Slow and fast carbohydrates: What's the difference?

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Posted by Linda O'Byrne (Atkins Nutritionist)

Carbohydrates are a collective name for all kinds of sugar, and starch but one type of carbohydrate isn't the same as another. By understanding thie difference, it makes it easier to get the right kinds of carbs. In this article we explain the difference between fast and slow released carbohydrates.

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What are carbohydrates?

But what are carbohydrates exactly? Carbohydrates are a source of energy for the body. You can find carbohydrates in foods such as pasta, bread, rice, sugar, fruit, potatoes, vegetables but also in cakes, sweets, cakes and soft drinks. The carbohydrates consist of one or more glucose units. The glucose is used as fuel for the body. It's an easy, quick fuel for our bodies. Yet, the body has a store of carbohydrates, in the form on glycogen, you can also get energy from fat and make glucose in the liver.

Interested in a low carb diet? Read more about the diet in this article.

What are fast released carbs?

Fast releasing carbohydrates are called simple carbohydrates. By eating fast released carbohydrates , you increase your blood sugar rapidly and get a quick release of energy. In response, your body makes insulin, which lowers the glucose level. They are fast releasing because you get a burst of energy and the energy lasts only a short time. The result is that you quickly get very hungry, so you will need to eat again. Wheat products like pasta, white rice, potatoes, as well as cookies and candy contain fast releasing carbohydrates.

Too many simple carbs may lead to high cholesterol, hypertension and obesity. But how? Fast releasing carbohydrates are important sources of glucose but when too many simple sugars are consumed, the excess glucose is stored as bodyfat.

What are slow released carbohydrates?

Slow released carbs are also known as complex carbohydrates. These are healthy carbohydrates and are absorbed much more slowly into the body. As a result, the glucose contained in the carbohydrates is absorbed more slowly into the body and it doesn't cause a rapid spike in insulin. Complex carbohydrates are found in foods such as wholemeal and spelt grains, sweet potatoes, green vegetables, legumes, nuts, seeds and whole grain rice.

When you eat products with slow released carbohydrates; combined with protein and fat; glucose from the slow carbohydrates are slowly absorbed into your body. This is a healthy way of eating and thus reduces the risk of obesity.

Foods that contain fast releasing carbohydrates

Try to avoid fast releasing carbohydrates as much as possible. But how do you know exactly which foods are high in these types of carbs? Generally foods with high sugar content and white grains contain fast releasing carbohydrates. See below a list:

  • Candy
  • Cake
  • Pastries

Soft drinks and juices (with added sugar)

  • White rice
  • White bread
  • Ice-cream


  • Most breakfast cereals:
  • cornflakes
  • Muesli

Fruit and dried fruit

  • Sugar
  • Syrup
  • Honey
Foods which contain slow released carbohydrates

See below a list foods which contain slow released carbohydrates:

  • Leafy vegetables
  • Lettuce
  • Spinach
  • Kale
  • tomatoes
  • nuts
  • walnuts
  • Brazil nuts
  • Pecans
  • Green beans
  • Whole-wheat pasta
  • Brown rice

Low carbohydrate diet

There are foods that contain no carbohydrates. These products you may eat on a low carbohydrate diet. Here's a list at a glance:

  • Meat
  • Fish
  • Poultry
  • Shellfish and crustaceans
  • oil
  • Eggs

Would you like to know the amount of carbs of a specific product? Use our carb counter!

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Glycemic index

The glycemic index (GI) indicates how quickly certain food causes your blood sugar to rise. It is a measure to indicate how quickly carbohydrates are digested in the intestine and the glucose is absorbed into the blood. The GI of glucose is the maximum value of 100. Thus, the lower the GI of a product, the slower the carbohydrates are included. Foods which contain complex carbohydrates have a lower GI.

  • Products with GI to 50. These include broccoli, sweet potato, avocado and lentils.
  • Products with a GI between 50 and 70. These are, for example, whole-wheat pasta, cereal, pineapples, bananas, etc.
  • Products with a GI between 70 and 100 products with these high GI value include mashed potatoes, French fries, white bread, pasta, rice and cereal.

The cooking time will affect the GI. Thus the GI of baked potatoes is different from boiled potatoes.

lose weight with a low-carb diet

A low-carb diet is a diet where you limit your intake of carbohydrates, and especially the simple carbs/sugars. Some of these carbohydrates are replaced with vegetables, healthy fats and proteins. Eating low carbs is not only suitable for people who want to lose weight, but also for people who want to eat a healthy and varied diet.

A low carbohydrate diet promotes healthy, balanced nutrition and includes vegetables, meat, fish, eggs, dairy, nuts and seeds. Want to know more about which foods are best to eat? Take a look at this comprehensive list of healthy low-carb products.

Provide balance

So be careful that you avoid simple carbohydrates. Most foods with slow released carbohydrates can be eaten, starting with leafy green vegetables and adding more 'good' carbs as you go through each phase of Atkins. Which phase you start, depends on how much weight you want to lose.

Often the problem is that people eat too many simple (fast) carbohydrates, but do not burn these carbohydrates. When you have a limited amount of carbs and enough exercise, it's easy to find your healthy weight. The trick is to find the right balance!