**Background:** Attaining higher rates of fat oxidation (FAT-ox) during exercise has cardiometabolic benefits and may enhance endurance performance by sparing glycogen. Dietary strategies incorporating anthocyanin-rich fruits have shown promise for increasing FAT-ox, but prior research focused on New Zealand blackcurrants (NZBC). Wild blueberries (WB) contain similar anthocyanin content and are more widely available in the U.S., yet no study had examined their effects on FAT-ox during exercise. This study aimed to determine whether 14-day WB consumption increases FAT-ox during submaximal cycling in trained males.
**Methods:** Eleven healthy aerobically trained males (age 26.55 ± 7.95 years, VO₂peak 54.43 ± 7.99 mL/kg/min, body fat 10.15 ± 3.37%) completed a non-randomized, quasi-experimental, free-living trial. After a 2-week diet washout (avoiding anthocyanin-rich foods), participants performed a 40 min cycling bout at 65% VO₂peak following a 12 h fast. They then consumed 25 g/day freeze-dried WB powder (375 mg anthocyanins, equivalent to ~1 cup fresh fruit) for 14 days and repeated the exercise protocol. FAT-ox and carbohydrate oxidation (CHO-ox) rates were calculated from expired gases using standard equations. Blood lactate, plasma non-esterified fatty acids (FFA), glycerol, and urinary F2-isoprostanes, creatinine, and free/total carnitine were measured pre- and post-exercise. Repeated measures ANOVA with post hoc Tukey HSD tests were used (α < 0.05).
**Key Results:** WB consumption significantly increased FAT-ox at 20 min (WB: 0.49 ± 0.23 vs. C: 0.38 ± 0.22 g/min, +19.7%, p = 0.049), 30 min (WB: 0.49 ± 0.26 vs. C: 0.35 ± 0.20 g/min, +43.2%, p = 0.010), and 40 min (WB: 0.50 ± 0.25 vs. C: 0.38 ± 0.23 g/min, +31.1%, p = 0.012). Correspondingly, CHO-ox was significantly lower at 20 min (WB: 1.65 ± 0.83 vs. C: 1.84 ± 0.96 g/min, p = 0.0239), 30 min (WB: 1.54 ± 0.81 vs. C: 1.89 ± 0.96 g/min, p = 0.0141), and 40 min (WB: 1.52 ± 0.79 vs. C: 1.78 ± 0.93 g/min, p = 0.0451). RER was significantly lower at 20 (p = 0.0289), 30 (p = 0.0097), and 40 min (p = 0.0168) in the WB condition. Blood lactate was significantly lower at 20 min (WB: 2.6 ± 1.0 vs. C: 3.0 ± 1.1 mmol/L, p = 0.0053), 30 min (WB: 2.2 ± 0.9 vs. C: 2.9 ± 1.0 mmol/L, p = 0.0047), and 40 min (WB: 1.9 ± 0.8 vs. C: 2.5 ± 0.9 mmol/L, p = 0.0132). No significant differences were found in plasma FFA, glycerol, urinary F2-isoprostanes, creatinine, free/total carnitine, heart rate, power output, cadence, RPE, or ventilation between conditions. Dietary analysis showed significantly higher carbohydrate intake during WB (4.41 vs. 3.67 g/kg, p = 0.0043) due to the 92 g CHO from the WB powder, but mixed-model analysis indicated that protein (g/kg) and percent protein significantly affected FAT-ox (p = 0.0074), while fat and carbohydrate did not.
**Clinical Implications:** This study provides the first evidence that wild blueberry consumption can significantly increase fat oxidation during moderate-intensity exercise in trained males, with effect sizes comparable to or exceeding those reported for NZBC. The 19.7–43.2% increases in FAT-ox, coupled with lower blood lactate, suggest potential benefits for endurance performance by sparing glycogen and reducing metabolic fatigue. The findings are particularly relevant for U.S. athletes and active individuals given the greater accessibility of wild blueberries compared to NZBC. However, the study's limitations include its non-randomized design, small sample size (n=11), free-living conditions with self-reported diet and activity, and the absence of direct performance measures. The higher carbohydrate intake in the WB condition (from the powder itself) did not diminish the FAT-ox effect, suggesting the anthocyanin content (375 mg/day over 14 days) may be the active component. Future research should include randomized controlled designs, direct performance outcomes, and investigations into the mechanistic pathways (e.g., AMPK/CPT-1 activation, nitric oxide-mediated blood flow).