These days, carbohydrates have a bad reputation as a cause of weight gain, obesity, and related health problems. However, it’s also one of the macronutrients that your body needs. In this article, we’ll discuss the different types of carbohydrates to get to know them better.
So, what are carbohydrates? Carbohydrates, like other nutrients, are chemical substances. The term carbohydrate, which means “hydrated carbon,” reflects the atoms it contains. The atoms that make up carbohydrates are carbon, hydrogen, and oxygen―the last two are the atoms that also make up water.
Based on their chemical structure, carbohydrates can be classified into simple carbohydrates and complex carbohydrates. These two different types of carbohydrates can be further classified into four groups. Simple carbohydrates include monosaccharides and disaccharides, while complex carbohydrates include oligosaccharides and polysaccharides.
Simple Carbohydrates
Simple carbohydrates, as their name suggests, are carbohydrates that have a simple chemical structure. They’re also commonly referred to as sugars. Simple carbohydrates include two types of carbohydrates, i.e. monosaccharides and disaccharides.
A. Monosaccharides
The term monosaccharide comes from the words “mono” which means “one” and “saccharide” which means “sugar.” Monosaccharides are carbohydrates that consist of only one sugar molecule. The most common and important monosaccharides in foods are:
1. Glucose
Glucose, also known as “blood sugar,” is the most abundant monosaccharide in foods. However, glucose rarely exists as a standalone entity in foods; it usually exists as part of disaccharides or complex carbohydrates. Glucose serves as an important source of energy for your body, especially your brain, nerve, and red blood cells.
2. Fructose
Fructose is the sweetest monosaccharide. It exists naturally in fruits and honey. It also occurs (through processing) in high-fructose corn syrup and various processed foods and beverages that use the syrup, such as cereals, soft drinks, candies, etc.
3. Galactose
Just like glucose, galactose rarely exists as a standalone entity in foods. It usually exists as part of the disaccharide lactose, which is the main carbohydrate of milk.
B. Disaccharides
Disaccharides are carbohydrates consisting of two bonded monosaccharide molecules. The word “di” in the term disaccharide means “two.” The most common and important disaccharides in foods are:
1. Lactose
Lactose consists of one glucose molecule and one galactose molecule. It’s the main carbohydrate of milk. The word “lac” in the term lactose means “milk.” Lactose is also commonly called “milk sugar.”
2. Sucrose
Sucrose consists of one glucose molecule and one fructose molecule. Since it contains fructose, sucrose is the sweetest disaccharide. Sucrose occurs naturally in fruits and vegetables. White sugar or brown sugar that people consume regularly is made from sucrose that is refined from sugarcane or sugar beets.
3. Maltose
Maltose consists of two glucose molecules. It rarely exists as a standalone entity in foods. Maltose usually occurs as a result of the digestion of starch by your body. It also occurs through the fermentation process in the production of alcoholic beverages.
Complex Carbohydrates
Complex carbohydrates are carbohydrates that consists of three or more monosaccharides. They include two types of carbohydrates, i.e. oligosaccharides and polysaccharides.
A. Oligosaccharides
Oligosaccharides are carbohydrates consisting of 3 to 10 monosaccharides. The word “oligo” in the term oligosaccharide means “several.” The most common oligosaccharides in foods are:
1. Raffinose
Raffinose consists of a glucose molecule, a fructose molecule, and a galactose molecule. It exists in cabbage, brussels sprouts, broccoli, whole grains, and beans.
2. Stachyose
Stachyose consists of two galactose molecules, a glucose molecule, and a fructose molecule. It exists in many legumes.
B. Polysaccharides
Polysaccharides are carbohydrates that contain many (hundreds or thousands) glucose molecules and sometimes several other monosaccharides. The word “poly” in polysaccharide means “many.” The most important polysaccharides in foods are:
1. Glycogen
Glycogen is the storage form of glucose in animals and humans; it does not exist in plants. However, when an animal dies, its glycogen is broken down by enzymes in its body. So, very little glycogen remains in meat. Most glycogen in your body does not come from food but is made by your body from excess glucose.
2. Starches
Just like glycogen for animals and humans, starch is the storage form of glucose in plants. There are two types of starch, i.e. amylose and amylopectin. The digestion of amylopectin is faster, so it increases blood glucose faster than amylose.
Foods that are sources of starch include grains (wheat, rice, corn, etc.), tubers (potatoes, yams, etc.), and legumes (beans, peas, etc.).
3. Fibers
Fiber is the skeletal structure of plants, so it exists only in plants. Not all fibers are polysaccharides, but most of them are.
Due to their molecular bonds, most fibers are indigestible; they pass through your digestive system without being digested and absorbed by your body. Hence, they contribute little or no energy to your body. Nevertheless, they have many health benefits.
Some fibers, though, are fermentable. They can be fermented and digested by bacteria in the colon. Based on their solubility in water, fibers can be classified into soluble fibers and insoluble fibers. Soluble fibers are usually more fermentable than insoluble fibers.
Digestion and Absorption of Carbohydrates
An article on the types of carbohydrates wouldn’t be complete without discussing how they are digested and absorbed by your bodies. In this section, we’ll discuss the process of digestion and absorption of carbohydrates.
The process of carbohydrate digestion begins in your mouth. When you chew starchy food, the amylase enzyme in your saliva breaks down the starch into maltose. Disaccharides, though, aren’t digested in the mouth.
Very little digestion of carbohydrates takes place in your mouth because the food doesn’t stay there for long. After the food enters your stomach, the stomach acid will deactivate your salivary amylase enzyme. No digestion of carbohydrates takes place in your stomach.
The process of carbohydrate digestion continues again when the food enters your small intestine. Most digestion of carbohydrates occurs in the small intestine. Here, the amylase enzyme that comes from the pancreas breaks down the remaining starch into maltose.
Other enzymes then break down maltose and other disaccharides into monosaccharides. The enzyme maltase breaks down maltose into two glucose molecules; the enzyme sucrase breaks down sucrose into fructose and glucose; the enzyme lactase breaks down lactose into galactose and glucose.
After that, all these monosaccharides enter the bloodstream and travel to the liver. The liver then converts most non-glucose monosaccharides into glucose. If there is an immediate need for energy, the glucose is sent to your body’s cells for energy. If there is no immediate need for energy, the glucose is stored as glycogen in the liver, muscles, and brain.
However, the capacity of your body to store glycogen is limited. Glycogen can only provide energy for about a day or less. Once the glycogen storage limit is reached, the remaining excess glucose will be stored as fat.
Regarding fibers, most fibers can’t be digested by your body. So, they just pass through your digestive system and are excreted in feces. Some fibers, though, can be fermented by the bacteria in your colon. This fermentation produces gas, water, and short-chain fatty acids.
Since they are indigestible, most fibers do not contribute energy to your body. The fermented fibers contribute energy but only a little, about 1.5 to 2.5 calories per gram. However, fiber has many health benefits, such as preventing constipation and reducing blood cholesterol.
Other carbohydrates that are also difficult to digest are FODMAP, which stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Among them are raffinose and stachyose that we mentioned above. Both are fermented by bacteria in the large intestine.
Closing Remarks
The classification of the types of carbohydrates above is based on their chemical structure, as is commonly done in nutrition science. This is not the only way to classify carbohydrates. For example, MedlinePlus and the American Diabetes Association classify carbohydrates into three types, i.e. sugars, starches, and fiber.
Whichever way you classify carbohydrates, they end up in your body primarily as glucose and fiber. Consuming too much glucose is associated with diabetes, obesity, or other related health problems; while fiber has many health benefits.
The general recommendation is to prioritize fiber-rich carbohydrates. However, this is not as simple as eliminating certain types of food or eating only certain types of food. Many carb-foods contain more than one type of carbohydrate. Fruits, for example, contain sugar and fiber; while grains contain starch and fiber.
References
Thompson, J. L., Manore, M. M., & Vaughan, L. A. (2017). The Science of Nutrition (4th ed.). Pearson Education.
Whitney, E., & Rolfes, S. R. (2019). Understanding Nutrition (15th ed.). Cengage Learning.