The carbohydrates or sugars (colloquially called carbs) are the most abundant biomolecules in nature, consisting mainly of carbon, hydrogen, and oxygen. Sorted by size, carbohydrates can be denominated monosaccharides, oligosaccharides or polysaccharides.
They comprise a class of large organic compounds, and are one of the main dietary requirements of organisms. Their function is to provide energy for the body, especially the brain and the nervous system. The liver breaks down carbohydrates into glucose (blood sugar), which is used to generate energy in a process called cellular respiration.
There are different types of carbohydrates, some of which are healthier than others. Sugars are found naturally in fruits, vegetables, milk, and milk products. Foods such as cakes and cookies have had sugars added. Starches are complex carbohydrates that are broken down in your into simple sugars. Starches are found in certain vegetables, such as potatoes, beans, peas, and corn, and in breads, cereals, and grains. All of these sugars can be converted to glucose. In contrast, dietary fibers (cellulose) are carbohydrates that your body cannot digest. They pass through your body without being broken down into sugars. Fiber is important for maintaining digestive system function. The fiber grain, fruit, and vegetables can reduce the body's absorption of fructose, even from fruit which is naturally high in the sugar. Fiber also helps get rid of excess fats in the intestine, reducing the risk of heart disease, and helps push food through the intestines, which prevents constipation.
Carbohydrates are classified as simple or complex. The classification depends on the chemical structure of the particular food source and reflects how quickly the sugar is digested and absorbed. Simple carbohydrates have one sugar molecule (monosaccharides) or two (disaccharides) while complex carbohydrates have three or more sugars (oligosaccharides and polysaccharides).
Simple carbohydrates are broken down quickly by the body to be used as energy. Examples of single sugars (monosaccharides) from foods include fructose (found in fruits) and galactose (found in milk products). Disaccharides (double sugars) include lactose (found in dairy), maltose (found in certain vegetables and in beer), and sucrose (table sugar). Honey is also a disaccharide, but unlike table sugar, it contains a small amount of vitamins and minerals. Simple carbohydrates that contain vitamins and minerals occur naturally in fruits, milk and milk products, and vegetables. Simple carbohydrates are also found in processed and refined sugars such as candy, table sugar, syrups (not including natural syrups such as maple), and regular (non-diet) carbonated beverages, such as soda.
Complex carbohydrates include starch and dietary fiber (cellulose), which are made up of sugar molecules that are strung together in long, complex chains. Complex carbohydrates are found in foods such as peas, beans, whole grains, and vegetables. Both simple and complex carbohydrates are turned to glucose (blood sugar) in the body and are used as energy. Complex carbohydrate foods provide vitamins, minerals, and fiber that are important to the health of an individual. The majority of carbohydrates should come from complex carbohydrates (starches) and naturally occurring sugars, rather than processed or refined sugars, which do not have the vitamins, minerals, and fiber found in complex and natural carbohydrates. Refined sugars are often called "empty calories" because they have little to no nutritional value.
Starch must be broken down through digestion before your body can use it as a glucose source. Starchy foods include:
- Whole grain breads and cereals
- Starchy vegetables
Dietary fiber is a component of plants (cellulose) that can not be digested by most multicellular organisms. Only a small amount of fiber is metabolized in the stomach and intestine. The rest is passed through the gastrointestinal tract and makes up a part of the stool. Dietary fiber adds bulk to your diet. Because it makes you feel full faster, it can be helpful in controlling weight. Fiber aids digestion, helps prevent constipation, and is sometimes used for the treatment of diverticulosis, diabetes, and heart disease.
There are two different types of fiber -- soluble and insoluble. Both are important for health, digestion, and preventing diseases. Soluble fiber retains water and turns to gel during digestion. It also slows digestion and helps your body absorb vital nutrients from foods. It can be found in foods such as oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. Insoluble fiber appears to speed the passage of foods through the stomach and intestines and adds bulk to the stool. It is found in foods such as wheat bran, vegetables and whole grains.
In general, you want to limit carbohydrates that increase your blood glucose levels. If your blood glucose stays high for too long, injury to the heart can develop. To keep your blood glucose in check, limit the amount of table sugar and foods with added sugar you eat. You can tell if a food has added sugars by looking at the ingredients list on the package. You also should limit the amount of white potatoes you eat. Eating white potatoes occasionally is fine because they contain important vitamins and minerals. But your body rapidly digests the starch in white potatoes, raising your blood glucose level.
Healthy carbohydrates include:
- Natural sugars in fruits, vegetables, milk, and milk products
- Dietary fiber
- Starches in whole-grain foods, beans, peas, and corn
Refined sugars provide calories (energy), but lack vitamins, minerals, and fiber. Such simple sugars are often called "empty calories" and can lead to weight gain. Also, many refined foods, such as white flour, sugar, and polished rice, lack B vitamins and other important nutrients unless they are marked "enriched." It is healthiest to obtain carbohydrates, vitamins, and other nutrients in as natural a form as possible -- for example, from fruit instead of table sugar.
It is recommended that you get 14 grams of dietary fiber for every 1,000 calories that you consume each day. If you need 2,000 calories each day, you should try to include 28 grams of dietary fiber. 
|Daily calorie needs||Daily dietary fiber needs|
- Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2010) (in Portuguese). Biologia Molecular da Célula [Molecular Biology of the Cell] (5th ed.). Porto Alegre: Artmed. p. 55. ISBN 978-85-363-2066-3.
- Karp Gerald (2008). Cell and Molecular Biology:Concepts and Experiments (5th ed.). New Jersey: John Wiley & Sons. p. 42-47. ISBN 978-0-470-04217-5.
- Carbohydrates by Medline Plus
- Carbohydrates by the Office on Women's Health in the U.S. Department of Health and Human Services.
- Image Number K3839-3 by the U.S. Department of Agriculture
- Complex carbohydrates by Medline Plus
- Soluble vs. insoluble fiber by Medline Plus
- Rubin, J., Matsushita, K., Ballantyne, C. M., Hoogeveen, R., Coresh, J., & Selvin, E. (2012). Chronic Hyperglycemia and Subclinical Myocardial Injury. Journal of the American College of Cardiology, 59(5), 484–489. http://doi.org/10.1016/j.jacc.2011.10.875