The ketogenic diet is a hot topic. It’s being talked about by everyone, from coaches to athletes to scientists. Is the ketogenic diet a good option to improve performance in strength sports?
What is the Keto Diet?
The ketogenic diet, or “keto diet”, is a dietary model based on the total or near total restriction of carbohydrates consumed in favour of an increase in dietary fat sources and, usually, a maintenance of protein intake.
Depending on the author, you might see the ketogenic diet referred to as VLCHFD (very low carb, high fat diet).
How do you do it?
To follow a ketogenic diet, you need to:
- Consume less than 50g of net carbohydrates per day,
- Have minimum concentrations of β-hydroxybutyrate (ketone bodies) of 0.5mmol/L, usually reaching up to 3mM under normal conditions.
Figure I. Functional nutritional status according to plasma hydroxybutyrate concentrations.
If you’re in ketosis, you’re doing the ketogenic diet right…
Most people don’t have a blood ketone body tester at home; or don’t want to go to the pharmacy to buy a urine ketone body test (which is less accurate and doesn’t follow the above reference values).
The most practical thing to do is to monitor what you eat and make sure you don’t eat any carbohydrates.
Keto and sports performance
The reason the ketogenic diet is such a hot topic is due to their being two extreme positions on the matter held by athletes and coaches.
- Either keto is the best, and everyone should use it.
- Or keto is the worst, and no one should use it.
It’s difficult to pretend there aren’t grey areas regarding the diet, and this polarises views.
Removing a nutrient from the diet is obviously going to position themselves either for or against it depending on the benefits and detriments they’ve heard about it.
The reality is that carbohydrates, whose consumption modulates hepatomuscular glycogen concentrations, are a determinant of sporting performance, especially in moderate to high intensity and medium duration sports and competitions.
Figure II. Changes in muscle glycogen concentrations over 6 days of training with insufficient replenishment until day 4 and replenishment in search of supercompensation over the final 2 days.
As Mata et al. (2019) note:
“When exercising at high intensities, CHO become the main energy substrate, and thus glycogen depletion is considered an important limiting factor of performance.”
They go on to note that if the objective is to maximise performance during a training session or competition, it’s advisable to provide an optimal amount of carbohydrates before and during exercise.
We’re talking about moderate/high intensity exercise, but… Is strength training included in that?
Let me summarise it quickly: until just a few years ago, we knew little or nothing; now, we know enough to draw preliminary conclusions in the absence of further research.
Strength sports and ketogenic diets, friends or enemies?
Strength training is intense, we can’t deny that.
We understand strength training as training with loads: powerlifting, bodybuilding and fitness, weightlifting and the less metabolic part of CrossFit.
And we know that intense strength training burns a lot of calories;
Up to 40kcal/min of work! (Reis et al., 2011).
They come mainly from intramuscular ATP, the phosphagen system and glycolysis (Tesch et al., 1986).
A standard weights session with 15 sets for one muscle group results in up to 40% depletion in the glycogen of the trained muscles.
All this indicates, a priori, that carbohydrates are an important nutrient in strength training, right?
This is what’s known as “keto-adaptation”: the ability to use fatty acids and ketones efficiently (when we’re naturally not prepared for it) during high-intensity exercise.
Figure III. Proposed mechanisms from which keto-adaptation can improve sports performance.
What do the studies show?
The thinking is clear: the ketogenic diet must decrease strength training performance by reducing the availability of glucose as an energy substrate.
However, McSwiney et al. (2019) conducted a well-analysed literature review, where they presented the following data:
The Ketogenic Diet did not reduce performance in…
- …athletes trained at intensities of 50-84%1RM, even in complex exercises such as CMJ or push-ups.
- …athletes trained at intensities >85%1RM (it even increased in one study).
- …olympic lifts.
- …CrossFit exercises (400m runs, maximum bending test, 1RM power clean…)
Although I say there’s “no decrease in performance”, the fact is that we always talk about statistically significant effects, and no statistically significant effect doesn’t mean there’s no difference.
As most of the determinants of the strength demonstrations are not controlled, we can’t to establish a conclusive cause-effect relationship between the ketogenic diet and the results.
But, there’s enough literature to be able to say that:
This is despite the fact that in general, the trend is lower than that produced by a standard Western diet.
Ketogenic diets and muscle mass gain
Glycogen is not only important as a store of energy, it’s a key mediator at the biomolecular level that also serves as a metabolic barometer (the hepatic), regulating energy balance and basal metabolic rate.
You heard that right!
But again, and as I’ve said many times… biomolecular models don’t always replicate in vivo.
And here we have the example again:
Paoli et al. (2019) conducted a review of the effects of the ketogenic diet where they observed that there is conflicting evidence in the available trials about the effects of this dietary model on muscle mass.
In general, the effects tend to be neutral.
Studies that report changes in the amount of muscle mass (whether positive or negative) do not give precise explanations of the mechanisms influencing the changes and/or have a high risk of bias, because they’ve not calculated the amount of calories consumed, haven’t monitored the workouts, the amount of protein in the diet…
They are low quality studies.
Figure IV. Table showing the effects on muscle mass of various research studies using ketogenic diets.
Even so, there are mechanisms through which the ketogenic diet can have an influence, especially by reducing certain aspects that negatively condition muscle mass (such as chronic low-grade inflammation, (per-)oxidation, increased expression of genes that inhibit muscle development, etc.).
Figure V. Proposed biomolecular mechanisms through which ketogenic diets influences muscle mass. A tick indicates that influences positively; a cross that it influences negatively.
The ketogenic diet has the potential (at least at the biomolecular level in animal models) to promote the retention of lean mass in:
- Sick people;
- Elderly people;
- Particular conditions such as stress, hypoxia, ultra-distance athletes…
Strength and Muscle Mass
I’m talking about muscle mass as it’s important to control it, because there’s a strong relationship between a person’s lean mass and their ability to generate strength.
It’s in the interest of a strength athlete to maintain a high protein intake, and diets that help promote muscle mass gain will help them perform better in their sporting discipline.
- Durkalec-Michalski, K., Nowaczyk, P. M., & Siedzik, K. (2019). Effect of a four-week ketogenic diet on exercise metabolism in CrossFit-trained athletes. Journal of the International Society of Sports Nutrition, 16(1), 16.
- Escobar, K. A., Vandusseldorp, T. A., & Kerksick, C. M. (2016). Carbohydrate intake and resistance-based exercise: Are current recommendations reflective of actual need? British Journal of Nutrition, 116(12), 2053–2065.
- Hearris, M. A., Hammond, K. M., Fell, J. M., & Morton, J. P. (2018). Regulation of muscle glycogen metabolism during exercise: Implications for endurance performance and training adaptations. Nutrients, 10(3).
- Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: Nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11(1), 20.
- Kephart, W., Pledge, C., Roberson, P., Mumford, P., Romero, M., Mobley, C., … Roberts, M. (2018). The Three-Month Effects of a Ketogenic Diet on Body Composition, Blood Parameters, and Performance Metrics in CrossFit Trainees: A Pilot Study. Sports, 6(1), 1.
- Mata, F., Valenzuela, P. L., Gimenez, J., Tur, C., Ferreria, D., Domínguez, R., … Sanz, J. M. M. (2019). Carbohydrate availability and physical performance: physiological overview and practical recommendations. Nutrients, 11(5).
- McCleary, S. A., Sharp, M. H., Lowery, R. P., Silva, J. E., Rauch, J. T., Ormes, J. A., … Wilson, J. M. (2014). Effects of a ketogenic diet on strength and power. Journal of the International Society of Sports Nutrition, 11(1), P41–P41.
- McSwiney, F. T., Doyle, L., Plews, D. J., & Zinn, C. (2019). Impact Of Ketogenic Diet On Athletes: Current Insights. Open Access Journal of Sports Medicine, Volume 10, 171–183.
- Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259.
- Paoli, A., Cancellara, P., Pompei, P., & Moro, T. (2019). Ketogenic diet and skeletal muscle hypertrophy: A Frenemy relationship? Journal of Human Kinetics, 68(1), 233–247.
- Pascoe, D. D., Costill, D. L., Fink, W. J., Robergs, R. A., & Zachwieja, J. J. (1993). Glycogen resynthesis in skeletal muscle following resistive exercise. Medicine and Science in Sports and Exercise, 25(3), 349–354.
- Pons, V., Riera, J., Capó, X., Martorell, M., Sureda, A., Tur, J. A., … Pons, A. (2018). Calorie restriction regime enhances physical performance of trained athletes. Journal of the International Society of Sports Nutrition, 15(1), 12.
- Reis, V. M., Júnior, R. S., Oliveira, D. R., & Zajac, A. (2011). Energy Cost of Resistance Exercises: An Uptade. Journal of Human Kinetics, 29A(Special Issue), 33–39.
- Sherrier, M., & Li, H. (2019). The impact of keto-adaptation on exercise performance and the role of metabolic-regulating cytokines. American Journal of Clinical Nutrition, 110(3), 562–573.
- Smiles, W. J., Hawley, J. A., & Camera, D. M. (2016). Effects of skeletal muscle energy availability on protein turnover responses to exercise. Journal of Experimental Biology, 219(2), 214–225.
- Tesch, P. A., Colliander, E. B., & Kaiser, P. (1986). Muscle metabolism during intense, heavy-resistance exercise. European Journal of Applied Physiology and Occupational Physiology, 55(4), 362–366.
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