Carbohydrates are the primary source of fuel for our cells, such as nerve cells and red blood cells. Muscles also rely on a supply of carbohydrates to perform high-intensity activities such as sprinting and jumping. Excess carbohydrates are stored in the liver and skeletal muscles as glycogen. When that storage capacity is full, any excess will be stored as fat.
Types
There are three primary kinds of carbohydrates: monosaccharides, disaccharides and polysaccharides. Monosaccharides (simple sugars) are the simplest form of sugars, which consist of one molecule. This is the form that is absorbed into the bloodstream. There are three main sugars used by our bodies: glucose, fructose and galactose.
Disaccharides are made up of two monosaccharide combinations. Two glucose molecules form maltose, a sugar commonly found in the early stages of alcohol fermentation. Sucrose (table sugar) is formed by glucose and fructose bonding together. Lactose, formed by galactose and glucose, is found in milk and other dairy products.
Polysaccharides (complex sugars) are huge links of sugar molecules attached to each other. They are often in this form as energy storage in plants (starch) and animals (glycogen). In plants, non-starch polysaccharides such as cellulose, pectins and gums constitute the structures of plants.
Fiber
There are two types of dietary fiber: soluble and nonsoluble. Soluble fiber--found in legumes, oats, rye, broccoli, carrots and potatoes--absorbs water and is fermented by bacteria in the gastrointestinal tract. Insoluble fiber--found in whole wheat, nuts, seeds, potato skins and fruit rinds--does not absorb water and does not get digested in the gastrointestinal tract. In an apple, the apple skin (cellulose) is insoluble while the flesh inside is soluble (pectin).
Fiber helps to increase bulk in food to make you feel full faster and reduce appetite, good attributes for a weight management program. It also lowers LDL cholesterol and slows the absorption rate of sugar in the bloodstream, which help lower the risks of heart disease and diabetes.
Sources
Carbohydrate sources are abundant, and they all come from plants and their products. Nearly every culture's diet is more than 50 percent carbohydrates, with the highest percentages in East Asia and Mediterranean countries. Carbohydrates that are commonly eaten are bread, rice, pasta, sugar, fruits and vegetables. Processed foods such as potato chips, candy, cookies and crackers contain little nutritional value compared with whole grains. These should be eaten sparingly.
Sports Nutrition
Glucose is the major source of fuel for all sports and activities, whether it is anaerobic (heavy weight lifting, 100-meter sprint) or aerobic (jogging, walking). Therefore, athletes need a high amount of carbohydrates to perform. Dietitians recommend that athletes consume at least 5 grams of carbohydrates per kilogram of body weight. Triathletes and marathoners may need more, as many as 6 to 10 grams per kg of body weight. This is essential to prevent chronic fatigue and load the liver and muscles with glycogen. Athletes should choose complex carbohydrates because of their higher nutritional value, including B vitamins, folate and iron.
Misconceptions
Many low-carb gurus advocate that eating carbohydrates will make you fat, but that is not necessarily so. While eating a lot of carbs (or any type of food) can be converted into fat for storage if they are not used for energy, this process would not happen if the foods were eaten in moderation. Low-carb diets promote rapid weight loss because the dieter's body breaks down proteins in muscles to be used for fuel. Because muscle tissues are mostly water, the dieter loses weight rapidly. Also, by taking out carbohydrates as a food source, the amount of net calories consumed will be reduced, which causes the weight loss. When a normal diet is resumed, the protein tissue is rebuilt, and the weight is gained back.
Remember: Carbs do not make you fat--excess calories do.
References
- "Perspectives in Nutrition"; Gordon Wardlaw and Margaret Kessel; 2002
- "Ultimate Sports Nutrition"; Ellen Coleman; 2004
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