Carbohydrates for Sports
- Kayla
- Oct 7, 2019
- 4 min read
Updated: Oct 22, 2019
Function
Carbohydrates are important as they provide fuel for the central nervous system and act as a versatile substrate for muscular work, this supports exercise over a range of various intensities due to its utilisation by both anaerobic and aerobic pathways.
As a fuel source carbohydrate is advantageous over fat since it provides a larger yield of ATP per volume of oxygen that can be delivered to the mitochondria (the cells' powerhouses), thus improving exercise efficiency. It also prevents protein catabolism in the body by decreasing gluconeogenesis, therefore sparing muscle tissue.
There is significant evidence that performance of prolonged or intermittent high-intensity exercise is enhanced when athletes maintain high carbohydrate availability, while depletion of glycogen stores and blood glucose is associated with fatigue, impaired skill and concentration, increased perception of effort and decreased work rate.
Sources
Carbohydrates are found in both healthy and unhealthy foods, sources include bread, beans, popcorn, potatoes, noodles, jellies, cookies, pasta, soft drinks, corn, bananas and grapes. They also come in a variety of forms including fibre, starches and sugars.
The healthiest sources of carbohydrates are mostly natural, unprocessed or minimally processed whole grains, legumes, vegetables and fruit. These types of carbohydrates should make up a significant amount of the diet as they promote good health by providing a source of vitamins, minerals and fibre.
Unhealthier sources of carbohydrates include refined white bread and pastries, fizzy drinks, and other highly processed or refined foods. These items contain easily digested carbohydrates.
As an athlete, both sources are included in the diet. While more complexed carbs such as whole grains should make up most of the carbohydrates in the diet, they often take longer to digest and so aren’t usually desirable for an athlete’s during-exercise energy source. Instead, you would opt for easily digestible carbohydrates such as sports drinks during exercise. Within the hour or so prior to training or an event, it is advisable not to ingest foods too high in fibre as it may induce gut issues, however, this depends on the athlete in question. Every athlete should test what works for them.
Storage
The amount of carbohydrate stored in the body is relatively limited and can be manipulated on a daily basis. The dependence an athlete has on their carbohydrate stores depends on the exercise type, the duration of the exercise session, the fitness level of the athlete and the level of exertion of the athlete. However, I will talk more about that later in a separate blog post.
Ways in which an athlete may manipulate their carbohydrate stores include carb-loading and carb-periodisation.
Carbohydrate Loading
The purpose of this is to promote a significant increase in the glycogen content in both liver & muscle to give athletes greater endurance. Endurance athletes include multi-event competition over a sustained period (marathon, ultra-endurance events, triathlon). Carbohydrate loading isn’t as simple as over-indulgence of sugar. In order for it to be effective, it must be done properly. Exercise is usually tapered down over the 6 days prior to the event, with carbs supplying ~50% of all energy for the first 3 days. For the last 3 days, exercise is reduced even further & carbohydrates should provide 70-80% of energy. This type of dietary manipulation should only be done for endurance events, but shouldn't be done for regular training as you are compromising other nutrients.
Carbohydrate periodisation
Carbohydrate periodisation refers to the process of manipulating carbohydrate intakes around specific training session. There are a number of ways you can periodise training such as fasted training sessions. There are some potential negative effects with this method of training such as compromised immune function, compromised recovery and compromised Muscle Protein synthesis (MPS). It has been shown that insufficient carbohydrate stores during training will decrease performance. For competitive athletes it is always best to be fueled properly for both training and competition to get the most out of each session. Carbohydrate periodisation strategies should only be tested in training and done so under the supervision of a sports nutritionist. Implementing these strategies during competition is not advised as this could compromise performance.
Intake
Usually carbohydrates will make up 45-65% of total daily calories. Ideal daily intakes may be calculated based on the duration of training or a specific goal. Intakes will also vary throughout a day based on that day's training/event.
Duration of Training
1 hour/day = 5-7g/kg/day
1-3 hours/day = 6-10g/kg/day
4+ hours/day = 8-12g /kg/day
Goals
To maximise daily glycogen recovery in order to enhance prolonged daily training, or "load" the muscle with glycogen before a prolonged exercise competition = 7-10g/kg/day.
To meet fuel needs and general nutrition goals in a less fuel demanding sport – e.g light jogging, or many hours of low intensity exercise – 5-7g/kg/day.
5-6 hours of moderate intensity exercise or prolonged intense exercise e.g. Tour de France cyclists. The carbohydrate intake goal would be to provide energy for the high energy requirements of the athlete, to allow daily muscle glycogen recovery, and also to refuel the athlete during exercise - 10-12+ g/kg/day.
To enhance early recovery after exercise, when the next session is less than 8 hrs away and glycogen recovery may be limiting.1-1.2g/kg soon after exercise, and continued intake so that ~1g/kg/2hrs is achieved in snacks or a large meal.
To provide an additional source of carbohydrate during prolonged moderate and high intensity exercise, particularly in hot conditions or where pre-exercise fuel stores are sub optimal e.g. team sports events lasting more than 1 hour – 30-60 g/hr in an appropriate fluid or food form.
Timing
Pre-event fuelling: 1-4 hours before exercise, the athlete should have 1-4g/kg.
During exercise*: If exercise lasts for more than 1 hour, then 30-60g/hr should be ingested, often sports drinks (6-8% carbs) are helpful as they also provide hydration. If exercise lasts less than an hour then carbohydrates shouldn't be required.
Post-exercise: 1-1.2g/kg immediately after exercise (along with 0.3g protein/kg, read protein blog-post for information on protein requirements).
*The athlete should practice to find a refuelling plan that suits their individual goals including hydration needs and gut comfort.
Calculating carbohydrate requirements is tricky, and therefore it is always advised that each individual athlete sees a qualified sports nutritionist who can assess them and provide them with a dietary plan to help them reach their needs.
Information sourced from:
Thomas, D.T., Erdman, K.A. and Burke, L.M., 2016. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Medicine and science in sports and exercise, 48(3), pp.543-568.
My personal Sports Nutrition notes from University College Cork
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