Is fiber essential to your health?
A deep-dive into the latest understanding of how plant fiber affects digestion and gut health
The Mayo Clinic tells its followers that dietary fiber is essential to our health. It supposedly normalizes bowel movements, lowers cholesterol, helps control blood sugar levels, aids in achieving healthy weight, and helps you live longer. That’s a lot of promise for a substance that the human body cannot digest. Dig a little deeper, and you’ll find the story of fiber is much like that of saturated fat - based on correlation, not causation, and to this day scientifically unproven.
High-fiber recommendations originated in the 1970s with a charismatic individual, Denis Burkitt, who developed a theory based on personal observation of tribes in Africa. Despite the lack of rigorous clinical research, the cereal industry found his logic was good for business, and the rest is history.
Many people worry about fiber intake and fear constipation when switching to a keto/carnivore way of eating, so we wanted to check the latest thinking to better understand the confusion around this aspect of nutrition. Here is a summary of what we found:
Fiber is not a nutrient. Fiber comes from the cell walls of plants. It is considered a form of carbohydrate (along with starch and sugar), but it does not contain vitamins, minerals, or calories. According to the experts at Virta Health, the body does not need any dietary carbohydrates, including fiber, to thrive.
There are two types of fiber, both are indigestible: Soluble fiber dissolves in water and forms a gel-like matter in the gut. Chia, flax, guar gum, and psyllium are some examples. This type of fiber cannot be digested by enzymes in the small intestine, although it may be broken down somewhat by bacteria that live elsewhere in the gut. Insoluble fiber is roughage (think celery, lettuce, leafy greens). It does not dissolve but passes through the body more or less intact. (What goes in must come out!) Insoluble fiber irritates the large intestine and tends to dry out the digestive tract. It also can bind to essential minerals making them unavailable to the body.
Fiber does not initiate elimination or alleviate constipation. Did you know, dietary fat (not fiber) is responsible for starting the elimination process? Gut Sense author Konstantin Monastyrsky explains: “Dietary fat stimulates the release of bile from the gallbladder, which, in turn, stimulates the gastrocolic reflex. This, in turn, stimulates peristaltic mass movement, which, in turn, stimulates defecation.”
Adding high amounts of fiber to an already blocked elimination system makes the symptoms worse. Don’t confuse higher volume, more frequent bowel movements with improved bowel function, as measured by better consistency, less discomfort, etc. Instead of turning to fiber supplements, try eliminating dairy, drinking more water, discovering food sensitivities, improving thyroid function, lowering stress, and giving your body time to adjust to a major change in nutrition (like keto).
Eating concentrated forms of fiber does not offset sugar and starch intake. In whole foods, fiber is subtracted from total carbs to determine net carbs for the purpose of tracking your keto macros. But watch out for keto-branded foods that pack psyllium husk, glucomannan, pectin, modified wheat starch, inulin, chicory root, soluble corn fiber, cassava root fiber, oat fiber or flaxseed meal into their formulas to make the NCs appear lower. Added fiber in a manufactured food-like substance is not the same as ingesting fiber as part of a whole food. As Dr. Georgia Ede explains in her article, Pulp Fiction, “We were not meant to swallow concentrated extracts of plant fiber. We were designed to eat whole foods.”
As a side note, checking the Senza Trends page for your fiber intake over time is a good way to find out if the packaged keto foods you’re eating contain high amounts of hidden fiber.
Fiber can reduce blood sugar spikes a little by slowing the digestion process. This aspect of fiber may help people eating a high-carb Standard American Diet (SAD), but once you switch to a keto/carnivore way of eating, you don’t need to rely on fiber for this marginal benefit. Restricting your carb intake to maintain ketosis will balance blood sugar more effectively than adding any amount of fiber.
Fiber can lower LDL cholesterol. True, but the science of cholesterol also has changed, and LDL isn’t necessarily the metric to watch for preventing heart disease. More on this topic in a future issue of Fix the Food, but some of the best resources include: Peter Attia’s blog; Eat Rich, Live Long by Ivor Cummins and Jeff Gerber; and Dave Feldman’s Cholesterol Code.
Fiber doesn’t help you feel full. Fiber makes people feel gassy and bloated. Protein helps you feel full. It’s important to note the difference.
Fiber is not proven to support weight loss. Studies that have attempted to show a connection here repeatedly fail because of inconsistent and limited observational data.
Fiber may be beneficial for gut health in some people, but it’s not the end-all/be-all. Microbiome researcher Lucy Mailing explains that while fiber supports the lining of the colon by fermenting into short chain fatty acids like butyrate, an alternative way to support the same cells is through protein fermentation into isobutyrate and ketones in the blood.
“Fiber has been mis-stated as the only way to support gut health,” she says. “The ideal diet promotes metabolic flexibility.”
The story of fiber is a good reminder that our food/nutrition culture struggles to understand nuance.
The benefits of fiber have been overstated by an industry that profits from adding it to manufactured products and calling these foods “heart healthy.” The effects of eating plant fiber depend on whether the individual has high or low levels of inflammation, is metabolically flexible or not, and has any known sensitivities to antinutrients in plants.
Fiber in the context of a whole food is different from fiber that’s extracted through an industrial process and then added to processed foods in concentrated form.
More fiber isn’t necessarily better, especially when the digestive tract is strained or blocked.
If you know that your body tolerates dietary fiber well and you can switch easily between fat-burning and sugar-burning states, by all means enjoy these foods in their whole forms. But if gastric distress is a regular occurrence, consider experimenting with a lower fiber intake - and give it time to assess the results. Above all, don’t blame protein and fat for the side effects of eating carbs.
More Fiber Resources:
Fiber Menace: The Truth About the Leading Role of Fiber in Diet Failure, Constipation, Hemorrhoids, Irritable Bowel Syndrome, Ulcerative Colitis, Crohn's Disease, and Colon Cancer - by Konstantin Monastyrsky
Diagnosis Diet: Dr. Georgia Ede’s take on fiber
Do You Need Fiber on the Carnivore Diet? All Things Carnivore presents an evidence-based point of view on fiber.
Fiber Myths and Truths: Do We Really Need Fiber? Doctor Kiltz
Do you need plant fiber for a healthy gut? Dr. Paul Saladino interviews Lucy Mailing, PhD, on the Fundamental Health Podcast. Start at 37:21 for the discussion of fiber.