We know that plant "roughage" is important to our health, but most of us still fall far short of meeting our daily dietary recommendations for this nutrient. Modern day diets are very different from those of our ancestors, who ate far more fiber just a few generations ago than we do today (McKeown et al., 2022). Today, in the U.S. we each consume on average, about 17 grams of fiber daily, although our ancestors would consumer upwards of 100 grams daily. When we consider how much fiber we need to move our bowels daily, or what is required to improve cardiac health, we should aim towards about 30 grams daily, but when we consider fiber's impact on our gut microbiota, that number eludes us a bit.
I remember in school, nursing school even, learning that fiber wasn't utilized by our body; it was too rough. However, it moved through our body taking cholesterol and toxins with it, which was protective. All the things resistant to our human enzymes were moved through, but in the few decades since nursing school, scientists have started to bicker about what defines fiber. Most definitions include carbohydrates with three or monomeric units, including fructans and inulins (McKeown et al., 2022).
There is confusion among both healthcare consumers and healthcare providers about fiber, and most don't appreciate the complexity of dietary fiber, likely believing fiber is a simple, or at least a single, nutrient. When we read food labels, fiber is listed very generically, as if all dietary fibers are the same. They aren't considering the source, type, quality, or physiologic effects. Add to this complexity, that isolated or synthetic fibers can be added to foods and beverages as ingredients, and the same fibers might have multiple names (McKeown et al., 2022).
There are several distinct classes of fiber that deliver different health benefits. Although each one contributes towards the recommended daily intake, different isolated fibers deliver very different health benefits based on their individual properties. Soluble, viscous fibers such as oat B-glucan reduces serum cholesterol and improves blood sugar control, whereas insoluble fibers such as coarse wheat and rye brans bulk up our stool and can improve regularity (McRorie & McKeown, 2017). While fiber can also reduce blood sugar after meals and insulin levels, lower blood pressure, increase energy levels, improve the gut microbiota and improves our ability to absorb minerals, most aren't clear what the difference is between whole grains and refined grains. Most are eating highly processed, refined grains and too few fruits and vegetables.
Adding a tablespoon of flax or chia seeds to salads or oatmeal each day can provide an estimated 5 grams of extra fiber. Peek at the labels on your high fiber cereals, or choose wheat or bran cereals as they can have as much as 11 grams of fiber per serving. Legumes are protein sources, but often overlooked as a source of fiber. A half-cup of cooked legumes contains nearly 5 grams of fiver. Try a variety of nuts and seeds, as well as fruits and vegetables with each meal.
Why the Fuss?
Foods with natural fibers such as fruits, vegetables, legumes and whole grains have long been known to deliver health benefits, and they offer a wide array of nutrients and phytochemicals (Mayor, 2019). Populations who eat more plants and fiber-rich diets have greater protection from developing chronic disease (Qian et al., 2019 & Kim et al., 2019). Whole grains contain numerous vitamins, minerals, phenols, antioxidants, and phytoestrogens (Hullings et al., 2020).
Fiber improves cardiac health (Wu, et al., 2015), lowers risk for stroke (Zhang et al., 2013) and type 2 diabetes (Reynolds et al., 2019 & Veronese et al., 2018), as well as colorectal cancer (Reynolds et al., 2019) and diverticulitis disease. Higher amounts of fiber in your diet has been shown to lower risk to essentially all mortality, and this high amount was only about 30 grams a day. I would caution you then, to be mindful when following diets that reduce fiber, such as the Paleo or Keto diets, even gluten-free diets.
Colorectal cancer is the third most commonly occurring cancer among both men and women in the United States (Howlander et al., 2019) and not only is fiber important, upwards of 50 grams per day (Reynolds et al., 2019), but so is folate (Hullings et al., 2020). Studies have found fiber via cereals especially helpful.
Fiber is also important for gut health in that it helps ferment, so that short chain fatty acids are created, crucial to our health. The metabolites from this effort (butyrate, propionate, and acetate) feed the ecosystem that lives within your gut but is also absorbed through the gut to nourish your entire body (Fehlbaum et al., 2018). These buzz words in functional health, n-Butyrate, propionate, and acetate support the immune system, and provide mucosal protection in the gut, as well as anti-microbial peptides. When we have low diversity within our microbiome, it reduces these fatty acids, which ultimately leads to inflammation and makes the gut susceptible to pathogenic microbes, even carcinogenic metabolites (O'Keefe, 2019).
What's really fascinating is fiber helps to create acetate, the fatty acid mentioned, and this one fatty acid helps regulate our appetite, so low fiber equals poor regulation. Propionate also plays a role in appetite regulation, as well as being anti-inflammatory and anti-carcinogenic so all those health concerns you may have or you have have genetic susceptibility would be improved by adding fiber to your diet. Huge! With regards to colorectal cancer, increasing fiber to 50 grams daily means a reduction in cancer risk by at least 13% over 15 years, and exclusively through cereal foods or whole grains (Reynolds et al., 2019).
Can Fiber Supplements Offer the Same Advantages?
Food will always be better than supplements, but supplements are better than no fiber. Recommending effective supplements is complicated though, as only a handful have shown health benefits (McRorie & Fahey, 2015).
Focus instead increasing legumes in your diet and eating at least half your grains whole. Take some times to learn about which foods in your pantry are whole grains and which are refined, particularly if you have little ones. Which wheats have higher fiber, such as amylose wheat. Whole grains would include a cup of oatmeal, quinoa, popcorn, barley and whole wheat spaghetti. Half an avocado though, has nearly 5 grams of fiber, and an apple with the skin has 4.4 grams. A pear, even better, with the skin has 5.6 grams of fiber and a cup of raspberries has 8 grams. A medium banana has 3 grams. Spinach, raw, has just 1 gram of fiber in two full cups but a cup of cooked broccoli has over 5 grams. Butternut squash, raw, has 4 grams in a cup and cubed sweet potatoes, raw, has 4 grams per cup. Black beans offer 9grams of fiber in a half cup, lima beans 4.5grams, chickpeas 5.2grams, soybeans 5.1grams, and kidney beans 4.9grams. If we look at nuts and seeds, a tablespoon of flaxseed offers 3 grams, chia seeds 3.4grams, a quarter cup of almonds 3.8grams and walnuts 2.0grams. Chunky peanut butter offers a single gram of fiber in a full tablespoon.
Take one baby step. Maybe buy some flaxseed and put that in your refrigerator. Grind a little bit up and sprinkle it on your cereal in the morning, maybe in your yogurt, or add it to your smoothie. Do this for a month, then add one more boost until you reach your target. Fiber is crucial to improving health and it really isn't the most challenging thing we can do for ourselves. Let me know your favorite tips in the comments.
References
Aune, D., Sen, A., Norat, T., & Riboli, E. (2020). Dietary fiber intake and the risk of diverticulitis disease: a systematic review and meta-analysis of prospective studies. European Journal Nutrition, 59, 421-432.
Fehlbaum, S., Prudence, K., & Kieboom, J. (2018). In vitro fermentation of selected prebiotics and their effects on the composition and activities of the adult gut microbiota. International Journal of Molecular Science, 19.
Hullings, A. G., Sinha, R., Liao, L. M., Freedman, N. D., Graubard, B. I., & Loftfield, E. (2020). Whole grain and dietary fiber intake and risk of colorectal cancer in the NIH-AARP diet and health study cohort. The American Journal of Clinical Nutrition, 112(3), 603-612.
Kim, H., Caulfield, L. E., Garcia-Larsen, V., Steffen, L. M., Coresh, J., & Rebholz, C. M. (2019). Plant-based diets are associated with a lower risk of incident cardiovascular disease, cardiovascular disease mortality, and all-cause mortality in a general population of middle-aged adults. Journal of American Heart Association, 8.
Mayor, S. (2019). Eating more fibre linked to reduced risk of non-communicable diseases and death, review finds. BMJ, 364, 1159.
McKeown, N. M., Fayey, G. C., Slavin, J., & van der Kamp, J-W. (2022). Fibre intake for optimal health: how can healthcare professionals support people to reach dietary recommendations? BMJ, 378.
McRorie, J. & Fahey, G. (2015). Fiber supplements and clinically meaningful health benefits: identifying the physiochemical characteristics of fiber that drive specific physiologic effects. In: Taylor C. (ed). The CRC handbook on dietary supplements in health promotion. CRC Press.
McRorie, J. W. & McKeown, N. M. (2017). Understanding the physics of functional fibers in the gastrointestinal tract: an evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber. Journal of Academic Nutrition & Diet, 117, 251-264.
O'Keefe, S. J. (2019). The association between dietary fibre deficiency and high-income lifestyle-associated diseases: Burkitt's hypothesis revisited. Lancet Gastroenterology & Hepatology, 4, 984-996.
Qian, F., Liu, G., Hu., F. B., Bhupathiraju, S. N., & Sun, Q. (2019). Association between plant-based dietary patterns and risk of type 2 diabetes: a systematic review and meta-analysis. JAMA International Medicine, 179, 1335-1344.
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. Lancet, 393, 434-445.
Veronese, N., Solmi, M., & Caruso, M. G. (2018). Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses. American Journal of Clinical Nutrition, 107, 436-444.
Wu, Y., Qian, Y., & Pan, Y. (2015). Association between dietary fiber intake and risk of coronary heart disease: a meta-analysis. Clinical Nutrition, 34, 603-611.
Zhang, Z., Xu, G., Liu, D., Zhu, W., Fan, X., & Liu, X. (2013). Dietary fiber consumption and risk of stroke. European Journal of Epidemiology, 28, 119-130.
Comments