ABSTRACT
Background
Sodium bicarbonate (SB) supplementation may enhance short-term, high-intensity exercise performance through improved extracellular buffering capacity, but its effect on continuous running performance has not been systematically evaluated. We conducted a systematic review with meta-analysis of randomized, double-blind, placebo-controlled trials examining the effects of oral single-dose SB supplementation on continuous running performance.
Methods
We searched Medline, Embase, and the Cochrane Central Register of Controlled Trials for eligible trials published through 31 December 2024. The primary outcome was performance on a continuous running test. Secondary outcomes included gastrointestinal (GI) symptoms and GI-associated study withdrawal rates. Running performance was analyzed using random-effects meta-analysis with adjustment for GI-related study withdrawals using intent-to-treat methods and publication bias using the trim-and-fill method. Treatment effects were reported using the standardized mean difference (SMD) statistic where 0.00–0.19 represents negligible benefit, 0.20–0.49 small benefit, 0.50–0.79 medium benefit, and ≥ 0.80 large benefit. We used univariable meta-regression to examine factors associated with treatment effect magnitude. The certainty of evidence was assessed using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach.
Results
Among 11 studies with 126 participants, all used a cross-over design. Most (84%) subjects were male, SB dose was typically 0.3 g/kg, and performance test durations ranged from 1 to 30 minutes (median: 4 minutes). GI symptoms occurred more frequently with SB than placebo (29.5% vs. 2.6%; odds ratio = 5.9; p = 0.003; low certainty), as did GI-related study withdrawal (8.7% vs. 1.6%; odds ratio = 2.9; p = 0.049; moderate certainty). After adjusting for GI-related study withdrawal and publication bias, the treatment effect of SB was negligible and not statistically significant (SMD = 0.18; 95% CI: −0.01, 0.36; p = 0.06; I2 = 0%; moderate certainty). In meta-regression, male sex (p = 0.03) and higher body mass (p = 0.04) were associated with greater SB performance benefits. In the 8 studies that enrolled males only, the treatment effect of SB was small and statistically significant (SMD = 0.40; 95% CI: 0.18, 0.63; p < 0.001).
Conclusions
SB supplementation has a negligible benefit on continuous running performance in a mixed-sex population, the ergogenic effect may be more pronounced in males, GI symptoms are common, and some users may not tolerate supplementation. Athletes should carefully weigh the potential performance benefit of SB against the risk of GI symptoms and establish individual tolerance during training before considering use during competition.
KEYWORDS: Ergogenic aid, metabolic alkalosis, running, sodium bicarbonate
1. Introduction
Sodium bicarbonate (SB) is a potential ergogenic aid for short-term, high-intensity exercise due to its ability to attenuate acidosis via improved extracellular buffering [1]. While several reviews have reported improved athletic performance with SB supplementation [2–6], the magnitude and consistency of these ergogenic benefits are highly variable. Interpreting the existing evidence is challenging due to the substantial heterogeneity in study designs, dosing regimens, exercise modalities, and performance metrics. While most research on SB has examined cycling performance, studies have also evaluated performance in other activities such as team sports, swimming, resistance exercise, and running [3]. In running studies specifically, evaluating results from continuous versus repeated sprint tests creates further challenges in data interpretation. Furthermore, methodological limitations often compromise the reliability of existing findings as many studies lack proper randomization and blinding procedures or selectively report outcomes by excluding data from participants who withdraw due to gastrointestinal (GI) symptoms. Additionally, most studies of SB are conducted with small samples, which presents a considerable risk of publication bias [7]. To address these limitations, we conducted a systematic review with meta-analysis of randomized, double-blind, placebo-controlled trials examining the effects of oral single-dose SB supplementation on continuous running performance, with results adjusted for GI-related study withdrawal and publication bias.
2. Methods
This systematic review with meta-analysis was prospectively registered at www.reviewregistry.com (reviewregistry1943). The methodology and reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines [8].
2.1. Study eligibility criteria
Eligible studies utilized a double-blind, randomized, placebo-controlled design, investigated oral single-dose SB supplementation, and assessed continuous running performance. These criteria were selected to identify the highest quality studies on the topic while focusing on continuous rather than interval running protocols to better simulate competitive racing conditions. We excluded studies that used multi-day supplementation protocols, non-oral administration routes (e.g. intravenous infusion or topical application), or reported outcomes from repeated sprint or interval running protocols. We also excluded studies published only in abstract form or those representing duplicate publications. No language restrictions were applied to the searches.
2.2. Search strategy and study selection process
A systematic literature search was conducted using Medline, Embase, and the Cochrane Central Register of Controlled Trials. The search strategy is detailed in Supplement Table S1. Additional searches were performed in the Directory of Open Access Journals and Google Scholar, with manual screening of reference lists from included studies and relevant review articles. Two researchers (LM, DG) experienced in systematic review methodology independently evaluated titles and abstracts for eligibility using EndNote v21 (Clarivate, Philadelphia, PA, USA) for reference management and screening. Potentially relevant articles underwent full-text assessment. Per Cochrane guidance [9], disagreements regarding eligibility were resolved through discussion and consensus between reviewers. The searches included papers published through 31 December 2024, with the final search completed on 11 January 2025.
2.3. Data extraction and outcomes
The researchers independently extracted data from eligible studies using standardized, piloted forms, with discrepancies resolved through discussion and consensus. The risks of selection, performance, detection, attrition, reporting, and other potential sources of bias were evaluated using the Cochrane Collaboration tool [10]. The primary outcome was performance on a single-bout continuous running test. For studies reporting multiple performance metrics, we analyzed data from the highest-intensity continuous performance test to maintain methodological consistency and reflect conditions where metabolic acidosis is more likely to limit performance. In studies utilizing submaximal exercise before the performance test, only the performance test outcome was analyzed. Secondary outcomes included GI symptoms between the time of supplement ingestion through test completion and GI-related study withdrawals.
2.4. Statistical methods
We conducted a random-effects meta-analysis using restricted maximum likelihood estimation to calculate the standardized mean difference (SMD) and 95% confidence interval (95% CI) in continuous running performance between SB and placebo conditions. Because studies reported continuous running performance using different testing methods (e.g. time trials, time to exhaustion, graded exercise tests), the SMD statistic standardized results relative to their variability to enable pooling across studies. SMD values of 0.00–0.19, 0.20–0.49, 0.50–0.79, and ≥ 0.80 represent negligible, small, medium, and large treatment benefits, respectively [11].
The meta-analysis used intent-to-treat methods by first adjusting results to assume no performance benefit in participants who withdrew due to GI symptoms, with subsequent adjustment for publication bias using trim-and-fill missing study imputation [12]. Publication bias was also evaluated by visual funnel plot inspection and Egger’s regression test [13]. We conducted a one-study-removed sensitivity analysis to assess the influence of individual studies on meta-analysis outcomes. The frequency of GI symptoms and GI-associated study withdrawals between SB and placebo conditions were analyzed using odds ratios and 95% CIs.
Heterogeneity among studies was assessed using the I2 statistic [14]. In order to explore potential sources of heterogeneity, we performed univariable meta-regression examining participant characteristics (age, sex, body mass, body mass index, training status), supplementation protocol variables (SB dose, dosing form, time to ingest SB, time between ingestion and running performance test, concomitant food intake, placebo type, washout period duration), study characteristics (sample size, publication date), and performance test characteristics (submaximal running prior to performance test, performance test duration). A two-sided p-value of less than 0.05 was considered statistically significant. Statistical analyses were performed using Stata v18.5 (Stata Corp, College Station, TX, USA), and the risk of bias assessment used Review Manager v5.4 (The Cochrane Collaboration, London, UK).
We assessed the certainty of evidence for each outcome using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach [15]. Outcomes from randomized controlled trials start as high-certainty evidence and may be downgraded based on the risk of bias, inconsistency, indirectness, imprecision, or publication bias. We rated each outcome across these domains and assigned a final certainty rating of high, moderate, low, or very low. For continuous running performance, we based the rating on the effect estimate adjusted for publication bias and GI-related withdrawals.
3. Results
3.1. Study and participant characteristics
After screening 465 articles, 11 randomized, double-blind, placebo-controlled trials [16–26] met the inclusion criteria (Supplement Figure S1). Notable exclusions included three studies that used single-blind methods [27–29] and one double-blind study where sodium citrate and potassium citrate rather than SB were the main components of an alkaline mixture [30]. Studies enrolled mainly competitive runners, and all used a cross-over design. Among 126 participants, most (84%) were male, with mean age ranging from 20 to 31 years (median 22 years) and mean body mass index ranging from 19 to 24 kg/m2 (median 21.5 kg/m2) (Table 1).
Table 1.
Study and subject characteristics in randomized double-blind trials of single-dose oral sodium bicarbonate ingestion on running performance.
| Study | N | Sex (M:F) |
Mean age (yr) |
Mean BMI (kg/m2) |
Mean body mass (kg) |
Training status |
|---|---|---|---|---|---|---|
| Bird [16] | 10 | 10:0 | 21 * | — | 63 * | Club-to-national standard middle-long distance runners |
| Brisola [17] | 15 | 15:0 | 23 | 23 | 71 | Moderately active |
| Freis [18] | 18 | 17:1 | 28 | 22 | — | Trained runners |
| George [19] | 7 | 7:0 | 22 | — | 78 | Healthy subjects involved in a variety of competitive sports |
| Goldfinch [20] | 6 | 6:0 | 22 | 22 | 75 | Trained 400-meter runners |
| Lassen [21] | 21 | 13:8 | 25 | 21 | 67 | Elite orienteers; 10–25 yrs experience |
| Potteiger [22] | 7 | 7:0 | 25 | 20 | 65 | Competitive distance runners |
| Shing [23] | 10 | 10:0 | 21 | 22 | 61 | Trained runners with O2 max > 50 ml/kg/min |
| Tiryaki [24] | 11 | 0:11 | 22 | 20 | 54 | Collegiate track athletes (competing in 200–1500 m races) or trained non-athletes |
| van Montfoort [25] | 15 | 15:0 | 31 | 24 | 74 | Trained distance runners; routine 5–10 km races at club or national level |
| Wilkes [26] | 6 | 6:0 | 20 * | 19 | 61 | Varsity track athletes competing in 800- and 1500-m races |
*Estimated values.
Abbreviations: BMI = body mass index; F = female; M = male; O2 max = maximal oxygen consumption.
SB dosing was consistent across studies, with most (9 of 11) using 0.3 g/kg body mass (range: 0.2–0.4 g/kg). The most commonly used placebos were sodium chloride or calcium carbonate. SB or placebo was administered in powder (6 studies) or capsule (5 studies) form, mixed with water, juice, or flavored drinks (typically 250–1000 ml), and primarily taken without food. The mean time between product ingestion and initiation of the running performance test ranged from 60 to 146 minutes (median 90 minutes). Running performance assessment methods included fixed-distance time trials (5 studies), time-to-exhaustion at fixed workloads (4 studies), fixed-duration time trials (1 study), and a standardized graded exercise test (1 study). Performance test durations ranged from 1 to 30 minutes (median 4 minutes), with washout periods between SB and placebo conditions ranging from 2 to 9 days (median 6 days) (Table 2).
Table 2.
Single-dose oral sodium bicarbonate and placebo dosing regimens.
| Study | Dosing medium | Dosing form |
SB dose (g/kg) | Placebo type & dose |
Mean pre-exercise timing (min) | Mean time to ingest SB (min) |
Food co-ingestion | Running performance test | Mean test duration (min)* | Washout (days) |
|---|---|---|---|---|---|---|---|---|---|---|
| Bird [16] | Diluted orange juice (400 ml) | Powder | 0.3 | Sodium chloride (0.1 g/kg), calcium carbonate (0.2 g/kg) | 90 | 60 | No | 1500 meter time | 4.3 | ≥3 |
| Brisola [17] | Water (500 ml) | Capsule | 0.3 | Dextrose (0.3 g/kg) |
85 | 10 | No | Time to exhaustion at 110% O2 max | 2.8 | ≥2 |
| Freis [18] | Water (700 ml) | Powder | 0.3 | Sodium chloride (4 g) | 60 | 60 | No | Maximum running speed in graded exercise test | 17.3 | 7–9 |
| George [19] | Water (500 ml) | Capsule | 0.2 | Not reported (0.2 g/kg) | 120 | 60 | No | Time to exhaustion at running velocity corresponding to 4 mmol/L blood lactate | 28.1 | — |
| Goldfinch [20] | Water-based low-energy drink (250 ml) | Powder | 0.4 | Calcium carbonate (0.4 g/kg) | 90 | 60 | No | 400 meter time | 1.0 | 7 |
| Lassen [21] | Water (volume not reported) | Capsule | 0.3 | Calcium carbonate (0.3 g/kg) | — | — | Yes | 3.5 km time trial | 13.0 | 3–7 |
| Potteiger [22] | Water (1000 ml) | Capsule | 0.3 | Wheat flour (0.5 g/kg) | 125 | 10 | No | Time to exhaustion at 110% lactate threshold (89% O2 max); preceded by 30 minutes at lactate threshold | 8.5 | 7 |
| Shing [23] | Water (550 ml) | Powder | 0.3 | Sodium chloride (0.045 g/kg) | 60 | — | Yes | Maximal distance in 30 minutes; preceded by 30 minutes at 65% O2 max | 30.0 | ≥7 |
| Tiryaki [24] | Sugar-free Kool-Aid (volume not reported) | Powder | 0.3 | Sugar-free Kool-Aid (volume not reported) | 146 | 4 | No | 600 meter time | 2.0 | 7 |
| van Montfoort [25] | Water (750 ml) | Capsule | 0.3 | Sodium chloride (0.21 g/kg) | 135 | 90 | No | Time to exhaustion; protocol intended to elicit maximum effort in 1–2 minutes (19–23 km/hr at 2–3% grade) | 1.3 | 2–5 |
| Wilkes [26] | Water ad libitum (mean: 504 ml) | Powder | 0.3 | Calcium carbonate (0.3 g/kg) | 90 | 120 | No | 800 meter time | 2.1 | 5 |
*Mean duration across sodium bicarbonate and placebo conditions.
Abbreviations: SB = sodium bicarbonate; O2 max = maximal oxygen consumption.
3.2. Risk of bias
All studies were graded as low risk of bias for selection, performance, and detection bias. The primary risk of bias involved incomplete outcome data where participants who withdrew due to GI symptoms were excluded from data analyses (2 of 11 studies). In addition, studies that did not report GI symptoms or GI-related withdrawals were classified as having unclear risk of selective reporting bias (5 of 11 studies) (Figure 1).
Figure 1.
Risk of bias summary.
Review authors’ judgments about each risk of bias item for each included study. Green circle indicates low risk of bias, yellow circle indicates unclear risk of bias, and red circle indicates high risk of bias.
3.3. GI symptoms and GI-related study withdrawals
GI symptoms before or during the performance tests were more frequent with SB than placebo (29.5% vs. 2.6%; odds ratio = 5.9; 95% CI: 1.8, 18.8; p = 0.003). Study withdrawal due to GI symptoms (resulting in missing running performance data in all cases) occurred more frequently with SB than placebo (8.7% vs. 1.6%; odds ratio = 2.9; 95% CI: 1.0, 8.1; p = 0.049). The most common GI symptoms following SB ingestion were diarrhea (9.0% of participants), unspecified GI symptoms (9.0% of participants), nausea/vomiting (6.4% of participants), and stomachache (5.1% of participants).
3.4. Sodium bicarbonate effects on continuous running performance
In the unadjusted meta-analysis, SB supplementation resulted in a small statistically significant benefit on continuous running performance (SMD = 0.32; 95% CI: 0.13, 0.50; p < 0.001). After intent-to-treat adjustment for GI-related study withdrawals, the treatment effect remained small and statistically significant (SMD = 0.29; 95% CI: 0.11, 0.47; p = 0.001). Heterogeneity among studies was minimal (I2 = 3%) (Figure 2). All studies fell within the 95% CI of the overall effect size, with no statistical outliers identified (Supplement Figure S2). In the one-study-removed sensitivity analysis, no single study significantly influenced the overall result, with SMDs ranging from 0.25 (p = 0.008) to 0.35 (p < 0.001) following iterative removal of one study at a time (Supplement Table S2). Visual inspection of the funnel plot showed asymmetry suggesting publication bias due to small-study effects. Publication bias was confirmed by Egger’s test (p = 0.03) and the publication-bias adjusted trim-and-fill analysis, which estimated that 4 unpublished studies demonstrating no benefit of SB may exist (Figure 3). After adjustment for publication bias, the benefit of SB on running performance became negligible and not statically significant (SMD = 0.18; 95% CI: −0.01, 0.36; p = 0.06; I2 = 0%).
Figure 2.
Forest plot of the effects of oral single-dose sodium bicarbonate ingestion on continuous running performance: As-reported (top) vs. Intent-to-treat (bottom) analyses.
Values reported as the SMD between sodium bicarbonate and placebo conditions. The SMD and 95% CI are plotted for each study. The size of the square is proportional to the weighting of each study in the meta-analysis. The overall SMD (diamond apex) and 95% CI (diamond width) are calculated using a random effects model. The effect of sodium bicarbonate on running performance was small-to-medium and statistically significant relative to placebo in the as-reported (SMD = 0.32; 95% CI: 0.13, 0.50; p < 0.001; I2 = 3%) and intent-to-treat (SMD = 0.29; 95% CI: 0.11, 0.47; p = 0.001; I2 = 0%) analyses.
Abbreviations: CI = confidence interval; SMD = standardized mean difference.
Figure 3.
Publication-bias adjusted trim-and-fill funnel plot of treatment effect of sodium bicarbonate on continuous running performance using intent-to-treat analysis.
The SMD and standard error for the effect of sodium bicarbonate on continuous running performance are plotted in blue for observed studies and orange for imputed studies. After adjusting for publication bias, the SMD for sodium bicarbonate decreased from 0.29 (95% CI: 0.11, 0.47; p = 0.001) to 0.18 (95% CI: -0.01, 0.36; p = 0.06). Evidence of potential publication bias was confirmed in Egger’s test (p = 0.02).
Abbreviations: CI = confidence interval; SMD = standardized mean difference.
Meta-regression identified two variables associated with greater SB treatment benefit: a higher percentage of male participants (Z = 2.12; p = 0.03) (Figure 4) and higher body mass (Z = 2.08; p = 0.04) (Figure 5). No other participant-, study-, or performance-related variables were associated with SB treatment benefit (all p > 0.05) (Table 3). In a post hoc analysis of the eight male-only studies, the intent-to-treat and publication bias-adjusted treatment effect was small and statistically significant (SMD = 0.40; 95% CI: 0.18, 0.63; p < 0.001).
Figure 4.
Bubble plot of the association between participant sex and the treatment effect of sodium bicarbonate on continuous running performance using intent-to-treat analysis.
The SMD of the effect of sodium bicarbonate on continuous running performance and the percentage of male participants are plotted in blue for each study. The circle size is proportional to the study weighting in the random-effects model. The red line represents the regression line of best fit and blue shading represents the 95% CI. The treatment effect (SMD) of sodium bicarbonate was positively associated with percentage of male participants (p = 0.03). While the clustering of studies near 100% male participation limits the statistical power of the meta-regression, it is notable that the two studies with the lowest proportion of male participants reported the smallest effect sizes.
Abbreviations: CI = confidence interval; SMD = standardized mean difference.
Figure 5.
Bubble plot of the association between body mass and the treatment effect of sodium bicarbonate on continuous running performance using intent-to-treat analysis.
The SMD of the effect of sodium bicarbonate on continuous running performance and the mean body mass of participants are plotted in blue for each study. The circle size is proportional to the study weighting in the random-effects model. The red line represents the regression line of best fit and blue shading represents the 95% CI. The treatment effect (SMD) of sodium bicarbonate was positively associated with participant body mass (p = 0.04).
Abbreviations: CI = confidence interval; SMD = standardized mean difference.
Table 3.
Association of participant- and study-related factors on the effect of sodium bicarbonate on continuous running performance.*
| Variable | Z-score | P-value** |
|---|---|---|
| Higher percentage of male subjects | 2.12 | 0.03 |
| Higher body mass | 2.08 | 0.04 |
| Smaller sample size | 1.91 | 0.06 |
| Longer SB ingestion time | 1.60 | 0.11 |
| Higher body mass index | 1.18 | 0.24 |
| Higher absolute SB dosage | 1.09 | 0.28 |
| Earlier publication date | 1.05 | 0.29 |
| Submaximal running prior to performance test | 0.79 | 0.43 |
| Trained runners vs. non-runners | 0.77 | 0.44 |
| Sodium-based placebo | 0.68 | 0.50 |
| SB ingestion fasted vs. with food | 0.66 | 0.51 |
| SB dosing form (capsule vs. powder) | 0.65 | 0.52 |
| Older age | 0.51 | 0.61 |
| Longer performance test time | 0.50 | 0.62 |
| Fewer washout days between performance tests | 0.29 | 0.78 |
| Shorter time between SB ingestion and exercise | 0.02 | 0.99 |
*Results derived from random effects meta-regression.
**p < 0.05 indicates the variable was statistically associated with greater running performance improvement after sodium bicarbonate versus placebo conditions.
Abbreviations: SB = sodium bicarbonate.
3.5. Certainty of evidence
Based on the GRADE criteria, the certainty of evidence for the effect of SB on continuous running performance was rated as moderate. All included trials were randomized, double-blind, placebo-controlled, and used crossover designs. Furthermore, this rating was based on the analysis that adjusted for both GI-related withdrawals and publication bias. However, the confidence interval ranged from no meaningful effect to a small benefit, which warranted a downgrade for imprecision. The certainty of evidence for GI symptoms was rated as low, with downgrades applied for both incomplete outcome reporting and imprecision due to wide confidence intervals. The certainty of evidence for GI-related withdrawals was rated as moderate, with a single downgrade for imprecision due to wide confidence intervals (Table 4).
Table 4.
GRADE summary of findings table.
| Outcome | Subjects (Studies) |
Risk of bias |
Inconsistency | Indirectness | Imprecision | Publication bias |
Effect (95% CI) |
Absolute effect per 1,000 (95% CI) |
Certainty |
|---|---|---|---|---|---|---|---|---|---|
| Continuous running performance |
126 (11 RCTs) |
Not serious | Not serious | Not serious | Serious* | Not serious** |
SMD = 0.18 (−0.01 to 0.36) |
— | Moderate |
| GI symptoms | 78 (6 RCTs) |
Serious*** | Not serious | Not serious | Serious* | Not serious |
OR = 5.9 (1.8 to 18.8) |
109 more (20 to 305) |
Low |
| GI-related withdrawals |
126 (9 RCTs)† |
Not serious | Not serious | Not serious | Serious* | Not serious |
OR = 2.9 (1.0 to 8.1) |
29 more (1 to 100) |
Moderate |
*Downgraded due to wide confidence intervals.
**The primary outcome was adjusted for publication bias.
***Downgraded for incomplete outcome reporting (data reported in only 6 of 11 RCTs).
†The same sample size (n = 126) appears for continuous running performance and GI-related withdrawals. However, this reflects different subsets since those who withdrew due to GI symptoms were excluded from the performance analysis but included in the GI-related withdrawal outcome.
Abbreviations: CI = confidence interval; GI = gastrointestinal; OR = odds ratio; RCT = randomized controlled trial; SMD = standardized mean difference.
4. Discussion
In this systematic review with meta-analysis of randomized, double-blind, placebo-controlled cross-over trials with adjustment for GI-related participant withdrawals and publication bias, the treatment benefit of SB supplementation on continuous running performance was negligible and not statistically significant. Male sex and higher body mass were significantly associated with greater performance benefits, with a statistically significant treatment benefit when analyzing male-only studies. GI side effects and GI-associated study withdrawal occurred more frequently with SB than placebo. Overall, these findings demonstrate that after adjusting for confounding variables, SB supplementation has a negligible benefit on continuous running performance in a mixed-sex population, the ergogenic effect may be more pronounced in males, GI symptoms are common, and some users may not tolerate supplementation.
Two prominent sports organizations previously published reviews on SB supplementation with mixed-modality exercise. The International Olympic Committee concluded that SB may have adequate support to suggest that marginal performance gains may be possible [2]. The International Society of Sports Nutrition also concluded that SB improves exercise performance in men and women [3]. To the author’s knowledge, this is the first meta-analysis specifically focused on the effects of SB on continuous running performance, representing Level 1a evidence [31]. Furthermore, we are unaware of any reviews that adjusted for multiple important sources of biases such as lack of randomization, improper blinding, attrition, and publication bias. While the magnitude of improvement in the unadjusted analysis (SMD = 0.32) was comparable to previous reviews of mixed-modality exercise, the adjusted analysis demonstrated a considerably diminished ergogenic benefit (SMD = 0.18). Failure to adjust results to account for GI-related study withdrawal had a modest negative impact on the treatment effect. However, the impact of publication bias on the results was substantial, leading to a dramatically reduced effect size since studies with larger treatment benefits were more likely to be published than those with null effects. Overall, these findings suggest that the ergogenic benefit of SB may be overestimated in the literature. Future reviews of SB supplementation should account for these factors to provide unbiased estimates of treatment effects. Additionally, reviews that focus on performance in specific sports following SB supplementation are encouraged to minimize heterogeneity among studies.
GI symptoms and GI-associated study withdrawal occurred more frequently with SB than placebo. The studies reporting participant withdrawal due to GI distress [18,25] excluded these subjects from analyses rather than following intent-to-treat (as randomized) principles. This biases the results since the reported performance benefits reflect only those participants who tolerated the supplement. Given that participants reporting GI symptoms with SB may experience impaired performance [32], these studies likely overestimated the true ergogenic benefit of SB. It is also plausible that the true benefit of SB is even lower than that reported here since we assumed there was no difference between SB and placebo among those withdrawing due to GI symptoms. To the extent that performance after SB may have been worse than placebo due to these symptoms, the treatment benefit of SB may be attenuated further. Further, the fact that GI symptoms were only reported in 6 of the 11 studies is concerning since symptoms may have occurred in studies that did not report this information. Unfortunately, too few studies reported GI symptom data to conduct meta-regression to discern whether participant or study factors were associated with GI symptom risk with SB. These findings suggest that the decision to use SB should balance the trade-offs between a negligible benefit in continuous running performance versus the nearly 30% likelihood of experiencing GI symptoms, some of which may lead to discontinued use of the supplement. Thus, tolerance for SB should be well established during training before use in competition. Given the high frequency and under-reporting of GI symptoms as well as the potential for GI-related SB discontinuation, future studies should report GI symptoms and analyze data using intent-to-treat methods to provide a more balanced assessment of the benefits and risks of SB supplementation.
Although over half of the included studies were published prior to 2000, meta-regression showed no influence of publication year on the effect of SB, suggesting consistent findings over time. However, recent innovations in sports nutrition have led to the development of various SB delivery systems intended to alleviate GI distress. Several studies have reported less GI distress when SB was provided as enteric-coated capsules compared to gelatin capsules [33–35]. Unfortunately, the single study in our review that used enteric-coated capsules did not report GI symptom data [21]. Additionally, specialized carbohydrate hydrogels containing SB have shown promise in reducing the risk of GI discomfort during cycling [36–38], but no randomized trials examining running performance with these delivery systems have been performed. The frequency of GI symptoms among various SB delivery systems and exercise modalities warrants additional investigation.
The lack of female participants in our review, as well as others [1,3–6], represents a significant limitation of the SB literature. Meta-regression identified male sex and higher body mass as factors associated with greater SB efficacy. However, we were unable to perform multivariable meta-regression since only 11 studies were available. Therefore, whether these associations represent independent or related effects remains unclear. Sex-specific treatment differences may be associated with physiological variations in muscle mass, glycolytic capacity, muscle fiber type distribution, baseline buffering capacity, or hormonal influences on acid-base balance [5]. However, our ability to draw conclusions about female-specific effects is limited by their severe underrepresentation in the literature and general lack of reporting on these potential mediating factors. Interestingly, other research is also inconclusive on whether sex differences influence the ergogenic potential of SB. A meta-analysis of primarily cycling studies by Saunders et al. [5] found a small ergogenic effect in females (SMD = 0.37), which is comparable to our unadjusted results. However, several studies have reported sex-dependent responses to SB favoring males [39,40] although small sample sizes likely limited the ability to identify statistical benefit among females. Overall, the sex-specific effects of SB in the current meta-analysis should be considered hypothesis-generating and warrant further study.
A primary strength of this meta-analysis was the inclusion of only randomized, double-blind, placebo-controlled trials with minimal heterogeneity, providing Level 1a evidence [31] on the effects of SB on continuous running performance. Additionally, we adjusted the meta-analysis to account for GI-related participant withdrawals. Finally, we adjusted the meta-analysis results to account for publication bias using the trim-and-fill method. This method has been shown to provide unbiased estimates of the true effect size [12,41], and its use substantially altered the conclusions regarding SB efficacy.
There were several limitations of this meta-analysis that warrant discussion. First, while all included studies were double-blinded, the effectiveness of blinding was rarely reported. Given the distinctive taste and potential for GI side effects with SB, it is plausible that blinding may have been inadvertently compromised in some cases. Second, females were considerably underrepresented in the included studies, and suggests the need for more research specifically examining SB effects in women. Third, the results of this meta-analysis are generalizable only to single-dose oral ingestion of SB on continuous running performance. Outcomes based on chronic ingestion, non-oral administration, repeated-interval running, and non-running exercise performance should not be extrapolated from this research, and warrant future similar rigorous review. Fourth, while placebo-controlled comparisons reduce the risk of certain biases, such designs may not reflect real-world conditions as placebos are not administered in competitive settings. However, in the three studies that included a no-supplement control arm [16,20,26], there was a negligible difference between placebo and control performance (SMD = 0.06; 95% CI: −0.36, 0.48; p = 0.78), suggesting that the SB benefits reported in this meta-analysis are likely minimally influenced by placebo effects. Finally, cross-over designs typically provide similar statistical power to parallel-group designs, but with approximately one-fourth to one-third the sample size requirements since subjects serve as their own controls. Still, most studies in this review remained underpowered to detect even large effect sizes, with only 2 of the 11 cross-over trials demonstrating a statistical benefit of SB. These limitations, in combination with the finding of publication bias where larger treatment benefits were reported in smaller studies, suggest future randomized trials should utilize larger diverse samples with adequate statistical power estimated using realistic treatment effect assumptions.
5. Conclusions
SB supplementation has a negligible benefit on continuous running performance in a mixed-sex population, the ergogenic effect may be more pronounced in males, GI symptoms are common, and some users may not tolerate supplementation. Athletes should carefully weigh the potential performance benefit of SB against the risk of GI symptoms and establish individual tolerance during training before considering use during competition.
Supplementary Material
Acknowledgments
The authors thank Deborah Gains for assistance with the systematic review.
Funding Statement
The author(s) reported there is no funding associated with the work featured in this article.
Authors’ contributions
LM conceived and designed the study. LM drafted the manuscript with input from RB, SK, MB, and WH. All authors provided critical review of the manuscript, and have read and approved the final version.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
Supporting data from this meta-analysis will be made available upon submission of an acceptable data-sharing proposal specifying the project rationale, planned analyses, and intended use.
Supplementary material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/15502783.2025.2538606
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Data Availability Statement
Supporting data from this meta-analysis will be made available upon submission of an acceptable data-sharing proposal specifying the project rationale, planned analyses, and intended use.