Fiber: you know the drill. Eat just enough of it, and your bowel movements will be more cohesive. Eat too much of it, and you’ll face an “obstruction of justice.” This is something we know from common sense and from experience. What fewer people know is that fiber works with your digestive tract in ways that reduce your risk of intestinal diseases.
First, a quick review: what is fiber? Simply put, fiber is any organic material your body can’t digest. Plant food sources contribute the most fiber to your diet because all plants contain cellulose, a sugar that makes up the cell walls of all plant cells. Herbivorous animals like rabbits have special digestive systems that allow them to thrive on stuff like this, but we, for better or worse, do not. Humans can get fiber from beans, whole grains, and brown rice.
So we know that fiber literally makes up the bulk of our waste. But that’s not its only function. Fiber is also what your digestive tract uses to clean itself. Several places in the body are sites of rapid cell division, and the digestive tract is one of them. Lining the inside of our digestive tracts are cells called epithelial cells, which die, are sloughed off, and grow back roughly every five days. Fiber facilitates this process simply by gliding along the intestinal walls and scrubbing the surface as it goes.
This is important not only for the general upkeep of your plumbing, but also for reducing the risk of serious diseases. Fiber has an impact on one’s risk of diabetes because high-fiber foods tend to have low glycemic indexes. They also improve glycated protein levels, a characteristic of bodies that handle glucose well. There is some controversy regarding the importance of fiber for reducing the risk of certain cancers of the digestive tract, and according to recent scientific reviews there is no statistically significant link between fiber and cancer (Kendall, Esfahani & Jenkins 2010). Regardless, foods high in fiber tend to be better for you, so the moral remains the same: eat foods that are high in fiber!
Fiber does not directly contribute to energy intake, but it plays an essential role in the absorption of macronutrients. Dietary fiber changes the constitution of the matter that passes through your gut—makes it more viscous—and this has two effects: first, it increases the viscosity of the organic matter in your gut, which causes more macronutrients to be absorbed; second, it increases digestion time, which further increases nutrient absorption—another twofold benefit of dietary fiber (Kaczmarczyk, Miller & Freund, 2012).
What should you do? The answer is simple: love your gut. Look for natural foods before supplements because our bodies have evolved to digest real, whole foods. Eat beans, crunchy vegetables, whole grains, brown rice, bran, and steel-cut oatmeal. Fiber is easy to find and relatively cheap, and the benefits are, frankly, difficult to do without.
Kaczmarczyk, M. M., Miller, M. J., & Freund, G. G. (2012). The health benefits of dietary fiber: Beyond the usual suspects of type 2 diabetes mellitus, cardiovascular disease and colon cancer. Metabolism, 61(8), 1058-1066. doi: http://dx.doi.org/10.1016/j.metabol.2012.01.017
Kendall, C. W. C., Esfahani, A., & Jenkins, D. J. A. (2010). The link between dietary fibre and human health. Food Hydrocolloids, 24(1), 42-48. doi: http://dx.doi.org/10.1016/j.foodhyd.2009.08.002