Active Voice: The Quest for Optimal Nutrition & Minimal GI Distress during Endurance Competitions?

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Dr. Asker Jeukendrup is one of the world’s leading sports nutritionists. He is currently Global Senior Director of the Gatorade Sports Science Institute, where he continues to provide leadership in sports nutrition research and education. His research at the University of Birmingham, UK, where he was (and still is) a professor, has had significant impact on the field of sports nutrition. In the February issue of Medicine & Science in Sports & Exercise® (MSSE), he and his co-investigators presented findings of a descriptive study that investigated nutritional intake and gastro-intestinal complaints of endurance athletes.

It has long been known that carbohydrate intake during prolonged endurance exercise and prevention of dehydration can improve performance. Guidelines have been developed that recommend carbohydrate and fluid intakes. For example the 2009 ACSM Position Stand on Nutrition and Athletic Performance recommends an intake of 30-60 g CHO/h and a fluid intake to minimize weight loss. More recently, the carbohydrate intake guidelines have been modified and are more specific, recommending higher intakes (up to 90 g/h) for more prolonged exercise (for more, see Jeukendrup 2010 and 2011). It has been questioned whether such high intakes can be achieved by athletes. This may especially be a concern since it has become clear that one of the main challenges the endurance athlete faces in these longer events is gastro-intestinal discomfort and problems. Some studies have suggested a link between nutritional intake before and during races and the prevalence of these GI symptoms.

We set out to determine athletes’ actual intake in endurance events and to establish how many athletes suffer from GI discomfort. We were also interested in studying the relationship between intake and GI discomfort. One of the first observations was the very large inter-individual variation in intake patterns and preferences. We also observed large variation in GI symptoms displayed and the severity of those symptoms. Perhaps the most important finding was that carbohydrate intake from all sources (drinks, gels, energy bars, etc.), was high and exceeded ACSM guidelines in almost all endurance events (apart from marathon running) and was much closer to the newer recommendations. The intake was not associated with GI problems.

Interestingly, however, there was a correlation between carbohydrate intake and performance. From our recent study published in MSSE it was impossible to determine whether higher carbohydrate intake improves performance or whether better performers are able to tolerate a higher intake. It may actually be a combination of these factors. Recent experiments have demonstrated a dose-response relationship between carbohydrate intake and performance. Individuals who struggle to ingest carbohydrate during prolonged endurance sports may have difficulties being competitive in these sports. The good news for athletes is that there are indications that the gut can be “trained.” After a period of high carbohydrate intake (during exercise and in the diet), absorption and tolerance may be improved. More research is needed to get more insights into these mechanisms as well as the practical implications – for example, what are the best methods to “train the gut?”

All in all, this study provided useful insights into what athletes actually ingest during races. Because there appears to be a discrepancy between the advice and what is actually ingested, there is an important role for educating athletes and helping them to find ways to achieve the newer recommendation using various individualized strategies.