Glucose Plus Fructose Ingestion for Post-Exercise Recovery—Greater than the Sum of Its Parts?

Abstract

Carbohydrate availability in the form of muscle and liver glycogen is an important determinant of performance during prolonged bouts of moderate- to high-intensity exercise. Therefore, when effective endurance performance is an objective on multiple occasions within a 24-h period, the restoration of endogenous glycogen stores is the principal factor determining recovery. This review considers the role of glucose–fructose co-ingestion on liver and muscle glycogen repletion following prolonged exercise. Glucose and fructose are primarily absorbed by different intestinal transport proteins; by combining the ingestion of glucose with fructose, both transport pathways are utilised, which increases the total capacity for carbohydrate absorption. Moreover, the addition of glucose to fructose ingestion facilitates intestinal fructose absorption via a currently unidentified mechanism. The co-ingestion of glucose and fructose therefore provides faster rates of carbohydrate absorption than the sum of glucose and fructose absorption rates alone. Similar metabolic effects can be achieved via the ingestion of sucrose (a disaccharide of glucose and fructose) because intestinal absorption is unlikely to be limited by sucrose hydrolysis. Carbohydrate ingestion at a rate of ≥1.2 g carbohydrate per kg body mass per hour appears to maximise post-exercise muscle glycogen repletion rates. Providing these carbohydrates in the form of glucose–fructose (sucrose) mixtures does not further enhance muscle glycogen repletion rates over glucose (polymer) ingestion alone. In contrast, liver glycogen repletion rates are approximately doubled with ingestion of glucose–fructose (sucrose) mixtures over isocaloric ingestion of glucose (polymers) alone. Furthermore, glucose plus fructose (sucrose) ingestion alleviates gastrointestinal distress when the ingestion rate approaches or exceeds the capacity for intestinal glucose absorption (~1.2 g/min). Accordingly, when rapid recovery of endogenous glycogen stores is a priority, ingesting glucose–fructose mixtures (or sucrose) at a rate of ≥1.2 g·kg body mass−1·h−1 can enhance glycogen repletion rates whilst also minimising gastrointestinal distress.

Alterations of Renal Epithelial Glucose and Uric Acid Transporters in Fructose Induced Metabolic Syndrome

“…Unlike glucose, fructose has low glycemic index but it causes insulin resistance in the liver and adipose tissue in the long term [19]. Despite the disparities, addition of glucose to fructose ingestion facilitates intestinal fructose absorption [20]. In our experiment, we found that chronic fructose consumption upregulated not only GLUT2, GLUT9 but also SGLT1 and SGLT2, implying that fructose may also enhance glucose reabsorption simultaneously.…”

Fructose and metabolic health: governed by hepatic glycogen status?

“…With regards to hepatic metabolism of carbohydrate, ingestion of glucose in either free form, or as the various polymers such as maltose, maltodextrin and (amylose) starch can be considered physiologically similar stimuli because hydrolysis of glucose polymers is not thought to be rate‐limiting to intestinal absorption (Gonzalez et al . ). Furthermore, free glucose is rarely ingested alone as a sugar and, for this reason, it has been proposed that the ingestion of glucose alone is more reflective of non‐sugar intake from a physiological perspective (Tappy, ).…”

“…This provides mechanistic evidence for how hepatic fructose uptake potentiates hepatic glucose uptake, which supports evidence in humans that glucose–fructose co‐ingestion approximately doubles hepatic glycogen repletion rates compared with glucose ingestion alone (Gonzalez et al . ).…”

“…), and there are even some recommendations for fructose‐containing carbohydrates to optimise performance and recovery during competition and intensive training in athletes (Gonzalez et al . , ). In an attempt to solve this conflict on the role(s) of dietary fructose, this symposium review will aim to unify the related symposium reviews (Fuchs et al .…”

Outcome of the public consultation on a draft protocol for the Scientific Opinion on dietary sugars

“…fructose is known to act differently as glucose regarding liver metabolism (Geidl-Flueck and Greber, 2017;Gonzalez et al 2017;Laughlin, 2014)). In a narrative review about digestion, absorption and metabolism of different types of free sugars (subquestion 3), it should be possible to integrate the different effects of different sugars in the final conclusion (e.g.…”