By Patricia Thomson, PhD
Most of us probably have at least a vague notion of what fiber is and that we should eat more of it. Maybe you grab a bran muffin or down a glass of water with a powdery fiber supplement mixed in to keep yourself “regular.” While it’s true that fiber can prevent or address instances of constipation, that barely scratches the surface of the role this amazing nutrient plays in maintaining our health by preventing and even reversing many of the most prevalent and deadly “lifestyle” diseases in America.
WHAT IS FIBER ANYWAY?
All fiber originates in plants and is the part of the plant that is not digestible by the body. Fiber comes in two different forms: soluble fiber and insoluble fiber—both of which are integral to our health. Soluble fiber is the part of the plant that dissolves in water and becomes gelatin-like, whereas insoluble fiber is the part of the plant that stays whole throughout the digestive process. Oatmeal, for example, is a whole grain containing soluble and insoluble fiber, as well as protein, carbohydrates, and fat. A half cup of rolled oats has about 3 grams of fiber, or roughly 10 percent of the recommended amount we should consume daily. In addition to its fiber content, this little grain also packs a powerful nutritional punch, with 5 grams of protein and 3 grams of fat, as well as antioxidants and iron.
It bears noting that food products derived from animals—beef, chicken, pork, fish, cheese, milk—contain no fiber whatsoever. Even many foods that are plant-based—breads, cakes, boxed or packaged food, olive and other vegetable oils—have little to no fiber because they are highly processed.
Plants have different ratios of soluble and insoluble fiber, and, therefore, when discussing dietary fiber content, both forms are included in the one value. Eating a whole food, plant-based diet ensures you are getting enough of both kinds of fiber.
HOW DOES FIBER WORK?
Fiber serves as both a sponge and
a plunger in your body during the digestive process.1,2 As it moves through the digestive tract, soluble fiber acts like a sponge, soaking up and binding extra cholesterol, fats, and other waste from the digestive process; dead bacteria and cells; and inorganic substances and toxins. Insoluble fiber plunges out the digestive tract by softening and adding bulk to the stool and helping lubricate the colon, which allow the stool to move smoothly through the gastrointestinal tract and out of the body. In the absence of sufficient fiber, waste can build up in the lower intestine and become toxic to the body.1,2
You can see now why adding fiber to your diet prevents constipation. Constipation is commonly considered to be easily preventable, with increased dietary fiber intake being a safe and effective option. However, apparently the word on fiber has not gotten out to everyone. Medical visits for issues related to constipation have increased over the past 20 years, and the cost of these visits are passed on to the patient and to the medical system as a whole.28 One study found that if individuals with constipation increased their fiber consumption through simple changes in dietary practices instead of seeing a doctor and taking prescription or over-the-counter laxatives, nearly $13 billion could be saved annually in direct medical costs.28 It seems that not only does increasing your dietary fiber benefit your digestive health, it benefits your wallet too!
FIBER AND THE GUT MICROBIOME
By now, you’re probably thinking, “OK, OK, I get it: Fiber prevents constipation.” But, additionally, fiber plays a major role in our overall health through its relationship with our gut bacteria. Our digestive tracks are home to billions of microorganisms—our gut microbiome—that are instrumental in regulating our bodies.3 The fiber we consume helps to nourish the beneficial bacteria so that they can do their job. Not only do these microbes help to digest our foods and provide vital nutrition to our bodies, they also help to regulate our immune systems; produce necessary vitamins; secrete hormones; control our weight, cholesterol, and blood sugar levels; and decrease our susceptibility to mental disorders and other diseases.3
Our gut microbiome evolves with our changing tastes and diets. When we add fiber-containing foods to our diet, we are basically feeding our gut microbiome. The more gut microbes we have, the thicker our digestive tract mucus wall is. Why is this important? This mucus wall establishes a firm barrier between our bodies and the bacteria that make up the gut microbiome. The thicker the wall, the greater the protection from inflammation and risk of disease. Conversly, without enough fiber in our diet, the gut microbiome would not have the fuel needed to survive
or reproduce. In an animal study,4 researchers reported that destruction of the gut microbiota of mice occurred when fed a high-fat diet. Without healthy gut microbiota, the digestive enzymes needed to coat the intestines of the mice were not produced, which allowed gut bacteria to pass into the body, leading to inflammation and metabolic syndrome.4 Thus, it is important to feed our gut bacteria with sufficient fiber to maintain our health and wellness.7–9
It is important to note that not all fiber is created equal. Fermentable fiber is a form of fiber that can be digested by the gut biome and used as fuel by the microbes to proliferate. Remember, the more beneficial microbes you have the healthier you will be. The best sources of fermentable fiber include beans and legumes.
Viscous fiber takes on a gel-like form moving very slowly through the gut, slowing down digestion and allowing the absorption of nutrients and creating a sense of satiety. Foods containing viscous fiber include Brussel sprouts, legumes, oats, and flaxseed.
Resistant starch, another type of fiber, acts like a fermentable fiber and has many health benefits, like improving digestive health, lowering insulin resistance, and reducing blood sugar levels. Examples of resistant starch foods include white potatoes, white rice, some legumes, cashews and raw oats. Including all three types of fibrous foods will ensure a healthy and happy gut microbiome.6,7
FIBER AND DISEASE PREVENTION Heart disease.
Dietary fiber is an important factor in the prevention of coronary heart disease.10–13 In a Harvard study involving 43,757 male health professionals over a six-year period, an inverse relationship was found between dietary fiber consumption and coronary heart disease—in other words, people who consumed more fiber had less heart disease.10 Fiber sources included vegetables, fruits, and whole grain cereal, although the relationship was more significant with the cereal fiber. Likewise, another study found a nine-percent lower risk of both coronary heart disease and cardiovascular disease with every additional seven grams of fiber that participants consumed each day.11
Cholesterol has also been linked to a higher risk of coronary heart disease. Studies examining the relationship between dietary fiber and lower cholesterol concluded that increasing dietary fiber by at least 3 grams a day resulted in a significant lowering of LDL cholesterol.12,13
Cancer. Increasing fiber intake can also reduce your risk of many types of cancer, including breast, esophageal and esophagus, endometrial, and ovarian.14–18 Analysis of data from 90,534 premenopausal women from the Nurses’ Health Study II revealed that increased fiber intake during adolescence and in early adulthood resulted in lower incidence of breast cancer.14 In a meta-analysis that looked at rates of Barrett’s esophagus and esophageal cancer in relation to fiber intake among a total of 16,885 participants, investigators found that a 10-gram- per-day increase in dietary fiber consumption was associated with a 31-percent reduction in incidence of Barrett’s esophagus and esophageal cancer.16 In a meta-analysis of 142,189 study participants, investigators also observed that a 10-gram-per-day increase in dietary fiber intake was linked to decreased ovarian cancer risk.18
Diabetes.
If you suffer from Type 2 diabetes, adding fiber to your diet can help reduce your reliance on insulin and might actually reverse your disease. Studies have shown that fiber plays an instrumental role in the prevention of Type 2 diabetes by controlling blood sugar and insulin levels in the blood. A low-fat diet with a dietary fiber intake of more than 25 grams per day, primarily from whole grains and insoluble cereal fibers, showed a 20- to 30-percent reduction in diabetes incidence.19–21
In the United States, African-American women are especially at risk for Type 2 diabetes, compared to other races. In the Black Women’s Health Study, 59,000 African-American women were assessed for Type 2 diabetes risk by comparing glycemic load, glycemic index, and cereal fiber.22 Diabetes risk was lower in women who consumed more cereal fiber. Plant-based diets offer positive benefits for individuals with diabetes. Evidence suggests that an increase in dietary fiber, among other factors, helps regulate glycemia.23
Weight loss.
If you want to lose weight, adding fiber to your diet can help. Research has shown that increased dietary intake of fiber can prevent obesity.24,25 There exists an inverse relationship between dietary fiber intake and body weight and body fat, and dietary fiber has been shown to help with weight management and hunger satiation.24,25
WHAT ELSE SHOULD YOU KNOW ABOUT FIBER?
The National Institute of Medicine recommends daily fiber consumption for men and women. For men 50 years of age or younger, 38 grams of fiber per day is recommended; for men older than 50 years, 30 grams per day should be consumed. For women 50 years of age or younger, 25 grams of fiber is the recommended daily amount, while for women older than 50 years, the target consumption should be 21 grams of fiber daily.26
Unsurprisingly, few Americans consume the recommended amounts of fiber. In 2010, the United States Dietary Guidelines for Americans classified dietary fiber as a nutrient of concern because more than 90 percent of American adults and children failed to meet their daily dietary fiber recommendations.27 The standard American diet, or Western diet, consists largely of processed foods, meat, and dairy (including cheese and eggs) and high levels of fat, salt, and sugar. And because there is no natural fiber in most of these food products, a diet that comprises mostly processed foods and animal products and very little fresh vegetables and fruits will likely result in fiber deficiency.
For those individuals hoping to maintain their current diet and increase fiber intake through supplements containing fiber extracts in pill or powder form, be aware that fiber studies have focused on the benefits of fiber provided through food intake, not fiber isolates
or extracts. Natural fiber-containing foods—fruits, vegetables, whole grains—also contain other nutritionally valuable components such as proteins, vitamins, minerals, and antioxidants, which suggests that fiber supplements are not as nutritionally effective as consuming whole, plant-based foods.
Adopting a whole-food, plant-based diet can help you achieve a healthier, disease-free life. When you base your meals around vegetables, fruits, whole grains, legumes, nuts ,and seeds, you are filling your body not only with beneficial fiber but also with a variety of other nutrients. If you would like to add more fiber to your diet, do so gradually through the addition of whole grains, fruits, vegetables, legumes, nuts, and seeds and drink plenty of water. Choose softer legumes such as lentils for easier digestion. Rinse and drain canned beans thoroughly before using. Add small amounts of fiber-containing foods at each meal. Gradual introduction of more fiber will help your gut bacteria adapt more quickly and reduce gassiness and bloating. Once your body adapts, you will begin to feel better and any discomfort should be relieved.
Of course, any time you make significant changes to your diet you should let your doctor know. Your doctor might need to adjust your medications as you move to a healthier diet that includes more unprocessed, plant-based food
REFERENCES
1. National Lipid Association. Adding soluble fiber to lower your cholesterol. In: Clinician’s Lifestyle Modification Toolbox. NLA Nutrition Task Force. 2018. https://www. lipid.org/sites/default/files/adding_soluble_fiber_ final_0.pdf. Accessed 9 Dec 2019.
2. Matala N. Increase fiber to decrease cholesterol. 19 Sep 2018. https://www.raleighmedicalgroup.com/blog/ entryid/528/how-to-lower-cholesterol-with-fiber. Accessed 9 Dec 2019.
3. Hair M, Sharpe J. The human microbiome. 20 Jan 2014. University of Washington. Center for Ecogenetics and Environmental Health. https://depts.washington.edu/ ceeh/downloads/FF_Microbiome.pdf. 9 Dec 2019.
4. Zou J, Chassaing B, Singh V, et al. Fiber-mediated nourishment of gut microbiota protects against diet- induced obesity by restoring IL-22-mediated colonic health. Cell Host Microbe. 2018;23(1):41-53.
5. Birt DF, Boylston T, Hendrich S, et al. Resistant starch: promise for improving human health. Adv Nutr. 2013;4(6):587–601.
6. Bird AR, Brown IL, Topping DL. Starches, resistant starches, the gut microflora and human health. Curr Issues Intest Microbiol. 2000;1(1):25–37.
7. Robertson MD, Bickerton AS, Dennis A, et al. Insulin- sensitizing effects of dietary resistant starch and effects on skeletal muscle and adipose tissue metabolism. Am J Clin Nutr. 2005;82(3):559–567.
8. Clark MJ, Slavin JL. The effect of fiber on satiety and food intake: a systematic review. J Am Coll Nutr. 2013;32(3):200–211.
9. Parnell JA, Reimer RA. Prebiotic fiber modulation of the gut microbiota improves risk factors for obesity and the metabolic syndrome. Gut Microbes. 2012; 3(1):29–34.
10. Rimm EB, Ascherio A, Giovannucci E, et al. Vegetable, fruit, and cereal fiber intake and risk of coronary heart disease among men. JAMA 1996;275:447–451.
11. Threapleton DE, Greenwood DC, Evans CE, et al. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ 2013;347:f6879.
12. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol- lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr 1999;69:30–42.
13. Whitehead A, Beck EJ, Tosh S, Wolever TM. Cholesterol- lowering effects of oat β-glucan: a meta-analysis
of randomized controlled trials. Am J Clin Nutr 2014;100(6):1413–1421.
14. Farvid MS, Eliassen AH, Cho E, et al. Dietary fiber intake in young adults and breast cancer risk. Pediatrics 2016;137(3):e20151226 .
15. Hajishafiee M, Saneei P, Benisi-Kohansal S, Esmaillzadeh A. Cereal fibre intake and risk of mortality from all causes, CVD, cancer and inflammatory diseases: a systematic review and meta-analysis of prospective cohort studies. Br J Nutr 2016 Jul;116(2):343-52. Epub 2016 May 19.
16. Sun L, Zhang Z, Xu J, et al. Dietary fiber intake reduces risk for Barrett’s esophagus and esophageal cancer. Crit
Rev Food Sci Nutr 2017;57(13):2749–2757.
17. Li H, Mao H, Yu Y, Nan Y. Association between dietary
fiber and endometrial cancer: a meta-analysis. Nutr
Cancer. 2019 Oct 4:1-9.
18. Zheng B, Shen H, Han H, et al. Dietary fiber intake and
reduced risk of ovarian cancer: a meta-analysis. Nutr J.
2018 Oct 30;17(1):99. doi: 10.1186/s12937-018-0407-1. 19. Kaline K, Bornstein SR, Bergmann A, et al. The
importance and effect of dietary fiber in diabetes prevention with particular consideration of whole grain products. Horm Metab Res 2007;39(9):
687–693.
20. Weickert MO, Pfeiffer AFH. Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. J Nutr 2018;148(1):7-12. doi: 10.1093/ jn/nxx008.
21. Rebello CJ, Johnson WD, Martin CK, et al. Acute effect of oatmeal on subjective measures of appetite and satiety compared to a ready-to- eat breakfast cereal: a randomized crossover trial. J Am Coll Nutr 2013;32(4):272-9. doi: 10.1080/07315724.2013.816614.
22. Krishnan S, Rosenberg L, Singer M, et al. Glycemic index, glycemic load, and cereal fiber intake and risk of type 2 diabetes in US black women. Arch Intern Med. 2007;167:2304–2309.
23. Barnard ND, Katcher HI, Jenkins DJ, et al. Vegetarian and vegan diets in type 2 diabetes management. Nutr Rev 2009 May;67(5):255–263. doi: 10.1111/j.1753- 4887.2009.00198.x.
24. Slavin JL. Dietary fiber and body weight. Nutrition 2005;21(3):411–418.
25. Davis JN, Hodges VA, Gillham MB. Normal-weight adults consume more fiber and fruit than their age- and height-matched overweight/obese counter parts. J Am Diet Assoc 2006 Jun;106(6):833–840.
26. Institute of Medicine. The National Academies. 5 Sep 2002. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. http://www.nationalacademies.org/hmd/ Reports/2002/Dietary-Reference-Intakes-for-Energy- Carbohydrate-Fiber-Fat-Fatty-Acids-Cholesterol-Protein- and-Amino-Acids.aspx. Accessed 5 Dec 2019.
27. United States Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 7th ed. Washington, DC: US Government Printing Office; 2010.
28. Schmier JK, Miller PE, Levine JA, et al. Cost savings of reduced constipation rates attributed to increased dietary fiber intakes: a decision-analytic model. BMC Public Health 2014;14:374.
PATRICIA R. THOMSON, PhD
is a certified nutritionist, earning her nutrition certification through e-Cornell Center for Nutrition Studies, her plant- based culinary certification through the Rouxbe Culinary School, and her teaching certification through the Physicians
Committee For Responsible Medicine Food For Life program. She earned her PhD in Biological Sciences, and offers plant-based nutrition education to the community. She is also the Founder of the first-ever Food as Medicine Summit & EXPO, coming to Dallas in April of 2020. Visit www.foodasmedicinesummittx. comorwww.tswellness.orgtolearnmore. NHR
