Back in 2003, scientists discovered that certain carbohydrate combinations can be absorbed more quickly during exercise. Before this discovery, it was believed that the maximum amount of carbohydrate that could be delivered to muscle was about 60 grams per hour (or 240 kcal per hour). Given the energy expenditure of over 1000 kcal/h in some endurance sports, it has been speculated that consuming more carbohydrates would improve performance. You just had to find a way to take in more.

Science behind carbohydrate ratios

No matter what protocols were used and what type of carbohydrates, nothing seemed to be able to utilize more than 60g/hr in the body. Several researchers began to investigate this limitation and found that neither gastric emptying, nor muscle glucose uptake, nor muscle metabolism was 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). This protein becomes saturated with high glucose intake. And this limit is 60 g of glucose per hour. GLUT5 is another transporter that transports fructose. The theory was developed that by using both transporters simultaneously it would be possible to absorb more carbohydrates, which should then result in greater delivery to the muscle and greater utilization by the muscle.

In fact, the first studies combining glucose and fructose showed exactly this. When combining glucose and fructose, oxidation rates were 50% higher than when taking glucose alone! This opened up many possibilities: different carbohydrate combinations could be tested and the amounts consumed were increased up to 3 g/min or 180 g/h in the first few years (don't try this at home!!).

The highest oxidation rates were observed at an intake of 144 g/h, but the best results were probably achieved at 108 g/h as this resulted in the lowest residual volume. If we ideally consume 100 grams of carbohydrates, we want all of the carbohydrates to be utilized and for there to be as little residual volume as possible in the intestines. The more carbohydrates remain in the stomach, the greater the likelihood of intestinal problems. The highest oxidation efficiency was observed with the intake of 108 g/h as glucose and fructose in a ratio of 2:1.

Later on O'Brien (O'Brien et al, 2013) investigate 1:0,8 carbohydrate ratio. The 1:0.8 ratio increases exogenous carbohydrate oxidation by 17% compared to a 2:1 ratio. It also increases average power output over 10 maximal sprint efforts by 3% compared to a 2:1 ratio (O'Brien et al.). The 1:0.8 carbohydrate matrix reduces symptoms of bloating and nausea compared to the 2:1 ratio.

The results of all of these studies suggested that 90 grams per hour was a safe amount to consume, as very few athletes experienced gastrointestinal problems. As intake above 90 g/h increased, we observed an increased number of people who did not tolerate the amounts well. From a purely practical perspective, the recommendation was 90g of carbohydrates per hour.

The proposed ratio was 2:1 glucose - fructose or maltodextrin - fructose for two reasons: First, the amount of glucose had to be just enough to saturate the glucose transporter, and we have the highest oxidation efficiency at similar ratios and amounts.

Is 2:1 the optimal ratio? Or is it 1:0,8

There is no optimal ratio. The optimal ratio changes depending on the amount consumed. At 90g of carbohydrates per hour we recommend to use 2:1 ratio. If individual consume more than 90 g of carbohydrates per hour (100+ or 120g) we reccomend to use 1:0.8 or 1:1 ratio.

There are many brands that claim to have the best ratio, but the reality is that there is no best ratio. A 1:0.8 glucose - fructose ration was used in a study by Dave Rowlands. Conclusion showed that under the conditions of this particular study, oxidation was slightly higher at 1:0.8 glucose - fructose than at 2:1. However, this does not mean that this ratio is the best under all conditions and it changes when different amounts are taken.

So what conclusions can we draw about the carbohydrate ratio?

There is no optimal ratio. The optimal ratio changes depending on the amount of carbohydrate consumed. For now, we can conclude that intake needs to be individualized based on tolerability. This tolerance can be trained by training the gut, but intake should be based on what is easily tolerated.

We should always aim for a glucose intake of around 60-70 g/h, but no higher, and we can add fructose as well. Below are some examples:

  • If I can tolerate 90g/h, I would consume 60g/h of glucose and 30g/h of fructose. This would be a 2:1 ratio.
  • If I can tolerate 110-120g/h or even more, I would consume 60g/h of glucose and 50-60g/h of fructose. This would be a 1:0.8 to 1:1 ratio.

At La Primafit you can find all mentioned ratios from the best brands that supply the best Pro Tour teams - Amacx (Team Visma-Lease a Bike, Q36.5 Pro Cycling, EF Eudcation EaspPost) 6d Sports Nutrition (Team Soudal Quick Step), Neversecond (Bahrain Victorius), Precision Fuel & Hydration (Team dsm-firmenich PostNL Lottos Dstny), 226ers (Team Cofidis, Movistar Team), Santa Madre (Team Israel Premier - Tech), Winforce (Groupama FDJ), Maurten, and also the most famous triathlon brands such as 226ers, Precision Hydration and Maurten. This way you can be sure that you can find what is best for you and what is most tolerable.