Impact of Fiber on Overall Health

Impact of Fiber on Overall Health

Joy Stepinski, MSN, RN-BC

April 4, 2023

Gut health has been widely publicized in recent years. As the largest microbiome within the human body, the intestine houses an abundance of microbes that have important functions. These microbes direct biological processes [1], including immune function, glucose and lipid metabolism, and brain and nervous system communication.

The balance of microbes within the gut is very important to whole health. In fact, one study examined 76 fecal samples and suggested that altered microbial populations were associated with depression [2]. Other research findings show that changes within the microbiota can lead to inflammatory diseases, such as cancer, allergies, autoimmune diseases, obesity, metabolic syndrome, and inflammatory bowel disease [1, 3].

The rise of disease appears to be connected to the loss of beneficial microbes. Western diet is thought to play an enormous role in causing lack of diverse bacteria within the gut microbiome [1]. Among a variety of factors, low intake of fiber and increased consumption of fat and sugar contribute to the depletion. According to the USDA Dietary Guidelines for Americans [4], “more than 90 percent of women and 97 percent of men do not meet recommended intakes of dietary fiber” (p. 101).

What exactly is fiber? Fiber comes from plant-based compounds [5]. It is categorized as soluble or insoluble, although plant cell walls often contain both [6].  Insoluble fiber, like wheat bran, absorbs water to provide bulk and laxation. Soluble fiber, on the other hand, dissolves in water to form a gel-like substance and is fermented by the microbes within the microbiome. Examples include raw fruits and vegetables, oats, and barley.

The relationship between the abundant microbes and the body is significant for health. Various microorganisms create a balanced environment, including bacteria, bacteriophages, fungi, viruses, and archaea. Their role helps inhibit growth of pathogens and control inflammation within the gut [7].

The fermentation of fiber by these microbes leads to benefits. This process is important for regulating metabolic functions, like blood glucose, and maintaining intestinal homeostasis. One metabolite, or substance produced by fermentation, is a short chain fatty acid (SCFA). SCFAs are vital to digestive tract cell health because they provide energy. They also play a role in intestinal cell proliferation, differentiation, and gene expression to influence gut motility and protect the integrity of the intestinal barrier.

Notably, one study [8] researched the difference of stool samples among 58 children with autism in comparison with 39 children considered healthy. The results found that children with autism had lower levels of SCFA, suggesting that there are less beneficial bacteria to produce SCFA’s, a low intake of soluble fiber, and/or increased absorption of SCFA into the bloodstream because of increased gut permeability. Gut permeability refers to the ability of material to pass through the intestinal wall.

A separate review discussed the benefits of fiber on patients diagnosed with diabetes type 2 [9]. Consumption of saturated fat is associated with insulin resistance, which leads to a rise in blood glucose levels. However, studies have demonstrated that increased fiber consumption improves the ability for insulin to function properly.

The role of fiber is significant in men’s and women’s health. The intake of fiber appears to help prevent breast cancer. One study investigated the diet differences between Asian and Caucasian women [10] living in the United States. Asian women typically experience breast cancer less. The purpose of the study was to understand the relationship of estrogen levels between the different diets. The authors found that Caucasian women consumed higher amounts of animal foods, while Asian women ate significantly less fat and calories, and 30 to 40% more fiber. Premenopausal Asian women also excreted estrogen compounds in their feces significantly more than the Caucasian women (feces of postmenopausal women was not measured). Other studies report that low-fat and high- fiber diets may reduce the risk of benign prostatic hyperplasia (BPH), common among men [11].

Fiber can provide cognition benefits as people age. Researchers investigated the effects of fiber on disabling dementia among Japanese subjects [12]. Disabling dementia was defined as dementia requiring care under the national insurance. The dietary intake of 3,739 participants was followed for a median of 19.7 years. When comparing the fiber intake of the 670 cases of dementia to those without, the authors reported that dietary fiber intake was inversely associated with risk of disabling dementia.

Other research investigated the effects of fiber on the gut microbiota of patients with advanced colorectal adenoma versus a healthy group. Both groups totaled 344 subjects. Dietary fiber intake, SCFAs, and gut microbiota were compared. Results showed an altered fecal gut microbiota among cancer patients, as well as lower amounts of fecal SCFAs. The authors concluded that diets low in dietary fiber led to these findings [13].

In the China Study, a large research study that occurred in the 1980s, investigators found that people in rural China consumed fiber three times higher than Americans [14]. Blood cholesterol was noted to be inversely associated with dietary fiber intake. Yet it was directly associated with dietary fat, animal protein, and meat. As a result, the authors noted that Western diseases are diseases of nutritional extravagance. They concluded that diets containing a variety of good-quality plant foods are correlated with the lowest disease rates.

High fiber diets are ones centered around whole plant foods (fruits, vegetables, and whole grains). Because fiber is such an important contributor of gut microbial diversity, consider eating meals comprised mostly of plants. The plants will feed the microbes, which maintain a crucial balance within the body. When the body is more balanced, it can heal!

References

1.  Makki, K., Deehan, E. C., Walter, J., & Bäckhed, F. (2018). The impact of dietary fiber on gut microbiota in host health and disease. Cell Host & Microbe, 23(6), 705-715. https://doi.org/10.1016/j.chom.2018.05.012

2.  Jiang, H., Ling, Z., Zhang, Y., Mao, H., Ma, Z., Yin, Y., ... & Ruan, B. (2015). Altered fecal microbiota composition in patients with major depressive disorder. Brain, behavior, and immunity, 48, 186-194. https://doi.org/10.1016/j.bbi.2015.03.016

3.  Sonnenburg, E. D., & Sonnenburg, J. L. (2014). Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metabolism, 20(5), 779-786. https://doi.org/10.1016/j.cmet.2014.07.003

4.  USDA. (2020). Dietary guidelines for Americans 2020 – 2025. https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf

5.  Hornick, B., Liska, D., Dolven, C., & Wrick, K. L. (2011). The fiber deficit, part I: whole grain contributions to health and fiber intakes. Nutrition Today, 46(6), 293-298. https://doi.org/10.1097/NT.0b013e318239635f

6.  Hills Jr, R. D., Pontefract, B. A., Mishcon, H. R., Black, C. A., Sutton, S. C., & Theberge, C. R. (2019). Gut microbiome: Profound implications for diet and disease. Nutrients, 11(7), 1613. https://doi.org/10.3390/nu11071613

7.  Parada Venegas, D., De la Fuente, M. K., Landskron, G., González, M. J., Quera, R., Dijkstra, G., ... & Hermoso, M. A. (2019). Corrigendum: Short chain fatty acids (SCFAs)-mediated gut epithelial and immune regulation and its relevance for inflammatory bowel diseases. Frontiers in Immunology, 10, 1486. https://doi.org/10.3389/fimmu.2019.01486

8.  Adams, J. B., Johansen, L. J., Powell, L. D., Quig, D., & Rubin, R. A. (2011). Gastrointestinal flora and gastrointestinal status in children with autism–comparisons to typical children and correlation with autism severity. BMC Gastroenterology, 11(1), 1-13. https://doi.org/10.1186/1471-230X-11-22

9.    Bessesen, D. H. (2001). The role of carbohydrates in insulin resistance. The Journal of Nutrition, 131(10), 2782S-2786S. https://doi.org/10.1093/jn/131.10.2782S

10.   Goldin, B. R., Adlercreutz, H., Gorbach, S. L., Woods, M. N., Dwyer, J. T., Conlon, T., ... & Gershoff, S. N. (1986). The relationship between estrogen levels and diets of Caucasian American and Oriental immigrant women. The American Journal of Clinical Nutrition, 44(6), 945-953. https://doi.org/10.1093/ajcn/44.6.945

11.   Barnard, R. J., Kobayashi, N., & Aronson, W. J. (2008). Effect of diet and exercise intervention on the growth of prostate epithelial cells. Prostate Cancer and Prostatic Diseases, 11(4), 362-366. https://doi.org/10.1038/pcan.2008.6

12.   Yamagishi, K., Maruyama, K., Ikeda, A., Nagao, M., Noda, H., Umesawa, M., ... & Iso, H. (2023). Dietary fiber intake and risk of incident disabling dementia: The Circulatory Risk in Communities Study. Nutritional Neuroscience, 26(2), 148-155. https://doi.org/10.1080/1028415X.2022.2027592

13.   Chen, H. M., Yu, Y. N., Wang, J. L., Lin, Y. W., Kong, X., Yang, C. Q., ... & Fang, J. Y. (2013). Decreased dietary fiber intake and structural alteration of gut microbiota in patients with advanced colorectal adenoma. The American of Clinical Nutrition, 97(5), 1044-1052. https://doi.org/10.3945/ajcn.112.046607

14.   Campbell, T. C., Parpia, B., & Chen, J. (1998). Diet, lifestyle, and the etiology of coronary artery disease: the Cornell China study. The American Journal of Cardiology, 82(10), 18-21. https://doi.org/10.1016/S0002-9149(98)00718-8