When athletes train at high altitudes where there’s less oxygen in the air, their bodies work extra hard. Researchers looked at 20 different studies involving 329 people to see which foods and supplements help the body adapt better. They found that eating carbohydrates (like bread, pasta, and fruits) before or during exercise at altitude helps people use oxygen more efficiently and feel less tired. Adding glutamine (a protein building block) to carbs might help oxygen levels in the blood even more. Iron supplements also showed promise for helping the body’s oxygen-carrying capacity. The good news: these aren’t expensive or complicated—just smart eating choices.

The Quick Take

  • What they studied: Do different foods and supplements help athletes perform better and feel less exhausted when exercising at high altitudes where oxygen is scarce?
  • Who participated: 329 healthy people aged 16 and older from 20 different studies, all exercising at altitudes above 5,000 feet where oxygen levels are noticeably lower
  • Key finding: Carbohydrate supplements improved how efficiently the body uses oxygen by a meaningful amount—about 1.13 times better than no supplement—and made exercise feel less exhausting. Combining carbs with glutamine showed even better results for blood oxygen levels.
  • What it means for you: If you’re training at high altitude, eating carbs before and during exercise may genuinely help you perform better and recover faster. This is most relevant for athletes, mountain climbers, and people moving to high-altitude areas. However, these findings are based on relatively small studies, so talk to your doctor or sports nutritionist before making major changes.

The Research Details

Researchers searched for all published studies up to June 2025 that tested different dietary supplements on people exercising at high altitudes (above 5,000 feet). They only included high-quality studies where some people got the supplement and others got a fake placebo to compare results fairly. They then combined the results from all 20 studies using special statistical methods called network meta-analysis, which allows researchers to compare multiple treatments even if they weren’t all tested against each other directly.

The researchers measured several things: how much oxygen the body could use during maximum effort (VO2max), heart rate, blood oxygen levels, how much iron the blood could carry, and how hard the exercise felt to the person doing it. They used a ranking system to figure out which supplements worked best for each measurement.

To ensure reliability, they also checked the quality of evidence for each finding using a standard scientific checklist. This helps readers understand which results are more trustworthy than others.

High altitude is genuinely stressful for the human body because there’s less oxygen in the air. Athletes and people living at altitude need their bodies to adapt quickly and work efficiently. By combining results from multiple studies, researchers can see patterns that might not be obvious in any single study. This network meta-analysis approach is particularly valuable because it shows not just whether supplements work, but which ones work best for different body functions.

The evidence was rated as ‘moderate quality,’ which means the findings are reasonably reliable but not perfect. The studies included were all randomized controlled trials, which is the gold standard for testing supplements. However, the total number of participants (329) was relatively small, and the studies varied in how they measured results. The researchers were transparent about these limitations, which increases confidence in their conclusions.

What the Results Show

Carbohydrate supplements showed the clearest benefit: they improved oxygen use efficiency by about 1.13 times compared to placebo, and this improvement was large enough to matter in real athletic performance. The supplements also reduced how hard exercise felt (rating of perceived exertion dropped by 0.77 points on the scale), making workouts feel more manageable.

When researchers combined carbohydrates with glutamine (an amino acid), this combination ranked highest for improving blood oxygen levels (SpO2) and reducing exercise difficulty. The ranking system gave this combination an 84.54% score for oxygen levels and 69.37% for exercise difficulty—meaning it was the best option among all tested interventions.

Iron supplementation showed the highest rankings for heart rate control (56.54%) and blood iron-carrying capacity (66.67%), suggesting it might help the body transport oxygen more efficiently. However, these benefits weren’t statistically significant, meaning they could partly be due to chance.

Importantly, the improvement in oxygen use from carbohydrates exceeded what scientists consider a ‘clinically meaningful’ improvement—meaning it’s not just a tiny statistical difference, but something that could actually affect athletic performance.

The research revealed that different supplements work best for different body functions. While carbs alone were best for maximum oxygen uptake, the carb-plus-glutamine combination was better for maintaining blood oxygen during exercise. This suggests that athletes might benefit from different strategies depending on their specific goals—whether they want to maximize overall fitness or maintain steady oxygen levels during activity. The variation in results also suggests that individual differences matter; what works best might depend on the person’s fitness level, how long they’ve been at altitude, and their specific training goals.

This research builds on earlier findings that nutrition matters for altitude performance, but it’s the first comprehensive comparison of multiple dietary strategies using modern statistical methods. Previous studies often tested single supplements in isolation, making it hard to know which was truly best. This network meta-analysis provides a more complete picture by ranking all options against each other. The finding that carbohydrate benefits exceed the minimum clinically important difference aligns with sports nutrition theory but provides stronger evidence than previously available.

The studies included were relatively small (averaging about 16 participants each), which limits how confident we can be in the results. The research only included healthy, active people, so results might not apply to sedentary individuals or those with health conditions. Most participants were young adults, so benefits for older athletes are unclear. The studies measured effects over different time periods, and some supplements were tested in only one or two studies, making those results less reliable. Additionally, the research didn’t examine long-term effects—only short-term performance during altitude training. Finally, publication bias is possible, meaning studies showing positive results might be more likely to be published than those showing no effect.

The Bottom Line

For athletes training at high altitude: Consider carbohydrate supplementation before and during exercise (moderate confidence). The evidence suggests meaningful performance improvements. For those wanting to maximize blood oxygen levels: A combination of carbohydrates plus glutamine may offer additional benefits, though evidence is slightly less robust (moderate confidence). For general altitude acclimatization: Iron supplementation may help, particularly if you have low iron levels, but evidence is weaker (low confidence). These recommendations should be personalized—consult a sports nutritionist or doctor before starting any supplement regimen, especially if you take other medications.

This research is most relevant for: competitive athletes training at altitude, mountain climbers, people relocating to high-altitude areas, and fitness enthusiasts doing high-altitude training. It’s less relevant for people living at sea level or those with iron overload conditions (who should avoid iron supplements). People with diabetes or those taking blood thinners should consult their doctor before using supplements. Younger athletes (under 16) should have parental guidance and medical supervision.

Carbohydrate supplementation effects appear within hours to days of starting—you might notice improved exercise tolerance within your first few high-altitude workouts. Blood oxygen improvements typically develop over days to weeks as the body adapts. Maximum benefits for overall fitness usually appear after 2-4 weeks of consistent supplementation at altitude. Iron supplementation takes longer—typically 4-8 weeks—because the body needs time to build new red blood cells. Don’t expect overnight transformation; these are performance enhancements, not miracle cures.

Want to Apply This Research?

  • Log carbohydrate intake (grams consumed) before/during workouts and track perceived exertion on a 1-10 scale, plus blood oxygen readings if available via a pulse oximeter. Record these daily to see if carb timing correlates with better performance and lower fatigue ratings over 2-4 weeks.
  • Set a reminder to consume 30-60 grams of carbohydrates (like a banana, sports drink, or energy bar) 30-60 minutes before high-altitude exercise sessions. Track which carbohydrate sources you use and how you feel during workouts to find what works best for your body.
  • Create a weekly summary comparing weeks with consistent carbohydrate supplementation to weeks without it. Monitor three metrics: average perceived exertion during workouts, workout duration/intensity completed, and subjective recovery feeling. Over 4-8 weeks, patterns should emerge showing whether supplementation helps your individual performance.

This research summary is for educational purposes and should not replace professional medical advice. Before starting any supplement regimen, especially at high altitude, consult with your doctor, sports nutritionist, or healthcare provider. This is particularly important if you have existing health conditions, take medications, are pregnant or breastfeeding, or are under 18 years old. Individual responses to supplements vary significantly. The studies reviewed involved healthy, active participants; results may not apply to everyone. Supplements are not regulated the same way as medications, so quality and purity can vary between brands.