Effects of a 0.8-ratio fructose : lactose blend on exogenous- and endogenous-carbohydrate utilisation and high-intensity endurance performance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Auckland, New Zealand. EMBARGOED until 14th March 2026
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2024
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Massey University
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Background: Ingestion of fructose and glucose/maltodextrin at ratios close to unity during high-intensity endurance exercise enhances exogenous-carbohydrate oxidation and endurance metrices, relative to single carbohydrates or fructose-glucose/maltodextrin blends at different ratios. Traditionally, both fructose and lactose have been avoided due to intolerance and gastrointestinal disturbances, but in tolerant individuals these carbohydrates increase fat and spare endogenous-carbohydrate oxidation relative to other carbohydrates suggesting possible synergistic benefits of a fructose-lactose blend. Aim: To determine the metabolic and performance outcomes of an ingested fructose-lactose blend in comparison to a fructose-maltodextrin blend and an isocaloric maltodextrin-only control on high-intensity endurance exercise. Methods: In a three-way crossover design, twelve endurance-trained male cyclists (mean age 49-years SD 11, VO₂ₘₐₓ 57 ml/kg/min SD 5.6) cycled at 57.5% peak power for 2-h, followed by 10-repeated maximal work tasks lasting average 2.4 min SD 47.1 each, whilst drinking every 15-min 200 mL of 11.3% carbohydrate solutions comprising of fructose-lactose (FRUC:LACT), fructose-maltodextrin (FRUC:MALT), or maltodextrin only (MALT). During the 2-h ride, substrate oxidation was determined from indirect calorimetry and naturally-high abundance ¹³C carbohydrate labelling of ingested carbohydrates. Results: There was strong evidence for a moderate-large increase in mean sprint power with FRUC:LACT vs MALT (5.2%; 99% confidence limits 2.0%, 8.5%), but an unclear difference in FRUC:LACT and FRUC:MALT (-1.7%; -4.8%, 1.3%). There was strong evidence for a large-very large increase in exogenous-carbohydrate oxidation rate with FRUC:LACT vs MALT (58%; 90% confidence limits 45%, 72%), and some evidence for a slight to small increase vs FRUC:MALT (6.3%; -1.0%, 13%). There was good evidence for slight to small decreases in endogenous-carbohydrate oxidation rate with FRUC:LACT vs MALT (-11%; - 18%, -3.6%) and vs FRUC:MALT (-10%; -18%, -2.8%), respectively. The two carbohydrate blends lowered fat oxidation rate, relative to MALT, but there was no clear difference between blends. Interestingly, there was some evidence for a slight to small reduction of nausea during the 2-h ride and sprints and a reduction of muscle soreness during the sprints with FRUC:LACT vs FRUC:MALT. Conclusion: A 0.8-ratio fructose-lactose blend is a viable alternative to equivalent fructose maltodextrin blends producing substantial benefits to high-intensity endurance performance, relative to isocaloric maltodextrin. The fructose-lactose blend produced small increases in exogenous-carbohydrate oxidation and endogenous glycogen sparing, vs fructose maltodextrin. Further investigations into ratios and other potential lactose or galactose blends are warranted to explore metabolic responses and alternative carbohydrate sources to support endurance exercise performance.
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Embargoed until 14th March 2026