Interest in the 2-hr marathon (Caesar, 2019) has focused attention on an important sports nutrition strategy; consumption of carbohydrate (CHO) during exercise to contribute to the substantial fuel costs of some endurance events. Events of sufficient intensity and duration to be limited by CHO availability benefit from an exogenous CHO supply (Stellingwerff & Cox, 2014), with mechanisms including fuel provision once muscle glycogen is depleted (Coyle et al., 1986), spared liver (Gonzalez et al., 2015; Wallis et al., 2006) and muscle (King et al., 2018; Tsintzas et al., 1995, 1996) glycogen use, and central nervous system benefits (Burke & Maughan, 2015). A sliding scale of intake is recommended, according to event fuel needs and specific mechanisms underpinning performance benefits (Thomas et al., 2016). Upper targets for fuel-demanding events (80–90+ g·hr–1 CHO), which aim to maximize the contribution of exogenous CHO to substrate use, are often challenged by the ability to consume, tolerate, and absorb large amounts of CHO (de Oliveira & Burini, 2014). Factors include the availability of foods/drinks to meet CHO targets in practical amounts/volumes, the effect of the mode and intensity of exercise on gastrointestinal (GI) comfort and function (de Oliveira & Burini, 2009), the role of specific “gut training” (Cox et al., 2010), and characteristics of the CHO source. Here it has been shown that the use of CHO blends (“multiple transportable CHO” such as glucose [G] and fructose [F]) can maximize gut uptake via the use of different intestinal transport mechanisms, assisting with substrate delivery and the management of gut comfort (Jeukendrup, 2010).
Recently, specialized sports foods claiming to address such factors via the use of “hydrogel technology” have become commercially available (Sutehall et al., 2018). These supplements, combining typical CHO sources with pectin (a soluble fiber) and alginate (a polymer derived from seaweed) undergo gelation on contact with low pH solutions, such as stomach acid, to encapsulate the CHO (Marciani et al., 2019). Enhanced rates of gastric emptying could deliver this “hydrogel” to the small intestine where it dissolves in the higher pH environment for absorption, leading to reduced gut discomfort, enhanced muscle CHO delivery, and performance benefits (Figure 1). Indeed, according to testimonials, the commercial product has been quickly adopted by elite athletes (Sutehall et al., 2018) and publicized in sporting successes including the 1:59 marathon project, leading to marketing claims that it is the “world’s fastest sports fuel” (Maurten, 2020). Noting that this has largely occurred in the absence of scientific validation of these claims, we undertook a review of newly published investigations of hydrogel CHO to determine whether they achieve better GI characteristics, substrate delivery, and performance effects under exercise conditions than traditional sports drinks and gels.
Mechanisms of CHO hydrogel formation and delivery to the small intestine. Despite benefits to gastric emptying with hydrogel-encapsulated CHO, the rate-limiting step of exogenous CHO oxidation lies in the intestinal transport of monosaccharides. CHO = carbohydrate.
Citation: International Journal of Sport Nutrition and Exercise Metabolism 30, 5; 10.1123/ijsnem.2020-0102