Guidelines 10 years ago stated that carbohydrate intake during exercise should be 30-60 grams per hour, this developed to intakes of 90 g/h in some situations, but recently a paper was published that suggested intakes of 120 g/h in mountain marathon runners. Time to investigate….
Carb use from drinks gels and bars
In a couple of earlier blogs, we discussed that carbohydrate oxidation from drinks, gels and bars that are ingested, can be utilized (oxidized) by the body at rates up to 60 g/h. If an endurance athlete ingests 100 g/h for example they will burn up to 60g/h. The rest is likely remaining in the intestine and this has been linked to gastro-intestinal problems. In this previous blog we discussed that the limitation is in intestinal absorption and that this limitation can be overcome by using carbohydrate types that use different intestinal transporters for absorption. In short: certain combinations of carbohydrate can be oxidized at much higher rates. In one study it was found that combinations of glucose and fructose can be oxidized up to 105 g/h. This happened at very high intakes of 144g/h.
90 grams per hour
The latter studies were done for academic purpose: to find out where the limit is. Such high intakes are, however, not practical and we therefore set the recommendations at around 90 g/h, as a compromise between providing enough carbohydrate, but not so much that it would cause gastro-intestinal distress in a lot of athletes. It is important to note that, in theory, higher intakes than 90 g/h could have beneficial effects as we had seen higher oxidation rates with higher intakes.
A few years ago carbohydrate intake recommendations were up to 60 g/h, now we are talking about 90 or even 120 g/h
The new study in mountain marathon runners
Anecdotally athletes have reported higher intakes than 90 g/h (we saw up to 130 g/h in one athlete in Ironman Hawaii), but the study published recently, by Aitor Viribay and colleagues showed that higher intakes are certainly possible. What did they do? They hypothesized that a higher carbohydrate intake could enhance performance but also reduce muscle damage after exercise. They therefore designed a study to compare the effects of high carbohydrate intake of 120 g/h with 90 g/h and 60g/h intake in 26 male elite ultra-endurance athletes during a mountain marathon. This race was organised by the researchers, but all athletes, including 2 world champions mountain trail running and an international stage winner were highly competitive in this event.
They were randomly allocated to one of the experimental groups and were trained to use that target intake during training. So, the high carbohydrate intakes were not new to them. The runners completed the mountain marathon that included 4000m of altitude difference.
The researchers measured exercise load by asking about ratings of perceived exertion and several markers of muscle damage (creatine kinase (CK), lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), urea and creatinine). EIMD markers were analysed before the race and 24 h afterwards and it was found that the 120 g/h group had significantly lower CK, LDH and GOT values 24 h after the mountain marathon race compared to 60 or 90 g/h.
Internal load and muscle damage 24h after the race were lower in the group that ingested 120 g/h carbohydrate
The ratings of perceived exertion during the event allowed the investigators to calculate an internal load and it was concluded that internal exercise load during the mountain marathon was significantly lower with 120 g/h compared with 60 and 90 g/h as well.
These findings are really interesting: first of all because it shows that it is possible to take in larger amounts of carbohydrate during real events. It also suggests that there are benefits in terms of performance and in terms of muscle damage.