What are carbohydrates?

Carbohydrates are a polarising subject. For some people, carbs are life, while others say they are the devil. In this article we explore what are carbohydrates, their roles, types and sources.

What are carbohydrates?

Carbohydrates, a.k.a. “carbs” are one of the macronutrients in our food. As the name “carbohydrate” implies, carbs contain carbon, hydrogen and oxygen, hence the sciency abbreviation “CHO”.

The word “carbohydrates” is a noun often used to describe carbohydrate-containing foods. Many of these foods are staples in many traditional cuisines, for example rice, bread, pasta, noodles, potatoes, and taro.

Roles of carbohydrates

The main role of carbohydrate is energy production in the body. The amount of energy that carbohydrates contribute is 16-17 kJ (approximately 4 kcal) per gram.

Types of carbohydrates

Simple vs complex

In practical terms, all carbohydrates are composed of sugars. We can classify carbohydrates based on the number of sugars they contain.

Simple carbohydrates come in lots of 1 (monosaccharides) and 2 (disaccharides) sugars.

Monosaccharides include glucose, fructose and galactose.

Disaccharides include:

• Sucrose (a.k.a. table sugar): glucose + fructose
• Lactose (the sugar in milk): glucose + galactose
• Maltose: glucose + glucose

Complex carbohydrates are also known as polysaccharides, which means “many sugars”. These include glycogen, starch, and dietary fibre.

• Glycogen: carbohydrate stored in animal tissue (e.g. muscles, liver)
• Starch: carbohydrate stored in plant tissue
• Dietary fibre: present in plants, normally resistant to digestion in our gastrointestinal tract

Simple carbohydrates are easier to absorb and therefore represent a quicker source of energy. Complex carbohydrates need to be broken down before they can be used as energy. In general, this means a slower absorption.

Low vs high GI

The glycaemic index (GI) indicates the extent at which a carbohydrate-containing food raises blood sugar. In general, low GI carbohydrates are recommended for good health and high GI carbohydrates are recommended when a quick source of energy is required, such as certain types of exercise.

Low GI foods include multigrain and sourdough bread, rolled oats, pasta cooked al dente, basmati rice, quinoa, seeded crackers, legumes (beans, lentils, chickpeas), sweet potatoes, corn, milk, and most fruits.

High GI food include white bread, processed breakfast cereals, potatoes, white rice, most crackers and biscuits, most baked goods, cordial, and soft drinks.

Sources of carbohydrate

This is where part of the confusion comes from. For some people, “carbs” equals rice, pasta, bread and potatoes. Hence, when they say they eat or not eat carbs, are pretty much just referring to those handful of foods.

In reality, carbohydrates are present in many foods, including of course grains and cereals, but also vegetables, legumes, fruits, dairy and alternatives, nuts and seeds, beverages, and even some protein sources. The graph below shows the carbohydrate content and the carbohydrate contribution to total energy (in %) per 100g of selected foods.

The moral of the story is that many foods contain carbohydrate, including non starchy vegetables (e.g. capsicum, green beans, cauliflowers and tomatoes), dairy foods (e.g. milk, yoghurt and plant-based milks) and processed protein sources (e.g. crumbed/battered fish, chicken nuggets, sausages). So… think again when you say you eat “zero” carbs.

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