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A Diet Lacking in Fiber Wreaks System-Wide Havoc, Scientists Find

It's more than just weight gain—it's chronic inflammation and weak immunity.

Photo: U.S. Air Force, Airman 1st Class Grace Lee.

The first two episodes of the Netflix documentary series Rotten touch upon important issues in our relationship to food. The first focuses on the dangers of colony collapse in bee populations as well as international companies filling bottles with ingredients that definitely are not honey. The second deals with food allergies, particularly focused on the largest: peanuts.

While these are distinct issues, two themes weave these stories together. First, the impact of our environment on health. Humans have gone to great lengths to separate from nature. Yet we interact with whatever environment we live within. Effects of sedentary existences lived apart from the planet’s rhythms include the slow destruction of our bodies and pretty much every species we come into contact with.

The booming almond industry needs pollinators, which stressed beekeepers (and bees) travel hundreds or thousands of miles to accomplish in California’s central valley each season—adding to the stress. Colony collapse is rampant given the diseases these nomadic bees are now sharing. This is but one example of interdependence that we often overlook. No pollination, no honey, no almonds, no—a lot. 

The rapid onset of food allergies over the course of only one generation provides another example of our exile from nature’s rhythms. We would never eat foods apart from the environment they were grown or captured within until recently. Industrial monocultures are likely, at least in part, to blame for this stunning increase in any or all of the eight allergens, which leads us to the second theme in these episodes: our microbiome. 

These 8 foods make up 90% of all food allergies in the U.S. Image:

The bacteria that live inside of our guts is arguably the most important feature of our entire body. While the brain receives the bulk of praise, scientists have more recently raised an inquisitive eyebrow regarding all the data emerging on the microbiome. The relationship between our nervous system and gut (which has its own nervous system) is exceptionally influential on health. 

Our microbiome also directly interacts with our environment. While Purell has proven beneficial for soldiers in foreign territories, constantly sanitizing your hands weakens your immune system when in home territory. Synopsis: let your kids play in dirt. You play in dirt too. Those bacteria are strengthening.

Yet we have many weird relationships with our environment and the foods we eat, often in the invented cause of “purity.” One example is juicing, heralded as the perfect (and profitable) “cleansing” mechanism. Drink juice for five or ten days and your body “resets.” But juice is no different than soda, as you’ve removed the most beneficial part of the fruit: fiber. 

We’ve long known fiber is essential to our diet, in order to “get things moving.” Otherwise known as roughage, dietary fiber is comprised of soluble and insoluble fiber. Both play critical roles in defecation. While too much fiber can cause intestinal gas and bloating, too little, a hallmark of a highly processed diet heavy on sugar, means we’ll turn to laxatives instead of eating the fruits, plants, and grains that offer an abundance of it. 

Fiber also reduces the risk of heart disease, arthritis, and diabetes, and has been shown to lower mortality rates. But its role in digestion is particularly important. The food we consume is broken down by enzymes, its nutrients absorbed by our intestines. The molecules we cannot absorb, fiber, either pass through or, as it turns out, become food for gut microbes. 

A recent study published in Cell Host and Microbe investigates mice on a low-fiber, high-fat diet. The gut bacterial population crashed, triggering immune reactions. A similar experiment, published in the same journal, discovers that the effects of a low-fiber diet are wide-ranging: 

Along with changes to the microbiome, both teams also observed rapid changes to the mice themselves. Their intestines got smaller, and its mucus layer thinner. As a result, bacteria wound up much closer to the intestinal wall, and that encroachment triggered an immune reaction.

Continuation of this diet causes chronic inflammation; the mice also got fatter and developed high blood sugar. In both cases, the inclusion of a fiber called inulin dramatically improved their health and gut bacteria population. The researchers, which include Georgia State University’s Andrew T. Gewirtz, realized that fiber serves as an essential food for an entire population of bacteria. 

"One way that fiber benefits health is by giving us, indirectly, another source of food, Dr. Gewirtz said. Once bacteria are done harvesting the energy in dietary fiber, they cast off the fragments as waste. That waste — in the form of short-chain fatty acids — is absorbed by intestinal cells, which use it as fuel," writes Carl Zimmer for The New York Times.

The “peaceful coexistence” of bacteria in the microbial system is disturbed on a low-fiber diet. Famine breaks out. Bacteria dependent upon fiber starve, followed by the bacteria that depend upon them for sustenance. A colony collapse. What follows isn’t a disappearance, but an aggravation. 

"Inflammation can help fight infections, but if it becomes chronic, it can harm our bodies. Among other things, chronic inflammation may interfere with how the body uses the calories in food, storing more of it as fat rather than burning it for energy," writes Zimmer.

Obesity isn’t the only thing fiber fights. It is also believed to help combat or prevent immune disorders. A fiber supplement probably won’t cut it, however, since what our microbiome truly craves is a variety of fiber sources, which, fortunately, can be found in the produce aisle. 

We begin life with a disadvantage regarding fiber. In his book, Catching Fire, British primatologist Richard Wrangham writes that our relatively small colon means we cannot utilize plant fiber nearly as effectively as great apes. Cooked food provides an important means for intaking more fiber (and other nutrients) than raw plants, but thing is, we have to eat those plants. 

A diet filled with processed foods and fiber supplements is not going to cut it. Our microbiome craves what it has evolved to need in order to survive. Without those requirements those bacteria perish, initiating system-wide havoc in our bodies. Sans fiber we’re not honoring the environment that gave birth to us, and that environment is certainly speaking back. 


Derek Beres is the author of Whole Motion: Training Your Brain and Body For Optimal Health. Based in Los Angeles, he is working on a new book about spiritual consumerism. Stay in touch on Facebook and Twitter.

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