Complex Carbohydrate Absorption


What happens to sugar as soon as we eat it? If it’s so important, the body will produce energy from it immediately, right? The answer to the first question is best explained by dividing it into two parts: what happens to complex carbohydrates and what happens to simple carbohydrates as soon as we eat them? We have already covered the absorption of simple carbohydrates earlier.

First, we’ll discuss the breakdown of complex carbohydrates (whole grains, brown rice, and starchy vegetables). In the mouth, the complex carbohydrates are acted upon by digestive organs including the teeth and tongue for mastication (chewing), starch-digesting enzymes known as salivary amylases, and other digestive enzymes primarily residing in the saliva. The saliva also contains low levels of the B vitamins, vitamin C, and vitamin K to help assist in the proper utilization of these sugars. The teeth are important because they are meant to grind up the fiber of the grains and vegetables to release the carbohydrates from the cells. Plants also have another type of carbohydrate as fiber called cellulose in their cell walls of which humans don’t use as nutrients but act, instead, to aid in the movement of digested foods through the intestine. Therefore, our teeth are needed to cut through the plant cell walls to enable appropriate digestion of the starches.

In a neutral to slightly acidic environment, salivary amylase begins to break down the long-chain complex carbohydrates known as polysaccharides into smaller chains. This is done by the addition of water molecules. The smaller carbohydrate chains are then swallowed following mastication and continue to be digested by salivary amylase as they reach the stomach. Once in the stomach, the salivary amylase is inactivated by the higher acidity of the stomach.

complex carbohydrates

From the stomach, the remaining small and long-chain polysaccha- rides are further acted upon by pancreatic amylase that is secreted into the duodenal portion of the small intestine. Enzymes within the cell membranes of the duodenum will further breakdown the fragmented polysaccharides into the monosaccharides glucose, fructose and galactose, simple carbohydrates also known as simple sugars as they pass through the small intestine. The fragmented complex carbohydrates are slowly and systematically broken down to monosaccharides for distribution into the bloodstream. Insulin levels can stay in better control this way.

Digestion and absorption of complex carbohydrates continues uniformly and without straining insulin secretion. The amount of surface area provided by the intestinal cell membranes due to their microscopic finger-like projections is about the size of a tennis court. This is where the absorption of simple sugars occurs into the bloodstream. The stomach, however, has very little ability to absorb any nutrients.

In the bloodstream, almost all of the circulating simple sugar is exclusively glucose. Fructose needs to pay a visit to the liver in order to be converted to glucose. Therefore, the metabolism of fructose is much slower than for glucose. Glucose from galactose is derived from the milk sugar lactose. It, too, converts slowly to glucose. Refined grains are absorbed much more rapidly into the bloodstream than whole grains because the carbohydrate complexes in refined grains have been previously split apart during the refining process.

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