Study selection
Figure 1 illustrates the number of publications considered and excluded at each phase of the literature search. The initial search yielded 20,731 records, with 12,551 duplicates (from various databases) being eliminated. Following the review of titles and abstracts, 133 full-text articles were retrieved for eligibility assessment. After a thorough examination of each document, 66 studies were excluded for various reasons: 20 studies lacked useful data (no available outcome measures), 19 studies did not meet our inclusion criteria (non-randomized controlled trials), 10 studies involved non-elite athlete participants, and 11 studies included underage participants. Additionally, 4 studies were non-English papers, and 2 studies were conference abstracts (Supplementary Material 2). As a result, a total of 67 published papers ultimately satisfied the inclusion criteria. Among them, 5036,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85. papers were included in the quantitative network meta-analysis. Additionally, 17 papers86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102 were included in the qualitative systematic review.
Flowchart of screening process.
Study characteristics
The characteristics of the included studies are shown in Table 1. A total of 1026 elite combat athletes were recruited in the 67 studies reviewed. A total of 508 elite athletes were recruited from grappling events, of whom 287 were from judo37,38,40,41,43,44,47,53,56,57,58,62,64,65,67,68,72,73,74,78,79,80,−81,85, 113 from jiu-jitsu39,41,48,52,56,60,69,71, 83 from wrestling36,51,61,66 and 25 from jujitsu and wrestling without a clear sample of combat types83,84. A total of 445 elite athletes were recruited in the striking event, of whom 257 were from taekwondo42,45,46,49,50,54,55,59,65,75,76,77,82, 70 from boxing86,94,95,96,98, 26 from karate89,97, 36 from kendo86,93, 36 from fencing88,101,102 and 20 from sanda92. Additionally, there were 57 athletes of mixed martial arts90,91,99 and 16 combat athletes100 without a clear description of the type of combat.
From the gender distribution of the sample, more male athletes participated. Forty studies recruited male athletes (598 athletes), two studies37,68 recruited female athletes (16 athletes), 12 studies combined male and female athletes (136 male and 99 female athletes), and 14 studies did not specify the sample gender (177 athletes).
In 67 included studies, we examined the benefits of 26 different dietary supplements for elite combat sports athletes. Among these, caffeine emerged as the most frequently studied dietary supplement, with 24 studies focusing on caffeine (CAF) alone42,44,46,47,49,50,52,54,56,57,60,64,65,67,69,70,78,80,84,85,89,95,99,102 or sodium bicarbonate + caffeine (SB_CAF)65,89. Thirteen studies explored sodium bicarbonate (SB) alone41,45,48,55,65,66,73,74,81,86,89,96 or beta-alanine + sodium bicarbonate (BA_SB)41, creatine + sodium bicarbonate (CR_SB)45, and highly alkaline water (HAW)100. Six studies investigated beta-alanine (BA) alone41,53,62,72,94,98. Another six studies delved into carbohydrate (CHO) alone, carbohydrate + electrolyte (CHO_E)39,61,76,79,88,101or branched-chain amino acids + carbohydrate + arginine (BCAA_CHO_ARG)61. Arginine (ARG)36,40,58 and beetroot juice (BRT)59,71,82 were reported in three studies, respectively. Two studies examined the supplementation of vitamin C + vitamin E (VITC_VITE)75,92. Similarly, two studies explored vitamin D (VITD) alone or vitamin D + probiotics (VITD_PB)90,91. The remaining studies investigated Antilactate (ANT)51, citrulline malate (CM)38, creatine (CR)45, Coenzyme Q10 (CoQ10)87,93, creatine malate (CRM)43, beta-hydroxy-beta-methylbutyrate (HMB)37, hydrogen-rich water (HRW)68, omega-3 fatty acids + policosanol (O3FA_PC)97, polyphenol (PP)63, sodium citrate (SC)83, and branched-chain amino acids + arginine + citrulline (BCAA_ARG_CIT)77, respectively.
To reveal the advantages of different dietary supplements for elite combat athletes, this study conducted a network meta-analysis of the following outcome measures: rating of perceived exertion38,39,41,42,46,47,49,50,53,54,55,56,57,64,65,67,70,73,76,78,79,81,83,84,final heart rate36,42,43,46,52,53,54,56,57,59,63,64,67,68,75,76,78,79,82,83,84, blood lactate concentration 36,38,40–44,46,48,51,53–58,60−62,64–66,68,71–75,77,78,80–84, mean power37,41,42,44,45,51,58,59,61,62,66,74,76,81,83,84,85, peak power37,41,42,44,45,51,58,61,66,74,76,81,83,84,85, number of throws38,43,52,57,64,65,66,67,72,78,81, special judo fitness test index38,43,52,53,57,64,67,68, Taekwondo-number of kicks45,49,50,70,76, number of attacks46,47,54,55,67,80, and grip strength39,56,60,69,73,80.
In terms of countries and regions, 19 studies were carried out in Brazil, 9 studies in Poland, 7 studies in Taiwan, 6 studies in Tunisia, 5 studies in Spain and the United Kingdom, 4 studies in Iran, 2 studies in Estonia, Japan, and Serbia, 1 study in Hong Kong, North Cyprus, Italy, Republic of Korea, Saudi Arabia, and Greece, respectively.
Risk of bias in studies
Out of the 67 randomized controlled trials we included, 64 provided a clear description of the randomization component in the sequence generation process. Two studies62,101 outlined nonrandom components, while one study39 lacked sufficient information to justify the generation of random sequences. Nineteen studies36,37,39,40,45,51,53,58,62,74,76,85,88,92,97,98,100,101,102 did not offer enough details to determine if reasonable allocation concealment was performed, but the remaining studies implemented reasonable allocation concealment methods. Thirteen studies36,37,39,40,45,51,53,58,62,85,97,100,101 failed to report information regarding blinding, whereas the other studies indicated that blinding was implemented. Seven studies46,52,60,64,69,86,89 ensured the blinding evaluation of outcomes, while others did not specify this aspect. Two studies66,67 experienced a high number of participants lost to follow-up, whereas the remaining studies were free of lost-to-follow-up bias. All studies were devoid of reporting bias and other biases. Detailed results can be found in Figs. 2 and 3.
Meta-analysis
Rating of perceived exertion
Twenty-four studies reported on the effects of different dietary supplements on the rating of perceived exertion in elite combat athletes, involving eight different dietary supplements, mainly CAF, SB, CHO, and SB_CAF, with other supplements explored in only a small number of studies (Fig. 4). The results from the meta-analysis on the consistency model indicated that, when compared to a placebo, no supplement demonstrated a statistically significant improvement in the rating of perceived exertion (Figure S1 and Table 2). According to the SUCRA rankings, BA_SB (SUCRA = 87.4%), SC (SUCRA = 57.8%), and BA (SUCRA = 55.7%) were the top three in terms of improving the rating of perceived exertion (Figure S2). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Funnel plot did not provide evidence for apparent publication bias (Figure S3).
Network diagram of the efficacy of different dietary supplements in improving the rating of perceived exertion. BA beta-alanine, BA_SB beta-alanine + sodium bicarbonate, CAF caffeine, CHO carbohydrate, CM citrulline malate, PLA placebo, SB sodium bicarbonate, SB_CAF sodium bicarbonate + caffeine, SC sodium citrate.
Final heart rate
Twenty-one studies reported on the effects of dietary supplements on the final heart rate of elite combat athletes, involving 10 different dietary supplements, mainly CAF, CHO, VITC_VITE and SC, with other supplements explored in only a small number of studies (Fig. 5). The results of the meta-analysis utilizing the consistency model indicated that, in comparison to the placebo, supplementation with CAF alone (SMD: 0.27, 95% CrI: 0.12, 0.41) was significantly associated with an increase in final heart rate (Figure S4 and Table 3). According to the SUCRA rankings, CAF (SUCRA = 81.6%), ARG (SUCRA = 78.6%), and BRT (SUCRA = 73.1%) were identified as the top three interventions for enhancing final heart rate (Figure S5). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Funnel plot did not provide evidence for apparent publication bias (Figure S6).
Network diagram of the efficacy of different dietary supplements in improving final heart rate. ARG arginine, BA beta-alanine, BRT beetroot juice, CAF caffeine, CHO carbohydrate, CRM creatine malate, PLA placebo, PP polyphenol, SC sodium citrate, VITC_VITE vitamin C + vitamin E.
Blood lactate concentrations
Thirty-five studies investigated the impact of various dietary supplements on blood lactate concentrations in elite combat athletes. The research encompassed sixteen different dietary supplements, primarily CAF, SB, BA, and SB_CAF. Other supplements were only minimally explored in a limited number of studies (Fig. 6). The meta-analysis results of the consistency model showed that, compared to placebo, supplementation of SB_CAF (SMD: 2.3, 95% CrI: 1.5, 3.2), CAF (SMD: 0.72, 95% CrI: 0.53, 0.93), BA (SMD: 0.58, 95% CrI: 0.079, 1.1), and SB (SMD: 0.54, 95% CrI: 0.30, 0.81) was associated with the statistically significant increase in blood lactate concentrations (Figure S7 and Table 4). Based on SUCRA ranking, SB_CAF (SUCRA = 99.9%), CAF (SUCRA = 85.0%), and BA (SUCRA = 74.7%) ranked the top three in enhancing blood lactate concentrations (Figure S8). The overall heterogeneity was moderate (I² = 35%), indicating some variability between the included studies, though the consistency of the network meta-analysis results remains reasonable. Importantly, funnel plot did not provide evidence for apparent publication bias (Figure S9).
Network diagram of the efficacy of different dietary supplements in improving blood lactate concentrations. ANT antilactate, ARG arginine, BA beta-alanine, BA_SB beta-alanine + sodium bicarbonate, BCAA_ARG_CIT branched-chain amino acids + arginine + citrulline, BCAA_CHO_ARG branched-chain amino acids + carbohydrate + arginine, BRT beetroot juice, CAF caffeine, CHO carbohydrate, CM citrulline malate, CRM creatine malate, HRW hydrogen-rich water, PLA placebo, SB sodium bicarbonate, SB_CAF sodium bicarbonate + caffeine, SC sodium citrate, VITC_VITE vitamin C + E.
Mean power
Seventeen studies investigated the impact of various dietary supplements on mean power in elite combat athletes, examining 13 different supplements, primarily SB, BA, and BA_SB. Other supplements were only minimally explored in a few studies (Fig. 7). The results of the meta-analysis utilizing the consistency model indicated that, in comparison to placebo, the supplementation of CR_SB (SMD: 2.2, 95% CrI: 1.5, 3.1), CR (SMD: 1.0, 95% CrI: 0.38, 1.6), and SB (SMD: 0.42, 95% CrI: 0.18, 0.66) was significantly associated with an increase in mean power (Figure S10 and Table 5). According to the SUCRA rankings, CR_SB (SUCRA = 99.9%), CR (SUCRA = 90.1%), and SB (SUCRA = 75.4%) occupied the top three positions in enhancing mean power (Figure S11). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Funnel plot did not provide evidence for apparent publication bias (Figure S12).
Network diagram of the efficacy of different dietary supplements in improving mean power. ANT antilactate, ARG arginine, BA beta-alanine, BA_SB beta-alanine + sodium bicarbonate, BCAA_CHO_ARG branched-chain amino acids + carbohydrate + arginine, BRT beetroot juice, CAF caffeine, CHO carbohydrate, CR creatine, CR_SB creatine + sodium bicarbonate, HMB beta-hydroxy-beta-methylbutyrate, PLA placebo, SB sodium bicarbonate, SC sodium citrate.
Peak power
Fifteen studies investigated the impact of dietary supplements on peak power in elite combat athletes, encompassing 12 different supplements, predominantly SB, BA, and BA_SB. Other supplements were examined in a limited number of studies (Fig. 8). The results of the meta-analysis for the consistency model indicated that, in comparison to placebo, the supplementation of CR_SB (SMD: 1.6, 95% CrI: 0.85, 2.3), CR (SMD: 1.1, 95% CrI: 0.45, 1.7), and SB (SMD: 0.35, 95% CrI: 0.11, 0.57) was significantly associated with an increase in peak power (Figure S13 and Table 6). According to the SUCRA ranking, CR_SB (SUCRA = 98.4%), CR (SUCRA = 91.9%), and SB (SUCRA = 70.4%) emerged as the top three interventions for enhancing peak power (Figure S14). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Importantly, funnel plot did not provide evidence for apparent publication bias (Figure S15).
Network diagram of the efficacy of different dietary supplements in improving peak power. ANT antilactate, ARG arginine, BA beta-alanine, BA_SB beta-alanine + sodium bicarbonate, BCAA_CHO_ARG branched-chain amino acids + carbohydrate + arginine, CAF caffeine, CHO carbohydrate, CR Creatine, CR_SB creatine + sodium bicarbonate, HMB beta-hydroxy-beta-methylbutyrate, PLA placebo, SB sodium bicarbonate, SC sodium citrate.
Special judo fitness test
Number of throws
Eleven studies investigated the impact of various dietary supplements on the throwing performance of elite combat athletes, encompassing six different supplements: CAF, SB_CAF, SB, CRM, CM, and BA (Fig. 9). The results from the meta-analysis of the consistency model indicated that only the supplementation of CAF alone (SMD: 0.35, 95% CrI: 0.081, 0.61), in comparison to placebo, was linked to a statistically significant increase in the number of throws as shown in Figure S16 and Table 7. According to the SUCRA ranking, the top three interventions for increasing the number of throws were SB_CAF (SUCRA = 85.8%), BA (SUCRA = 78.2%), and SB (SUCRA = 59.6%) as illustrated in Figure S17. The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Importantly, funnel plot did not provide evidence for apparent publication bias (Figure S18).
Network diagram of the efficacy of different dietary supplements in enhancing the number of throws. BA beta-alanine, CAF caffeine, CM citrulline malate, CRM creatine malate, PLA placebo, SB sodium bicarbonate, SB_CAF sodium bicarbonate + caffeine.
Special judo fitness test index
Eight studies investigated the impact of various dietary supplements on the special judo fitness test index in elite combat athletes, exploring five different supplements: CAF, BA, CM, CRM, and HRW (Fig. 10). The results of the meta-analysis of the consistency model indicated that, when compared to placebo, no supplement demonstrated a statistically significant improvement in the special judo fitness test index (Figure S19 and Table 8). According to the SUCRA ranking, CM (SUCRA = 81.2%), BA (SUCRA = 73.6%), and HRW (SUCRA = 48.9%) were identified as the top three supplements for improving the special judo fitness test index (Figure S20). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Funnel plot did not provide evidence for apparent publication bias (Figure S21).
Network diagram of the efficacy of different dietary supplements in improving special judo fitness test index. BA beta-alanine, CAF caffeine, CM citrulline malate, CRM Creatine malate, HRW Hydrogen-rich water, PLA Placebo.
Taekwondo kick test – number of kicks
Five studies investigated the impact of various dietary supplements on the number of kicks in elite combat athletes. These studies encompassed five distinct supplements, namely CAF, SB, CR, CR_SB, and CHO (Fig. 11). The results of the meta-analysis for the consistency model indicated that, in comparison to the placebo, the supplementation with CAF alone (SMD: 1.4, 95% CrI: 0.19, 2.7) was the only intervention associated with a statistically significant increase in the number of kicks (Figure S22 and Table 9). According to the SUCRA ranking, CR_SB (SUCRA = 75.2%), CAF (SUCRA = 71.5%), and SB (SUCRA = 70.3%) were the top three interventions in promoting an increase in the number of kicks (Figure S23). The overall heterogeneity was low (I² = 9%), indicating minimal variability between the included studies and supporting the consistency of the network meta-analysis results. Importantly, funnel plot did not provide evidence for apparent publication bias (Figure S24).
Network diagram of the efficacy of different dietary supplements in enhancing the number of kicks. CAF caffeine, CHO carbohydrate, CR creatine, CR_SB creatine + sodium bicarbonate, PLA placebo, SB sodium bicarbonate.
Simulated competition – number of attacks
Six studies investigated the impact of various dietary supplements on the number of attacks in elite combat athletes. The studies examined two different supplements, namely CAF and SB (Fig. 12). The meta-analysis results of the consistency model showed that, compared to placebo, no supplement was associated with the statistically significant increase in the number of attacks (Figure S25 and Table 10). Based on SUCRA values, the rankings were CAF (SUCRA = 78.4%) and SB (SUCRA = 49.6%) (Figure S26). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Importantly, funnel plot did not provide evidence for apparent publication bias (Figure S27).
Network diagram of the efficacy of different dietary supplements in enhancing the number of attacks. CAF caffeine, PLA placebo, SB sodium bicarbonate.
Grip strength
Six studies investigated the impact of various dietary supplements on grip strength in elite combat athletes, encompassing three distinct supplements: CAF, SB, and CHO (Fig. 13). The results of the meta-analysis pertaining to the consistency model indicated that, in comparison to a placebo, no supplement demonstrated a statistically significant increase in grip strength (Figure S28 and Table 11). According to SUCRA values, the rankings were as follows: SB (SUCRA = 90.3%), CAF (SUCRA = 71.2%), and CHO (SUCRA = 1.8%) (Figure S29). The overall heterogeneity was low (I² = 0%), indicating no variability between the included studies and supporting a high level of consistency in the network meta-analysis results. Funnel plot did not provide evidence for apparent publication bias (Figure S30).
Network diagram of the efficacy of different dietary supplements in enhancing grip strength. CAF caffeine, CHO carbohydrate, PLA placebo, SB sodium bicarbonate.
Subgroup analysis
We performed subgroup analyses of rating of perceived exertion, final heart rate, blood lactate concentration, mean power, and peak power by type of striking and grappling. The subgroup analysis results show that, for elite striking combat athletes, compared to placebo, the supplementation of SB (SMD: 0.69, 95% CrI: 0.11, 1.3) and CAF (SMD: 0.45, 95% CrI: 0.17, 0.73) was associated with the statistically significant improvement in blood lactate concentration; the supplementation of CR_SB (SMD: 2.2; 95% CrI: 1.4, 3.1), SB (SMD: 1.2, 95% CrI: 0.53, 1.9), and CR (SMD: 1.0, 95% CrI: 0.32, 1.7) was associated with the statistically significant increase in mean power; the supplementation of CR_SB (SMD: 1.6, 95% CrI: 0.17, 3.0) was associated with the statistically significant increase in peak power. However, in comparison to the placebo, no dietary supplements demonstrated a statistically significant improvement in the rating of perceived exertion and final heart rate among elite striking combat athletes. For elite grappling combat athletes, compared to the placebo, the supplementation of CAF (SMD: 0.39, 95% CrI: 0.20, 0.57) was linked to a statistically significant rise in final heart rate; the supplementation of SB_CAF (SMD: 2.4, 95% CrI: 1.4, 3.5), CAF (SMD: 0.93, 95% CrI: 0.60, 1.3), and SB (SMD: 0.60, 95% CrI: 0.24, 0.99) was correlated with statistically significant improvements in blood lactate concentration; the supplementation of SB was associated with a statistically significant increase in mean power (SMD: 0.31, 95% CrI: 0.063, 0.55) and peak power (SMD: 0.36, 95% CrI: 0.12, 0.61). Nonetheless, when compared to the placebo, no dietary supplements were identified to yield a statistically significant improvement in the rating of perceived exertion for elite grappling combat athletes (for detailed description, see Supplementary Material 4).
Overview of other combat sports
Among the 17 studies included in our systematic review, for boxing, SB was associated with a statistically significant increase in blood buffering capacity and punch efficiency compared with a placebo. It also helps restore acid-base balance, resulting in significant improvements in subsequent athletic performance86,96. Compared to placebo, BA was associated with a statistically significant improvement in lower extremity peak power and upper extremity power maintenance, punch performance, and blood lactate levels94,98. Compared to placebo, CAF was associated with a statistically significantly improvement in anaerobic exercise performance, subjective cognitive function, and emotional state95. In fencing, compared to a placebo, CAF helps maintain skills and reduce overall perceived fatigue102. Compared to placebo, CHO was associated with a statistically significant enhancement of the accuracy of specific skills (lunge test)88. In the context of karate, compared to a placebo, CAF, SB, and CAF_SB were associated with a statistically significant extension of the time to exhaustion of karate athletes in the Karate-specific aerobic test, while causing an increase in blood lactate levels89. O3FA_PC had a positive effect on mood state and attention97. In the case of kendo, compared to a placebo, Coenzyme Q10 may have an inhibitory effect on changes in toll-like receptor 4 positive / cluster of differentiation 14 positive (TLR-4+/CD14+) cells to a certain extent87. At the same time, it is effective in reducing muscle damage indicators (serum creatine kinase activity and serum myoglobin (Mb) concentration) and oxidative stress indicators (lipid peroxidation)93. In mixed martial arts, compared to a placebo, VITD_PB improves lactate utilization and has a positive impact on anaerobic performance90. VITD_PB significantly reduces inflammation (decreased calprotectin concentrations), alters gut microbiome diversity, and improves exercise tolerance91. In the context of sanda, compared to the placebo, VITC_VITE was associated with a statistically significant reduction in serum creatine kinase levels and a statistically significant increase in serum myoglobin levels92 (Table S2).
Side effects
Among the 67 studies included, 11 studies discussed side effects, and 7 of them found varying degrees of side effects after taking dietary supplements. The observed side effects were mainly linked to supplementation with BA (sensory abnormalities)41,72, SB (stomach discomfort, hiccups, heartburn, diarrhea, bloating, abdominal discomfort, and urge to defecate)41,55,65,96, CAF (moderate headache, diarrhea, and abdominal pain)70, CAF_SB (gastrointestinal bloating)65, and SC (moderate nausea, burping, severe bloating, urgency to defecate, and diarrhea)83 (Table S3).
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