Understanding Carbohydrates, Sugar, and Fiber

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All three of the macronutrients —that includes fat  and protein—can be used for energy. However, carbohydrates are the body’s go-to energy source. They fuel you throughout daily activities, and during short to moderate lengths of exercise. They are the preferred fuel source for movement, biosynthesis of proteins, brain function, and more. There are about four calories (16.8 joules/gram) per gram of digestible carbohydrates.

Carbohydrates are found in a wide range of foods. Anybody who’s tried a low-carb diet knows that. But carbs aren’t evil. In addition to providing energy, some of the healthiest sources of carbohydrates are also rich in other nutrients for the body. They can include large amounts of fiber (a beneficial type of complex carbohydrate), vitamins, minerals, and phytonutrients.

You just have to watch the kind of carbs you eat. Not all choices are equally beneficial. Many processed foods contain large amounts of carbohydrates with very few other nutrients. Those don’t provide a lot of nutritional bang for your caloric buck.

Types of Carbohydrates—It’s Not Just Sugar

Carbohydrates are chemicals made of carbon, hydrogen, and oxygen atoms. They are normally classified by their polymer (the scientific name for a large molecule) length.

Simple sugars are short, containing one to two units. Oligosaccharides have a long, complex name, but are the middle of the carbohydrate road with three to ten units. Polysaccharides are where things get complex. They have more than ten units.

Simple Sugars You’ve Heard All About

Glucose (also known as dextrose) and fructose are two simple sugars that you may recognize. They are called monosaccharides, because they contain only one sugar polymer. (Mono meaning one.) Other monosaccharides include galactose, xylose, mannose, and more. Monosaccharides can be found by themselves in foods, or as the building blocks for larger carbohydrates.

Disaccharides are formed from two monosaccharides. (Di meaning two.) Sucrose and lactose are two common sugars that are considered disaccharides. Sucrose is made of one glucose molecule and one fructose molecule. Lactose, a sugar found in milk, is made of glucose and galactose molecules.

Sugars vary in the amount of sweetness humans can taste. Fructose is about 1.5 times sweeter than sucrose (table sugar), while lactose (sugar in milk) is 1/8 as sweet as sucrose. Sucralose, an artificially modified disaccharide, is 600 times sweeter than sucrose.


Oligosaccharides are medium-length carbohydrates (3-9 units). They provide you with energy and fiber. Maltodextrin is a commonly eaten oligosaccharide. It is comprised of three to 17 glucose units. The linking of monosaccharides means maltodextrin is rapidly broken down and absorbed by the body.

Oligosaccharides are used inside the body to bind with proteins and fats. The structures they form, play an important role in healthy immune response, cell membranes, cell signaling, skin, and more.

Polysaccharides Store Lots of Energy

Polysaccharides are energy powerhouses. They’re built of long chains of monosaccharides of varying lengths. They can be as short as 10 units, or as large as 10,000+ units.

Starch is a type of polysaccharide that plants use for energy storage. Potatoes, rice, wheat, and other grains are high starch foods. Like simple sugars and maltodextrin, starch can be quickly digested and used for energy for your body.

While plants use starch for energy storage, humans use the molecule called glycogen. This polysaccharide is created by your body from the sugars that you eat. Glycogen is found in large amounts in the liver to provide energy for your entire body.

Fiber Is a Complex, And Beneficial Carbohydrate

Different types of fiber are also classified by their length. And like other sugars, their lengths make them oligosaccharides or polysaccharides. What makes fiber different from other carbohydrates, is that it can’t be fully broken down by your bodies. This offers a number of potential health benefits.

Fiber can play a role in maintaining a healthy weight. Because fiber is not completely broken down, this limits the energy your body can acquire from this type of carbohydrate. Fiber can also play a role in weight maintenance by helping you feel full longer.

Insoluble fiber is made of molecules like cellulose and chitin. You can find it in grains, fruit, and vegetables. Insoluble fiber, as the name suggests, is not absorbed by the body. That doesn’t mean it doesn’t help out. It passes through the digestive tract, where it plays a role in digestive health by feeding your gut bacteria.

Soluble fiber can help promote regularity and bind with cholesterol to support heart health. It is found in the skin of fruits, oatmeal, psyllium, and inulin.

Food Sources

Foods highest in carbohydrates include bread, pasta, rice, cereal, fruit, some vegetables, and also candy and sweets. When choosing which of these to include in your diet, it’s important to consider which other nutrients are also in the food. While the primarily role of carbohydrates is to provide energy, your food choices can have a much larger impact on nutritional status and health.

Fruits and vegetables are filled with vitamins, minerals, and phytonutrients. For example, a medium banana (118 g) provides about 27 grams of carbohydrates, three grams of those carbohydrates are fiber. It has over 400 mg of potassium, 400 mg of vitamin B6, and also some manganese, folate, vitamin c, and other nutrients. Compare that with candy. The same amount of carbohydrates in candy or pastries will not have the same nutrients as the fruits and vegetables.

Fruit and vegetables versus candy is an obvious choice. Choosing between grain products can be more difficult. While many grains are fortified (added vitamins and minerals), whole-grain products can still offer significant benefits. Whole grains have more fiber. They can include higher amounts of B vitamins, and minerals like selenium, potassium, and magnesium.

Pick Your Energy Sources Wisely

You need to eat carbohydrates to fuel your daily life. When choosing these foods, you should ask yourself two questions. How much energy do you need, and which foods offer the most micronutrients?

Sports, a workout, or other physical activity provide a good reason to eat energy-dense carbohydrates, like juice, energy drinks, or foods full of simple carbohydrates. They’re easy to break down, and generate quickly accessible energy.

More sedentary activity can be fueled with vegetables and whole grains. They provide a moderate amount of energy, while filling you up longer because of their fiber and bulk.

Carbs aren’t all about energy. Your body needs micronutrients, too. One way to get them is to eat a varied diet, focusing primarily on fruits and vegetables. The stomach has a limited amount of space for food, and you get to choose whether those foods will be nutrient rich or not.


“Carbohydrates in human nutrition – Chapter 1 – The role of carbohydrates in nutrition”. Food and Agriculture Organization of the United Nations. FAO.

“Carbohydrates”. The Nutrition Source. Harvard School of Public Health.

“Carbohydrates”. MedlinePlus. U.S. National Library of Medicine.

National Institutes of Health. Office of Dietary Supplements.

“Oligosaccharide”. Encyclopædia Britannica.

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