Comparative efficacy of different dietary interventions for cardiopulmonary fitness at high altitude: a systematic review and network meta-analysis

Abstract

Background: A plateau hypoxic environment can increase the physiological burden on athletes. Although nutritional interventions have been recognized as a potential strategy to improve plateau acclimatization, evidence in support of specific dietary patterns is still lacking. This study compared the effects of different dietary interventions on cardiopulmonary fitness during plateau exercise through systematic evaluation and network meta-analysis methods.

Methods: This study systematically reviewed relevant literature up to June 2025 and included 20 randomized controlled trials (RCTs) conducted at altitudes above 1,500 meters involving healthy participants aged 16 years and above who engaged in physical activities. The primary outcomes included cardiopulmonary indicators [maximal oxygen uptake (VO_2max), heart rate (HR)], blood biomarkers [peripheral oxygen saturation (SpO₂), hematocrit (HCT)], and subjective perception indicators [rating of perceived exertion (RPE)]. For each outcome, the pooled effects of each intervention compared to others were estimated. Mean difference (MD) or standardized mean difference (SMD) with 95% Credible Intervals (95% CrI) were calculated. The Surface Under the Cumulative Ranking Curve (SUCRA) was used to rank the dietary interventions and quantify their relative effectiveness. In addition, the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was applied to assess the quality of evidence.

Results: A total of 20 randomized controlled trials involving 329 participants were included, evaluating eight dietary interventions. Moderate-quality evidence indicated that carbohydrate supplementation significantly improved the percentage of maximal oxygen uptake (VO_2max) compared to placebo (SMD = 1.13, 95% CrI: 0.25 to 2.05) and reduced RPE scores (MD = -0.77, 95% CrI: -1.83 to -0.09). Moderate-quality evidence indicated that carbohydrate supplementation combined with glutamine ranked highest in improving SpO₂ (SUCRA 84.54%) and RPE (SUCRA 69.37%), while iron supplementation showed the highest SUCRA rankings for HR (56.54%) and HCT (66.67%). However, these interventions did not demonstrate statistically significant advantages. Notably, the observed increase in VO_2max exceeded the minimally clinically important difference (MCID) of 1.0 ml/kg/min reported in previous studies, suggesting that the effect of carbohydrate supplementation on VO_2max may have clinical relevance.

Conclusions: Differences exist in the effects of different dietary interventions on cardiopulmonary fitness during altitude exercise. The current network meta-analysis indicates that carbohydrate-based strategies show beneficial effects, with carbohydrate plus glutamine supplementation demonstrating greater advantages in SpO₂ and RPE, while carbohydrate alone is more supported in improving VO_2max. Therefore, carbohydrate-based strategies may serve as effective options to promote altitude acclimatization, whereas iron supplementation may have potential benefits in improving HCT and HR.

Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD420251069629, identifier: CRD420251069629.

Keywords: cardiopulmonary fitness; high-altitude; network meta-analysis; nutritional interventions; randomized controlled trial.

Figure 1

Flow diagram for identification of studies in the systematic review.

Figure 2

Risk of bias (ROB) analysis highlighting results in all domains examined within the nine identified studies (A) and overall risk of bias for included studies (B).

Figure 3

Network meta-analysis of various interventions on cardiopulmonary fitness. (A) Network of interventions for VO_2max. (B) Network of interventions for RPE. (C) Network of interventions for SpO₂. (D) Network of interventions for HR. (E) Network of interventions for HCT. (F) Forest plot displaying weighted standardized mean difference and 95% credible interval for the effect of various interventions vs. placebo on VO_2max levels. (G) Forest plot displaying weighted mean difference and 95% credible interval for the effect of various interventions vs. placebo on RPE levels. (H) Forest plot displaying weighted mean difference and 95% credible interval for the effect of various interventions vs. placebo on SpO₂ levels. (I) Forest plot displaying weighted mean difference and 95% credible interval for the effect of various interventions vs. placebo on HR levels. (J) Forest plot displaying weighted mean difference and 95% credible interval for the effect of various interventions vs. placebo on HCT levels. CHO, carbohydrate; Fe, iron.

Figure 4

League table displaying pairwise comparisons among various interventions on VO_2max (A), RPE (B), SpO₂ (C), HR (D), and HCT (E). Statistically significant differences are bolded (**). CHO, carbohydrate; Fe, iron; **P < 0.01.

Figure 5

Surface Under the Cumulative Ranking Curve (SUCRA) illustrating the cumulative probability of each intervention being among the best in terms of RPE (A), SpO₂ (B), HR (C), and HCT (D) levels. CHO, carbohydrate; Fe, iron.

Figure 6

Funnel plot detailing publication bias in the studies reporting the impact of dietary nitrate on VO_2max (A), HR (B), SpO₂ (C), RPE (D), and HCT (E) levels. CHO, carbohydrate; Fe, iron; RC, rhodiola crenulata- and cordyceps sinensi.