The History of Gut Bugs--Part 2 of 3

A man and his microbes (or maybe Tail Wagging the Dog?)

Three key features make humans ideal hosts for intestinal microbes[2]:

●        An adaptive immune system

●        A desire to survive by adapting to external forces

●        Lots of food and a stable environment

If microbes had a hand in the evolution of living creatures, their crowning achievement was us.

Microbes have one goal.  Survival.  They will be here long after we are gone, but I'm pretty sure they want to keep us around as long as possible.  Undoubtedly, the lives of gut bugs are much simpler with easily controllable human pods to live in.

The goals of human intestinal microbes and our goals as humans align perfectly.  A human gut bug’s wish list is simple:  A well-fed, long-living, healthy, sociable host who has a strong desire to mate.  The colonization process begins before birth, microbes begin populating places they normally are not seen such as mammary glands, birth canal, and even in the bloodstream.  When a baby is born, the first thing it encounters is a barrage of microbes who want to get inside of the new life form.  They want to become incorporated and create a superorganism.   

Every facet of our lives and behavior is influenced by the lessons our microbes learned in the last 3 billion years[3].  Our social habits, hand-shaking, kissing, hugging, sniffing, licking, and the need for kinship may certainly be all gut-bug driven to access more gut bugs and protect us against pathogens[4].  Often our interpersonal behaviors seem a bit odd, but for our intestinal inhabitants, they may have deep evolutionary meaning.

Gut bugs also hit the jackpot with humans in terms of fueling their existence. Humans are omnivores, meaning we can eat a wide range of foods of plant and animal origin.  Our intestinal microbes need this diversity to keep their living conditions stable.  A diet too high in animal or too high in plant may rock their world[5]!  Back when we were hunters and gatherers, gut microbes might have had an easier time making their human hosts understand their need for different foods.  In the modern day, we are killing them and ourselves with our desire for foods that neither benefit them nor us.   It’s almost a case of the student outsmarting the teacher.

GUT BUG FOOD THROUGHOUT HISTORY

100,000 years ago, we had spread across Africa and into the Middle East.  70,000 years ago we were well established throughout Asia.  50,000 years ago, mankind called most of Europe and Australia home.  At 25,000 years ago, we inhabited the cold regions of Siberia and shortly thereafter, traveled across the Bering Land Bridge into North America.  By 12,000 years ago, we were rooted on nearly every square inch of the Earth’s landmass.

All throughout this amazing journey, our Paleolithic predecessors ate a similar diet...small and large mammals, reptiles, amphibians, fish, birds, grub, insects, plants, tubers, and roots of all kinds.  Everywhere man went, he had access to a vitally important food source: Foods for our intestinal friends. Foods we now consider prebiotics...the fibers, resistant starches and other indigestible bits and pieces of common plant and insect-based foods.  

Prebiotics were extremely important to early man.  Our microbes that keep us healthy and motivated evolved on diets high in fiber and starch[7].  Without this fuel to feed our trillions of microbial friends, we are at a distinct disadvantage in keeping up our end of the deal—the gut bugs’ survival.

Across Africa, Asia, Australia, Europe, and the Americas, prebiotic fiber and starch sources grew plentifully.  They grew above ground and underground. As dry climate swept through after each cold spell, grass-like sedges, prairies and acres of grasslands replaced dense forest.  Besides potatoes and tubers, the new grass-like sedges and grasses provided nutrient rich bulbs, rhizomes and corms. Tiger nuts, sedge bulbs, bananas, plantains, sago, taro, cassava, mung beans, amaranth, squash, cattails, corn, seeds, and nuts were ushered in as the air became more arid and photosynthesis evolved in the dry climes, these are now known as C4 plants[8][9].  When our expansion stopped and man became more dependent on agriculture, our reliance on the plants of our past diminished.

Currently 95% of Earth's plants are the type known as “C3,” however our human food crop plants are nearly all “C4.”  Photosynthesis allows the capture of energy (CO2 and sunlight) to be placed in glucose as chains and polymers or glucose in plants, known as starches and polysaccharides. C4 plants are much more efficient at converting sunlight to compounds humans can use as energy. 

Covered in dirt and soil microbial organisms, sedge bulbs were consumed raw, uncleaned and whole. Dirt and soil based organisms covered these underground storage gems. Early man likely ate it all and on a regular basis. In their soil community, soil organisms consume starches, fiber and as well each other[12]. Encrusted on a starchy tuber, dirt bugs rode into history. Together they represent a synergistic powerhouse of both prebiotics and probiotics.

As progress marched forward into the 21st Century, the consumption of prebiotics is only a fraction of what our ancestors co-evolved with.  Tasty, marketable foods have replaced our old staples, and our gut bugs don’t enjoy it one bit!

Remember earlier, we said that humans made a perfect scaffold for gut bugs to call their native land.  Our propensity to eat a wide range of foods that could not be digested by us made our large intestines a perfect place for microbes to call home. Intestinal microbes rely on a fresh influx of fiber fuel daily for both our survival and their longevity[15].  The modern diet provides food for us, however it’s inadequate for them.This has been the biggest miscalculation by man in our long history despite the wealth of food in modern nations.   

This single faux pas has perhaps lead to widespread disease, early death, and loss of reproductive capacity.  A diet which starves the gut bugs is a diet which dooms mankind.  An agricultural industry which relies on chemical herbicides, pesticides, and fertilizer to grow genetically modified organism (GMO) crops that emit intestinal toxins is an industry which is devastating to the intestinal cities in our guts[16].  Relying on a herd of animals force-fed antibiotics, growth hormones, and fed GMO grains while being raised in a high-stress environment will ensure a meat supply of inferior grade that passes it’s weaknesses to the consumer.  Similarly, a health care industry dependent on antibiotics which indiscriminately kill both good bugs and bad bugs is an industry which delivers unbalance to man.

BRAIN-GUT CONNECTION

The trillions of microbes in our gut are credited with influencing the development of the brain, brain chemistry, and a whole range of behavioral systems such as satisfaction, serenity, sadness, pain, and stress.

The small intestine, where we absorb all of our food, has 100 million nerve connections. As the interface with the outside world, it is no wonder that the number of neurons in the gut exceeds that of both the spinal cord and peripheral nervous system combined. Microbes that live there produce hundreds of chemicals, or neurotransmitters, that the brain uses to regulate such things as learning, memory, mood, sleep, and dreaming[19].  The same amount of dopamine, the reward chemical, housed in the gut is the same as the brain's. Nearly all (95%) of our happy mood chemical, serotonin, is manufactured in the gut by a combination of microbial action and intestinal modifications.

This nervous system in our innards is the same one that originally emerged in vertebrates over 500 million years ago. However, as our ancient cranium and brain tissues tripled in size, we believe it is highly likely the 'second brain' and its special inhabitants increased in complexity and magnitude as well[20]. Gastroenterologist Emeran Mayer, MD, director of the Center for Neurobiology of Stress at UCLA once remarked,

“When you consider the gut's multifaceted ability to communicate with the brain, along with its crucial role in defending the body against the perils of the outside world, it's almost unthinkable that the gut is not playing a critical role in mind states[21]."

MIND CONTROL BY MICROBES

It may be fanciful thinking that our gut bugs are actually controlling our thoughts and behaviors, but consider if you will for a moment, the amazing life-cycle of the lancet liver fluke (Dicrocoelium dendriticum[22]).  The tiny lancet liver fluke is a parasite that infects mostly cows, although human’s have been known to harbor this pathogen also[23]. It spends its entire adult life inside the host's liver.  After the liver fluke mates, its eggs are excreted in the feces of its host.

The route in which the fluke takes to get from an egg on the ground to an adult living happily in a cow’s liver is nothing short of miraculous.  The first step in completing its life cycle involves being eaten by a snail, feeding on cow dung.  Once eaten, the egg hatches and the larval liver fluke drills into the gut wall of the snail which irritates the snail.  When the snail senses the parasitic intruder it builds a protective cyst around it and excretes it onto the ground.   

Along comes an ant who is following the snail’s trail and using the snail slime as a source of hydration.  The ant finds the cyst, which resembles one of his favorite foods, snail poop, and he eats it.  The liver fluke eats his way out of the cyst and spends a few days drifting around inside the ant’s body fluids until it finds the ant’s “sub-esophageal ganglion,” a cluster of nerve cells similar to a human’s brain, and attaches itself to it.   

The fluke is now in control of the ant.  As evening approaches, the ant, who has behaved normally all day—foraging and feeding with his hill-mates—instead of returning to its colony, the fluke controls the ant and commands it to climb and clamp onto the tip of a very tall blade of grass. In this manner, a grazing cow should come along shortly and eat the grass with the infected ant and thus complete its life cycle.  However, if a cow does not come along before dark, when a nocturnal grazer such as a rabbit or a deer might eat it instead, the liver fluke-controlled ant will unclamp its jaws and return to its anthill as if nothing had happened.  It will repeat the evening grass-climbing act until the ant dies, or a cow eats it.

This bizarre behavior of a single liver fluke inside a single ant seems like a novelty, but similar life cycles are played out by thousands of species of parasites on hundreds of different animals every day[24].  And to then realize that the lowly liver fluke also has microbes living inside it truly makes this story all-the-more bizarre[25].

With these illustrations, the true power of the brain-gut connection should be apparent and the possibility that our gut bugs are more than passive companions becomes a reality.

In humans, toxoplasmosis[26] is caused when the single-celled bacterium Toxoplasma gondii is passed from a cat to a human and infects the human’s brain leading to possible encephalitis (inflammation of the brain) and neurological diseases, and can affect the heart, liver, inner ears, and eyes.  Toxoplasmosis is also associated with attention deficit hyperactivity disorder, obsessive compulsive disorder, schizophrenia, and suicidal behavior.  Toxoplasmosis is also known as ‘Crazy Cat Lady Syndrome[27]’.

Who's really in charge?

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^[25] Abebe, Eyaulem et al. "An insect pathogenic symbiosis between a Caenorhabditis and Serratia." Virulence 2.2 (2011): 158-161.

^[26] "CDC - Toxoplasmosis." 2010. 17 Jan. 2014 <http://www.cdc.gov/parasites/toxoplasmosis/>

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