A recent set of studies was reported in the NY Times in January 2018, opening a window of understanding of not only how fiber works, but how health depends on a complex interaction between the trillions of bacteria in our gut and the cells of our gut.  https://nyti.ms/2Eujmqy

What is Fiber?

Fiber is a poor word to describe what fiber is.  The common sense of the word fiber brings to mind rope, string, textiles.  But the fiber we are talking about when we are talking about food is not string.

Fiber in food refers to a large group of molecules that all share one property- they are very long chains of sugars.

A sugar is a chemical or molecule that is made up of a ring of carbon atoms that are also linked to hydrogen and oxygen.  You may recall that a very famous combination of hydrogen and oxygen is called water.  So when combinations of hydrogen and oxygen occur in chemicals, those joint appearances of these two atoms are often called hydrates, or water-like combinations.   If you combine carbon atoms with hydrates, you get a combination called carbon hydrates, but its easier to call them carbohydrates.

If the carbon in the carbohydrate is in a ring and the hydrogen and oxygen are arranged in a certain way, that carbohydrate tastes sweet, and we call that type of carbohydrate a sugar.

Some sugars are burned by our cells very, very efficiently.  The sugar our cells love most is glucose.  It is transformed into energy, and in most situations is the only fuel our brain burns to create all our thinking energy.  Other sugars are burned but not so easily, like fructose.

Now, you may wonder, what does this have to do with fiber?  So far nothing.  But we are getting close.

The next step towards learning what fiber in the diet is brings us to long chains of molecules, called polymers.   Take glucose and starch as the easiest example.  Starch is nothing but zillions of units of glucose, one attached to the next, in a very straight line.  It is amazing to think that if you take a molecule of glucose, attach it to another, and another, and another, eventually the chain gets so long it is now starch.  That is what a potato and banana and the bread we eat are mostly made out of.  So starch is a polymer because a long chain of linked repeating units of a molecule are a polymer, and starch is indeed a long chain of linked glucose molecules each unit of which is identical.

Starch works as a food because the body chops up the chain, converting the starch into a pile of zillions of glucose molecules, ready to be burned for energy production.

The orientation of each unit in a polymer makes a big difference.  If you take a long line of glucose molecules, but instead of linking them straight on, you flip every other glucose molecule before linking them into a chain, you don’t get starch, you get cellulose.  Here is a wonderful bit of biology wonder.  If our body had the ability to chop up the cellulose polymer into its glucose units, we could eat grass and live on celery and lettuce and leaves.  Most plants are made up of a lot of cellulose, but we can’t chop up that polymer, so it is useless as an energy source.  What a dramatic difference from starch, which is also a long chain of glucose units, but a chain we can chop, and so a chain we can eat and live on.

Now we can answer that question, what is a fiber in the diet?  Fiber in the diet is a polymer of a sugar that cannot be burned to transform into energy in our body.  So starch is not a fiber, we can chop up that chain and get energy from it.  But cellulose is a fiber, we cannot chop up that chain.

So, take any sugar, link it in a very long chain, make a sugar polymer, and if the unit sugar, or the chain, cannot be burned as fuel, that chain is a fiber in our diet.

Fibers then, are chains of sugars linked in a polymer.

How does dietary fiber work to help us?

Here is where the story gets fairly amazing.

Fibers play their role in the strange and wonderful world of the collaboration between the bacteria of the gut and the human cells of the gut.

You might wonder, aren’t bacteria germs?  Don’t they cause disease and infection?  The answer is that they can cause harm, but there are literally trillions of bacteria in our gut, and these bacterial cells are essential to the normal function of our human gut cells.  They collaborate!

And, without this collaboration, the human cells that line our guts can wither and our guts become sickly.

The bacteria in our guts and our human cells lining our guts need each other, but at the same time can irritate each other, sort of like people in some ways, right?

The article in the Times, https://nyti.ms/2Eujmqy, outlines a rather remarkable dance between these two groups of cells, bacterial and human, in our gut, and the star of the dance is highly unlikely, it is mucus!

The story goes something like this:

Fiber, that chain of sugars our body cannot digest, is digested by gut bacteria.  They chop up the chain of sugars in fiber and feast on the freed sugars.  The gut bacteria thrive when we send fiber down to them (that is, eat dietary fiber).   That proliferation of healthy gut bacteria, in turn, leads to our human gut cells thriving.  When these human gut cells are happy, they have the extra energy to make a nice comfy bed of mucus to line the human gut cells.  This keeps the human gut cells and bacterial gut cells a bit apart, keeping both sides very happy.

Now, what happens if you just eat chips, candy, and swill soda?  That is, if you don’t eat any fiber?

Then the bacteria in your gut miss out on a wonderful feast of sugar, and they wither.  When they wither, your human gut cells wither, and make less mucus.  The mucus lining thins and the gut bacteria draw closer, even touch, the human gut cells.  The immune system now notices the gut bacteria and react causing the lining of the gut to get inflamed, creating a whole list of possible troubles and gastrointestinal inflammatory diseases.

So eat fiber, it feeds the good bacteria in your gut, which makes your human gut cells thrive, and sharply reduces gut inflammation and disease.

What are good foods to eat to get dietary fiber in your family’s diet?

No surprises here, the great sources of dietary fiber are found mainly in fruits, vegetables, and whole grains.

Here is a good list of specifics and how much fiber each food contains:

https://health.gov/dietaryguidelines/2015/guidelines/appendix-13/

BOTTOM LINES

1. Not all bacteria are germs, or bad.  In fact, the human body consists of 10 trillion cells and we walk around with 100 trillion bacteria on us, nearly all of which are vital to us being healthy and alive.
2. The cells of the gut bacteria are critical to the health and function of our human gut cells.
3. Dietary fiber is actually not like string or rope or fabric, it is any long chain of sugars our body cannot absorb.
4. When you eat dietary fiber, the gut bacteria can break it down and feast on the chain of sugars released.  
5.  This makes the bacteria in your gut very happy, which makes the human cells that line our gut very happy.  The human cells celebrate by making a comfy lining of mucus that keeps the hordes of gut bacteria a bit away.
6.  If you don’t eat fiber, the bacteria in the gut wither, the human cells lining our guts wither, and the mucus lining gets very thin or absent.  This allows the bacteria in the gut to come close enough to the human cells lining the gut for our immune system to get upset and attack.  This attack creates gut inflammation, the source of many, many gut diseases.

So, eat dietary fiber, just another reason to eat mainly fruits, vegetables, and whole grains.

To your health,
Dr. Arthur Lavin