Purpose: In athletes, caloric restriction (CR) improves physiological mechanisms, although its effects on professional soccer players are unclear. This study aims to evaluate the effects of CR on physical performance, fatigue, and inflammation in male professional soccer players compared with a no-restriction diet. Methods: This was a controlled, randomized, parallel-group study with 28 participants. The experimental group received a CR diet (-25% of recommended energy intake; mean caloric intake: 2650 kcal/d). Controls received a normal caloric (NC) diet (mean caloric intake: 3500 kcal/d). Both groups received a protein supplement. Six weeks of intervention were followed by 6 weeks without intervention. Thereafter, the participants were allowed to eat ad libitum. The study evaluated leukocytes, lymphocytes, creatine phosphokinase (CPK), urea, testosterone, lactate dehydrogenase (LDH), rate of perceived exertion (RPE), countermovement-jump (CMJ), and squat jump (SJ). Results: Average age was 27.6 ± 4.4 years. After 6 and 12 weeks, differences between the two groups were insignificant in terms of the immune response, fatigue (CPK, urea, testosterone, and cortisol), and inflammation (LDH) (p > .05). The CR group had lower RPE levels at 12 weeks (0.01 vs. 0.62 points; p = .001) than the NC group. Conclusion: CR is an effective intervention for male professional soccer players, because it decreased RPE while preserving biochemical parameters.
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