What does a 2:1 carbohydrate ratio actually mean?
You have probably seen “2:1 carbohydrate ratio” printed on sports nutrition products.
But what does it actually mean and why does it matter to you as an athlete?
In sports nutrition, a 2:1 carbohydrate ratio means a fuel source (like a sports drink, gel, or bar) is made of two parts glucose (or maltodextrin) to one part fructose.
Eating carbohydrates is only the beginning
As we explored in Part 1, consuming carbohydrate does not guarantee that all of it will reach your working muscles.
Carbohydrate must first be digested and absorbed through the wall of the small intestine. This happens with the help of specialised transporters.
Think of these transporters as doorways. Each doorway moves a particular type of carbohydrate through the intestinal wall and each has a limited capacity.
Sending more carbohydrates towards a doorway that is already operating near capacity does not necessarily mean more will pass through.
The glucose doorway
Glucose and glucose-based carbohydrates primarily use a transporter called sodium-glucose linked transporter 1, shortened to SGLT1.
On their own, glucose-based carbohydrates can typically be used for energy at a rate of up to approximately one gram per minute, or 60 grams per hour.
This may be sufficient for many sessions, however during prolonged endurance exercise, an athlete may benefit from consuming more than 60 grams per hour.
Simply consuming more glucose does not make the SGLT1 doorway any wider.
Where does maltodextrin fit in?
A sports nutrition product may list maltodextrin rather than glucose as its main carbohydrate source.
Maltodextrin is made from chains of glucose molecules. During digestion, it is rapidly broken down into glucose and absorbed using SGLT1.
It can therefore be considered a glucose-based carbohydrate. It also allows a relatively large amount of carbohydrate to be included in a sports drink without making it excessively sweet.
Fructose opens another doorway
Fructose uses a different transporter called glucose transporter type 5, or GLUT5. Despite its name, GLUT5 is primarily responsible for transporting fructose through the intestinal wall.
Because fructose uses a different transporter, it can be absorbed alongside glucose.
In the traditional 2:1 model, approximately two parts of the carbohydrate come from maltodextrin or another glucose-based source and one part comes from fructose.
At an intake of 90 grams per hour, this would provide approximately:
- 60 grams from maltodextrin or another glucose-based carbohydrate
- 30 grams from fructose
Instead of trying to move all 90 grams through the glucose pathway, the carbohydrate is distributed across two pathways.
We have not made the original doorway wider. We have opened another doorway.
Why is that important?
Using more than one transporter can increase the amount of ingested carbohydrate the body absorbs and uses during prolonged exercise.
This becomes particularly relevant when carbohydrate requirements exceed approximately 60 grams per hour. That said, it does not mean every athlete needs to consume 90 grams per hour.
The right amount depends on the duration and intensity of the exercise, your performance goals and your individual tolerance.
When carbohydrate intake exceeds what the digestive system can comfortably process, it may contribute to bloating, nausea, cramping and other gastrointestinal issues. Higher intakes should therefore be practised during training, this is often referred to as training your gut.
It should be noted that oxidation is not the same as absorption, but we’ll explore the difference in more detail in a later piece.
The bottom line
A 2:1 ratio combines approximately two parts maltodextrin or glucose-based carbohydrate with one part fructose.
Glucose uses SGLT1 while fructose uses GLUT5. By using both pathways, the body may be able to absorb and use more carbohydrate during prolonged exercise than it can from glucose based carbohydrate alone.
It does not mean every athlete needs 90 grams per hour (we’ll explore that further in part 3). It means that when more carbohydrate is required, the body has access to more than one doorway.
No hype. Just science.
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