffie, MS, RDN, LDN

Jaime began her career as a Dietitian at the St. Cloud, Minnesota V.A. and later transferred to the Orlando V.A. in Florida. Jaime thri... [Read Full Bio]