Effect of New Zealand Blackcurrant Extract on Physiological Responses at Rest and during Brisk Walking in Southeast Asian Men: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

New Zealand blackcurrant (NZBC) extract affects cardiovascular and metabolic responses during rest and exercise in Caucasian men. Ethnicity and nutritional habits may affect responses to nutritional ergogenic aids. We examined the effects of NZBC extract on cardiovascular, metabolic, and physiological responses during seated rest and moderate-intensity exercise in Southeast Asian men. Seventeen healthy Thai men (age: 22 ± 3 years; body mass index (BMI): 21.8 ± 1.1 kg·m−2) participated. Resting metabolic equivalent (1-MET) was measured (Oxycon™ mobile, Germany), and an incremental walking protocol was completed to establish the relationship between walking speed and MET. In a double-blind, randomized, placebo-controlled, crossover design, cardiovascular (Physioflow, n = 12) and physiological responses (Oxycon, n = 17) were measured during both seated rest and a 30-min treadmill walk at five metabolic equivalent (5-MET), with either a seven-day intake of placebo (PL) or two capsules of NZBC extract (each 300 mg capsule contains 35% blackcurrant extract) with a 14-day washout. Paired t-tests were used with significance accepted at p < 0.05 and a trend for 0.05 > p ≤ 0.10. During 30 min of treadmill walking at 5-MET, no differences were observed for heart rate and substrate oxidation. With intake of NZBC during treadmill walking, there was a trend for increased stroke volume by 12% (PL: 83.2 ± 25.1; NZBC: 93.0 ± 24.3 mL; p = 0.072) and cardiac output increased by 12% (PL: 9.2 ± 2.6; NZBC: 10.3 ± 2.8 L·min−1; p = 0.057). Systemic vascular resistance decreased by 10% (PL: 779 ± 267; NZBC: 697 ± 245 dyn·s·cm−5; p = 0.048). NZBC extract had no effect on metabolic, physiological, and cardiovascular parameters during seated rest and exercise-induced fat oxidation in Thai men, in contrast to observations in Caucasian men. During treadmill walking, Thai men showed cardiovascular response, indicating vasodilatory effects during moderate-intensity exercise with the intake of NZBC extract. Our findings suggest that the ergogenic responses to anthocyanin intake from New Zealand blackcurrant may be ethnicity-dependent