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.