Way back, about 10 thousand years ago, eating lots of fiber was a way of life. Our hunter-gatherer ancestors lived off sour, fibrous and wild plants, lean wild game and fish, and they were immersed in microbes from the world around them. We have been agrarian for about 1% (10k years) of the time that homo sapiens have been on earth. In this time, our diet has become increasingly focused on refined carbohydrates and finely-ground hybridized wheat products. Our slowly adapting human genes have not been able to keep pace with the “sudden” and dramatic change in our diet.
Living in Tanzania with the Hadzabe people, anthropologist and microbiologist, Jeff Leach, has studied one of the last hunter-gatherer groups still foraging for 95-100% of its food. The most profound dietary difference between the Hadza and the rest of the world is not only a lack of processed foods, but also their tremendous consumption of dietary fiber. While eaters in developed countries consume an average of 10-15 grams of fiber/day, the Hadza eat approximately ten times that.
They consume an average of 100-180 grams of a diverse array of plant fibers daily.
It’s this fiber that gives them the huge diversity of microbes that protects them against chronic inflammatory diseases such as diabetes, cardiovascular disease, and perhaps even Alzheimer’s.
Recent scientific research has increased our understanding of just how fiber influences brain function.
The answer lies in the beneficial bacteria that reside in the gut.
These microbes depend on dietary fiber for survival.
When we eat an interesting and diverse array of plant fibers, these pass through the small intestine where most of our digestion and assimilation of nutrients occurs. The undigested fiber arrives in the colon, and is a smorgasbord for our gut bugs. The bacteria ferment, i.e feast on, these fibers and as a result, produce a special nutrient that profoundly affects our health (especially brain function!):
Short-Chain Fatty Acids (SCFA)
How do SCFA affect the gut?
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SCFA are a key fuel source for cells in the colon. Additionally, they are protective against gut inflammation and colon cancer. They also help acidify the colon which discourages overgrowth of pathogenic bacteria, like salmonella, and also helps us absorb calcium and magnesium from our diet.
How do SCFA affect the brain?
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SCFA have an anti-inflammatory impact that affects both body and brain. Systemic inflammation affects the brain and manifests as brain fog.
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SCFA directly impact brain inflammation by calming the immune cells of the brain (microglia). Over-active microglia (i.e. from post-traumatic brain injury) can perpetuate inflammation, leading to impaired cognitive function.
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SCFA bind to regulatory T cells (T-regs) in the gut. T-regs are a class of white blood cells that modulate autoimmune reactions. One type of autoimmune disease that affects the central and peripheral nervous system is Multiple Sclerosis (MS).
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SCFA decrease interleukin 1B, the inflammatory cytokine, which is linked to Alzheimer’s disease.
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SCFA delay aging of the brain.
Many factors affect the production of SCFA in your colon, including the type and number of microorganisms, the type and amount of fiber in the diet, and the time it takes food to travel through your digestive system.
The following types of fiber are best for the production of short-chain fatty acids in the colon:
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Inulin: You can get inulin from many plants, such as artichokes, garlic, leeks, onions, radishes, tomatoes, dandelion root, burdock root and asparagus.
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Fructooligosaccharides (FOS): FOS are found in various fruits and vegetables, including bananas, onions, garlic and asparagus.
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Resistant starch: You can get resistant starch from grains, barley, rice, beans, green bananas, legumes and potatoes that have been cooked and then cooled. The cooling part is key!
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Pectin: Good sources of pectin include apples, apricots, carrots, oranges and applesauce.
One of the marvels of the microbiome is its tremendous ability to adapt and change. Since they divide quickly, bacteria in the gut microbiome can double in number every 30-40 minutes. This means you can change to a less inflammatory profile in as little as 72 hours!
The key is to feed the beneficial bacteria plenty of soluble fiber, and starve the bad guys by avoiding refined sugars and processed foods.
Remember the following key points:
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Bacterial species that thrive on your diet will crowd out others very quickly, so eat the foods that beneficial bacteria thrive on: plant fibers! Don’t know which foods have high fiber? Here’s a great chart.
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Our modern diet of refined processed foods, plus our habit of eating the same foods every day, has literally starved our beneficial microbes! As a result, we have an increase of pathogenic bacteria that thrive in the more alkaline gut, thereby creating inflammation and leaky gut.
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If your gut bugs don’t get enough fiber, they turn to an alternate source of CHO (carbohydrate), the mucus lining of you large intestine – yum!
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The cardiovascular system, musculoskeletal system, immune system and nervous system all depend on SCFA production in the gut.