Preface: I did not write this, some guy at reddit did. Here’s the original source: http://www.reddit.com/r/Fitness/comments/dhwm9/fiber_is_not_a_nutrient/
You understand that we begin the digestion process by processing the food (chewing it) into fine (hopefully) particles, then enzymes & acids in the digestive tract break those particles down into smaller particles still until you have individual molecules of fat, individual molecules of protein, and individual molecules of sugar.
The reason for this digestion process is to break the food down into it’s smallest possible unit so that it will actually pass through the lining of the digestive tract and enter the bloodstream.
Sugar is a carbohydrate. In fact, all carbohydrates are composed of repeating units of sugar.
The bond connecting the glucose (sugar) molecules in starch (you might call them so-called “complex carbohydrates”) is very weak, the process of breaking those bonds is rapid and begins as soon as you put it in your mouth and begin to chew (see: amylase).
The bonds connecting the repeating units of sugar comprising fiber (also a carbohydrate – made of sugar) are different and stronger, so different and strong, in fact, that you and I cannot digest them, therefor they never enter the bloodstream.
Many people envision the fiber entering the bloodstream and cleaning the arteries much like a Scrubbing Bubbles commercial – nope.
So what’s the benefit?
Well, if there’s enough fiber, that is, the fiber in a given food is not overwhelmed by sugar or starch, the fiber will act as a mechanical inhibitor, slowing down the digestion and absorption of the sugars/starches in the food/meal. This is beneficial because it creates a “time release” effect of the nutrients of the meal, especially important in regards to sugar, because excess blood sugar is toxic if chronic, and fattening, because of excess calories, andexcess insulin.
An average “Fiber One” bar, for instance has:
9 grams of fiber
20 grams of sugar (10 grams of sugar + 10 grams of starch (sugar)
While the box (Fiber One marketing), of course, brags about a bar being 35% of your “Daily Value of Fiber”, as if fiber were a nutrient, like protein, sugar, fat, vitamin B, vitamin C, iron, etc…(see, all these things enter the bloodstream, fiber doesn’t), what you’ve got here is too much sugar and too little fiber in relation to that sugar.
Take spinach, for instance (a carbohydrate). A serving of spinach or broccoli, or asparagus, has about 3 grams of fiber and 3 grams of sugar….along with the lion’s share of it’s mass & weight coming from vitamin/mineral-rich water. So much nutrition, in fact (in the vitamin/mineral profile), that’s it’s an embarrassing comparison for any of the grains.
Fiber is not a nutrient. Fiber is “bulk” in our diet. There are nutrients found in foods that contain fiber, but fiber is not a nutrient.