Soluble Fiber

    I didn’t learn about the importance of dietary fiber in medical school, probably because there was very little instruction on nutrition. I’ve certainly heard plenty about fiber since. Most reviews divide fiber into two categories: soluble and insoluble. “Soluble” things can be dissolved in a liquid, like salt or sugar, so “soluble fiber” baffled me. How could fiber be dissolved?

    Then I realized my confusion might be due to my definition of “fiber.” I began using fibers in elementary school. I embroidered, knit, crocheted, made macrame, and sewed clothing, with varying levels of skill. I even latch-hooked a small rug during my medical internship, that hangs in my office today. Fiber, to me, was a filamentous substance that was used to make cloth. Substances like that won’t dissolve in water.

    I asked Google for definitions of fiber, and here’s what came up:

1. a thread or filament from which a vegetable tissue, mineral substance, or textile is formed

2. dietary material containing substances such as cellulose, lignin, and pectin, that are resistant to the action of digestive enzymes

    So dietary fiber is a substance that the human gut cannot digest, including both insoluble and soluble fiber. Insoluble fiber is what my handiwork-trained brain thought of, such as the stringy material in celery. Soluble fiber becomes gel-like in water, but it can’t be digested and so meets the medical definition of “fiber.”

SOURCE: https://edelweisspublications.com/keyword/49/1981/Dietary-Fiber

    As it turns out, soluble fiber is especially important for the gut microbiome. Human enzymes can’t digest it, but the gut bacteria can. They in turn make many substances, like butyrate, that help keep colon cells healthy.

    I thought I was alone in my misunderstanding of “fiber” until a recent discussion with a patient. After our conversation, I decided to share this explanation with all of you.

    So, to get more fiber into your diet, include sources of soluble fiber, such as beans, fruits and vegetables, and whole grains. That’s what your gut bacteria like to eat.

    Some of you might be wondering what happens to fiber when vegetables are juiced. It makes sense that juicing would remove insoluble fiber. But if some fiber is soluble, wouldn’t it wind up in the juice?

    I started my research by consulting Dr. Google. I found several websites that included percentages of how much soluble fiber is removed in juicing. I looked for the scientific references in those posts. There weren’t any.

    Then, I looked for scientific references myself, and found nothing that properly addressed my question. This didn’t surprise me, because who would fund such research?

    Finally, I wrote the author of one of the more technical articles I found. The answer: we don’t know. More research is needed.

    In the meantime, I plan to drink my vegetable juice, in addition to eating my vegetables.