what are carbohydrates?

Carbohydrates are one of three macronutrients. They are the main energy source in the body and they are used first before protein and fat.

After I drill the health benefits of carbohydrates in your brain I’m going to follow up with the most frequently asked questions I get about carbs. By the end of this article, I hope to shift your thinking about this misunderstood macronutrient and empower you to know which carbs to eat and which to avoid.

The word “carbohydrate” comes from the Greek word sakharon, which means “sugar”.

simple and complex carbs

simple carbohydrates

All simple carbohydrates are made of just one or two sugar molecules such as monosaccharides or disaccharides

They are rapidly digested and are a quick source of energy

Quick digestion and absorption often leads to a rapid spike in blood glucose (aka sugar high)

Food examples: are usually processed food or refined sugars with little nutritive value

First of all, let’s talk science. I know chemistry can be scary, but I turned molecules into emojis,  so stay with me.

Imagine that each little hexagon shape in the picture above is one sugar molecule. A monosaccharide is just one ‘sugar molecule,’ such as glucose.

mono means one

complex carbohydrates

Complex sugar molecules take longer to digest and absorb into the bloodstream

Not all sugar is usually released to the bloodstream at once meaning usually no rapid spike in blood sugar

Food examples: unprocessed foods that are high in fiber and other nutrients, vitamins, and minerals. For this reason, complex carbohydrates should be the majority of your carbohydrate intake.

Complex carbohydrates are longer chains of sugar molecules. Oligosaccharides and polysaccharides are both long molecules with several sugar units linked together. These are called complex carbohydrates.

Oligo = few (three to ten sugar molecules linked together)

Poly = many (more than ten sugar molecules linked together)

Complex carbohydrates have to undergo more steps in the digestive process than simple carbohydrates. They are not broken down and used for energy as quickly as simple carbohydrates.



mono [one] saccharide [sugar]

Monosaccharides are one unit of sugar. Monosaccharides are the most basic unit of carbohydrates because they can’t be further broken down to a smaller compound. They are simple carbohydrates.



di [two] saccharide [sugar]

Disaccharides are two sugar units linked together by a glycosidic bond. They are simple carbohydrates. Maltose is a sugar found in some cereals and candies, lactose is present in milk, and sucrose is a table sugar that is purified from cane or beet sugar.



poly [many] saccharide [sugar]

Polysaccharides are _____. They are simple carbohydrates.

digestion of carbohydrates

The process of carbohydrate digestion begins in the mouth. As we chew our food an enzyme called salivary amylase is secreted into our saliva. Then the food travels down the esophagus, into the stomach, and is released into the small intestine.

This is where the magic happens.

In the beginning of the small intestine the pancreas secretes an enzyme called pancreatic amylase. This enzyme breaks polysaccharides down to disaccharides. Later in the small intestine the disaccharides are then broken down to monosaccharides that are able to pass through the intestinal wall into the bloodstream.

There are some carbohydrates that can’t be digested and absorbed by the small intestine, thus, we don’t derive an energy from them. Dietary fiber and resistant starch is partially digested in the small intestine which also feeds intestinal bacteria. The undigested fiber continues through the small intestine into the colon and becomes a bulking agent for stool.

POST LINK: More about starch and fiber

using carbohydrates as energy

All carbohydrates we eat must be broken down to the same simple sugars before entering the bloodstream to be used as fuel.

Any sugar molecules that are linked together will into pass through the wall of the small intestine because they are too big. Monosaccharides (one sugar unit) such as glucose, fructose, or galactose are the only sugar that are small enough to pass straight into the bloodstream.

However, most foods naturally contain either disaccharides or polysaccharides which are too big to pass through the intestinal wall. These larger sugar molecules must be broken down into monosaccharides before they can enter the bloodstream.


Disaccharides are two sugar units linked together. It only takes one enzymatic reaction to hydrolyze the bond holding the two sugar molecules together.

They are considered simple carbohydrates because the bond is easily broken. When the disaccharide is broken into two monosaccharides they can now individually travel into the bloodstream from the small intestine.


Polysaccharides are complex carbohydrates can have hundreds or thousands of sugars linked together in a long chain.

These large molecules cannot get through the intestinal walls, so many enzymatic reactions have to occur for all of the bonds are broken so each individual sugar unit can pass into the bloodstream. As you might guess, breaking all the bonds on a large molecule take a lot longer than simple carbohydrates. Thus, there is a slower release of sugar into the bloodstream.


When I eat a donut by itself for breakfast, it doesn’t take long before I get a surge of sugar into my bloodstream. Why? Because donuts are simple carbohydrates, and as we just learned, simple sugars are quickly digested and assimilated into the bloodstream.

Hello sugar high.

how carbohydrates affect blood sugar

how to avoid blood sugar spikes