In 2003, we discovered that certain combinations of carbohydrate could be absorbed faster in a sports setting. Before this discovery it was believed that the maximal amount of carbohydrate that could be delivered to the muscle was around 60 grams per hour (or 240kcal per hour). With energy expenditures over 1000 kcal/h in some endurance sports it was speculated that delivering more carbohydrate would help performance. This blog outlines the science behind carbohydrate ratios for sports performance.
The science behind carbohydrate ratios
No matter what protocols were used and what type of carbohydrate, no one seemed to be able to deliver more than 60g/h. We and several other researchers started to investigate this limitation and discovered it was neither gastric emptying, neither muscle glucose uptake, neither muscle metabolism that were the limiting factor. It had to be absorption. The absorption of carbohydrates is facilitated by transport proteins. Glucose is transported by a sodium dependent glucose transporter 1 (SGLT1). Perhaps this protein was becoming saturated at high glucose intakes? There were not many alternatives. GLUT5 is another transporter that transports fructose. The theory was developed that if both transporters would be used at the same time it would be possible to absorb more carbohydrate and this should then lead to greater delivery to the muscle, and greater use by the muscle.
Indeed, the first study to combine glucose and fructose showed exactly this. When glucose and fructose were combined oxidation rates were 50% higher compared with just glucose ingestion! This opened up a lot of opportunities: different combinations of carbohydrates could be tested and the amounts ingested were increased up to 3 g/min or 180g/h in those early years (don’t try this at home!!).
The highest oxidation rates were seen with intakes of 144 g/h, but the best results were probably obtained with 108 g/h because this resulted in the lowest residual volume. When we ingest 100 grams of carbohydrate ideally we want all of this carbohydrate to be used and we want as little of this as residual volume in the intestine. The more carbohydrate remains in the stomach, the greater the chances of intestinal problems. The highest oxidation efficiency was observed with the intake of 108g/h as glucose and fructose in a 2:1 ratio.
Ratio of carbohydrates
We then had to summarise the findings of all these studies into practical recommendations and it seemed that 90 grams per hour was a safe amount to ingest with very few athletes displaying gastro-intestinal problems. With increasing intake above 90 g/h we saw an increased number of individuals who did not tolerate the amounts well. So we landed at the recommendation of 90 g/h purely from a practical point of view.
The ratio we suggested was 2:1 glucose:fructose or maltodextrin:fructose because of 2 reasons: first the amount of glucose needed to be just enough to saturate the glucose transporter and we had seen the highest oxidation efficiency with similar ratios and amounts.
Is 2:1 the optimal ratio?
There is no optimal ratio. The ratio that is optimal will change depending on amounts ingested. If 90 g/h is ingested it should be around 2:1, but if more is ingested, for example 120 g/h, 1:1 is likely better. There are many commercial preparations with claims of the best ratio, but the reality is that there is no best ratio. A common ratio is 1:0.8 glucose:fructose and this is the result of one study by Dave Rowlands who used this ratio and showed that in the conditions of that particular study, oxidation was slightly higher for the 1:0.8 glucose:fructose compared with 2:1. But of course this doesn’t mean that this ratio is the best in all conditions and it will change when different amounts are ingested.
There is no optimal ratio. The ratio that is optimal will change depending on the amount of carbohydrate ingested.
To date, we hear more and more about the higher the intake the better, and this may be the case, but evidence is currently lacking. We have studies to show that 2:1 is better than a single carbohydrate at intakes around 90 g/h. But so far, performance effects for even higher intakes (>90 g/h) have not been demonstrated. Hopefully future studies will investigate this, carefully controlling all variables, including how accustomed subjects are to ingesting large amounts of carbohydrate.
So, what can we conclude about carbohydrate ratios?
For now, we can conclude that the intake needs to be individualised based on tolerance. This tolerance might be trained by training the gut, but the intake should be based on what is easily tolerated. Especially at the elite level higher intakes should be targeted. It is the target intake that will then determine what the optimal ratio is.
We should always aim for a glucose intake around 60-70 g/h but not higher and we can add fructose on top of this. Below are some examples:
If I can tolerate 80 g/h, I would ingest 60g/h of glucose and 20 g/h of fructose. This would be a 3:1 ratio.
Wheres if I can tolerate 100 g/h, I would ingest 60g/h of glucose and 40g/h of fructose. This would be a ratio of 3:2.
Most commercial preparations are 2:1 or 1:0.8 glucose:fructose. 2:1 would be best if 90 g/h would be ingested and 1:0.8 would probably be preferred if closer to 110 g/h is ingested.
If you enjoyed this blog, we have an upcoming webinar on What's new in marathon nutrition? where we will discuss the latest on carbohydrate ratios, as well as the effect of caffeine and hydrogel technology on performance, the possible use of CGM for fuelling strategies, and more! Click HERE for more...
