The Ketogenic Diet and Strength Training: Why it Doesn’t Stack Up

The ketogenic diet has become a hot topic. The discussion around it is a perfect example of the lack of any measured conversation in the nutrition-sphere, caught as we always are between dogmatists and detractors.

Dietary fat is, more so than any element of the human diet, an emotive topic. The fact that the ketogenic diet is a high fat diet automatically deprives it of credibility for safety or efficacy in the eyes of many, particularly in the medical community. I find this somewhat of an add dichotomy given that the ketogenic diet has been a gold-standard in clinical nutrition since the 1920’s for childhood epilepsy.

The discussion around it tends to reflect a lack of education, which isn’t helped by rabid keto-ers who gloat about eating a pound of bacon a day. This only reflects their own ignorance, not the nutritional enlightenment they insist “going keto” has bestowed upon them.

Let me say at the outset that I think the ketogenic diet is fascinating, and this post is not aimed at addressing it’s benefit or lack of benefit in a broad, general sense. So let me say what this post isn’t. This is NOT a post about the benefits of the ketogenic diet in relation to certain diseases, for which there is some fascinating and growing evidence of a potential therapeutic effect. This is also NOT a post in relation to the ketogenic diet in endurance sports, for which the jury is still out: the evidence isn’t convincing for performance enhancement, but there may be some exceptions (Burke, 2015).

This post is solely concerned with the ketogenic diet in strength training. Given the resurgent popularity of the diet in strength and conditioning, it’s important rely on the evidence and not anecdote from “keto” subreddits. Note that the vast majority of data in relation to the ketogenic diet and exercise focuses on aerobic/endurance exercise, so studies actually looking at strength as a measurable are limited.

So, is the ketogenic diet [KD] going to benefit strength training? And by benefit, I mean increase your lifts, increase your strength, hypertrophy?

Problem 1: Physiological Mechanisms

The KD in it’s classical form is a “fasting-mimicking diet”, meaning that the underlying physiological processes mimic those of being in the fasted state. As far as muscular hypertrophy goes, this isn’t a positive. I wrote about the mechanisms of muscle protein synthesis [MPS] here, so quick recap: the pathways that are critical to this effect are the Akt/mTOR pathways, and MPS activates when inhibition of translation initiation of these pathways through AMPK is released (Dreyer et al., 2006). By mimicking fasting, the KD activates AMPK which inhibits the mTOR pathway (Paoli, Bianco & Grimaldi, 2015).

This inhibition doesn’t appear to be dependant on energy restriction, so a KD with a caloric surplus may not overcome these effects, as carbohydrate restriction itself activates AMPK (Paoli, Bianco & Grimaldi, 2015). In addition to AMPK activation, a KD directly inhibits the anabolic signalling pathways IGF-1, Akt and mTOR (Sandri et al., 2013). In fact, the KD has been described as “an oxymoron when the athlete seeks muscle hypertrophy.” (Paoli, Bianco & Grimaldi, 2015).

Now, both resistance training itself and the amino acid leucine directly activate these pathways (Atherton & Smith, 2012). So at a hypothetical level, perhaps the combination of the two in a caloric surplus may allow for hypertrophy. But on a purely mechanistic level, it appears it would be difficult at the very least, and this is supported by the limited data examining strength/hypertrophy in athletes on a KD (Paoli et al., 2012).

The other mechanistic element that goes against the KD in strength sports is that strength is primarily a neurological adaptation (Gabriel, Kamen & Frost, 2006), and carbohydrates increase performance (amongst other mechanisms) by enhancing central nervous system drive (Jeukendrup & Chambers, 2006). Moreover, restricting exogenous carb intake while glycogen-depleting exercise is being performed results in minimal resynthesis of glycogen, meaning performance will eventually be impaired by low muscle glycogen content (McDonald, 1998).

So could something like carbohydrate mouth rinsing or minor carb intake pre-workout (as in Lyle McDonald’s ‘Targeted Ketogenic Diet‘) enhance strength performance? Maybe. We’re back to the absence of evidence issue.

Problem 2: The Existing Data

And thus we come to the crux of the issue: the lack of any convincing evidence that a KD could be used to enhance adaptations to strength/power training. A few particular studies seem to be consistently referred to, so we’ll look at each of them.

Study 1 (Zajac et al., 2014): A study in 8 well-trained male off-road cyclists, using a crossover design where all subjects spent 4-weeks on a KD [15% protein/15% carbs/70% fat] and 4-weeks on a standard mixed diet [20% protein/50% carbs/30% fat], followed by 3-days of testing at different exercises intensities. At maximal exercise intensities, the KD compromised power output, and effect that is consistent with impaired exercise performance during higher intensity exercise on high-fat diets, due to depleted muscle glycogen and reduced activity of glycolytic enzymes (Burke, 2015).

This trial did, however, use 15% carbohydrate, and blood analysis indicates the subjects only achieved very mild nutritional ketosis. However, the observation of impaired power output during anaerobic exercise is consistent with other studies examining KD in cyclists (Phinney et al., 1983; Havemann et al., 2006).

As an aside, as far as health concerns of KD go, this trial places a specific emphasis on polyunsaturated and monounsaturated fats over saturates, with a high omega-3 fatty acid intake, and noted improvements across the board in cholesterol profiles and biomarkers of cardiovascular health. Which makes perfect sense.

Study 2 (Rhyu & Cho, 2014): A study in 20 high school Taekwando athletes, 10 randomly assigned to a KD [40% protein/5% carbs/55% fat] and 10 to a non-KD [30% protein/40% carbs/30% fat]. The study was looking at weight loss in weight-categorised athletes, so each diet used a 25% energy deficit for 3-weeks. There’s no details provided on the resistance exercise, save for “2 hours of morning exercise, mostly for physical strength development.” So god knows what that means.

As with the macronutrient percentage breakdown in the cyclists trial, it is arguable that this study didn’t get the KD quite right: 40% protein may be too high, as over 25% protein may suppress ketogenesis (Phinney, 2004).

The results of this trial are hardly impressive. The non-KD lost more body fat (1.08%) than the KD group (0.4%), and the KD group lost a shocking 2.18kg of lean body mass [1.39kg LBM lost in the non-KD group]. More particular to strength, there was a significant decrease in peak power output.

A difficulty with the interpretation of the results is the significant weight and LBM losses over the 3-week course of the study in both groups, a factor which likely had a bearing on the decreases in power. While energy restriction for the purposes of short-term weight loss may explain the results of this study, it is important to note the studies without energy restriction have consistently demonstrated impaired performance of peak power at anaerobic intensities on a KD (Phinney et al., 1983; Zajac et al., 2014; Havemann et al., 2006).

Aside: I like that the authors acknowledge that decreases in body weight and fat seen with diets that replace carbs with fat are a result of reduced food intake, by implication acknowledging that there is no special “metabolic advantage” as some low-carb/ketogenic dogmatists would insist.

Study 3 – The Big One (Paoli et al., 2012): I call it “the big one” as this is the study that primarily gets waved in your face in support of a KD and strength training. Except, it’s garbage, like the rest of the KD/strength research.

This study examined 8 elite male gymnasts on a KD for 1-month, followed by testing the same group after 1-month on a typical Western diet. The diet phases were separated by 6-months. Even in the design, the diet phases were not treated similarly: the KD phase was supplemented with high-protein meal replacements, a daily multivitamin, and herbal extracts which included diuretics and energy-boosting compounds like ginseng, guarana and coffee. The “Western diet” phase were not provided with any additional supplements.

Another issue? The diet composition, again: 40% protein. The authors cite observations of muscle loss in research employing very low calorie, energy restricted KD with protein intake >1.2g/kg, but this study wasn’t restricting energy intake, nor does muscle loss at a low protein threshold necessarily mean more than double the intake is required.

The authors attribute the muscle-sparing effect to the state of ketosis, but this is a reach: the high dietary protein intake coupled with the unrestricted nature of the diet (and energy sufficiency) mean that it is difficult to attribute preservation of LBM to ketosis alone.

And now we come to the assessment of strength, which was calisthenic exercises. In elite gymnasts. Basically testing them on exercises they could do in their sleep. Power output tests like counterbalance jumps were assessed, for which the trend was negative in effect. And overall, the trends were positive in the Western diet phase. In fairness to the authors, they do note two important points:

1: That increasing muscle mass on a KD is “actually very difficult.” And;

2: That what the study really shows is that strength and muscle mass can be maintained on a KD.

Limitations of the Research:

No trial has actually looked at strength training. No trial of a KD in Olympic lifters or powerlifters, for example. So until that happens, we’re left making inferences from gymnasts doing push ups and cyclists, well, cycling. And they are all trials with very small sample sizes.

Another difficulty is that the KD diets employed in the study may not resemble a full ketogenic diet, particularly with the use of over 35% protein, where it has been suggested that the maximal threshold for protein on a KD is 25% (Phinney, 2004).

Perhaps the major limitation is the short duration of the trials, typically not more than one month. The relevance of this as far as the KD goes is that it may take that long for the full adaptation to ketogenesis to occur (Phinney, 2004), meaning that performance benefits could take longer to manifest.

Conclusions

Ultimately, we’re left with two conclusions to draw.

1: The physiological mechanisms don’t add up. The machinery of hypertrophy is inhibited on a KD (Paoli, Bianco and Grimaldi, 2015). In addition, the very minor glycogen resynthesis when carbohydrates are restricted post-workout is not sufficient to sustain anaerobic performance (McDonald, 1998).

2: The physiological limitations are consistent with the research. While a KD may maintain/preserve muscle mass, increasing muscle mass is very difficult even with unrestricted caloric intake (Paoli et al., 2012). And in glycogen-depleting activities, like cycling or Taekwando, power output at anaerobic intensities is impaired on a KD, regardless of whether energy is restricted or not (Phinney et al., 1983; Zajac et al., 2014; Havemann et al., 2006; Rhyo & Cho, 2014; Phinney, 2004).

In sum, if you’re engaged in anaerobic sports like sprinting, weightlifting, Crossfit, or powerlifting, a KD is not optimal (Phinney, 2004). Given the ridiculous lack of objectivity and measured discussion in nutrition generally, I’m going to leave you with this spot-on quote from Australian Institute of Sport researcher, Louise Burke:

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, rather than insist on a single ‘truth’ or solution….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. (Burke, 2015).

Amen.


References

Atherton, P. and Smith, K. (2012). Muscle protein synthesis in response to nutrition and exercise. The Journal of Physiology, 590(5), pp.1049-1057.

Burke, L. (2015). Re-Examining High-Fat Diets for Sports Performance: Did We Call the Nail in the Coffin Too Soon? Sports Med, 45(S1), pp.33-49.

Gabriel, D., Kamen, G. and Frost, G. (2006). Neural Adaptations to Resistive Exercise. Sports Medicine, 36(2), pp.133-149.

Havemann, L. (2006). Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. Journal of Applied Physiology, 100(1), pp.194-202.

Jeukendrup, A. and Chambers, E. (2010). Oral carbohydrate sensing and exercise performance. Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), pp.447-451.

Kiens, B. and Astrup, A. (2015). Ketogenic Diets for Fat Loss and Exercise Performance. Exercise and Sport Sciences Reviews, 43(3), p.109.

McDonald, L. (1998). The ketogenic diet. [Austin, TX]: [The Author].

Paoli, A., Bianco, A. and Grimaldi, K. (2015). The Ketogenic Diet and Sport. Exercise and Sport Sciences Reviews, 43(3), pp.153-162.

Paoli, A., Grimaldi, K., D’Agostino, D., Cenci, L., Moro, T., Bianco, A. and Palma, A. (2012). Ketogenic diet does not affect strength performance in elite artistic gymnasts. J Int Soc Sports Nutr, 9(1), p.34.

Phinney, S. (2004). Ketogenic diets and physical performance. Nutr Metab (Lond), 1(2).

Phinney, S., Bistrian, B., Evans, W., Gervino, E. and Blackburn, G. (1983). The human metabolic response to chronic ketosis without caloric restriction: Preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism, 32(8), pp.769-776.

Rhyu, H. and Cho, S. (2014). The effect of weight loss by ketogenic diet on the body composition, performance-related physical fitness factors and cytokines of Taekwondo athletes. Journal of Exercise Rehabilitation, 10(5), pp.326-331.

Sandri, M., Barberi, L., Bijlsma, A., Blaauw, B., Dyar, K., Milan, G., Mammucari, C., Meskers, C., Pallafacchina, G., Paoli, A., Pion, D., Roceri, M., Romanello, V., Serrano, A., Toniolo, L., Larsson, L., Maier, A., Muñoz-Cánoves, P., Musarò, A., Pende, M., Reggiani, C., Rizzuto, R. and Schiaffino, S. (2013). Signalling pathways regulating muscle mass in ageing skeletal muscle. The role of the IGF1-Akt-mTOR-FoxO pathway. Biogerontology, 14(3), pp.303-323.

Zajac, A., Poprzecki, S., Maszczyk, A., Czuba, M., Michalczyk, M. and Zydek, G. (2014). The Effects of a Ketogenic Diet on Exercise Metabolism and Physical Performance in Off-Road Cyclists. Nutrients, 6(7), pp.2493-2508.