Carbohydrates are the body’s main source of energy. They are broken down into glucose, which enters the bloodstream as blood glucose (or blood sugar). Carbohydrates can be grouped into simple and complex types, and how processed they are has a big impact on how quickly they raise blood glucose levels.

Simple carbohydrates

Simple carbohydrates are made up of one or two sugar units and are digested quickly, causing faster and higher rises in blood glucose.

Highly processed sources often contain added sugars and very little fibre or nutrients, such as:

• Confectionery (lollies, chocolate)
• Baked sweets (cakes, biscuits, muffins, pastries, doughnuts)
• Ice cream and packaged desserts
• Sweetened breakfast cereals
• Soft drinks and sugary beverages
• Fruit juice and fruit drinks

Not all simple carbohydrates are highly processed. Whole fruits (apples, berries, oranges, pears) also contain simple sugars, but in their whole-food form they come packaged with fibre and nutrients that help slow digestion and the rise in blood glucose.

For this reason, the main focus should be on reducing highly processed simple carbohydrates that contain added sugars and little or no fibre.

Complex carbohydrates

Complex carbohydrates contain longer chains of sugar units, along with more fibre, vitamins, and minerals. As a result, they tend to be digested more slowly and raise blood glucose more gradually.

Highly refined starchy foods such as white bread, white pasta, white rice, many crackers, and potato crisps technically contain complex carbohydrates. However, much of their fibre has been removed, so they can raise blood glucose almost as quickly as simple sugars.

Examples of healthier, less processed complex carbohydrates include:

• Whole grains (oats, brown rice, quinoa, barley, wholegrain bread)
• Starchy vegetables (potatoes, sweet potatoes, corn, peas)
• Most other vegetables and whole fruits
• Legumes (lentils, chickpeas, beans, soy foods)

Similar to simple carbohydrates, the focus should be on choosing minimally processed, fibre-rich complex carbohydrates.

Relevance to diabetes

To connect this back to what we’ve learned, remember those big balls of energy bouncing down the street, needing to get into the houses (cells) to provide power?

When we eat carbohydrates, they are broken down into glucose, which enters the bloodstream.

Complex carbohydrates from whole plant foods come packaged with fibre, nutrients, and some protein, and are naturally low in fat. These features help slow digestion and support steadier blood glucose levels. In contrast, highly processed carbohydrates are broken down more quickly, leading to faster and larger rises in blood glucose.

In people without insulin resistance (no gum in the lock), insulin acts like a key that opens the door of the cell. This allows glucose to leave the bloodstream and enter the cell, bringing blood glucose levels back to normal.

In people with insulin resistance (gum in the lock), the key does not work properly. As a result, more glucose remains in the bloodstream, levels stay high, and over time this can damage blood vessels and organs.