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Don’t Be a Carb Hater

The evidence that going low-carb benefits any athlete’s performance is weak, mostly anecdotal, and often driven by dogma.

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There is a camp amongst athletes that favors a high-fat, low-carbohydrate approach. Their enthusiasm is fueled almost entirely by the work of three researchers (Stephen Phinney, Jeff Volek, and Tim Noakes), who despite over 30 years worth of research have yet to produce any notable studies that demonstrate a low-carb diet to work better than—or even equally as well as—a high-carb diet.

Now don’t get me wrong—what these researchers study is incredibly important, and by no means has their research been worthless. In many cases they’ve revealed aspects of fat-adaptation that we might not know about otherwise. They’ve also done significant work to elucidate the potential benefits of low-carb diets for different disease states. So I do respect these researchers and the work they do—I just can’t find any solid justification for their hypothesis that a low-carb diet would benefit an athlete.

At best, what we’ve seen in athletes who go low-carb and become “fat-adapted” is a mere preservation of performance without any notable improvements. Furthermore, this “preservation” only applies to submaximal aerobic exercise—high-intensity exercise performance is usually severely compromised. Thus, the evidence that going low-carb benefits any athlete’s performance (let alone a climber’s) is weak, mostly anecdotal, and often driven by dogma.

I hope you, my climbing reader, are not a carb hater—but I’ve also learned to be proactive in my approach. You may not fear carbs today, but the anti-carb camps are pernicious. Let me start the immunization process by sharing some bullet points on why going low-carb is a terrible idea for a climber.

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Going Low-Carb? Say Goodbye to Power!

At first glance, carbohydrates are not a significant source of power for a climber. The only study that has examined energy system use in climbers found that carbohydrates only supplied about 10-20% of the total energy for a climb (through anaerobic glycolysis, anyway). By contrast, creatine supplied 40% and the generic “aerobic energy” pool (which could be either fat or carbohydrates) supplied about another 40%. Without further study, we can’t know for certain how much aerobic energy was supplied by either carbohydrates or fats, so that is perhaps a moot point…

…Or maybe it’s not. We know that carbohydrates are capable of producing over double the ATP (cellular energy) through aerobic respiration than fats are (16.7 mmol/sec vs 6.7 mmol/sec). In the energy systems article mentioned above, the researchers hypothesized that the aerobic system’s primary purpose in climbing is to regenerate the spent creatine molecules back into energy-containing creatine phosphate molecules. Given the short amount of time a climber has between holds to regenerate creatine, and given that carbohydrates are capable of restoring about 2.5x as much creatine as fats, which fuel do you think is more capable of sustaining power and power endurance? The answer should be clear.

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Low-Carb Diets Make Exercise Feel “Harder”

Several studies show that restricting carbohydrates increases perceived exertion. Briefly put, “perceived exertion” is how our body and brain communicate in order to prevent you from over-exercising and suffering catastrophic muscle failure. When dietary carbohydrates go down or ketones (a byproduct of a low-carb diet) go up, so does perceived exertion.

In case you think perceived exertion is something you can just push through, think again. “Perceived” exertion is essentially a proxy for “actual” exertion and determines to a large extent how long your body will let you exercise before you get fatigued. In trials, perceived exertion is inversely correlated with time to fatigue, meaning that the harder you think you’re working the sooner you actually fatigue—even if you’re doing the exact same amount of work as you could normally do in better conditions (like with a higher carbohydrate diet)!

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Fewer Training Adaptations Are Made on a Low-Carb Diet

Finally, low-carb diets may actively impair training adaptations, at least over the long-term (and at least in untrained endurance athletes). In one study, untrained cyclists undertook an 8-week diet and training routine where one group consumed a high-fat diet and the other a high-carbohydrate diet but otherwise exercised and ate the same. At the end of the study, the high-carb group had improved by a not-so-small 56% compared to the high-fat group! That’s a pretty remarkable difference.

How much does this study have to do with climbers? Perhaps not much, since we’re not endurance athletes—but consider the implications of the previous two points in conjunction with this one. If you can’t climb with as great of power, and you can’t climb for as long, then assuming all other factors are equal you will definitely improve less than a climber who can train longer and harder. I won’t go so far as to say you’ll improve 56% less (some of that figure can be explained away by metabolic adaptations), but my money will always be on the athlete who supplies their body with the necessary energy for high-intensity training.

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Climbing is tough, gritty, powerful work, and carbohydrates are simply more capable of fueling that work (aerobically and anaerobically) than fat is. If you skimp on carbs, you’re potentially limiting your climbing potential both in terms of power and endurance. Likewise, the evidence that a high-fat diet confers any special advantage to climbers (or any athlete) is limited.

I don’t predict the high-fat athlete craze to disappear anytime soon; in fact, I suspect it has yet to peak. But I do hope you resist the urge to make such dramatic changes to your diet when the evidence so clearly indicates that the “fat-adapted climber” is an idea without merit. If your goal is improved performance—pushing your limits as a climber—then you’re going to need the help of carbs.

As a certified sports nutritionist (MS, CISSN), Brian Rigby works with climbers and other athletes at Boulder’s Elite Sports Nutrition in Colorado and writes at Climbing Nutrition.

This article originally appeared on and Climbing Magazine in 2015. It is reposted here for free. Sign up with a Climbing membership, now just $2 a month for a limited time, and you get unlimited access to thousands of stories and articles by world-class authors on plus a print subscription to Climbing and our annual coffee-table edition of Ascent.  Please join the Climbing team today.

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