| Carbohydrates Explained | ||||||||
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- What are carbohydrates?
- Classification of carbohydrates
- Simple carbohydrates
- Complex carbohydrates
- Glycemic Index
- Recommended intake of carbohydrates
What are carbohydrates?
Carbohydrates are one of the essential nutrients that are necessary for sustaining life and must be supplied to the body (in the form of food that is eaten) each day.
Carbohydrates are nutrients which provide energy.
Carbohydrates are compounds that contain carbon, hydrogen and oxygen molecules arranged in a specific order, depending on whether they are simple or complex carbohydrates.
Carbohydrates are classed as macronutrients as the body requires them in relatively large amounts (in comparison to vitamins, which are micronutrients and less of these are required each day).
Classification of carbohydrates
Carbohydrates used to be classified in terms of being either:
These days, the new classification of carbohydrates is called the glycemic index.
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Simple carbohydrates are molecules which the body is able to digest very quckly - they do not need to be broken down too much to be digested and so have a rapid impact on blood sugar levels.
Simple carbohydrates are either:
Monosaccharides are the simplest types of sugars and can be broken down and absorbed very quickly by the body. They can be of the following three types:
- Glucose - the simplest form of sugar and also know as blood sugar, which is the energy source for all the body's activities - all cells of the body require glucose in order to function properly. Carbohydrates are generally broken down to glucose in the body, after they are ingested, in order for it to be used for energy
- Fructose - is the sugar that naturally occurs in fruits and in honey (it is also added to canned/bottle drinks, ready-to-eat cereals, ice-cream, desserts, as it is basically the main constituent of "high-fructose corn syrup"). Fructose is the sweetest tasting sugar and gives honey its sweet taste
- Galactose - this rarely occurs naturally and is part of the lactose molecule
Disaccharides are formed from two joined monosaccharide molecules and are the slightly more complicated than the monosaccharides, but still can be broken down to a simple form and absorbed fairly quickly. They can be of the following three types:
- Sucrose - formed from fructose + glucose. Tastes very sweet because of the fructose. Sucrose is found in:
- fruits
- vegetables
- grains
- Lactose - formed from galactose + glucose. This is found only in:
- milk
- Maltose - formed from glucose + glucose. Maltose is produced when starch breaks down and during the fermentation process of alcohol. It is found mainly in:
- barley
Complex carbohydrates are molecules which the body is able to digest very slowly - they need to be broken down quite a lot in order to be digested and so have a more gradual impact on blood sugar levels.
Complex carbohydrates contain many glucose molecules (polysaccharides) linked together and are:
Glycogen is the name for glucose that is stored in the liver. Glycogen is not considered a significant food source of carbohydrate. The only food that is eaten that contains negligible amounts of glycogen are animal protein foods - but as the amount of glycogen in these foods is negligible, it is not considered a viable way to get this nutrient.
This type of complex carbohydrate is found in plants. Grains are the richest source of starch. Main types of grains are:
- wheat
- rice
- corn
- millet
- rye
- barley
- oats
Other types of starch are legumes (all types of beans, peas) as well as tubers (potatoes, yams).
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The structural part of plants are their fibre. Fibre is found in all plant foods:
Fibre comes in two types - soluble and insoluble:
- Soluble fibre - this type of fibre dissolves in a liquid and is digested by the body
- Insoluble fibre - this type of fibre does not dissolve and so is not digested by the body
Today, the glycemic index and the glycemic load are used to describe the effect that carbohydrates have on blood sugar levels. The article on glycemic index explains this new concept.
Recommended intake of carbohydrates
Latest recommendations for carbohydrates, are that they should consist of about half of the daily calorie intake - which is approximately 45%-65% of the total daily calorie intake.
For example:
An adult on a 2000 calories a day diet needs:
- 225g carbohydrates (if 45% of calorie intake)
- 325g carbohydrates (if 65% of calorie intake)
More information
To learn more, go to the official Glycemic Index (GI) web site
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references
- McGuire M, Beerman KA, Nutritional Sciences: From Fundamentals to Food, 2007 Thomson Wadsworth USA
- Rolfes SR, Pinna K, Whitney E, Understanding Normal and Clinical Nutrition 7th Edition, 2006 Thomson Wadsworth USA