Carbohydrates make up one of the important macronutrients derived from food. These nutrients are a significant source of energy. The classification of carbohydrates may be done according to chemical structure (such as monosaccharides or polysaccharides) or physiologic function, such as simple sugars, starches, and fibers, which are found in fruits and vegetables.
What Are Carbohydrates?
Carbohydrates are biological molecules consisting of carbon, hydrogen, and oxygen atoms. Like proteins and fats, they are macronutrients that are part of our daily diet.
What Are the Functions of Carbohydrates in the Body?
Carbohydrates provide energy for the body, enabling metabolism, thus preventing the breakdown of protein as an energy source. Carbohydrates are the preferred source of fuel for the brain, muscle and other organs.
What Foods and Drinks Have Carbohydrates?
Carbohydrates are found in varying amounts in many foods, including vegetables, fruits, grains, legumes, beans, milk, milk products, and foods with added sugar (candy and soda). Carbohydrates found in foods includes sugar, starch, and fiber.
How Are Carbohydrates Used in the Body?
Complex carbohydrates in foods are broken down and converted to simple carbohydrates (glucose) before being absorbed in the blood and used as energy. Metabolism to glucose increases the blood sugar levels, which triggers the pancreas to release a hormone called insulin. This hormone facilitates the entry of glucose into the cells, which convert it to energy.
Classification of Carbohydrates
Carbohydrates are also called saccharides, which comes from sakkron, a Greek word that means sugar.
3 Building Stocks of Carbohydrates: Sugars, Starches and Fiber
Carbohydrates are usually classified into three broad categories: sugars, starches, and fiber.
- Sugars are simple carbohydrates like glucose, fructose and lactose. They cause a rapid rise in blood glucose levels.
- Starches are complex carbohydrates that are composed of several molecules of glucose. They cause a less rapid rise in blood glucose levels. On the other hand, resistant starch and fiber are not digested or broken down in the small intestine, but these have many positive health effects.
- Fiber is a non-digestible complex carbohydrate. Our gut does not possess the enzymes needed to break apart the links between sugar units. Undigested fiber travels through our gut and while doing so, provides health benefits.
Chemical Classification of Carbohydrates
The chemical classification includes monosaccharides, oligosaccharides and polysacchares.
1. Monosaccharides
Monosaccharides are simple sugars, which possess a free ketone or aldehyde group. Being the simplest of sugars, they cannot be further hydrolyzed. Their chemical formula is CnH2nOn or Cn (H2O) n. Monosaccharides are classified into tiroses, tertroses, pentoses, etc., and as ketoses or aldoses, depending on their ketone or aldehyde group.
Examples include glucose, fructose, galactose, glycerose, ribose, and ribulose.
2. Oligosaccharides
“Oligo” meaning few, oligosaccharides are sugars that break down into two to 10 molecules of monosaccharides when hydrolyzed.
An oligosaccharide that yields two monosaccharide molecules on hydrolysis is a disaccharide, while those that break down into three or four monosaccharides are called trisaccharides, tetrasaccharides, and so on. Disaccharides have a chemical formula of Cn (H2O) n-1 while trisaccharides and others are Cn (H2O) n-2, etc.
Oligosaccharide examples include sucrose, maltose, lactose, raffinose, and stachyose.
3. Polysaccharides
“Poly” meaning many, polysaccharides are compound molecules that yield more than ten monosaccharide molecules on hydrolysis. They are also classified depending on the type of molecules hydrolyzed. These include homopolysaccharides (with several monosaccharides of one type) or heteropolysaccharides (with different types of monosaccharides). (C6H10O5)x is their chemical formula.
Polysaccharide examples include starch, cellulose, pectin, glycogen, inulin, and hyaluonic acid.
Physiological Classification of Carbohydrates
The physiologic classification includes:
1. Simple Carbohydrates
These include sugars like monosaccharides, disaccharides and oligosaccharides like trisaccharides and tetrasaccharides. Simple carbohydrates are easily digested basic sugars that offer little health value for the body when taken in large amounts. Foods that are high in simple sugars and low in fiber increase your blood sugar levels. Although fruits and vegetables contain simple carbohydrates, they are healthier than processed foods like cookies and cakes because they contain fiber. This changes the way that your body processes the sugars because fiber slows down their absorption.
It is therefore important to limit your intake of simple sugars from processed foods like:
- Candy
- Soda
- Artificially sweetened syrups
- Table sugar
- White rice, bread, or pasta
- Pastries and other desserts
2. Complex Carbohydrates
The polysaccharides are complex carbohydrates that are considered good for health because it takes more time for the body to break them down. They usually have a low glycemic load, meaning that you get lower amounts of sugar, which is released at a slower rate, producing small increases in blood sugar levels, instead of the peaks and valleys characteristic of simple sugars.
Choose complex carbohydrates over foods with simple carbohydrates by making simple substitutions in your meals. For example, choose brown rice instead of your usual white rice, or eat whole-wheat bread or pasta instead of white bread or pasta.
Note:
Learn to read labels of packaged foods to determine the classification of carbohydrates contained—whether they are made of simple sugars or complex carbohydrates. Look at the first ingredient, and if it is whole-wheat flour, it's more likely to be a complex carbohydrate with fiber.