That’s a definition of digestion.
Fiber is something that is not absorbed through the small intestine into the blood stream. The most common one is cellulose which is a molecule that is used by plants to form their cell wall. Cellulose is a chain of glucose molecules linked together. Starch is also a chain of glucose molecules linked together. The difference between Cellulose and Starch is that in Cellulose the linkages are comprised of beta bonds, while Starch it is alpha bonds. The enzyme in humans that break apart glucose molecules can only break alpha bonds, not beta bonds.
Some animals (like cows) have bacteria that do produce an enzyme that can break beta bonds. These are the animals that can survive eating nothing but cellulose containing plants.
How is that an answer to the question: “Are you saying that all *ingested *food is broken down to component molecules?”
It seems to me that the following statement is false:
It’s obvious that this doesn’t happen to *every part *of food that gets put into the body.
What am I missing here?
I honestly don’t know.
To me it’s obvious that it does happen. Nothing can be absorbed into the body properly without being broken down this way. (A few proteins sometimes leak through and cause allergic symptoms, but that’s a pathological event.) Waste material occasionally does not get broken down if it is not properly mechanically pulverized (the occasional kernel of corn) but the body is not designed to deal with whole chunks of food materials as waste. It takes all food apart and reduces it as much as possible. Even the fiber is often fermented by the bacteria in the colon.
So I still don’t understand what you think actually happens. Why do you think digestion doesn’t work the way I say? What specifically do you think does not work like this? How does it work if not like this? What is the final composition of fiber in your understanding? What other foods do not get broken down?
I can’t begin to give you a better answer than what I have unless you give me some clue as to what your knowledge is. You say I’m wrong but you haven’t given me a hint as to what is right. I’m not trying to be snarky. I’m trying to explain but just telling me no gives me nothing to work with.
When you said that “every other part of food that gets put into the body”, I took that to mean “every other part of food that is ingested”, not “every other part of food that is aborbed”. Fiber is not absorbed into the body – it is excreted. Kinda the definition of fiber.
But, there’s still this:
Well, not by the human digestive system. It is processed, yes, but it is not broken down to individual molecules. If it is, then what is excreted? The explanation of feces that you provided says that fiber is “undigested food residue”. Undigested. What does that mean to you?
The definitions that I provided of fiber (and the Wikipedia article) all refer to it as something that the body can’t digest. Why do you insist that fiber is digested?
Many parts of food are not broken down by the human digestive system. You’ve already mentioned hard-shelled peas and corn, but, more important, the cellulose in plants is not broken down. (Hirka T’Bawa’s post seems to agree with this.)
That’s what I think, anyway. Please correct me if I’m wrong.
Just to clarify: It’s obvious that the fiber in food is “processed” by the body, meaning that it doesn’t exit in exactly the same form that it entered. But, that’s quite different from saying that it is broken down to component molecules.
Cellulose is a type of fiber. It is not digested in the sense that it is not broken down into the individual glucose elements that make up the cellulose polymer. But it is not left unchanged either. As I said cellulose in foods form large interconnected sheets that make the stringy plant fibers that give fiber its name. (Other fibers work similarly, although not identically. They are similar enough to be treated alike for this example, though.) These stringy fibers do not appear in the waste. Cellulose is processed to remove the bonds that cause the structures it has in plants and is reduced to the large multi-hundreds or thousands of glucoses that form the cellulose molecule.
You still haven’t explained what you think happens to the cellulose once it is eaten. That’s the step you keep not giving.
Okay, I’ll start with one of your previous questions:
My understanding is consistent with the Wikipedia article on Dietary fiber:
This is not consistent with your claim:
Okay, so what is fiber? Do you disagree with the Wikipedia article when it says:
And, let’s look at what it says about some of components of fiber when it comes to digestion:
Lignin:
When you say “broken down to component molecules”, you are using “broken down” differently from how it’s used above, and you are referring to a cellulose chain of D-glucose units, rather than to the D-glucose units themselves. This was part of my confusion.
In any case, dietary fiber consists of more than just cellulose. Not all fiber is “broken down to component molecules”. Not “certainly”.
I’ve already made explicit - more than once - that there are two definitions of digestion, and I’ve made the distinction between absorption by the body, which I’m calling hydrolysis, and the complete process of food processing from mouth to anus.
So we can eliminate those links that are redundant in that they simply restate that distinction.
And that leaves… well, nothing. All your links merely restate what I’ve already said.
The question remains. What do you think happens, in detail, to cellulose from the time it is taken it at the mouth until the time it is released in stool?
I also need to comment on an earlier post of yours. Food passing through the body relatively untouched is an extremely rare event. You can check this by merely looking at your stool on a daily basis. People like to comment on a pea emerging in recognizable form, but that’s like commenting on an airline crash. Everybody talks about it, but the norm is exactly the opposite.
Please don’t turn the tables on me.
My first post in this thread started with this quote of yours:
I’ll keep this simple: Please provide a cite for your claim.
Fiber is not broken down into individual molecules by the hydrolysis digestive processes; a small amount of breakdown occurs by fermentation by bacteria in the digestive system, and subsequently uptaken into the intestinal wall, but this contributes little to overall metabolic function. Fiber (if sufficient broken down by mastication or some other mechanical structural reducing process) can participate in condensation reactions in the colon, and in fact this is the primary benefit to soluble dietary fiber. Non-soluble fiber contributes only to the sense of satiety; it provides no known nutritional or health benefit.
To answer the o.p. breaking down fiber by blending or another mechanical process contributes somewhat to gross solubility but does not destroy the fiber content or nutritional value of soluble fiber, and may even make it more effective. Drink your juice.
Cite?
From Exercise Physiology: Energy, Nutrition, & Human Performance, 6th Ed (the most widely used exercise physiology textbook in the United States):
Fiber, classified as a nonstarch, structural polysaccharide, includes cellulose, the most abundant organic molecule on earth, first recognized by French chemists Anselm Payen and Jean-Francois Persoz in 1834. Fibrous materials resist chemical breakdown by human digestive enzymes, although a small portion ferments by action of intestinal bacteria and ultimately participates in metabolic reactions following intestinal absorption.
Stranger