Carbohydrate ratios in sport

Trinkflaschen in einer Kühlbox

To better understand the development of the various recommendations, compositions and ratios, it is worth taking a look back. 

In 2003, it was discovered that certain carbohydrate combinations could be absorbed more quickly than others in a sporting context. Prior to this discovery, it was believed that a maximum of 60 grams of carbohydrates per hour (or 240 kilocalories per hour) could be delivered to the muscles. 

Since carbohydrate consumption is significantly higher in endurance sports, scientists were interested in identifying the limiting factor for absorption. It turned out that neither gastric emptying, muscle glucose uptake nor muscle metabolism set the limits – absorption in the intestine is the decisive factor. 

How carbohydrates are absorbed: 

Absorption is facilitated by transport proteins: 

  • Glucose is absorbed via the SGLT1 transporter. 
  • Fructose is transported via GLUT5 

The hypothesis: by using both transporters simultaneously, more than 60 grams of carbohydrates can be absorbed per hour. 

In fact, the first study on the combination of glucose and fructose showed that oxidation rates were 50% higher than with glucose alone. This opened the door to testing different carbohydrate ratios. 

Different carbohydrate ratios tested 

It is not only the oxidation rate, i.e. the speed at which carbohydrates are used for energy, that is important, but also how many carbohydrates remain in the intestine. A high residue in the intestine increases the risk of gastrointestinal problems. 

Results from studies: 

  • 144 grams per hour often led to nausea – the oxidation rate could not be fully utilised. 
  • Up to 110 grams per hour was practical and efficient. 
  • The best oxidation efficiency was observed at a ratio of 2:1 glucose:fructose. 

120 grams of carbohydrates per hour –
recent findings from  

Recent studies show that with targeted training of the digestive system, 120 grams per hour is also possible. The optimal ratio for this amount is 1:0.8 glucose:fructose.  

Important note: This does not mean that everyone should consume 120 grams per hour. Often, 60–80 grams per hour is more appropriate, depending on the type of sport, exertion and individual tolerance. 

Practical recommendations 

Train the gut  

High amounts of carbohydrates only make sense if the gastrointestinal tract is prepared for them. The intestine is adaptable: regular high carbohydrate intake during training improves gastric emptying and increases the absorption capacity via the relevant transporters (SGLT1 for glucose, GLUT5 for fructose). This reduces the risk of undigested carbohydrates remaining in the intestine, a key trigger for gastrointestinal problems.  

In practical terms, this means that intake levels above 90 grams per hour should be tested gradually during training. Those who only consume 60 grams per hour in everyday life cannot expect to consume significantly higher amounts during competition. "Train the gut" is therefore a necessary prerequisite for tolerating and effectively utilising carbohydrate ratios of 1:0.8 and intake amounts of up to 120 grams per hour. 

Choosing the ratio 

The ratio of one part glucose to 0.8 parts fructose (1:0.8) is often described as the optimal ratio. This is correct insofar as it allows the highest possible absorption rate according to the current state of scientific knowledge. However, many athletes do not need 120 grams of carbohydrates per hour. 

This applies both to very long competitions (over ten hours), in which fat metabolism continues to play a central role, and to shorter competitions such as half marathons or Olympic distances, in which the body's own glycogen stores cover a larger part of the energy supply. 

Fructose puts more strain on the digestive tract than glucose and can therefore lead to gastrointestinal problems more frequently during training or competition. Even in the long term, a permanently high fructose intake is not advisable. Excess fructose can increase fat formation in the liver and be linked to non-alcoholic fatty liver disease (NAFLD) and insulin resistance – factors that increase the risk of prediabetes and type 2 diabetes. This topic is also increasingly being discussed in professional endurance sports. 

The rule for fructose is therefore: as much as necessary, as little as possible. 

At MNSTRY, we take this principle into account by not exclusively following the trend towards ever higher 1:0.8 products, but also consciously offering products with 4:1 and 2:1 ratios – tailored to different levels of exertion, intake amounts and individual tolerance. 

New developments in 2025 –
individualised carbohydrate utilisation 

In 2025, a C-13 isotope test procedure was introduced for practical use for the first time. This allows the measurement of how many carbohydrates athletes actually oxidise. 

Key findings 

  • Some professional cyclists were able to oxidise up to 180 grams per hour. 
  • High individual variability: not all athletes achieve these values. 

Limitations of the 2025 study 

  • No peer-reviewed paper – data comes from initial field tests. 
  • Very small sample size – mainly professional cyclists, not transferable to amateur sport. 
  • Short-term observations – no long-term data on the tolerability of extremely high intake. 
  • No general recommendation – results show possibilities, no new standard recommendation. 

Practical significance 

The available data underscores the importance of individualised nutrition strategies. For most athletes, 60 to 90 grams of carbohydrates per hour is a safe and practical basis. In this range, classic ratios such as 2:1 or 4:1 are generally well tolerated. An intake of 90 to 120 grams per hour is possible, but requires targeted training of the digestive system and adjusted carbohydrate ratios. Amounts above 120 grams per hour should be critically evaluated and only used under clearly defined conditions. 

Sources 

  • Jeukendrup AE, Moseley L. Multiple transportable carbohydrates enhance gastric emptying and fluid delivery. J Appl Physiol. 2003;95(2):822–828. 
  • Jeukendrup AE. Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care. 2010;13(4):452–457. 
  • Rowlands DS et al. Optimising carbohydrate intake during endurance exercise: recent advances. Curr Opin Clin Nutr Metab Care. 2022;25(6):431–438. 
  • Costa RJS et al. Systematic review: gut training and carbohydrate tolerance in athletes. Sports Med. 2023;53(1):15–34. 
  • Field study 2025 (C-13 test procedure, Cyclingnews report): "New test used by WorldTour pros sheds light on individuality of carbohydrate intake". 
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