Fiber: Why you should consume it for your physical, digestive, and potential mental health
July 24, 2019
I just finished a 6-week summer program at Boston University studying Biostatistics. Through the course of the program, we conducted a team research project on a specific data set. As soon as I saw the National Health and Nutrition Examination Survey (NHANES) data set, I knew I wanted to investigate some sort of nutritional association. NHANES is a nationally representative survey conducted every other year including physical examinations, laboratory tests, and various questionnaire data. Part of the survey is 2-24 hour dietary recalls. Using USDA food codes, daily amounts of macro and micronutrients are calculated. Another included questionnaire is the Patient Health Questionnaire (PHQ-9) which is a measure of depressive symptoms. My group decided to investigate the association between dietary fiber and depressive symptoms. My initial thought was that higher fiber diets, which are generally healthy diets, would be inversely related with depressive symptoms. Before I get into what we found, let’s talk about fiber in general, and why you should strive to meet daily recommendations!
What is Fiber?
Many people associate fiber with pooping and other GI movements. And while yes this is true, the benefits of fiber go far beyond that of just digestive health! Fiber is a carbohydrate (cellulose) that is indigestible by humans and passes relatively intact through the GI tract. Fiber is only found in plant foods (whole grains, legumes, vegetables, fruits). Some common food sources with high amounts of fiber per serving include lentils, chickpeas, artichokes, squash, berries, chia seeds, barley and leafy greens. Daily recommended values of fiber are 25 grams for females and 38 grams for males, however 95% of Americans do not reach recommended intake-the average being around 15 grams per day! (Mayo Clinic, 2018) This is largely reflective of the standard American diet, in which many Americans do not consume recommended fruits, vegetables, and legumes. Consuming recommended amounts of fiber does take a concentrated effort. However, if you choose to eat a more whole food, plant based diet, like we explain here, it is much easier to reach recommended levels!
95% of Americans do not reach recommended daily intake of fiber
Why Should You Eat Fiber?
As stated before, fiber helps regulate bowel movements and maintains GI health. However, it does much more than that! High fiber diets lower cholesterol levels, control blood sugar levels, help maintain a healthy weight (and increasing fiber may help those trying to lose weight), and a reduced risk of many chronic diseases, including heart disease, stroke, hypertension, GI disorders, obesity, type 2 diabetes, and certain cancers (Rao et al, 2008, Quagliani & Gunderson, 2016, Mayo Clinic 2018) . As a reminder, fiber is only found in plant foods (animal products contain no fiber whatsoever), and a diet filled with plants is the healthiest diet!
Fiber and Mental Health?
Previous research has shown that nutrition can affect the onset, severity, and treatment of depression and other mental disorders (Xu et al., 2018, Rao et al, 2008). Because of the association with good physical health, and an overall healthy diet, we thought it was plausible for fiber intake to be associated with mental health as well. Additionally, because fiber is so tightly linked with the GI tract, and the brain-gut connection, there could be a pathway where fiber regulates mental functioning. While my research group could not run a causal experiment on the affects of fiber, we could run statistical analyses to see if fiber intake is correlated with depressive symptoms.
What Did We Find?
Statistically, when looking at both sexes together, we did not find a significant association between fiber intake and depressive symptoms (after adjusting for multiple confounders). However, there could still be some clinical significance to consider! Despite failing to reach a threshold for significance, increasing fiber intake was associated with a decreased risk in the odds of having depressive symptoms. Interestingly enough, when we separated the analyses into males and females, we found that for males, there was statistical significance showing that increasing fiber intake decreases your odds for depressive symptoms. If you would like to see more specifics on the methods we used and our results, check out our presentation here!
What Can We Conclude?
While we did not have enough evidence to conclude that dietary fiber is associated with depressive symptoms, another published study found that for both sexes, dietary fiber is inversely associated with depressive symptoms, and found that at about 21 grams/day your risk for depression remains relatively low (Xu et al, 2018). While both our investigation and the one just mentioned are purely observational and cannot prove causality, they suggest another benefit to a high fiber diet. All in all, getting adequate (and perhaps more than adequate) amounts of dietary fiber is not only great for digestive and physical health, but also may have protective effects from depressive symptoms.
In other words, eat more fiber, it’s more than nature’s laxative 😉
*disclaimer: The project I worked on was a learning experiment and cannot be considered published findings. Always remember to do your research when you hear about new findings when it comes to nutrition and science, and make sure it is backed by sound methods and science! The study I mentioned is linked here.
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M., & Attia, J. (2013). A systematic review and meta-analysis of dietary patterns and
depression in community-dwelling adults. The American Journal of Clinical Nutrition, 99(1),
Mayo Clinic. (2018, November 16). How to add more fiber to your diet. Retrieved from https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983
Quagliani, D., & Felt-Gunderson, P. (2016). Closing
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Rao, T., Asha, M., Ramesh, B., & Jagannatha Rao, K. (2008). Understanding nutrition,
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Xu, H., Li, S., Song, X., Li, Z., & Zhang, D. (2018). Exploration of the association between dietary fiber intake and depressive symptoms in adults. Nutrition, 54, 48-53. doi:10.1016/j.nut.2018.03.009