Good carbs, bad carbs

Let’s have a quick look at how carbs are classified. Carbohydrates (carbs) are typically classified according to their specific chemical structure. The most simple method of this classification is one that I’m sure you would’ve all heard of. Simple carbs and complex carbs. Simple being sugars and complex being starches or fibres. This method actually refers to the number of sugar units in the molecule.


The main sources of carbs are as follows:

Simple (sugars) 

  • Fruit sugar
  • Milk sugar
  • Brown sugar
  • Table sugar
  • Honey

Complex (starches) 

  • Vegetables 
  • Seeds
  • Whole grains
  • Dried beans/peas
  • Potatoes
  • Cereals
Classic iced and sprinkled donuts

Simple carbs

Simple carbohydrates are very small molecules consisting of 1 or 2 sugar units. 

The 1 sugar units (monosaccharides) include:

  • Glucose (dextrose) 
  • Fructose (fruit sugar) 
  • Galactose

The 2 sugar units (disaccharides) include:

  • Sucrose (table sugar) – which actually comprises of a glucose and fructose molecule joined together. 
  • Lactose (milk sugar) – which comprises of a glucose and galactose molecule joined together. 

Complex carbs

Now, complex carbs (polysaccharides) are much larger molecules consisting of anywhere between 10 to several thousand sugar units joined together, (mostly glucose). They include starches such as Amylose and Amylopectin and non-starch polysaccharides (dietary fibre), such as, Cellulose, Pectin and Hemicellulose. 

Look at this diagram.

Look at this simple diagram below:

As a rule of thumb, monosaccharides are quickly absorbed into the bloodstream. Disaccharides have a slightly delayed absorption into the bloodstream, whilst polysaccharides are absorbed into the bloodstream slowly. However this may not always be the case.

So, simple or complex carb?

Many foods actually contain a mixture of both simple and complex carbs making this classification quite confusing. 

For example, biscuits and cakes contain flour, which is a complex carb. They also contain sugar though, which is a simple carb. Bananas is another example, they contain a mixture of sugars and starches depending on their degree of ripeness. 

Good carbs, or bad carbs?


As stated above it may be tempting to think that just because simple carbs have a smaller molecular size that they are absorbed more quickly than complex carbs and produce a large and rapid rise in blood sugar levels. Unfortunately this is not always the case. For example, apples (containing simple carbs) produce a small and prolonged rise in blood sugar, despite being high in simple carbs. Many starchy foods (complex carbs), such as potatoes and bread, are digested and absorbed very quickly and give a rapid rise in blood sugar. 

So, in fact the model of simple vs complex carbs is actually somewhat incorrect and misleading and has in fact been replaced by the Glycaemic Index (GI). 

We will go over the GI in more detail in another blog post. 

Until then, have a great day!

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