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Carbohydrates, They're Complex!

Grace Aguirre, MS, RD
June 2, 2021
June 16, 2023

Carbohydrates (carbs) are the sugars, starches, and fibers found in fruits, grains, vegetables, and milk products. They are one of three types of nutrients that provide energy for your body. The other two energy-providing nutrients are protein and fat. There are two main classes of carbohydrates: “simple” and “complex” carbs. In this article, we will break down the different types of “complex carbs.” To learn more about simple carbs, see “All About Simple Carbohydrates”.

Complex Carbs

When sugar molecules stand-alone or exist in a chain of two sugar molecules attached, they are considered “simple carbs.” Simple carbs are sweet, while complex carbs are not so much. Complex carbs are long chains of glucose molecules, like a strand of pearls. For the glucose to be absorbed into the blood and used for energy in the body, these strands first need to be broken down into “simple carbs.” Digestive enzymes in the gut work like scissors to break down these glucose strands into smaller molecules. Eventually, these small molecules will turn to sugar in the bloodstream.

There are two types of complex carbohydrates found in food: starch and fiber. These are both made up of many pieces of simple sugar put together.

A single pearl, or a simple, easy to digest, uncomplicated sugar molecule.
A string of pearls, or a starch. It is made of many sugars strung together. A little more complex than sugar, it is still easy to break and absorb.
A complex string of pearls, or complex carbohydrate. Difficult to break down, this is like the fiber in our food.


Starch is the way that plants store glucose. Though all starches are considered “complex carbs,” there are both “complex” and “simple” starches found in plants. Both types of starch impact blood sugar levels but at different rates. For those with certain medical conditions such as Diabetes Mellitus, the starch intake needs to be monitored, and the type of starch needs to be considered.

Simple Starch:

  • Has a simple structure resulting in quick digestion
  • Breaks down with heat exposure
  • Causes blood sugar to rise quickly compared to “complex” starch
  • Its scientific name is Amylopectin
  • It makes up about 80% of all starches in whole, natural plant food
  • Found in high levels in processed foods with refined carbs

Complex Starch:

  • Has a complex structure resulting in slower digestion
  • Is resistant to heat (remains intact after heat exposure)
  • Causes blood sugar to rise slowly compared to simple starches
  • Its scientific name is Amylose
  • Makes up about 20% of all starches in whole, natural plant foods


Fiber, the other type of complex carb, is also found in plants but is used more for structure than energy. Fiber is such a complex carbohydrate that human enzymes cannot break it down to use it for energy. Fiber is essential for human health, including its ability to help regulate blood sugars, control cholesterol, eliminate disease-causing toxins, promote healthy body weight, and reduce the risk of cancer, heart disease, and diabetes. See the article titled “A focus on fiber” to learn more.

Dietary Sources of Complex Carbs

The only sources of complex carbohydrates in the diet are plant foods. Each plant contains a mixture of complex starch, simple starch, and fiber, depending on the plant type and part of the plant being consumed.

Plant foods are broken into the following categories:

There is a lot of confusion about how much and what type of carbs should be consumed for optimal health. It is important to note that each individual has their own unique needs, but a few core principles can be applied when building the best diet for you.

To achieve optimal health, talk to your care team dietitians through the Unified Care app to discuss and develop a plan for meeting your individual carbohydrate needs!

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