Why it is important for athletes to consume carbohydrates during long duration and high intensity exercise when peak performance is the goal
The wide variety of products available, including a new form of carbohydrate source called hydrogels
The potential use of hydrogels and what the expected outcomes may be
For decades we have known that consuming carbohydrates during endurance exercise can improve performance and delay the onset of fatigue. Over time, products such as sports drinks, chews, gels, and bars have been developed as a source of carbohydrates to be consumed during activity.
Athletes must find a balance between meeting carbohydrate needs during exercise while minimizing the risk of gastrointestinal issues. It is often recommended for athletes to consume at least 30-90g of carbohydrates per hour in order to sustain performance during long duration activity. While this is the case, once athletes start to consume high quantities of carbohydrates during exercise (in excess of 60-90g carbs per hour) the risk of gastrointestinal (GI) distress increases.
This is especially the case for long duration activity lasting several hours, as GI function tends to decrease over time during activity. Recently, a novel form of carbohydrates has become popularized. Hydrogel products claim to allow athletes to consume high doses of carbohydrates, while simultaneously decreasing the risk of GI distress is an attractive proposition.
Hydrogel products add pectin (soluble fiber) and alginate (from seaweed) to the usual sources of carbohydrate (mix of maltodextrin and fructose). When reaching the stomach, it forms a hydrogel to allow the carbohydrate to pass into the small intestine where it is absorbed.
It has been shown that hydrogels reach the small intestine quicker than typical carbohydrate products which would then potentially reduce the risk of gastrointestinal distress. It has also been suggested that hydrogels may decrease gastric emptying rate which is how quick food leaves the stomach (Scott-Dalgleish, 2021). When gastric emptying time is reduced, carbohydrate or other food remains in the stomach for less time, resulting in lower risk of bloating/fullness, and quicker access to carbohydrate for energy use.
Sutehall and colleagues identified an improvement in gastric emptying rate when consuming a hydrogel at rest examined while at rest in comparison to other carbohydrate sources. While this result is intriguing, it was completed at rest, and is difficult to draw any conclusions on how it might benefit athletes during exercise activity. Recently a review paper discussing the six exercise trials which have utilized hydrogel products was published by King and colleagues. These studies were completed in runners, cyclists, and skiers.
McCubbin et al. (2019) reported no significant difference between isocaloric carbohydrate beverages in 9 trained males completing 3 hours of steady state running. No significant performance differences were noted in the time to exhaustion trial either.
In Baur et al. (2019) 9 endurance-trained male cyclists completed 3 experimental trials consisting of a 98-minute varied-intensity cycling protocol with no difference in performance or GI symptoms between isocaloric carbohydrate trials. Similar results were found in Mears et al. (2020) when 8 male cyclists completed 120 minutes of steady state cycling followed by a ~20 minute time trial.
Flood et al. (2019) had 14 cyclists (both men and women) complete 90 minutes of fixed intensity cycling followed by a 15-minute time-trial within a hot (32 °C), humid (70% relative humidity). Again, no difference in performance or markers of gut permeability were found between carbohydrate products.
Petterson et al. (2019) reported no difference in GI issues in 12 male/female elite cross-country ski athletes during roller-skiing in a cold climate in comparison to water. The last study examined within the review was Barber (2019) which was the only study conducted within a fasting state to focus on the CHO oxidation process and timing which concluded an insignificant effect during the steady-state running of 9 runners.
The paper highlights that despite all the hype and promise which come with hydrogels, at this time there is no significant evidence that endurance performance is improved, or that gastrointestinal side effects are reduced in comparison to placebo or other carbohydrate sources.
The authors of this review recommended that future papers may benefit from looking at even higher exercise intensities to determine whether that may discover a difference between hydrogels compared to other carbohydrate products.
At this time, it does not appear that hydrogel products are superior for performance or reducing GI distress risk in comparison to other high quality carbohydrate sources during activity. Despite this, hydrogels do not seem to impair performance compared to other carbohydrate products either, so athletes who may prefer these novel products can continue to use them with confidence.
King, A. J., Rowe, J. T., & Burke, L. M. (2020). Carbohydrate Hydrogel Products Do Not Improve Performance or Gastrointestinal Distress During Moderate-Intensity Endurance Exercise. International Journal of Sport Nutrition and Exercise Metabolism, 30(5), 305–314. https://doi.org/10.1123/ijsnem.2020-0102
Sutehall, S., Stuart D.R. Galloway, Andrew Bosch, and Yannis Pitsiladis (2020). Addition of an Alginate Hydrogel to a Carbohydrate Beverage Enhances Gastric Emptying. Medicine & Science in Sports & Exercise, 52(8), 1785–1792. https://doi.org/10.1249/mss.0000000000002301
Baur D.A., Toney H.R., Saunders M.J., Baur K.G., Luden N.D., and Womack C.J. 2019. Carbohydrate hydrogel beverage provides no additional cycling performance benefit versus carbohydrate alone. Eur. J. Appl. Physiol. 119(11–12): 2599–2608.
McCubbin A.J., Zhu A., Gaskell S.K., and Costa R.J.S. 2019. Hydrogel carbohydrate-electrolyte beverage does not improve glucose availability, substrate oxidation, gastrointestinal symptoms or exercise performance, compared with a concentration and nutrient-matched placebo. Int. J. Sport Nutr. Exerc. Metab. 30(1): 25–33.
Flood, T.R., et al. (2020). Addition of pectin-alginate to a carbohydrate beverage does not maintain gastrointestinal barrier function during exercise in hot-humid conditions better than carbohydrate ingestion alone. Applied Physiology, Nutrition and Metabolism.
Pettersson, S., Edin, F., Bakkman, L., & McGawley, K. (2019). Effects of supplementing with an 18% carbohydrate-hydrogel drink versus a placebo during whole-body exercise in –5 °C with elite cross-country ski athletes: A crossover study. Journal of the International Society of Sports Nutrition, 16(1), 46.
Barber, J.F.P., Thomas, J., Narang, B., Hengist, A., Betts, J.A., Wallis, G.A., & Gonzalez, J.T. (2020). Pectin-alginate does not further enhance exogenous carbohydrate oxidation in running. Medicine & Science in Sports & Exercise, 52(6), 1376–1384.