Dietary supplementation with New Zealand blackcurrant extract enhances fat oxidation during submaximal exercise in the heat

This study investigated the effect of 7 days’ supplementation with New Zealand blackcurrant extract on thermoregulation and substrate metabolism during running in the heat. Randomized, double-blind, cross-over study. Twelve men and six women (mean±SD: Age 27±6 years, height 1.76±0.10m, mass 74±12kg, V̇O2max 53.4±7.0mLkg−1min−1) completed one assessment of maximal aerobic capacity and one familiarisation trial (18°C, 40% relative humidity, RH), before ingesting 2×300mgday−1 capsules of CurraNZ™ (each containing 105mg anthocyanin) or a visually matched placebo (2×300mg microcrystalline cellulose M102) for 7 days (washout 14 days). On day 7 of each supplementation period, participants completed 60min of fasted running at 65% V̇O2max in hot ambient conditions (34°C and 40% relative humidity). Carbohydrate oxidation was decreased in the NZBC trial [by 0.24gmin−1 (95% CI: 0.21–0.27gmin-1)] compared to placebo (p= 0.014, d=0.46), and fat oxidation was increased in the NZBC trial [by 0.12gmin−1 (95% CI: 0.10 to 0.15gmin−1)], compared to placebo (p=0.008, d=0.57). NZBC did not influence heart rate (p=0.963), rectal temperature (p=0.380), skin temperature (p=0.955), body temperature (p=0.214) or physiological strain index (p=0.705) during exercise. Seven-days intake of 600mg NZBC extract increased fat oxidation without influencing cardiorespiratory or thermoregulatory variables during prolonged moderate intensity running in hot conditions.