I haven’t really addressed ketogenic diets aside from a few articles where I discuss the overall benefits of carbohydrates to climbing, which inherently suggests that diets that exclude carbohydrates are a poor choice if your top concern is performance. I’m still not really going to dig into ketogenic diets in this little article, but rather want to bring attention to a recent study on the topic entitled “Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults.”
The study above concludes, “Our findings lead us to assume that a KD does not impact physical fitness in a clinically relevant manner that would impair activities of daily life and aerobic training. However, a KD may be a matter of concern in competitive athletes.” This is a fair conclusion based on the study results, but let’s look a bit further into what this means for a climber.
What the Study Found
As with most studies on the subject, this study used cycling as the primary means to detect changes in fitness. In this case, the authors also used a handgrip strength test as a proxy to determine whether physical strength was affected, which will become relevant later on.
What the authors discovered is as follows (only significant results listed):
- A slight decrease (2.4%) in VO2 max that disappeared when changes in body weight were accounted for.
- A moderate decrease (4.1%) in peak power.
- A small increase (2.5%) in handgrip strength.
They also found a large and significant increase in LDL cholesterol of 10.7% (LDL is the bad stuff), and claimed to have witnessed a significant improvement in the average triglyceride to HDL cholesterol ratio, but got the calculation wrong—it still improved, just not by as much as they claimed, and given the already low significance (.039) it’s unlikely it would still be significant. Also, considering that neither triglycerides nor HDL cholesterol changed significantly on their own, it would be surprising if they changed in relation to each other. But this is really aside from the point!
What the Results Mean
In the authors’ estimation (and mine as well), there’s only really a couple of clinically relevant findings from this study:
- Athletes who need endurance above the aerobic threshold will be hindered by the ketogenic diet, but those who work mostly below the aerobic zone will not be.
- Long-term ketogenic dieting may negatively impact blood lipid levels, raising the risk for cardiovascular diseases.
Your everyday person who goes to the gym and jogs on a treadmill for an hour is unlikely to be affected because they spend the majority of their time running well under the aerobic threshold. Therefore, the authors conclude, we should not worry about the possible exercise-related repercussions of putting a patient on a ketogenic diet for weight loss—the patient will maintain their ability (and thus likely motivation) to exercise.
What about the apparent increase in handgrip strength? Wouldn’t that be great for climbers? Yes, it’s easy to agree that any real increase in handgrip strength would be beneficial, but we should doubt the clinical relevance of the 2.5% increase demonstrated here. For one, the method of testing was a 5-second max hold—well within the capacity of our creatine phosphate reserves to handle alone. For two, there was no control group (a weakness the authors noted). Without a control group, it’s impossible to know whether the diet itself improved handgrip strength (unlikely) or whether it was related to something else.
For what it’s worth, the authors only measured this parameter so they could verify that overall muscle function wasn’t impaired during the weight loss period—that the participants didn’t lose too much lean mass or the ability to use it. They did demonstrate this, but nothing further.
What’s the Relevance?
This is simply another study documenting the negative impact ketogenic diets have on performance. If you’re not concerned with performance, but only with weight loss, then the ketogenic diet may be useful—but no athlete should care about weight to a greater degree than performance, even if losing weight may slightly increase performance. If the cost of increased performance is decreased performance, you’re limiting your growth.
It should also be noted that this study provides further evidence that there is nothing inherently healthier about the ketogenic diet, and that it may in fact decrease certain health-related biomarkers. I don’t think these markers, in isolation, mean the diet is unhealthy—if you are otherwise healthy, a lone slight increase in LDL cholesterol isn’t going to break you, and certainly not if it’s still in a healthy range—but it does provide counterevidence to the oft-claimed health benefits ketogenic zealots would have you believe in.
Bottom line, this study suggests the ketogenic diet will slightly hinder performance for the majority of athletes, but will not impact relatively low-grade exercise for those who are seeking weight loss over performance. Since this study used no control, we cannot assess the ketogenic diet’s ability to encourage weight loss versus any other diet, but most large-scale studies suggest all nutritionally sound weight loss methods are comparable.
I have been on the KD for 3 years now. I was climbing 12b when i started. Currently climbing 13c.
Blood work is always good, and I have never felt better.
@Melvis well maybe 3 years later you were a worse climber and weaker. 3 years ago I had only done a few V8s and my hardest redpoint is now V11. No diet involved.
They just got the triglyceride/HDL ratio wrong? Like, mathematically incorrect? Surprised this would happen in a peer-reviewed journal.
Also, what do you think is the value of having a diet with strict, but simple rules? Seems like some people are probably seeing benefits from these keto diets because they’re switching from an unhealthy diet to a healthier one (even if it’s not the healthiest of all) – all because they’re finally aware of what they’re eating.
Is a keto/paleo/vegetarian/whatever diet actually a benefit to the majority of people who don’t care to figure out a totally science-based diet? Maybe they’re not the best, but they’re better than average, just because they force an otherwise ignorant person to pay a little more attention to what they’re eating. That could help you avoid a lot of obvious bad choices, right away.
It’s not the first time I’ve seen a math error in a peer-reviewed article, and usually they don’t make a significant difference in the findings; it’s just random errata. I often find them because I’m recalculating their values because I want a precise figure and only have an estimate derived from a graph, for example.
As for diets, I do think there is a benefit to having rules, at least for some people. In the end, there’s not really such a thing as a “perfect” diet, and any diet that moves a person towards their goals without long- or short-term health consequences can have value. I have no problem with the keto diet (or any other diet) as long as it provides a person with what they need—in the case of a performance-oriented climber, however, a keto diet generally will not since it will compromise power and endurance, and thus I would say it’s a poor dietary choice for a climber who wants to lose weight.
The other thing to keep in mind is that the more rules a diet has, the harder the transition off the diet is afterwards. As I’ve written before, I don’t really believe there is such thing as “just eating better” and losing weight—all diets, in the end, require habit changes, which require discipline, which requires motivation, which can flag and lead to regression—but if you make a handful of small changes it’s easier to return to a more “normal” diet after you lose weight than if you, say, completely eliminate carbohydrates. So that must be weighed as well: rule-based diets provide easy dietary goals, but don’t translate very far outside of themselves; more open-ended diets provide less direction, but can nurture overall healthy habits that continue outside the scope of the diet.
Too bad this was just a 6 week study. I guess the whole negative impact of a ketogenic diet on climbing performance has to do with the glycolytic pathway, which uses glycogen in the muscles for the power endurance we all want to much.
This is the biggest metabolic obstacle fur us climbers, but I read in a study (sorry, don’t remember which one) that is takes up to 3 months for the body to adapt and replenish muscle glycogen stores from gluconeogenesis (from breakdown of lipids or protein) at normal rates.
this would mean that we could use our muscle glycogen for power endurance and replenish it at the same rate as anyone who eats lots of carbs…
I myself started eating keto a month ago, and this is where I feel the negative impact on climbing, but I’m going to stick to it for at least 2 more months andsee what my n=1 will be.. I hope the study is right 😀
anyway it would be interesting to have a study for at least 3 months or more, which targets the glycolytic pathway.
There are some studies that suggest muscle glycogen can rebound a bit after adaptation to a ketogenic diet, but the majority show ongoing reduced levels and reduced usage. There are a couple biochemical reasons we would expect this:
First, we cannot turn fats into carbohydrates, only use their glycerol tails, which severely limits how much glycogen we could create. Most of this glycogen would likely be created in the liver, which would even further limit the amount being replenished in the muscles. Amino acids from proteins are better suited, but still converted at a loss, so it would take very high levels of protein intake before we really saw a difference (at which point you’re essentially using proteins as a carbohydrate, so you might as well use the “real thing”, so to speak).
Second, it’s well-established at this point that our day-to-day dietary intake affects our ability to metabolize fats and carbohydrates. When the diet is high-carb, we shift systems towards carb burning and away from fat. When the diet is high-fat, we shift systems away from carb burning and towards fat. Thus, even if we have muscle (or liver) glycogen available, our ability to use it is impaired—this is why we no longer call high-fat adaptations “glucose sparing” but rather “glucose impairing”.
At the end of the day, the best evidence against a ketogenic diet is still the complete lack of any study that shows a benefit except in extremely limited situations such as ultramarathons where energy availability is expected to be limited. For power sports, we’ve consistently seen a drop in power and power endurance. We might hope that these drawbacks eventually even out or go away, but we currently have no evidence (or reason to believe) they will—though you can be sure that some folks will continue to argue that more time or slightly tweaked low-carb strategies completely change it!
Regardless, good luck with your diet, and let us know how it goes!
Volek’s FASTER study, with a well-matched group of HC and LC ultra-endurance athletes (avg of 20 months on LCD) gathered actual data on muscle glycogen levels via 3 muscle biopsies, at baseline, immediately after a 3h 64% VO2max treadmill run, and 120 minutes post-exercise and showed that there was almost no difference in muscle glycogen levels (or recovery) between the groups. doi: 10.1016/j.metabol.2015.10.028.
Since then, there have been some other additional interesting studies published, like McSwiney’s 2018 “Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes.” which shows increased power to weight ratio when switching HC athletes into LC/HC arms with equivalent training over a 12 week period. doi: 10.1016/j.metabol.2017.10.010. or LaFountain’s TANK study, a 12 week program with ROTC cadets that showed significant body composition improvements w/ no loss in performance with military-specific obstacle course (this included measurements of jumping power, maximal strength via squats, bench press, and free weights, and sprint intervals) doi: 10.1093/milmed/usz046.
The 2019 narrative review “Keto-Adaptation and Endurance Exercise Capacity, Fatigue Recovery, and Exercise-Induced Muscle and Organ Damage Prevention: A Narrative Review” I think does a good job in looking at some of the potential biomechanistic benefits of a ketogenic diet for athletes, doi: 10.3390/sports7020040, but obviously there’s considerable variability for how individuals respond to nutritional regimes – LCDs obviously works very well for some athletes, and as Louise Burke (no fan of LCHF) ends in her 2015 review “Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon?” doi: 10.1007/s40279-015-0393-9:
“It is important to consider insights from research and athlete testimonials to identify different scenarios in which one approach might offer advantages over another or to explain divergent outcomes (Table 5), rather than insist on a single ‘truth’ or solution. Indeed, although there is a continual cry to rid sports nutrition of ‘dogma’ [4], it would seem counterproductive if new ideas were as dogmatic as the old beliefs they seek to replace. … In other words, there should not be a choice of one fuel source or the other, or ‘black versus white’, but rather a desire to integrate and individualize the various dietary factors that can contribute to optimal sports performance. … Considering that athletes might best benefit from a range of options in the dietary tool box is likely to be a better model for optimal sports nutrition than insisting on a single, one-size-fits-all solution.”