Without having any knowledge of the subject, most people understand that fiber is an important part of any fitness-enhancing diet. There are many different reasons why fiber is an inseparable nutrient to the human species, but unfortunately according to an Omnibus survey, only 5% of Americans consume an ideal amount of fiber as recommended by the US Dietary Guidelines.

Fiber has been singled out as a “nutrient of concern,” since 2005, but misunderstandings of what fiber actually is, what fiber does, where it comes from, and how much is required, all together serve to distort the picture of fiber in the diet.

Most Americans are aware that fiber is good for digestion and for promoting healthy bowel movements, but beyond the stick of celery with Buffalo wings and whole wheat bread, the statistics show they actually know very little.

The consequences of getting the fiber question wrong are far more than the occasional bout of indigestion, and can result in a variety of different upsets from immune-system health to hormonal production.

Fiber and the Gut

During a process called dehydration synthesis, glucose molecules can bind together to create larger molecules known as polysaccharides. Some examples of polysaccharides are cellulose, chitin, and starch—in other words, fiber. Polysaccharides and fiber have another name as well—complex carbohydrates.

The human digestive equipment is not very effective at processing complex carbs. As a result, they retain their structure as they travel down our GI tract. Simple carbs and sugars are often fully pulverized long before they reach the large intestine or colon; depriving the bacteria that live there of nourishment.

The colon is the eventual destination of dietary fiber, and it’s there that the fiber is fermented by the microbes that make up our gut microbiota, allowing for a rather fascinating biological process to occur.

When fiber is consumed by these microbes, their waste products are utilized by the body as nutrients. Short-chain fatty acids are one of these compounds; produced when dietary fiber is fermented in the colon. One short-chain fatty acid called butyrate acts as the primary energy source for colonic cells, and is key for colonic health and preventing colon cancer.

T-regulatory cells are members of the immune-cell family which calm the immune system, preventing them from aggressively targeting the host’s biology with excessive inflammation and damage. If dietary fiber is not consumed it’s likely the immune system is operating in a hyper-inflamed state.

It’s this hyper-inflammatory state that has been linked with the increased numbers of cases of chronic autoimmune diseases like IBS or MS, along with food allergies, asthma, and most metabolic disorders. In fact, inflammation seems to be the primary indicator and driver of aging, with most centenarians and supercentenarians displaying a telling lack of inflammation.

If starved of complex carbs, the only source of nourishment for the bacterial ecology within the gut is mucin cells within the mucus membrane which lines the inside of the GI tract. The obvious danger in this is that it enhances gut permeability going in both directions. Immune cells from inside the body inflame and target the bacteria in the gut, while bacteria which would otherwise be harmless if it remained in the gut, can seep into the bloodstream causing further inflammation as the immune system seeks to destroy the harmful agent.

Dig in the Dirt

Most foods that are minimal sources of fiber display the “Good source of fiber” USDA designation loudly on their packaging. While many cereals and whole grain/wheat bread and pasta may advertise 3-4 grams of fiber per serving, they are also loaded with inflammation-inducing simple carbohydrates, and are normally fortified with only one form of supplemental fiber, rather than a complement of different starches and cellulose that you’d find in vegetables.

The best sources of fiber are good old-fashioned, dirt-covered produce. Unlike packaged foods such as cereal or different snack bars, vegetables and fruits contain a variety of important phytonutrients including polyphenols, alkaloids, keratinoids, and tannins.

Split peas, lentils, and beans are the best commonly available sources of fiber by weight. Other great sources are vegetables like collard greens, broccoli, Brussels sprouts, and green peas. Starch-heavy vegetables like acorn and butternut squash, turnips, and parsnips, are also good choices. Finally, nuts and stone fruit, eaten with their skins on, can be a supplemental fiber source.