A New Way to Look at Carbohydrates

Carbohydrates are a varied combination of both very small and very large molecules that comprise about 40 to 45 percent of the energy supply for your body. In addition, certain types of carbohydrates, such as fiber and resistant starches don't get taken into your body for energy, but play important health-promoting roles in your gastrointestinal tract, supporting digestion and absorption, and helping you eliminate toxins and waste products.

Carbohydrates are are composed of carbon, hydrogen, and oxygen, which are arranged into small units called sugars, or monosaccharides. Small carbohydrates, like glucose or sucrose (table sugar) are composed of one or two sugar units, respectively, and are the molecules that give food a sweet taste. These molecules are sometimes called "simple sugars" because they are small (only one or two units), and are quickly digested, providing immediate energy to the body.

Larger carbohydrate molecules, which include fibers and starches, are composed of at least 10 monosaccharides linked together. These large carbohydrates, called polysaccharides (poly=many) may contain up to several hundred monosaccharides linked together in different ways. Another term commonly used to describe carbohydrates is oligosaccharides, a type of carbohydrate molecule that is in-between polysaccharides and monosaccharides in size, and features two to ten monosaccharides bonded together.

Let's look at each of these types of carbohydrates and how the food you eat influences the quality of these important nutrients you receive.

The Simple Sugars: Monosaccharides and Disaccharides

Monosaccharides

Monosaccharides are true simple sugars since, as one sugar unit only, they exist in the form in which they can be directly absorbed into your body upon ingestion. Unlike the other carbohydrates, they don't require being broken down during digestion, so when you eat a food containing monosaccharides, these sugars quickly get into your bloodstream, increasing your blood sugar and providing immediate energy. Examples of monosaccharides include glucose, fructose and galactose.

Monosaccharides are present in most foods in at least some amount, but are particularly high in foods such as ripe fruit, and honey. Monosaccharides are an important energy source, but when too much of these simple sugars are consumed at once--especially when they are not balanced by complex carbohydrates like oligosaccharides or polysaccharides that take longer to digest and thus help maintain longer-term energy production--monosaccharides can cause a large increase in blood sugar, followed by an abrupt drop. The result is a jolt of energy quickly followed by a feeling of being tired, shaky, or run-down soon afterward. This type of fluctuation in blood sugar, if it occurs frequently, can lead to blood sugar dysregulation conditions such as hypoglycemia and diabetes mellitus. Proceesed foods often add high amounts of monosaccharides such as fructose and glucose to promote a sweet taste, which sells more product, but does not sustain health.

Disaccharides

Disaccharides contain two monosaccharides (di=two) bonded together, and include sugars such as lactose (milk sugar), sucrose (table sugar), maltose and isomaltose (sugars formed from the breakdown of starch). Disaccharides are similar to monosaccharides; that is, they provide sweet taste to food and quick energy, which is why they are considered "simple sugars" as well. As such, disaccharides also are highly represented in processed foods, and their frequent consumption can lead to blood-sugar disregulation, the same as monosaccharides.

Since these carbohydrates contain two sugars, disaccharides require some digestion to break them into two one-sugar units for absorption, and since each disaccharide is unique, each has its own digestive enzyme. For example, the enzyme sucrase can cut sucrose into its two individual sugar units; lactase cuts lactose into its two sugars. For most disaccharides, these enzymes area readily secreted into the intestines after consuming a meal, and digestion of the disacchrides proceeds rapidly. The exception appears to be with lactose (milk sugar).

Many people lack the enzyme lactase and are therefore unable to breakdown lactose, a condition called lactose intolerance, which makes the consumption of dairy products problematic for many people. Lactose intolerance, which occurs more frequently as we age, is quite common in adults. In lactose intolerance, the undigested lactose is not absorbed and can promote growth of unfriendly bacteria in the upper intestinal tract, a condition called small bowel overgrowth. These bacteria ferment the lactose, producing gas in the small intestine that causes great discomfort, along with acid, which can cause heartburn and nausea. Even more problematic, the acid produced by this bacterial fermentation can degrade the lining of the small intestine, injuring the intestinal tract cells. This damage compromises the ability of the intestinal cells to produce enzymes for digestion, so even less disaccharide digesting enzymes are produced, and a cycle of maldigestion is perpetuated. Diets that limit disaccharides may be of benefit for persons with these concerns, and a person with lactose intolerance should not consume lactose-containing foods without having a source of lactase either in the food or taken with the food. Some studies suggest that Lactobacillus supplements are beneficial in this respect as well.

The Polysaccharides: Starch, Fiber and Resistant Starch Starch

Plants store their energy by stringing together many glucose units into a long complex of several hundred to several thousand sugar (glucose) molecules. Plant foods that contain stored energy, for example seeds that must provide energy for the young plant when it starts growing, are high in starch. When the young plant starts growing, the starch is broken down into glucose for energy.

Starch

When you eat foods that contain starch, like corn or potatoes, your body uses this starch in much the same way. Since your body must breakdown this very large molecule to individual sugar units before they can be digested, the digestion of starch takes longer than that of disaccharides; therefore, starch provides an extended, or sustained source of energy. Because they do not lead to immediate bloodsugar spikes followed by a low, but instead a more moderate, longer-term elevation of blood sugar, starches are thought to be better for health and energy.

Starches are called complex carbohydrates because they are so large. Two main types of starches exist in food: amylose and amylopectin. These starches differ in how the individual sugars they contain are linked together. This difference results in differences in how easy it is for your body to cut the starches into their individual sugar units. Amylopectin is more quickly digested than is amylose; therefore, foods that contain higer amylose than amylopectin are often suggested as substitutions for people with bloodsugar control problems, like diabetes.

Starch digestion is also influenced by how the starch is packed in the food. When food is whole, or in its natural state, marcromolecules are folded together, and starch can be encased in protein or fiber or other large molecules that must be digested before the starch itself becomes available for digestion. The result of this packaging, again, is to slow down the absorption of the individual sugar units from the starch, and to provide extended, sustained energy for a longer-term, moderate rise in blood sugar after a meal. In contrast, processed foods have removed this complex interaction. In processing, the macromolecules are initially pulled apart from each other, then added back separately. The result is starch that is more accessible for quick digestion and absorption, and causes quicker, higher rises in blood sugar, looking more like a disaccharide than a starch. Therefore, people with blood sugar control concerns, such as hypoglycemia, insulin resistance or diabetes can benefit from eating whole foods and avoiding high-starch, processed foods.

Fiber
Dietary fibers are also polysaccharides and are, therefore, considered complex carbohydrates; however, the sugar units in fiber are linked (bonded) together in such a way that your body can't break the bonds and digest them. Instead, fibers transit through your small intestines and make it all the way to your large intestine intact. This ability to move through your system to your large intestine helps speed the transit times of wastes excreted from your body; for this reason, fiber helps to support your health by reducing constipation and promoting the excretion of toxins and wastes.

Fibers that promote overall healthy digestion and waste excretion are found in vegetables, grains, and legumes and are well represented in whole foods. Often, when processed, foods have these fibers removed. For example, bran contains high levels of fibers and is removed when grains are processed. Fruit skins are also high in fiber, but are often removed when the fruit is processed for a fruit-containing product.

Much has been written about the health-promoting benefits of fiber, and ample numbers of studies support an association between high-fiber diets and a decrease in risk of many types of cancers, including colon cancer and breast cancer. Some of this benefit comes from the ability of fiber to bind and remove toxins, and to promote healthy digestion. Recent research suggests, however, that fiber provides its health-protecting benefits in other ways as well, and one of the most important appears to be its ability to promote healthy intestinal tract bacteria.

Your large intestine contains a multitude of beneficial bacteria that are required for your body's health. They are called the "friendly flora," or the beneficial symbiotic microbes, and they support the health of your whole body by promoting healthy immune function and providing important molecules to your intestinal tract cells to promote their growth, thus sustaining overall intestinal tract integrity. These microbes use some of the fibers you eat as fuel for their own growth, and through their own metabolism produce molecules called short-chain fatty acids (SCFA). SCFA production by these friendly flora has been associated with a decrease in cancerous colonic cells, reduction of serum cholesterol, and maintenance of healthy blood sugar levels and healthy intestinal tract cell walls.

Not all fiber is fermented by the friendly flora in your intestinal tract. Some, as discussed above, goes through your entire system unchanged, binding toxins and waste products as it goes, and promoting healthy elimination. Some fibers can be fermented by microbes of all types, while other fibers are preferentially fermented by the "friendly flora," the bacteria that are most beneficial to your body, including Bifidobacteria and Lactobacillus. When these friendly bacteria are given their favorite types of fibers, called "prebiotic fibers," they will flourish, significantly improving the health of your digestive tract. Excellent sources of these prebiotic fibers include foods such as Jerusalem artichoke, chicory, rice fiber, and soy fiber.

The classical way of talking about fiber to divide it into two types, soluble or insoluble fiber, a classification determined by how much water a type of fiber holds. New research, however, suggests that fiber has a multitude of activities besides holding water, and that this classical distinction is not adequate. Providing a full range of all types of fibers, including prebiotic fibers, will support your immune system, and enhance healthy digestion, absorption, and the removal of wastes and toxins. In fact, the health of your gastrointestinal tract is dependent upon your consumption of the variety of fibers well-represented in the World's Healthiest Foods.

Resistant Starch

A final category of polysaccharides, or complex carbohydrates, is that of resistant starch. Resistant starch gets its name because, although it is starch, it is resistant to digestion in the small intestine. The result of this resistance is that this type of starch acts more like fiber than starch, and travels through the intestinal tract until it reaches the large intestine where, like fiber, is may be fermented by the bacteria in the colon. Research has shown that resistant starch promotes the generation of SCFAs by the bacteria in the large intestine, and therefore has many of the same health-promoting abilities as fiber. Resistant starch is found in whole grains such as brown rice, barley, whole wheat, and buckwheat.

This page was updated on: 2004-04-05 20:46:25
© 2002 The George Mateljan Foundation