The main differences and benefits of soluble versus insoluble fiber
To successfully address the benefits , first lets discuss the mechanistic differences between soluble and insoluble fiber. Soluble fibers act as a dry sponge within the digestive tract absorbing water and nutrients along the way creating a viscus consistency. Soluble fibers having such high water holding capacity creating the gel like product slows the digestion and absorption process of nutrients. This absorption process attributes to reducing the amount of low density lipids (LDL - bad cholesterol) in the bloodstream which are then excreted rather than absorbed. Fibers high in solubility include; pectin’s, gums and beta glucans (Gropper, pg.117). Soluble fibers inherently are also known to be highly fermentable within the colonic microflora. SOME of these fibers are known to be rich in prebiotics which stimulate the growth of intestinal bacteria (probiotics) which have been associated with overall improvement in the GI tract.
Sources rich in soluble fiber
Berries
Bell peppers
Citrus fruits
Peas
Oats
Apples
Beans
Carrots
Avocados
Pears
Brussel sprouts
Conversely, insoluble fibers move through the GI tract quickly and are essentially unchanged once excreted through the body. Though are not substantially broken down within the intestines they still contribute to colonic health. Insoluble fibers are less fermentable or non-fermentable and play a vital role in the detoxication of the colon. The fibers can absorb carcinogens to prevent their interaction with the mucosa within the colon. The inability to breakdown these insoluble fibers also allows for the promotion of increased fecal volume. Increased fecal bulk increase frequency of passing bowel movements, reduces intestinal transit time, and decreased intraluminal pressure (Gropper, pg. 124). Insoluble fibers that promote these properties include; cellulose, psyllium, inulin, and oligosaccharides.
Sources rich in insoluble fibers
Oats
Whole grain products
Barely
Celery
Zucchini
Potatoes
Cauliflower
Popcorn
Broccoli
Now with a clear understanding of the different components of soluble and insoluble fibers, let's review how these mechanisms aid optimal bodily functions.
According to a meta-analysis conducted over the course of 37 years concluded that diets high in dietary fiber (specifically beta glucan and/ psyllium both of which are comprised mainly of soluble fiber) appear to reduce fasting blood glucose concentrations and glycosylated hemoglobin percentages (McRae et al, 2018). This is due to the slowing of the digestive and absorption properties soluble fibers conduct when creating a viscus substance. The delaying of glucose reduced the post meal plasma glucose and insulin levels (McRae et al, 2018). These mechanisms alone are means to promote increased soluble fiber consumption to help in blood glucose management and increase insulin sensitivity. The viscous gels formed from the soluble fibers have been proven to improve glycemic control, reduce the rate of glucose absorption and insulin secretion, and increase insulin sensitivity. All of which are highly beneficial for those who are diagnosed with or at high risk of developing Type 2 diabetes.
According to “Total, Insoluble, and Soluble Dietary Fiber Intake and Insulin Resistance and Blood Pressure in Adolescents”, an increased consumption of both forms of fiber inversely effected insulin resistance and fasting glucose levels. The study concluded that both insoluble and soluble fibers can benefit those with increased risk of type two diabetes and promote improved blood glucose management of those diagnosed with type two diabetes. (Dong et al, 2019).
When working on increasing fiber intake it is important to note it should be done in a gradual manner overtime. If someone consumes a diet naturally very low in fiber (> 10 g/day) consuming 20+ grams of fiber overnight can cause a multitude of uncomfortable side effects such as: excessive gas, bloating, and constipation. Which is the exact opposite effect of what we are aiming for when increasing fiber. The current U.S dietary guidelines recommend about 20-30 grams/day.
Regular consumption of adequate fiber, can improve benefits that promote optimal health and well being.
Take aways from this article include
Both forms of fiber are a necessary component of a healthy diet
Many food sources contain both insoluble and soluble fiber components
Soluble fibers provide steady blood glucose control hence prolonged energy
Soluble fibers help reduce LDL levels in the bloodstream, improving cardiovascular health
Insoluble fibers provide stool bulk allowing for anti-carcinogenic protection
Both forms of fiber are great sources of prebiotics, probiotics, and symbiotics
When working on increasing fiber in the diet do so slowly over time to prevent constipation
The recommended dietary intake is 20–30 g of fiber/day for adults
Recipe link below!
References
Abutair, A. S., Naser, I. A., & Hamed, A. T. (2016). Soluble fibers from psyllium improve glycemic response and body weight among diabetes type 2 patients (randomized control trial). Nutrition journal, 15(1), 86. https://doi.org/10.1186/s12937-016-0207-4
Bozbulut, R., & Sanlier, N. (2019). Promising effects of β-glucans on glycemic control in diabetes. Trends in Food Science & Technology, 83, 159–166. https://doi.org/10.1016/j.tifs.2018.11.018
Dong, Y., Chen, L., Gutin, B., & Zhu, H. (2019). Total, insoluble, and soluble dietary fiber intake and insulin resistance and blood pressure in adolescents. European journal of clinical nutrition, 73(8), 1172–1178. https://doi.org/10.1038/s41430-018-0372-y