The positive effects of carbohydrates assumption during long (more than 60 minutes) training are well known and from many years. As soon as during the ’20 suggestions were made that refuelling with sugars during a marathon run could improve the performances. From then, there has been a research activity focused on finding the correct balance for the energetic reserves of athletes’ body, studying the timing and quality of carbs assumption.
HOW TO CHOOSE
As a matter of fact it is, now, fully understood that the choice of which carbohydrate is to be assumed during training has a impact on the speed of conversion into available energy.
Some sugars are indeed easier for our muscle to be immediately used and this is linked, mainly, by the gut absorption rate of each type of carbs. As a general guidance, it is better to choose fast absorbing sugars, like glucose, fructose or saccharose, but some distinctions are due.
Glucose assumed during training cannot be converted by oxidation at a speed higher than 60 grams per hour, and this is a limit we need to consider, mainly for prolonged endurance events (like an Ironman) where we should aim at getting as much as 90 grams per hour assumption rate. The 60 gr/hour limit is linked to the gut absorption. For this reason, the most updated studies, indicate that it is better to eat a blend of different sugars, like glucose+fructose, maltodextrin+fructose or glucose and saccharose. The ingestion of different sugars activates different transporters, increasing the total transportation and absorption capacity of the gut. This leads to several advantages, not only limited to the better energy intake, but extending to the improvement of the hydration balance and the reduction of gut discomfort.
Having spoken of the quality, it is important to consider that also quantity is an issue to consider carefully. Various scientific researches have indeed shown that the minimum quantity useful to elicit a positive performance increase is of 20 grams, while the assumption of big quantities of carbs (120 or more grams/hour) would bot result in any advantage and might increase the risk of gut problems. The correct quantity should be calculated depending on the type and length of the training / race and kept within a range of 30 to 60 grams/hours.
How we get our carbohydrates, in which form, seems to be of lesser importance. You might choose what you prefer between gels, bars or drinks or combine different delivery media, either for convenience or for personal taste or personal tolerance level to each product category.
PLAN THE BEST STRATEGY FOR YOUR NEEDS
Whilst the scientific guidelines are quite clear, it is indeed true that converting them into practice and giving some general advice on how-to might be quite difficult; each athlete should build his/her personal nutrition strategy based on his/ her experience, on the discipline he/she practices and keep in mind the personal tastes! You might have the possibility to train, like in cycling, carrying with you useful quantities of food or, on the opposite, like in marathons, it might be impossible to carry any weight at all.
Plan your nutritional strategy according to the type and length of your competition and build your knowledge on the experience of the training sessions. Also if you are at your first race or event try your best to prepare your nutrition plan properly: before making mistakes consult a nutritional expert who can guide you down the correct path.
Currel, Jeukendrup (2008) Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc, 40 (2), 275-281
Jeukendrup (2004) Carbohydrate intake during exercise and performance. Nutrition, 20 (7-8), 669-677