Exercise and Sport Science, Faculty of Health Sciences, Universidad Francisco de Vitoria, 28223 Pozuelo, Spain.
Exercise Physiology Laboratory, Camilo José Cela University, 28692 Villanueva de la Cañada, Spain.
Nutrients. 2021 Feb 27;13(3):782. doi: 10.3390/nu13030782.
By using deceptive experiments in which participants are informed that they received caffeine when, in fact, they received an inert substance (i.e., placebo), several investigations have demonstrated that exercise performance can be enhanced to a similar degree as a known caffeine dose. This 'placebo effect' phenomenon may be part of the mechanisms explaining caffeine's ergogenicity in exercise. However, there is no study that has established whether the placebo effect of caffeine is also present for other benefits obtained with acute caffeine intake, such as enhanced fat oxidation during exercise. Therefore, the aim of this investigation was to investigate the placebo effect of caffeine on fat oxidation during exercise. Twelve young men participated in a deceptive double-blind cross-over experiment. Each participant completed three identical trials consisting of a step incremental exercise test from 30 to 80% of V.O. In the two first trials, participants ingested either 3 mg/kg of cellulose (placebo) or 3 mg/kg of caffeine (received caffeine) in a randomized order. In the third trial, participants were informed that they had received 3 mg/kg of caffeine, but a placebo was provided (informed caffeine). Fat oxidation rates were derived from stoichiometric equations. In received caffeine, participants increased their rate of fat oxidation over the values obtained with the placebo at 30%, 40%, 50%, and 60% of V.O (all < 0.050). In informed caffeine, participants increased their rate of fat oxidation at 30%, 40%, 50% 60%, and 70% of V.O (all < 0.050) over the placebo, while there were no differences between received versus informed caffeine. In comparison to placebo (0.32 ± 0.15 g/min), the rate of maximal fat oxidation was higher in received caffeine (0.44 ± 0.22 g/min, = 0.045) and in informed caffeine (0.41 ± 0.20 g/min, = 0.026) with no differences between received versus informed caffeine. However, the intensity at which maximal fat oxidation rate was obtained (i.e., Fat) was similar in placebo, received caffeine, and informed caffeine trials (42.5 ± 4.5, 44.2 ± 9.0, and 41.7 ± 10.5% of V.O, respectively, = 0.539). In conclusion, the expectancy of having received caffeine produced similar effects on fat oxidation rate during exercise than actually receiving caffeine. Therefore, the placebo effect of caffeine is also present for the benefits of acute caffeine intake on substrate oxidation during exercise and it may be used to enhance fat oxidation during exercise in participants while reducing any risks to health that this substance may have.
通过使用欺骗性实验，参与者被告知他们摄入了咖啡因，而实际上他们摄入了一种惰性物质（即安慰剂），几项研究已经证明，运动表现可以得到类似程度的提高，就像摄入已知剂量的咖啡因一样。这种“安慰剂效应”现象可能是解释咖啡因在运动中具有促进作用的机制之一。然而，目前还没有研究表明咖啡因的安慰剂效应是否也存在于急性咖啡因摄入所带来的其他益处，例如运动中脂肪氧化的增强。因此，本研究旨在探讨咖啡因对运动中脂肪氧化的安慰剂效应。12 名年轻男性参与了一项欺骗性双盲交叉实验。每位参与者完成了三次相同的试验，包括从 30%到 80%的 VO2 进行逐步递增运动测试。在前两次试验中，参与者以随机顺序摄入 3 毫克/千克纤维素（安慰剂）或 3 毫克/千克咖啡因（摄入咖啡因）。在第三次试验中，参与者被告知他们摄入了 3 毫克/千克咖啡因，但实际上提供了安慰剂（告知咖啡因）。脂肪氧化率是根据化学计量方程得出的。在摄入咖啡因的情况下，与安慰剂相比，参与者在 VO2 的 30%、40%、50%和 60%时增加了脂肪氧化率（均<0.050）。在告知咖啡因的情况下，参与者在 VO2 的 30%、40%、50%、60%和 70%时增加了脂肪氧化率（均<0.050），而与安慰剂相比，接受咖啡因和告知咖啡因之间没有差异。与安慰剂（0.32±0.15g/min）相比，接受咖啡因（0.44±0.22g/min，=0.045）和告知咖啡因（0.41±0.20g/min，=0.026）时的最大脂肪氧化率更高，接受咖啡因和告知咖啡因之间没有差异。然而，获得最大脂肪氧化率的强度（即 Fat）在安慰剂、接受咖啡因和告知咖啡因试验中相似（分别为 VO2 的 42.5±4.5%、44.2±9.0%和 41.7±10.5%，=0.539）。总之，期望摄入咖啡因会对运动中脂肪氧化率产生与实际摄入咖啡因相似的影响。因此，咖啡因的安慰剂效应也存在于急性咖啡因摄入对运动中底物氧化的益处中，它可以在减少任何健康风险的同时，在参与者中增强运动中的脂肪氧化。
