Here are the Cliff Notes for this post.

• 2:1 ratio became popular to fully saturate transporters in the gut to get to 90g/hr
• 2 studies were done in 2011 and 2013 that showed 1:0.8 ratio had a higher carbohydrate oxidation rate which led people to believe this was better (22 male cyclists total).
• But there was no statistically significant improvement in performance or gut distress and it lowered fat oxidation.
• Over 90g/hr there is potential for 1:0.8 to be better but this has since been questioned by recent studies showing no performance benefit (120g/hr in 1:0.8 vs 90g/hr in 2:1).
• Is consuming over 90g/hr actually needed?
• And to further confuse us, a recent study has shown that body weight is actually a factor for glucose uptake.

My opinion is up to 90g/hr 2:1 is better. Over 90g/hr I would probably lean to 1:0.8 but I’m not 100% on this. Whatever you do, train your gut.

Okay, let's get into it.

Identifying the glucose absorption threshold

In the early 2000’s, leading researchers found that when glucose was ingested at 60g/hr, all 60g of glucose was oxidised (burnt)

But when they tested 120g an hour the amount that was oxidised did not double. 

This led to the hypothesis that it is not the amount of glucose consumed, but the fact there is a bottleneck within digestive system that limited the amount of glucose that could enter the bloodstream to be used as fuel.

This led to studies on different carb sources that target different transporters in the digestive system.

The primary cause of GI distress in endurance athletes is having undigested carbohydrates sitting in the gut. Research showed that combining glucose and fructose resulted in a higher absorption rate being achieved compared to using one type alone.

Products that were “mutli-transporter” in a 2:1 ratio started to be used.

This ratio reduced the amount of undigested carbohydrates in the gut whilst allowing a relatively high intake per hour. This is due to different transporters and their capacity. This is key to understand as we dive into which ratio is better.

So how did the 1:0.8 ratio become popular?

This originally came from 2 studies by O’Brien et al in 2011 and 2013 (totalling 22 male cyclists). Results showed -

• Higher carbohydrate oxidation rates
• This came at a cost of lower fat oxidation however.
• Improved power (not statistically significant though)
• Potential for reduced GI stress (although I am far from convinced on this. Ill explain in a minute)

A review paper in 2015 then reported a small number of studies indicating that a lower glucose:fructose ratio may benefit performance in ~2.5h endurance events in conjunction with extremely high carb intake rate (90+ grams per hour) (Reference)

Is a 1:0.8 ratio better than 2:1...My opinion...no Here’s why.

Upto 90g per hour you don’t need more fructose

It is crucial to know that the glucose transporter SGLT-1 must be as close to saturation as possible before the benefits of fructose can be fully realised. 

Red shows when the SGLT1 isn’t saturated and there is a higher amount of fructose being consumed.

The proposed “less GI stress” in a 1:0.8 doesn’t stack up

Looking into the research, this doesn’t stack up. From the 2011 study they report on the increase in nausea for the 2:1 group (shown here under 0.5 ratio) during the sprints but then fail to mention this occuring for abdominal cramping in the 1:0.8 group. In other studies, there is no statistical significance. (Reference)

• Increase in nausea during the sprints shown here (2:1 being the highest).
• Increase in abdominal cramps during the sprints shown here (1:0.8 group)

In a 2022 study which had 120g/hr (1:0.8) vs 90g/hr (2:1) there was less stomach fullness and less nausea in the 2:1 group. This may have been down to less overall carbs or less fructose however. (Reference)

Side note - whatever you use, gut training should be a strategy you employ - read our article here on how to do this.

Other studies on 2:1 vs 1:0.8

A 2022 study showed the a 1:0.8 group had a higher carb oxidation but lower fat oxidation (similar to that in the 2013 study) whilst receiving no performance advantage.

A 2020 study showed that 120g/hr in a 2:1 ratio was achieved with little to no gastric upset experienced in a real-life race-paced mountain marathon event.

And to further confuse this whole thing evidence for recommending such high ingestion rates (i.e., > 90 g·h−1) remains inconclusive, as there appears to be no further improvement in performance, no sparing of endogenous carbohydrate stores and, in some cases, aggressive carbohydrate feeding during exercise can result in increased muscle glycogen utilisation. (Reference, Reference, Reference, Reference)

The MARCHON Endurance Fuel 30

Our two endurance gels (unflavoured and mixed berry caffeine) are formulated to provide 30g of carbohydrates. They have a great balance of not being too watery or sticky so you don't have to consume with water. They minimise flavour fatigue, and you aren't left with half the gel being stuck in the packet. 

Check them out here