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Carbohydrate: The Basics

Carbohydrate is a valuable nutrient for athletes to perform at training, in competition and to assist recovery. Carbohydrate energises the muscles and brain, delays fatigue and supports gaining muscle mass. Here we will show you which carbohydrate-containing foods will help you to eat smarter, train harder, and perform at your peak.

Carbohydrate is the body’s preferred fuel source for high-intensity exercise. Photo: Derek Morrison

As sports dietitians we have watched carbohydrates ebb and flow in popularity. Let us cut through the confusion and reveal the truth behind this vital nutrient. 

What is carbohydrate?

Carbohydrate is a nutrient found mainly in plant foods. As we eat them we break them down into single sugar units like glucose, before absorbing them into our bloodstream. Carbohydrate is the body’s preferred fuel source for high-intensity exercise. We also use carbs for energy in our brain, our red blood cells, heart and liver. Carbohydrate is one of the three main macronutrients found in food, along with protein and fat. For every gram of carbohydrate consumed, we get 16-17 kilojoules (4 calories) of energy. In our Types of Energy piece Dr Kirsty Fairbairn talks more about energy and macronutrients. We store carbohydrate energy as glycogen mainly in our muscles, with some also in our liver.

When you train or exercise one or more times a day you need a lot more energy and carbohydrate than usual. Eating carbohydrate enhances your ability to train and compete hard. The amount of carbohydrate you need will depend upon the exercise you do, your weight and the intensity and duration of exercise.

What foods contain carbohydrate?

Most of our dietary carbohydrate comes from plants, except lactose which comes from milk. Carbohydrates are made in plants from sunlight energy via photosynthesis. Those carbohydrates are stored in the plant for its own energy needs, or used to build the structure of the plant.

There are three major types of carbohydrate in plants: starch, sugar and fibre. Different parts of plants have different types of carbohydrate in varying quantities, depending on what the plant needs for its own growth and reproduction.


Starch is a common form of carbohydrate in our diet, usually from the part of a plant where it stores carbohydrate. Corn, peas, beans, potatoes and grains (including rice, oats, wheat and barley) are all good sources of starch. When humans eat starch, our bodies break it down as we digest it, into lots of little glucose or other sugar molecules. We can then absorb those sugars from our gut into our bloodstream and either use them or store them for our own energy.


Plants also contain different types of sugars. Fruit is a great example of that. In whole fruit, the sugar is stored inside intact cell walls that are built from fibre. Think of a balloon made of fibre with the sugar stored inside. This means the sugar in whole fruit is slower to be digested and released when we eat it, because the fibre balloon makes it harder for our digestive enzymes to get to.


Another important type of carbohydrate in our diet is fibre. Fibre comes from the structural part of plant stems, leaves, fruit and seeds. Vegetables, fruit, whole grains, nuts, and beans are all high-fibre foods. While fibre gives us a lot less energy (as kilojoules and calories per gram) than starch and sugar, it gives our gut amazing exercise and is very important to our general health. Fibre is a fantastic nutrient to eat a lot of.

When you think about it, it is a pretty amazing concept that we can use energy that comes from the sun, via plants, to help us exercise and live our lives.

Choose your carbs wisely. Photo: Derek Morrison


Food processing and carbohydrates

Processing impacts carbohydrate-containing foods a lot. This is because processing often removes the fibre from the plant (like processing white bread from wholegrain wheat or rye for example). Another example is processing fruit into fruit juice. The fibre structure or content is changed, meaning the sugar in that plant becomes a lot easier for us to break down during digestion. This makes it much faster for those sugars to hit our bloodstream; when slow release is better for our body.

Generally whole and less processed fruit and vegetables retain more fibre in its natural form. Other processed carbohydrate foods like cakes, doughnuts and biscuits have very little fibre, meaning the carbohydrates in them are much easier to access during digestion.

What carbohydrate-containing foods are best to eat?

Foods containing wholegrain, natural carbohydrates should make up a lot of an athlete’s food intake. It is important to recognise and choose nutritious carbohydrate food sources for good health. We call these “nutrient dense” foods because they have many other nutrients alongside those carbohydrates. See our Types of Energy piece to take the Nutrient Dense test.

Like anyone, active people and athletes need to consume a variety of foods to get all the nutrients we need to operate well. Whole fruit, whole vegetables and whole grains are all high in fibre and an important part of a healthy diet. They contain vitamins, minerals and other important nutrients (including antioxidants) that are good for our health. That doesn’t mean that you can’t enjoy a less nutrient-dense food like a doughnut from time to time.

There are also some situations where an athlete may find more refined, less nutritious carbohydrate foods useful, such as during busy competition tournaments or meets. Easy and quick to digest carbohydrate foods can help meet higher fueling needs. However, try to make sure your dietary carbohydrate comes from nutrient-dense foods most of the time in your usual training diet.

In Summary

Some foods that contain carbohydrate are more nutrient dense than others. Dietary carbohydrate comes in a range of different forms, such as sugar, starch and fibre. Plants are our largest source of nutritious carbohydrate and the less processed the better. Many plants foods (like legumes and beans) provide carbohydrate alongside protein, vitamins, minerals and fibre.

Food processing can change the dietary fibre in a plant food a lot, or remove it completely. This can impact the speed at which those carbohydrates are absorbed into your bloodstream. Slow absorption of carbohydrate into our blood is generally healthier than fast absorption.

Selecting the right carbohydrate-containing food for your training should be a choice guided by what your situation is at that point in time, whether you need more nutrients with your carbohydrates and what makes you feel energised and able to train hard each session. That will help you reach your goals. 

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