Multiple transportable carbohydrates, aka different types of single carbohydrates (i.e. glucose, fructose, maltodextrin) can be beneficial during endurance activity lasting >2.5 hours in duration. Currently recommended practices for carbohydrate intake during endurance exercise include:
Optional CHO mouth rinsing during exercise 30-75 min
30–60 g/h during 1–2.5 h of endurance exercise
Up to 90 g/h of multi-transportable CHO (e.g. glucose or maltodextrin:fructose blends) for exercise >2.5 h.
Previously it was thought that the body could only utilize 1 g of CHO/min (60 g/h) during exercise. However, this was based on research examining a glucose-only solution. When researchers started adding different single CHOs (ie fructose) to the mix, carbohydrate delivery and oxidation rates increased.
Intestinal absorption of carbohydrate is the limiting factor when it comes to how much exogenous carbohydrate your body can utilize during exercise. Glucose and fructose rely on different transport proteins (SGLT1 and GLUT5) for absorption in the gut. Because the glucose transporter is saturated when glucose ingestion exceeds > ~60 g/h, multiple transportable CHO (e.g. glucose-fructose) solutions are recommended when CHO intake rates are higher than ~60 g/h. The ideal solution is proposed to contain a 2:1 glucose to fructose, or maltodextrin to fructose ratio (ie 60 g of glucose or maltodextrin, and 30 g of fructose). It should be noted that the fructose addition to glucose provides benefit after the glucose transporter is saturated at ~60 g/h.
Finally, research has suggested that multiple transportable CHO vs. single CHO can result in performance improvements. One study in particular found an 8% performance improvement with a glucose:fructose solution (56.1 min) compared to a glucose only solution (60.7 min) during a 40 km bike time trial that followed 2 hours of cycling at 55% of max in trained male cyclists. Evidence also suggests reduced GI discomfort with multiple-transportable CHO mixtures compared to glucose alone. Athletes can choose CHO-based sports nutrition products in the form of liquids, gels, or solids based on personal preference, environmental conditions, and demands of the course and event.
PMID: 26373645; 22468766; 20574242; 18202575
