Our expert says:
I am including an article from the www.worldofendurance website, which provides valuable information. What is important to note in your question, is that if your energy supplies are inadequate during an endurance event, it will affect your ability to continue and certainly to maintain your level of performance, therefore an energy supply (no matter what the endurance activity), is crucial.
The article below, will give you an idea of how much energy you might need and emphasises that perhaps not all this energy should come from carbohydrates. Certainly fat and some protein, have a role too. Many of the latest energy bars have a combination of these nutrients.
Should you need further information, I suggest you phone our High Performance Centre at the Sports Science Institute on 021 649 5641.
Energy requirements during endurance events
Ciska Connoway RD (SA)
Can you identify with and appreciate the following: Your training program and mental preparation are excellent and if everything depended on willpower, you will certainly outsmart your opponents. You believe you are on your way to the top – yet you experience decreased performance, slow recovery time after training and competitions and low energy levels.
What makes it worse, is that you often struggle to enjoy participation because of symptoms like headaches, hunger, dizziness, blurred vision, low concentration levels, lack of co-ordination, nausea and tiredness.
Sciences’ understanding of the complexity of the life process is incomplete and the intricate nature of human biology and human nutritional needs should therefore be approached in humility. We’re all unique, so everyone’s dietary needs are different and the individual genetic predisposition of individuals should be accommodated.
One cause for your discomfort, amongst various others, may be attributed to the ratio of the macronutrients (carbohydrates, protein and fat) in your diet.
For the past decade, the majority of sports scientists and nutritionists focussed primarily on the consumption of and the role of carbohydrates for endurance sports.
A small percentage of them arrived at different conclusions regarding the composition of diets for endurance sports and struggled to obtain recognition for their views of the importance of protein and fat as well. A natural consequence of this fixation with carbohydrate complements and food in general was the production of sports supplements by manufacturers captured in the “carbohydrate paradigm”. As we all know – established perceptions and paradigms do not change easily.
More recent scientific data suggest that the high carbohydrate dietary guidelines given to sports people should seriously be questioned.
These conclusions were confirmed and shared at the Sports Nutrition Workshop at the 2000 Nutrition Congress in Durban. Many athletes are complaining of the above mentioned symptoms (commonly known as hypoglycaemia) and choose to follow a mixed or higher fat and protein eating plan. A suggestion was made that the focus should shift from excessive carbohydrate to a more individualised and balanced nutritional strategy.
A BALANCED NUTRITIONAL STATEGY?
This term mainly refers to a more balanced or appropriate ratio of the macronutrients namely: carbohydrate (CHO), protein and fat.
The importance of a balanced ratio of these macronutrients can be explained by addressing the following:
* Energy sources during endurance events.
* The effect of macronutrients on hormones like insulin and glucagon and therefore energy release.
* Other important functions of protein and fat.
Energy sources during endurance events
It was previously generally accepted and believed that carbohydrates were the only main source of energy during endurance events or aerobic exercise. During endurance events, however, where the intensity rarely goes beyond 75% VO2 max, all three of these macronutrients are being used as an energy source.
The total carbohydrate storage capacity of the body is quite limited. According to recent studies, a man of approximately 70 kg can store more or less 430 – 475 g CHO in his body as glycogen. Where ±300-400 g CHO is stored in muscle, 60-90 g in the liver and 15 – 20 g in the extracellular fluid (including blood).
This ± 450 g stored CHO will provide 7 650 kJ (1 g CHO provides 17 kJ).
If the athlete intends to finish an endurance event like the Comrades Marathon in 6 hours, he will need ±78, 75 kJ / minute. This amounts to ± 28 350 kJ (basal metabolic requirements and energy expended over 90 km) for the whole marathon.
If only derived from CHO, he will be using 4,7 g CHO / minute (78,75 - 17). The 450 g stored glycogen will only last him 96 minutes (450 - 4,7).
What if he ingested CHO in the form of an energy drink while running? Keeping in mind that the body can utilise only ±1 g ingested CHO / minute, he can only utilise an additional 360 g CHO (1 g / 360 minutes) which will only keep him going for another 77 minutes (360 - 4,7).
The stored CHO and CHO ingested during the race will provide 13 770 kJ. Therefore there is an energy deficit of 14 580 kJ.
The rest of the energy will be supplied mostly by fat (38 kJ per gram), where protein (17 kJ per gram) is catabolised to a smaller extent.
Normally the body has more than enough fat reserves to supply the extra needed energy. Assuming that this 70 kg man has a body fat percentage of 15%, this 10,5 kg fat will provide approximately 399 000 kJ (1 g fat supplies 38 kJ). Theoretically this amount of energy will be enough to run 14 successive Comrades Marathons!
The ratio of CHO : protein : fat utilised during an endurance event varies from person to person. This may be the result of factors i.e. genetic predisposition, biochemistry etc.
On the basis of individuality, two different groups of people can be identified, namely high carbohydrate burners and high fat burners. At the end of an endurance event like the Comrades Marathon the two different groups would have derived energy from the three macronutrients in the following ratios:
* High carbohydrate burner: CHO : PROT : FAT = 32 : 8 : 60
* High fat burner: CHO: PROT : FAT = 18 : 10 : 72
Therefore it is clear that the body can’t perform on carbohydrates alone, especially not in endurance events – evidence enough that all three macronutrients are being used as an energy source during endurance events.
Nutrition data provided by the Bio-Energetics Scientific Advisory Council of PVM.
The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal
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