The three most important monosaccharides in the diet are glucose, fructose, and galactose. When two sugar molecules combine this is called a disaccharide. Two common disaccharides are sucrose (glucose + fructose), which is common table sugar and lactose (glucose + galactose), the sugar found in milk. Monosaccharides and disaccharides are referred to as simple sugars and are typically sweet to the taste.
Carbohydrates containing more sugar molecules are called polysaccharides or complex carbohydrates. Glucose, the main energy fuel for the body is the primary monosaccharide found in complex carbohydrates. In a complex carbohydrate, the glucose molecules link together either in straight or branched chains, thus providing a quick source of energy as each of the glucose molecules is broken off and subsequently converted into energy.
Humans store complex carbohydrates in the form of glycogen, whereas plants store these carbohydrates as starch. In foods such as corn, wheat, rice, oats, and legumes, the starch is found in the seed where it provides an energy source for the growing plant. In plants such as potatoes and yams, the underground portion or tuber, is the energy storage source for the plant.
The second type of complex carbohydrate commonly found in the diet is fiber. Unlike starch, dietary fiber cannot be digested and used for energy. Humans lack the enzyme required to break the complex carbohydrate into its glucose units. Dietary fiber is classified by its ability to absorb water.
- Soluble fiber can be found in foods such as apples, oats, kidney beans, and barley.
- Insoluble fibers are the tough form of dietary fiber found in whole grains and vegetables. A role of insoluble fibers is to maintain your body's natural elimination process.
Dietary Forms of Complex Carbohydrates:
Many of the plant-based foods are comprised of a combination of simple sugars, starch, fiber, protein, vitamins, minerals, oils, and phytochemicals. To what extent a complex carbohydrate-containing food may or may not contain these constituents depends not only on the food source (e.g. seed vs. stalk of plant) but also how much the food product has been processed.
- Whole grain vs. refined products:
Whole grains are made of three components, each of which contains different nutrients. The bran is the outermost layer and contains most of the B vitamins and insoluble fiber (See figure). The germ is the plant embryo, which contains vitamin E, selenium, and thiamin and is also where the vegetable oils such as corn oil and soy oil are derived. The remainder of the grain is composed of the endosperm. The endosperm is primarily starch, but also contains most of the protein and some vitamins.
Whole grain products, such as whole-wheat flour, contain all three of the components, making them a good source of complex carbohydrates and protein, oils, fiber, and vitamins. During the milling process, the whole grain is ground which separates the bran and germ from the endosperm. Grinding the endosperm isolated in the milling process makes refined flours. Because most of the fiber, oils, and vitamins are lost in the refining process, flour is enriched with some of the nutrients (thiamin, niacin, riboflavin, and iron) lost in the processing.
The refining process also pertains to other grain products such as rice. White refined rice has the outer bran layer removed and is primarily starch, whereas intact brown rice retains the outer bran containing the vitamins and insoluble fiber. Refined rice is also enriched to replace some of the nutrients lost to the refining process.
- The components of vegetables and legumes:
The pulp portion of root vegetables such as potatoes and yams is a good source of starch and some vitamins, while the skin provides the majority of the vitamins and insoluble fiber. Legumes such as pinto beans are excellent sources of starch, soluble fiber, protein, and minerals and vitamins. Vegetables like broccoli, cauliflower, and green beans are high in fiber, vitamins, and minerals. Because their starch content is lower, they are also lower in calories than the starch-containing root vegetables.
How Much Carbohydrate Should We Eat?
It is recommended that carbohydrates make up 50-60% of your total caloric intake with the majority of the dietary carbohydrate coming from complex carbohydrates. Following is an example of how to calculate the approximate grams of carbohydrates you need in a day based on a 2,000 calorie diet:
Example: 2,000 calories x 55% = 1,100 calories. There are 4 calories in 1 gram of carbohydrate. 1,100 calories divided by 4 calories per gram of carbohydrate = 275 grams carbohydrate.
Information about the amount of total carbohydrates, sugars, and dietary fiber in a food product can be found in a food product’s Nutrition Facts Panel.
It is best when choosing grain products that the predominant ingredient is presented as “whole,” “whole grain,” or “whole wheat” on the food label. By consuming whole grain products you are ensuring an adequate fiber intake. Fiber intake should be approximately 25 grams per day, based on a 2000-calorie diet.
Finally, minimize the amount of refined sugars you consume. This can be done is by
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snacking on fruits and vegetables instead of that mid-morning candy bar or by drinking artificially sweetened beverages instead of the full sugar versions!
Source: Michele M. Doucette, PhD
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