Why Fiber?

Why Fiber?

By: Jeremy Partl, Registered Dietitian

We’ve all probably heard that we should eat more fiber in our diets. Most people’s conception of why we should eat fibrous foods revolves around one of two assertions: (a) it helps with digestion or (b) eating more fiber requires you to eat more fruits and vegetables—so it is indirectly beneficial.

However, in this article, I will share an acronym for fiber (F-I-B-E-R) that will go beyond those two assertions and provide you with evidenced-based reasons to meet the recommended fiber guidelines.

What is Fiber?

Dietary fiber is a non-digestible form of carbohydrate that comes from plant foods.

There are two major types of fiber.

Soluble fiber dissolves readily in water and forms a gel in the colon. Due to its gel-like nature, the digestion and release of other nutrients into the blood is slowed down. The best sources of soluble fiber are oats, nuts, seeds, beans, legumes, and some fruits and vegetables such as citrus fruits, apples, strawberries, peas, and potatoes.

Insoluble fiber doesn’t dissolve in water and helps your body to bulk up your stool. As a result, it helps to keep food moving through your digestive system. The best sources of insoluble fiber are the skins and peels of most fruits and vegetables, legumes, and whole grains, such as wheat bran, whole wheat bread, whole grain couscous, and brown rice.

F-I-B-E-R…Full of Benefits

Below, I am going to briefly cover a variety of ways that fibrous foods can positively impact our overall health and body composition. While you have probably heard of some of these, my goal is to educate you on some other, less-known benefits of fiber in our diet.

F- Fullness

What’s worse than being hungry? For many people, whether they or dieting or not, hunger is not something we tolerate very well. (Read more about hunger here: “Hunger 101.”) Luckily, modifying our fiber intake is something we can do to help increase the sensations of fullness and reduce hunger.

There are a few mechanisms that explain why higher fiber intakes result in increased levels of satiation. (Hervik, 2019)^[1] Soluble fibers, in particular, help to slow down the digestion and release of nutrients, prolonging the time that the food sits in our stomach and intestines. As a result, this can inhibit the release of hormones that prompt us to eat. High-fiber foods tend to take up more space in our stomachs. The stomach is much more responsive to the stretch of it and the space occupied in it rather than nutrient content of foods. In other words, your stomach is a “volume counter” and not a “calorie counter,” making low-density, high-fiber foods a perfect choice for filling up without eating a lot of calories.

Due to their plant structure, high-fiber foods tend to take longer to chew. As a result, this longer oral processing time allows an opportunity for the brain to pick up satiety cues from the stomach before more food is eaten.

As a result of the impact on satiety levels and the sense of fullness it provides, higher fiber intakes are proposed to be beneficial for weight loss and have been found to be effective at the minimum for enhancing weight control. (Slavin, 2005)^[2]

I- Insulin Resistance

The title of this section is somewhat misleading if taken for face value. Higher fiber intakes do not cause insulin resistance, but it is a modifiable lifestyle aspect that we can control that has been related to controlling and regulating blood sugar, improving insulin resistance, and decreasing the risk of developing type 2 diabetes. When combing through the depth of studies, a high intake of fiber (>30–40 grams/day) or diet rich in whole grains has been estimated to reduce insulin resistance and the risk of developing type 2 diabetes by around 20–30%. (Weickert, 2018)^[3]

Most often, we think of the impact of fibrous foods (especially those high in soluble fiber) primarily being related to controlling blood sugar excursions after meals. Simply, dietary fiber lowers blood sugar elevations because of its ability to form a gel and hinder or delay the absorption of dietary carbohydrates. (Weickert, 2018)^[4]

But there may be other factors such as the protective impact of higher fiber intakes on weight regulation (through increased satiety, lower energy density, etc.) that help to reduce insulin resistance. For example, since it is well recognized that excessive energy intake leading to adiposity is considered one of the strongest predictors of insulin resistance and type 2 diabetes development, higher fiber intakes may be protective because of its weight regulation mechanisms. (Sung, 2012)^[5]

B- Beneficial Bacteria

Fiber doesn’t always impact us directly. Instead, forthcoming research is showing that the impact fiber intake has on the bacteria in our digestive system may be influential on our overall health. One way that an increased amount of fiber in the diet aids our health is by creating a large diversity and population of beneficial bacteria in our gut (most commonly referred to as probiotics). These populations of beneficial bacteria grow on short-chain fatty acids, which are a by-product of the incomplete breakdown of fiber (a process called fermentation). In other words, fiber can act as a source of food (often called probiotics) for the survival and thriving of beneficial gut bacteria. (Read more about fermentation here: “Fermented Foods.”)

It has been observed in scientific trials that low fiber diets have been shown to reduce microbial diversity and lead to the disappearance of specific beneficial bacterial species—the complete opposite of what happens with higher fiber diets.

As a result, these alterations may result in physiological dysfunctions, contributing to the incidence of a surprisingly broad range of relevant diseases and conditions (heart disease, type 2 diabetes, and colorectal cancer), as well as increased body weight and total cholesterol. (Deehan, 2018)^[6]

E- Expectancy

There are two guaranteed things in life…death and taxes. While death is guaranteed, we can do our best to live the longest amount of time as possible.

There is a very strong depth of evidence supporting the notion that higher fiber intakes prolong life expectancy and reduce the risk of early death. For years, research has started to display how dietary fiber intake can promote overall health by preventing and mitigating chronic diseases and conditions, such as type 2 diabetes mellitus, cardiovascular disease, and colon cancer. (Kaczmarczyk, 2012; Reynolds, 2019) ^[7], ^[8]

The most recent meta-analysis of over four decades of research found a 15% to 30% reduced risk of death and chronic diseases in people who included the most fiber in their diets, compared with those with the lowest intake. In addition, a higher fiber diet was linked, on average, with a reduction of 22% in stroke risk, 16% lower risk of type 2 diabetes and colorectal cancer, and a reduction of 30% in death from coronary heart disease. (Reynolds, 2019) ^[9]

While experts can’t estimate the number of years one may gain with a high-fiber diet, it’s clear that consuming higher intakes of dietary fiber is a very smart strategy that you can control to extend your lifespan.

R- Regulation

Normal bowel movement frequency is considered to be in the range of 3x per week to 3x per day. However, it is also important to consider the ease of bowel movements, size, and shape of the stools. (McRorie, 2015.)^[10] For many people, regular bowel movements can be taken for granted. Thanks to factors such as increased stress levels, medication side effects, physiological changes as we age, etc., our regularity can become more irregular. While we can influence some of these listed above, changing our diet can be a helpful tool to take care of our bowel movements.

Dietary fiber improves “regularity” in a couple of ways. Insoluble fiber adds bulk to the stool. Soluble fiber causes absorption of water in the gut, creating a gel-like substance that helps bowels move more smoothly and easily. Fermented soluble fiber—those prebiotics we discussed—feed the good bacteria required for proper digestion and bowel movement.

Summing these up into one coherent thought: increasing the amount of fiber in your diet may help to keep you regular by bulking up the stool (insoluble fiber), getting it moving (soluble), and enhancing the digestive environment (prebiotics). (Web.)^[11]

Recommended Intake

Depending on calorie intake, gender, and age, fiber intake recommendations from the Institute of Medicine (IOM) range from 19 grams to 38 grams per day. (Lupton, 2002.)^[12] This amount is similar to other highly respected organizations like the American Heart Association and the American Diabetes Association, which suggest roughly between 25 and 30 grams per day. Making it simpler, the established standard tends to be about 14 grams of fiber intake per 1000 calories consumed.

Globally, many people struggle to meet established recommended amounts, with most individuals consuming less than 20 grams per day. (Stephen, 2017.)^[13] In fact, surveys from the US reports that only 5% of the population meets recommendations, averaging about 16.2 grams of fiber per day, causing experts to call inadequate intakes a public health concern. (Quagliani, 2017.) ^[14]

Going back to the largest collection of evidence we have, the comparisons of outcomes among individuals with different intakes of dietary fiber suggests that intake of total daily dietary fiber should be no less than 25–29 gams. Furthermore, even higher intakes of fiber seem to confer additional health benefits with no dangers of higher fiber intakes (with the exception of those who struggle with iron deficiency). (Reynolds, 2019.) ^[15]

Many strategies have been suggested to close what experts call the “fiber gap” between actual intake and established recommendations. The following table displays these tactics and gives practical, take-home messages and habits to help you meet your daily fiber intake. (Quagliani, 2017.)^[16]

Adapted from Quagliani, D., & Felt-Gunderson, P. (2017). Closing America’s fiber intake gap: communication strategies from a food and fiber summit. American journal of lifestyle medicine, 11(1), 80-85.

Added Fibers

With recommendations to increase your fiber intake, most people probably know that they should eat more vegetables, fruits, beans, legumes, and whole grains. However, what happens if you don’t like those foods? Or, what happens when you fear strong associations with potential consequences like bloating, flatulence, and abdominal rumbling?

Over the past couple of decades, manufacturers have been developing and selling various fiber products, adding fibers, known as isolated fibers or functional fibers, to foods and beverages to help boost individual intakes.

These fibers (such as soluble corn fiber, polydextrose, cellulose, inulin, and oligofructose, etc.) are extracted from starchy foods or manufactured from starches or sugars and sold as supplements or added to traditional foods like bread, tortillas, snack goods, protein bars, etc. Additionally, it can be confusing because the fiber from these sources is included on the nutrition label as fiber…which is technically true.

However, are the benefits of functional fibers the same?

To date, there is a lack of evidence linking this kind of added fiber to the prevention of chronic disease. Research suggests that functional fibers have the potential to influence risk factors for chronic disease by controlling hunger and promoting satiety, lowering cholesterol, and other mechanisms discussed above. (Yuan, 2014.) ^[17]

Thus, I like to think of functional fibers as a bridge. For people who are just starting to add more plant foods to their diet, foods that are fortified with fiber may help bridge the gap while they make efforts to increase their intake of whole food sources of fiber.

Wrapping Up

Fiber is such a beneficial, but neglected nutrient in the Western diet. By making simple additions and substitutions to your diet, you can increase your fiber intake and start to transform your life, one gram at a time.

References

^[1] Hervik, A. K., & Svihus, B. (2019). The role of fiber in energy balance. Journal of nutrition and metabolism, 2019.

^[2] Slavin, J. L. (2005). Dietary fiber and body weight. Nutrition, 21(3), 411-418.

^[3] Weickert, M. O., & Pfeiffer, A. F. (2018). Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. The Journal of nutrition, 148(1), 7-12.

^[4] Weickert, M. O., & Pfeiffer, A. F. (2018). Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. The Journal of nutrition, 148(1), 7-12.

^[5] Sung, K. C., Jeong, W. S., Wild, S. H., & Byrne, C. D. (2012). Combined influence of insulin resistance, overweight/obesity, and fatty liver as risk factors for type 2 diabetes. Diabetes care, 35(4), 717-722.

^[6] Deehan, E. C., Duar, R. M., Armet, A. M., Perez-Munoz, M. E., Jin, M., & Walter, J. (2018). Modulation of the gastrointestinal microbiome with nondigestible fermentable carbohydrates to improve human health. Bugs as Drugs: Therapeutic Microbes for the Prevention and Treatment of Disease, 453-483.

^[7] Kaczmarczyk, M. M., Miller, M. J., & Freund, G. G. (2012). The health benefits of dietary fiber: beyond the usual suspects of type 2 diabetes mellitus, cardiovascular disease and colon cancer. Metabolism, 61(8), 1058-1066.

^[8] Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 393(10170), 434-445.

^[9] Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 393(10170), 434-445.

^[10] McRorie Jr, J. W., & Fahey Jr, G. C. (2015). Fiber supplements and clinically meaningful health benefits: identifying the physiochemical characteristics of fiber that drive specific physiologic effects. In Dietary Supplements in Health Promotion (pp. 172-217). CRC Press.

^[11] https://www.fiberchoice.com/smart-choices/fiber-and-regularity/

^[12] Lupton, J. R., Brooks, J. A., Butte, N. F., Caballero, B., Flatt, J. P., & Fried, S. K. (2002). Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. National Academy Press: Washington, DC, USA, 5, 589-768.

^[13] Stephen, A. M., Champ, M. M. J., Cloran, S. J., Fleith, M., Van Lieshout, L., Mejborn, H., & Burley, V. J. (2017). Dietary fibre in Europe: current state of knowledge on definitions, sources, recommendations, intakes and relationships to health. Nutrition research reviews, 30(2), 149-190.

^[14] Quagliani, D., & Felt-Gunderson, P. (2017). Closing America’s fiber intake gap: communication strategies from a food and fiber summit. American journal of lifestyle medicine, 11(1), 80-85.

^[15] Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 393(10170), 434-445.

^[16] Quagliani, D., & Felt-Gunderson, P. (2017). Closing America’s fiber intake gap: communication strategies from a food and fiber summit. American journal of lifestyle medicine, 11(1), 80-85.

^[17] Yuan, J. Y. F., Smeele, R. J. M., Harington, K. D., van Loon, F. M., Wanders, A. J., & Venn, B. J. (2014). The effects of functional fiber on postprandial glycemia, energy intake, satiety, palatability and gastrointestinal wellbeing: a randomized crossover trial. Nutrition journal, 13(1), 76.