Nutrition

Simple Carbohydrates vs Complex Carbohydrates

Carbohydrates are one of the three macronutrients, alongside protein and fats the body needs to function properly. They’re the body’s preferred source of energy.— while we burn fat and protein for energy, the body prefers carbohydrates for fuelling basic metabolic functions. Carbohydrates can be broken down into different groups based on their structure – and how they are utilised in the body. Carbohydrates are usually categorised as either simple or complex. This article explains the difference between the two types, their benefits, and which foods are sources of each type.

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simple carbohydrates

 

What are carbohydrates?

Carbohydrates are one of the primary sources of glucose, which the body uses for energy. Foods high in carbohydrates typically contain high levels of starch, fibre, and sugars — these nutrients have different chemical structures and are processed by the body in different ways.1

Complex carbohydrates are nutritionally dense and typically contain higher levels of fibre and starch. Because of this they often take longer to digest. Foods higher in sugar digest more quickly, and are classified as simple carbs.

 

What are simple carbohydrates?

Simple carbs are also known as sugars, and include glucose, dextrose, and lactose. They digest quickly and can be used for energy or stored in the liver or muscles for future use. Because they can be easily converted into glucose, they’re considered “high GI (glycaemic index)” carbs. While you may think of sugars as added for flavour and sweetness, sugars also occur naturally in foods,: such as fructose in fruit or lactose in milk.

 

What can simple carbohydrates be useful for?

Simple carbs have a bad reputation, but they can be useful. If you’re getting ready for a workout (or in the middle of one) and need a quick burst of energy, a dose of a quick-digesting carb like dextrose can be ideal. If you your blood sugar is low (feeling weak or tired or shaky), some simple sugars can be helpful.

Exercise that lasts longer than an hour, such as marathon training, requires sources of simple carbs (like energy gels or dextrose) to keep muscles replenished.2

 

Simple carbohydrates to avoid

While our body needs all types of carbohydrates, some high-sugar foods that have limited health benefits should generally be avoided in high quantities. Check nutrition labels for the amount of “added sugar” in a food rather than overall carbohydrates. Avoiding foods with five or more grams of added sugar is a good general guideline to follow. Examples of foods high in these simple carbs include:

• Packaged baked goods, cookies, biscuits

• Sweetened fruit- flavoured beverages

• Sweetened breakfast cereals

• Cakes

• Sodas

 

What are complex carbohydrates?

Complex carbohydrates are larger chains of simple sugars, fibre, and starches. These larger molecules digest more slowly into glucose and raise blood sugar more slowly, making them ‘low GI’ carbs. They provide energy over time and can be more filling than simple carbs. Complex carbohydrates often occur in nutrient- dense, plant- based foods like fruits, vegetables, and grains. These foods also contain high levels of vitamins and minerals that are good for our health.

 

Benefits of complex carbohydrates

Complex carbohydrates are ideal for when you need sustained energy levels. Consuming complex carbs more than one hour before your workout can help you stay energised and ready for a challenge. Long-distance cardio, such as running or swimming for more than 30 minutes, uses complex and stored carbs for sustained energy. This is why marathon runners “carb load” before a long-distance race.

Complex carbohydrates are also key for recovery after a workout. They help get protein to the muscles for recovery, and are crucial for replenishing stored carbs burned during exercise.2 A carbohydrate source (alone or as part of a meal) within two hours of exercise can help restore your muscles’ glucose levels.3

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Complex carbohydrate foods

Most complex carbs contain both fibre and starches, but different foods have more of one type of complex carbs than the other.

Carbohydrate foods high in fibre are primarily fruits and vegetables. Fibre is a plant-based carbohydrate our body does not fully digest and contains few calories. These foods typically have simple sugars as well in smaller amounts. High-fibre carbohydrates are a great choice for sustained energy (consume a couple of hours before your workout) and recovery after a workout.

  • Apples
  • Pears
  • Citrus
  • Berries
  • Nuts
  • Seeds

Carbs high in starches include whole grains and some starchy fruits and vegetables. Varying levels of ripeness in some foods (such as bananas) can change the breakdown of starches and sugars. Carbs high in starches are great for sustained energy and for rebuilding the levels of stored glucose in the muscle (glycogen) after a workout.

  • Barley
  • Bananas
  • Beans
  • Corn
  • Oats
  • Potatoes
  • Peas
  • Quinoa
  • Rice

 

Take Home Message

Carbohydrates may have a bad reputation, but they play a crucial role in our bodies for both energy and recovery. While foods high in added sugars should be avoided in large quantities, complex carbs high in fibre and starches are nutrient- dense foods vitally important for our health and athletic performance.

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Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you’re concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.


  1. Neacsu, N. A. (2014). Effects of carbohydrate consumption. Case study: carbohydrates in bread. Bulletin of the Transilvania University of Brasov. Economic Sciences. Series V, 7(2), 39.
  2. Beck, K. L., Thomson, J. S., Swift, R. J., & Von Hurst, P. R. (2015). Role of nutrition in performance enhancement and postexercise recovery. Open access journal of sports medicine, 6, 259.
  3. Stephens, B. R., Sautter, J. M., Holtz, K. A., Sharoff, C. G., Chipkin, S. R., & Braun, B. (2007). Effect of timing of energy and carbohydrate replacement on post-exercise insulin action. Applied Physiology, Nutrition, and Metabolism, 32(6), 1139-1147.


Claire Muszalski

Claire Muszalski

Registered Dietitian

Claire is a Registered Dietitian through the Academy of Nutrition and Dietetics and a board-certified Health and Wellness Coach through the International Consortium for Health and Wellness Coaching. She has a Bachelor of Science in Biology and a Master’s degree in Clinical Dietetics and Nutrition from the University of Pittsburgh.

Talking and writing about food and fitness is at the heart of Claire’s ethos as she loves to use her experience to help others meet their health and wellness goals.

Claire is also a certified indoor cycling instructor and loves the mental and physical boost she gets from regular runs and yoga classes. When she’s not keeping fit herself, she’s cheering on her hometown’s sports teams in Pittsburgh, or cooking for her family in the kitchen.

Find out more about Claire’s experience here.


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