Researchers studied 21 elite race-walkers to see how different eating plans and caffeine affected their performance on a challenging hill-walking workout. They found that athletes eating more carbohydrates performed better than those on low-carb diets. However, when all athletes took caffeine before their workout, everyone walked faster and worked harder. Interestingly, caffeine helped the low-carb dieters improve their performance, but they still didn’t perform as well as the carb-eating athletes who also took caffeine. This suggests that while caffeine is a useful performance booster, eating enough carbohydrates remains the most important factor for athletic performance.

The Quick Take

  • What they studied: Whether caffeine could help athletes perform better when following a low-carbohydrate diet compared to a high-carbohydrate diet during intense hill-walking training sessions.
  • Who participated: 21 elite race-walkers (competitive walkers at a high level) who were tested over a 3-week period. They were split into two groups: one eating a high-carbohydrate diet and one eating a low-carbohydrate, high-fat diet.
  • Key finding: Athletes on a high-carbohydrate diet walked faster and performed better than those on a low-carb diet. When everyone took caffeine, they all walked faster, but the high-carb group still outperformed the low-carb group. Caffeine helped the low-carb group improve, but not enough to match the high-carb group’s performance.
  • What it means for you: If you’re an athlete training hard, eating enough carbohydrates appears to be more important for performance than taking caffeine. That said, caffeine can provide a helpful boost to your workout intensity. This research is most relevant to competitive athletes; casual exercisers may see different results. Talk to a coach or sports nutritionist before making major diet changes.

The Research Details

This study followed a carefully controlled approach. First, all 21 race-walkers completed a challenging 14-kilometer hill workout while eating their normal high-carbohydrate diet. Then, researchers split them into two groups: one group continued eating lots of carbohydrates, while the other switched to a low-carbohydrate, high-fat diet. Both groups repeated the same hill workout every week for 3 weeks. During weeks 2 and 3, the researchers gave all athletes either caffeine (3 milligrams per kilogram of body weight) or a placebo (fake gum with no caffeine) 20 minutes before their workout. This design allowed researchers to see how both diet and caffeine affected performance separately and together.

The researchers measured several things during each workout: how fast the athletes walked, their heart rate, how hard they felt they were working (using a rating scale), and their mental focus using a color-word test. They also checked blood samples to see how their bodies were using different fuels.

This type of study design is strong because it lets researchers compare the same people under different conditions, which helps rule out differences between individuals.

Understanding how diet and supplements work together is important for athletes who want to perform their best. Many athletes are interested in low-carbohydrate diets because they’ve heard they can help with weight loss or fat burning. However, this research shows that these diets might hurt athletic performance. By testing whether caffeine could fix this problem, researchers could give athletes practical advice about whether they should switch diets or use supplements to maintain their performance.

This study has several strengths: it was published in a respected nutrition journal, it used a controlled design where researchers carefully managed the conditions, and it tested real elite athletes doing their actual sport. However, the sample size is relatively small (only 21 people), which means the results might not apply to all athletes. The study also only lasted 3 weeks, so we don’t know if these effects would continue longer. The athletes studied were race-walkers, so results might differ for other sports. Additionally, the study didn’t measure whether athletes could maintain this performance over many weeks or months of training.

What the Results Show

The most important finding was that the high-carbohydrate group performed better than the low-carbohydrate group throughout the study. Interestingly, the low-carb group actually started out slightly faster at the beginning, but by week 1 of the diet change, they had slowed down significantly. Meanwhile, the high-carb group improved over the first two weeks, suggesting they adapted well to the training.

When athletes took caffeine, everyone walked faster and worked at a higher intensity compared to when they took the placebo. This happened in both diet groups. The caffeine boost was meaningful—athletes were able to push themselves harder during their workouts.

However, even with caffeine, the low-carb group never caught up to the high-carb group. The high-carb athletes with caffeine still performed better than the low-carb athletes with caffeine. This suggests that while caffeine helps, it can’t completely make up for the performance loss from eating fewer carbohydrates.

The researchers also found that caffeine and diet didn’t interact in unexpected ways—meaning caffeine worked about the same for both groups, just at different baseline performance levels.

The study measured heart rate and how hard athletes felt they were working. Both groups showed similar heart rate responses to caffeine, suggesting their bodies were working harder when they took it. The mental focus test (Stroop test) didn’t show major differences between groups, suggesting that the performance differences were mainly physical rather than mental. Blood metabolite measurements showed that the two diet groups were using different fuel sources during exercise, which is expected—the high-carb group was burning more carbohydrates while the low-carb group was burning more fat.

Previous research has shown that low-carbohydrate diets can reduce athletic performance in endurance activities, and this study confirms that finding in race-walkers. The new contribution here is showing that caffeine can partially help athletes on low-carb diets perform better, though not completely. This adds to growing evidence that caffeine is a useful performance tool for many athletes. However, the finding that high-carbohydrate availability remains superior even with caffeine reinforces what sports nutritionists have recommended for decades: carbohydrates are the preferred fuel for intense athletic performance.

The study only included 21 people, which is a small number. This means the results might not apply to all athletes, and some findings might have occurred by chance. The study only lasted 3 weeks, so we don’t know if these effects would continue if athletes stayed on these diets longer. All participants were elite race-walkers, so results might be different for other sports or fitness levels. The study didn’t look at whether athletes could recover properly between workouts on the low-carb diet. Additionally, the study used a specific amount of caffeine (3 mg per kilogram of body weight), so different amounts might produce different results. Finally, individual athletes might respond differently to these diets and supplements based on their genetics and training background.

The Bottom Line

For competitive athletes doing intense training: Eating a high-carbohydrate diet appears to be the best choice for performance (strong evidence from this study). Caffeine supplementation can provide an additional performance boost for both diet types (moderate evidence). If you’re considering a low-carbohydrate diet, be aware that it may reduce your training performance, though caffeine can help partially offset this effect (moderate evidence). For casual exercisers: These findings are based on elite athletes, so they may not apply to you. Focus on overall healthy eating and training consistency before worrying about these specific strategies.

This research is most relevant to competitive endurance athletes, particularly those doing intense training sessions. Race-walkers, runners, cyclists, and other endurance athletes should pay attention to these findings. Athletes considering switching to a low-carbohydrate diet should understand the potential performance trade-offs. Coaches and sports nutritionists working with athletes should consider these findings when advising clients. This research is less relevant to casual exercisers, strength athletes, or people exercising primarily for health and fitness rather than competition.

The performance changes happened quickly in this study. The low-carb group showed slower performance within the first week of changing their diet. The high-carb group showed improvement within 2 weeks. Caffeine’s effects were immediate—athletes performed better in the same workout session when they took caffeine. However, this study only looked at 3 weeks, so we don’t know how long these effects would last with longer-term diet changes. Athletes should expect to see performance changes within days to weeks of changing their diet, but the full adaptation period might take longer.

Want to Apply This Research?

  • Track your workout speed or intensity (measured as percentage of maximum effort) on training days, separated by diet type and whether you took caffeine. Record this weekly to see patterns in your performance over time. Also track how you feel during workouts (energy level, fatigue) to correlate with performance metrics.
  • If you’re an athlete, use the app to experiment with timing your caffeine intake 20 minutes before your most important workouts. Track whether you notice improved performance on days you take caffeine versus days you don’t. If you’re considering a low-carb diet, use the app to monitor your training performance before, during, and after the diet change to see if your workouts are affected.
  • Set up weekly performance tracking that compares your speed, intensity, and perceived effort across different diet phases and caffeine use. Create a simple dashboard showing your performance trends over weeks and months. If you change your diet, establish a baseline of your current performance first, then track changes weekly for at least 4-6 weeks to see the real impact. Note any other factors that might affect performance (sleep, stress, other training) to get a clearer picture.

This research is based on a small study of elite race-walkers and may not apply to all athletes or fitness levels. Individual responses to diet changes and caffeine vary significantly based on genetics, training background, and other factors. Before making major changes to your diet or starting caffeine supplementation, consult with a sports nutritionist, doctor, or qualified coach. This information is for educational purposes and should not replace professional medical or nutritional advice. If you have any health conditions, take medications, or are pregnant or nursing, talk to your healthcare provider before changing your diet or using caffeine supplements.