Digestion of Carbohydrates
What
Are Carbohydrates? - Complex Carbohydrates
- Monosaccharides
Disaccharides - Oligosaccharides
- Polysaccharides - Simple
Carbohydrates - Starch - Sugars
Dietary Fiber - Types
of Dietary Fiber - Best Sources
of Dietary Fiber - Benefits of
Dietary Fiber
Daily Fiber Needs - Fiber
& Weight Loss - Fiber
& Low Carb Diets
Simple carbs, being sugars (glucose), are absorbed into the bloodstream very quickly. The exception is fruit sugar (fructose) which needs to be converted into glucose first.
Complex carbs (especially low glycemic index complex carbs) many of which are starchy carbohydrates, need more time to be digested.
The Digestion Process
Digestion of Starches
The process begins in the mouth when an
enzyme in saliva (amylase) begins to break down starchy carbohydrates.
After swallowing, the starchy carbs reach
the stomach where hydrochloric acid combines with them and acts on the
protein in the food. The stomach also acts as a reservoir for food, squirting
out small amounts into the intestines at intervals.
In the small intestine (where most carb-digestion
occurs) the starch is processed by the enzyme amylase and converted into
maltose and sucrose.
The maltose and sucrose are then absorbed into the lining cells of the intestine and are further simplified, being converted into glucose.
Digestion of Sugars
Simple carbohydrates, or sugars, (eg. table sugar) are digested by an enzyme in the lining of the small intestine. Examples: Table sugar is broken down into glucose and fructose, each of which is then absorbed from the intestinal cavity into the blood. Milk contains another type of sugar, lactose, which is broken down by an enzyme called lactase, also found in the intestinal lining. See also Carb Blockers
When Glucose Enters the Bloodstream
Once the starchy or sugary carbs are digested
and converted to glucose, the glucose then enters the bloodstream and
the level of blood-glucose rises. This induces the pancreas to secrete
insulin into the blood which "mops up" the glucose and helps
convert it into the storage-type of carbohydrate, called glycogen,
which is deposited in the liver and in the muscles.
When the liver and muscle glycogen stores
are full, any extra glucose is converted into fat. This adds to fat stores,
but to a lesser extent than fat released from fatty foods.
The liver glycogen helps to keep blood-sugar
levels in the normal range. If blood sugar falls, glycogen is converted
into glucose which enters the blood. If blood sugar rises (say) after
a meal, insulin is again released from the pancreas which converts the
glucose into glycogen. And so on.
The human body typically packs about 400 grams (14 ounces) of glycogen
into liver and muscle cells. If you add up all the glucose stored in glycogen,
plus the small amount of glucose in the bloodstream, it equals about 1800
calories of energy.
Digestion of Nutrients in Starches or Sugars
Other nutrients in carbs, like vitamins and minerals, are dissolved in the small intestine by the juices from the pancreas, liver, and intestine, and then absorbed through the intestinal walls. Waste or indigestible products, including dietary fiber, move into the colon. They usually remain in the colon for a day or two until expelled by a bowel movement.
