Beginner's Guide: What Is a Carbohydrate?

ketogenicfasting
Jun 16
4 min read

Updated: 6 days ago

What Is a Carbohydrate?

People think of carbohydrates as bread, pasta, rice, potatoes, cereals, and sugary foods. While that is correct, it does not explain what a carbohydrate actually is.

Carbohydrates are one of the three primary macronutrients found in food, alongside protein and fat. Their molecules are made of carbon, hydrogen, and oxygen and serve as one of the body's primary sources of energy.

Every gram of carbohydrate provides approximately four calories.

Carbohydrates exist in three main forms.

Sugars
Starches
Fiber

Although they look very different on your plate, they are all members of the same carbohydrate family.

Sugars

Sugars are the simplest form of carbohydrate. They are made of one or two sugar molecules and are rapidly digested and absorbed by the body.

Common sugars include:

Glucose
Fructose
Sucrose (table sugar)
Lactose (milk sugar)

These sugars do not all taste equally sweet either.

Fructose is the sweetest of the common dietary sugars, followed by sucrose (table sugar). Glucose is less sweet, while lactose is the least sweet of the group.

Sucrose, commonly known as table sugar, is made of one glucose molecule bonded to one fructose molecule. This combination tastes sweeter than glucose alone and provides the level of sweetness people commonly associate with sugar.

Table sugar (sucrose) is a two-molecule sugar

On its own, fructose tastes significantly sweeter than table sugar (sucrose).

Sucrose provides a more balanced sweetness when used as a sweetener.

Starches

Starches are longer chains of glucose molecules (simplest form of sugar) linked together.

During the digestion process, the starches are broken down into glucose, the simplest form of sugar.

Foods such as bread, rice, pasta, potatoes, corn, grains and legumes contain significant amounts of starch.

Starches do not taste as sweet as sugar. Your digestive system breaks them down into glucose, the simplest form of sugar.

Corn starch is the cheapest starch to produce and is a common ingredient in processed foods.

You have probably heard the terms whole grains and refined grains, but what exactly is the difference between the two?

Refined grain is all starch (endosperm), and has no germ or bran (fiber).

At first glance they may look similar, but the processing of a grain changes its nutritional value significantly. During refining, the bran and germ are removed, stripping away much of the fiber, vitamins, minerals, healthy fats, and other naturally occurring nutrients. What remains is primarily the starchy endosperm — essentially a grain that has been hollowed out, leaving mostly starch and calories behind.

Food manufacturers refine grains because the removal of the bran and germ improves shelf life and creates a softer, more uniform product that is easier to process on an industrial scale.

Understanding this difference helps explain why some grain-based foods contain more fiber, vitamins, and minerals than others.

Fiber

Fiber is also a carbohydrate, but it behaves differently.

Unlike sugars and starches, fiber is not broken down into glucose by human digestive enzymes. Because of this, fiber contributes fewer usable calories and generally has no or very little impact on blood sugar.

What Happens to Carbohydrates During Digestion?

During digestion, most carbohydrates are broken down into glucose, the simplest and smallest form of sugar.

Glucose is the readily available fuel that can be used quickly or stored for later use.

Glucose molecules are small enough to pass through the intestinal wall and enter the bloodstream, where they are carried to cells throughout the body.

This is why ALL carby foods raise blood sugar, even though they may look very different on your plate.

Understanding Net Carbs

For people following a low-carb lifestyle, net carbs help estimate the amount of carbohydrate that affects blood sugar.

Understanding net carbs helps people make more informed decisions when choosing foods for a low-carb lifestyle.

Net carbs are calculated by subtracting dietary fiber from total carbohydrates.

For example:

Total Carbohydrates: 17 grams

Dietary Fiber: 9 grams

Net Carbs: 8 grams

Dietary fiber is subtracted from total carbohydrates because fiber is not broken down into glucose like sugars and starches.

Simple and Complex Carbohydrates

You may also hear carbohydrates described as either simple or complex.

Simple carbohydrates consist of one or two sugar molecules and are generally digested quickly. Examples include the sugars found in fruit (fructose), milk (lactose), and table sugar (sucrose). Many added sugars, such as table sugar, honey, maple syrup, and high fructose corn syrup, are simple carbohydrates.

Complex carbohydrates are made of longer chains of sugar molecules. Many of the starch-rich foods people eat every day, including bread, rice, pasta, potatoes, corn, grains, beans, and legumes, are examples of complex carbohydrates.

Key Takeaway

Carbohydrates exist in three main forms: sugars, starches, and fiber.

Sugars are made of one or two sugar molecules. Starches are longer chains of sugar molecules. Fiber is also a carbohydrate but is not broken down into glucose like sugars and starches.

During digestion, sugars and starches are broken down into glucose, the simplest form of sugar.