The New Carbohydrate Intake RecommendationsJeukendrup A.
School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UK
Carbohydrate intake during prolonged exercise has been shown to increase endurance capacity and improve performance. Until recently, the advice was to ingest 30-60 g of carbohydrate per hour. The upper limit was based on studies that demonstrated that intakes greater than 60-70 g/h would not result in greater exogenous carbohydrate oxidation rates. The lower limit was an estimated guess of the minimum amount of carbohydrate required for ergogenic effects. In addition, the advice was independent of the type, the duration or the intensity of the activity as well as the level of athlete. Since 2004, significant advances in the understanding of the effects of carbohydrate intake during exercise have made it possible to be much more prescriptive and individual with the advice. Studies revealed that oxidation rates can reach much higher values (up to 105 g/h) when multiple transportable carbohydrates are ingested (i.e. glucose:fructose). It has also been observed that carbohydrate ingested during shorter higher intensity exercise (1 h, 80%VO2max) can improve performance, although mechanisms are distinctly different. These findings resulted in new recommendations that are dependent on the duration and intensity of exercise and not only specify the quantity of carbohydrate to be ingested but also the type.
Question 1: Carbohydrate provision maximizes performance. If you use carbohydrate blends (glucose, maltodextrin, fructose), you can actually absorb more carbohydrate during exercise. What are the practical limits for carbohydrate intake during exercise?
Answer: If you use a mix of different carbohydrates, we call them multiple transportable carbohydrates, you can achieve very high absorption and oxidation rates, and that has been shown to result in better performance during prolonged exercise (>2.5 h). It is important to realize that this only happens if you ingest relatively large amounts of carbohydrates. If you consume less than 60 g of carbohydrates per hour, you do not see these effects. You only see it if you push the carbohydrate intake higher than 60 g of carbohydrate per hour. We typically recommend around 90 g/h during this type of activity. That is actually quite a lot of carbohydrate to take on board during exercise, especially if you are not used to it. If you are unaccustomed, you can get some stomach discomfort, maybe some intestinal cramps. So the challenge is to ingest relatively large amounts of carbohydrate without causing gastrointestinal distress. The only way to get around this is to get used to it and use this practice in training. If you are planning to use this practice during a race, do not use this practice during the race for the very first time. Always practice the nutrition strategy in a training situation, and do it about once a week so the body is used to handling these large amounts of carbohydrate.
Question 2: Glucose availability in the mouth seems to directly improve performance capacity. Under what conditions would a little carbohydrate already have a practical relevance towards improve performance?
Answer: In some situations you do not need to actually ingest the carbohydrates to get the effect, but this is very specific to short-duration events. Most of the studies have investigated something around 60 min of all-out exercise, so maybe you see the effects from 30 up to 75 min. But it has to be an all-out effort for that period of time. Then, you can get these performance effects even with a simple mouth rinse. So, you can chose to rinse your mouth with a carbohydrate drink or you can chose to drink little bits of carbohydrate, and that should help your performance.
Question 3: Does this work only with glucose, or does this work with other sweeteners?
Answer: It does not work with any sweetener because in studies we and others used the sweetener as the placebo, and the carbohydrate improves performance compared with that placebo. So, it is a very specific effect of the carbohydrate and not of the sweetness. We have also done these studies with carbohydrates that have no taste and you can still see the performance effect. In fact, there are also studies that show that if you give a carbohydrate that is not sweet, it activates certain areas of the brain. So it is definitely a carbohydrate effect and not a sweetness effect.
Question 4: What is your personal and practical recommendation for carbohydrate intake during exercise for athletes?
Answer: The answer is: it depends. It depends on the level of athlete you are, and it depends on the type of event that you are involved in. Generally, if you are a higher level athlete who works out at higher absolute intensities, you probably need a little bit more carbohydrate. The event duration also matters. So if the event is very short you need smaller amounts of carbohydrate than when the event is very long. When the event is 2.5 h or longer and you really want optimal performance, you probably have to push the carbohydrate intake to as high as 90 g of carbohydrate per hour, use carbohydrates that contain multiple transportable carbohydrates. If you are in an event that is between, say 2-3 h, then you can probably get away with 60 g/h. If it is shorter, then you can go to 30 g/h. So, it really depends on what event you are looking at and what level of athlete you are.
Question 5: Is there also a difference if you consume carbohydrates during exercise as a solid food or as a liquid supplement?
Answer: That is a good question. We have recently done those studies where we compared drinks versus gels versus bars, and it turns out that it does not really matter how the carbohydrates are delivered. Gels with water are almost exactly the same as a sports drink. If you give carbohydrate bars with water, it is almost the same as a sport drink as well. But I think it is important that the bars or solid foods that you choose are low in fat, low in fiber and low in protein because as soon as you increase the content of those ingredients, you will slow down the delivery of the carbohydrate.
Number of Print Pages : 9
Number of Figures : 1, Number of Tables : 0, Number of References : 28
Book Serie: Nestlé Nutrition Institute Workshop Series, Vol. 75, Year 2013
Editor(s): Tipton, K.D. (Stirling); van Loon, L.J.C. (Maastricht)
ISSN: 1664-2147 (Print), eISSN: 1664-2155 (Online)
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Book Title: Nutritional Coaching Strategy to Modulate Training Efficiency (75th Nestlé Nutrition Institute Workshop, Mallorca, December 2011)
Editor(s): Tipton KD, van Loon LJC (eds)
For additional information: