Carbohydrates – pt 1

Low carb, high protein, high fat, train low, compete high….the list is endless.  Not a day goes by in my practice that I don’t talk about importance and need for carbohydrates in a balanced diet.   Many athletes are confused about the amount of carbohydrate they need to support their training and to optimise their performance, while still trying to maintain their body composition and lose/ maintain weight.  There is always a tendency for triathletes to want to lose weight to lower their body fat level to improve performance.  However, following weight loss fad diets, can increase the risk of failing to recover adequately from training, which can lower immunity, decrease muscle mass and compromise performance.


I have decided to divide this section on carbohydrates into two parts as there is a lot of information I would like to share with you.  In the first part I will be covering the types of carbohydrates, and how your body uses them for energy.  In part two, I will be discussing the consumption of carbohydrates before, during and after exercise.

Types of carbohydrate

Carbohydrates are made up of individual sugar units. Different types of carbohydrate are grouped by the number of sugar units they contain and how these units are linked together.



A simple sugar or monosaccharide is a carbohydrate with one unit of sugar. Glucose (the main form in which carbohydrate circulates in our body as blood sugar) found in table sugar, honey, soft drinks and sweets Fructose (fruit sugar)
  A disaccharide is a carbohydrate with two units of sugar. Sucrose (table sugar)

Lactose (milk sugar)



Complex carbohydrates or polysaccharides have more than two units of sugar linked together. Starch found in cereal grains including bread, pita breads, wraps, rice, pasta, couscous, pap, crackers and breakfast cereals. Some fruits and vegetables especially potatoes, root vegetables and pulses contain a mixture of sugars and starches.
Dietary fibre Carbohydrates found in plant cell walls are known as non-starch polysaccharides (NSP). We cannot digest them but they are a major component of dietary fibre. Root vegetables, nuts and seeds, oats, fruit, cereals and whole wheat bread.

Why is carbohydrate important?

Carbohydrates are the primary source of energy for the body and the working muscles.  Your body converts carbohydrates into glucose to be used for energy.  Any glucose not used by the cells is converted into glycogen and is stored in the muscles and in the liver to be used later for energy.  Glycogen stores however, are limited and need to be replenished daily.   When glycogen stores are low and do not meet the needs of an athlete’s training program, this will result in fatigue, reduced ability to train hard, impaired competition performance, delayed recovery after exercise and a reduction in immune system function. It is, therefore, essential to consume carbohydrate before, during and after training or an event.

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How much carbohydrate?

Daily carbohydrate requirements will differ according to the amount, duration and intensity of training.  Activity levels change on a daily basis, therefore, carbohydrate intake will change accordingly.   Triathletes should adopt eating strategies that promote recovery and refuel during training session.  Athletes should focus on including complex carbohydrates (bread, pasta, rice, potatoes and cereals) at every meal.   These foods, however, tend to be bulky and high in fibre, so during intense training or an event, supplements can be used to increase carbohydrate intake without the development of gastrointestinal discomfort such as abdominal bloating, cramping and diarrhoea.

 Glucose metabolism

 What about Glycaemic Index? 

Glycaemic Index (GI) is a ranking of how quickly carbohydrate foods raise blood sugar levels after they have been eaten.  Foods with a high GI are digested very quickly and increase sugar levels very quickly, whereas foods with a low GI are digested slower and as a result will increase sugar levels more gradually.

With regard to sports nutrition, it is important to consider the athlete’s requirements.  For example, low GI carbohydrates are useful as a meal 60-90 minutes before exercise such as a whole wheat sandwich/ cereal whereas a high GI food such as jelly babies/ Coke Cola is useful as a quick energy release during exercise.  Individual requirements are based on the duration of the training/ competition and performance goals.


Potgieter, S.  Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition.  South African Journal of Clinical Nutrition 2013; 26(1):6-16.

Jeukendrup, AE.  Nutrition for endurance sports: Marathon, triathlon, and road cycling Journal of Sports Sciences, 2011; 29(S1): S91–S99.

Jeukendrup, AE et al. Nutritional Considerations in Triathlon. Review Article. Sports Medicine 2005; 35 (2): 163-181.

British Dietetic Association: Food Facts.

Australian Institute of Sports:

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