Take Your Training to the Next Level with Ketosis

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One of the most popular critiques of a ketogenic diet – a diet that’s high in fat and low in carbs – is that it isn’t good for athletes. The argument is usually that you need carbs to produce glycogen, a stored form of sugar that fuels your muscles. As a result, most doctors and trainers suggest high-carb diets for athletes.

If you’ve been working out while eating Bulletproof, Paleo, keto, or any other variation on a high-fat, low-carb diet, here’s some good news: brand new research shows that you not only don’t need carbs for athletic performance, you can actually gain an advantage if you cut them out. Let’s talk about how ketosis can kick your athletic performance into a higher gear.


Why you don’t need carbs to train hard

A groundbreaking new study out of UConn found that low-carb endurance athletes perform just as well as high-carb endurance athletes, if not better. The results challenge nearly 50 years of research saying the opposite.

Until now, most studies have concluded that you top out at around 10% of energy recruited from fat [1] and for the rest you rely mostly on glycogen, a form of sugar stored in your muscles and liver.  That’s the main reason high-carb diets have been the standard for athletes for so many years. With a low-carb diet, your glycogen stores empty quickly, you run out of fuel, and you start breaking down your muscles for energy. Right?

Well, maybe not. If you teach your body to prefer fat for fuel you can work out intensely without any problems, according to this new study.

The paper’s authors measured the performance of ultra-endurance runners who regularly run upwards of 100 miles. Here’s how they set it up:

  • Half of the participants ate low-carb (<20% of calories from carbs) for 6 months
  • The other half ate high-carb (>55% of calories from carbs) for 6 months
  • On test day, athletes ran for 3 hours. The researchers measured the runners’ energy expenditure and gathered blood, muscle tissue, saliva, and a variety of other samples. They then pieced everything together to better understand what each group was burning for fuel, and how hard they had to work

The results were impressive. The ketogenic runners showed, to quote the authors, “extraordinarily high rates of fat oxidation.” [2]

In other words, the low-carb athletes were fat-burning machines. They recruited tremendous amounts of energy from fat during the 3-hour run and showed no more fatigue than the high-carb runners did. What’s even more fascinating is that both groups had the same muscle glycogen levels during and after exercise, and they weren’t breaking down their muscles to do it.

The takeaway is that a ketogenic diet can help you:

  • Massively increase the fat you burn
  • Preserve muscle tissue
  • Keep exercising like a boss without metabolic downsides, even at an elite level. In fact, the study’s lead author said that several of the high-carb ultra-marathoners in the study switched over to a low-carb diet after seeing how well the ketogenic participants performed.


Other benefits to low-carb training

Training on a high-fat, low-carb (HFLC) diet can give you several other advantages.

  • Fat and cholesterol support your testosterone levels, which leads you to burn more fat. Carbs – especially simple carbs – cause your testosterone to drop [3], making you store more fat.
  • Your energy stores are deeper if you’re running on fat. The average person can only hold about 500 grams of glycogen at a time, but as we all know too well, fat stores are more or less bottomless.
  • You hold less water weight on a low-carb diet. Without that bloating you’ll be faster and lighter on your feet, which can make all the difference in the world if you’re a competitive athlete. You’ll also look leaner. That’s what’s really important.


How you can mix ketosis and exercise

If you want to burn more fat without sacrificing muscle or athletic performance, try the following:

  • Eat a high-fat, low-carb diet like the Bulletproof Diet.
  • Get 5-20% of your calories from carbs each day. The study’s participants ate 20% carbs, but they were running for hours on a regular basis. If you don’t fit that bill you may want to try fewer carbs and more fat so you stay in ketosis. You can also try skipping carb refeed days to get into deeper ketosis. Experiment and find a level that works for you.
  • Eat fat before exercising so your muscles have quick access to fuel. Bulletproof Coffee is a great pre-workout supplement.
  • Get your carbs from non-starchy, nutrient-dense veggies like broccoli, bok choy, fennel, and kale.


What about lifting weights?

You can build muscle on a high-fat, low-carb diet too. A not-yet-published study presented at the 2016 National Metabolic Therapeutics Conference found that people on a ketogenic diet and a lifting program put on lean mass without issue.

However, the same study found that people on a cyclical ketogenic diet (5 days of low-carb, then 2 higher-carb days) put on less muscle and were only in deep ketosis a couple days each week. Bulletproof recommends one carb refeed day each week with a maximum of around 150g of carbs, so you may not run into the same issue, but if you find you’re not putting on enough lean muscle you can try skipping the higher-carb day. Stay tuned for a more in-depth breakdown of the ketogenic weight-lifting study; it’s due to publish soon.

Upping your fat intake and limiting carbs is a powerful way to improve your performance, both in and out of the gym. It’s easy to get caught up in ratios and percentages when you’re eating low-carb. Remember that we all have different genetic backgrounds, and you very well may find that cyclical ketosis works better for you than being in ketosis all the time does. Focus on how you feel and play around with the fat-to-carb ratio until you find something that works for you. And remember to subscribe below if you want more cutting-edge info about how to upgrade your biology. Thanks for reading!

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By Bulletproof Staff

  • Wesley Hurrell

    While this study was certainly groundbreaking in terms of defining the upper limits of fat oxidation in well adapted ketogenic ultraendurance athletes, it’s important to highlight that it did NOT included any performance measures. As such, it does not answer the question as to whether a ketogenic diet will help you will a marathon or ultraendurance run vs the conventional high carb diet. A ketogenic diet makes good sense for lower intensity sports like ultraendurance running or ironman triathlon, but we still need more evidence for its superior performance effects when it comes to event lasting around 2 hours or less. Events such as marathon, olympic distance triathlon, 10km track event, 1500m swimming etc. Many of the athletes winning medals at the Olympics in these events are not ketogenic, because when your performing at VO2max and above, there’s little evidence to say that fat oxidation can support this kind of intensity. You still have to have healthy carb/glycogen stores and be a good carb burner.

    • Luc Henri

      Exactly! and what about all the power athlete sports? Like sprints, weightlifting, basketball, etc?

      • LeBron James is a LCHF power forward basketball player. Surely shows his intensity when he dunks.

        • Luc Henri

          He was on a paleo diet in the off season but there’s been no reports of him doing it in season

    • Jared

      You should look into Ben Greenfield. He’s a professional endurance athlete who also does weightlifting, and follows a ketogenic diet almost identical to Bulletproof. His book “Beyond Training” goes into all these things that you are asking about.

  • Luc Henri

    First off let me say that I am regularly in ketosis but have noticed that I perform better quantitatively and qualitatively during my high intensity workouts when I’ve had either protein or carbs pre-workout as opposed to majority fat.

    So what about the efficacy of high intensity exercise which is advocated in the Bulletproof Diet Book? Muscle glycogen is needed for this type of exercise, and 3 hour runs are not high intensity. It’s well established that fat oxidation is the primary energy source at this intensity level.

    Further Dave ROUTINELY mentions that the first marathoner DIED so what is the purpose of showing a study that looks at ultra distance running as exercise and not high intensity exercise, which I previously mentioned he advocates.

    This study shows that ketosis is great for running long distances but that’s all it’s saying.

    • Wesley Hurrell

      Well said Luc.

  • Kevin

    Guys, he said to wait for the study that examined weight lifting. Jesus.

  • Ray Willy

    My anecdotal experience. I’ve been a ice hockey player for the last 40 years. It’s high intensity sprints for 2 mins followed by approx. 2 mins of rest. Repeat the cycle for 60 minutes. The first time I played a game after being low carb/high fat for only 3 days it went okay. Endurance was there, but sprints were a bit weaker than usual. However, the next time I played I had been low carb/high fat/intermittent bulletproof fasting for 10 days and the results were much better. Sprints were back to normal and overall endurance was improved. I’ve been playing this way now for the last 8 months and I won’t go back to pre-game carb loading again! (My pre-game meal is a couple tbsp brain octane blended with collagen protein 3 hours before.)

    So what’s my point? It’s not just for endurance exercises. The article above implies that you need to be at least partially keto adapted in order to benefit. My experience speaks to that reality. If you’re a carb burner and you try this on a whim, the benefits probably won’t be there. Your experience however, will undoubtedly be unique to you.

    Some people seem to be reading the article with the interpretation that the study will imply “carbs always bad, fat always good for everyone in all situations!” The usefulness of a study like this is to demonstrate that there is more than 1 path to optimum results. Regardless of the type of exercise, some people will do well as carb burners, some will do well as fat burners, and many more will do their best finding some middle ground that works best for them.

  • Pete Gawtry

    I’m a Personal Trainer and Natural Bodybuilder. I have used ketosis for both putting on muscle and for losing weight [shredding]. I personally have more energy with it, but it’s not explosive! or out of the gates energy.
    Resistance training I have found that my energy levels don’t drop, the only thing that makes me stop is not being able lift my arms or legs anymore. It also perfect for low intensity cardio, like jogging to burn calories.
    Ketosis has helped me more than any other diet has or ever did.
    Just lately, I had to jump out of keto to carb up for a competition. I love it and seemed to be back immediately craving/loving carbs again. Just shows you how addicted we are to them.
    Good to be back in ketosis again and having more focus and energy.

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  • GMan

    Distance or endurance type of athletics require some level of ketotic state primarily because the average person cannot physically store enough glycogen to complete and event on the magnitude of a marathon or greater. Many marathon diet and running regimens reflect this. Taking a GU or whatever other simple sugar during an event is done essentially to bridge gap between glycogen stores being burned off too quickly and the amount of energy a runner is able to generate from burning fat. If you burn out your glycogen stores, you’re done… and it doesn’t matter who you are. It’s all about conserving glycogen stores. That’s why “the long run” is one of the most important training events in a long distance runner’s repertoire because it theoretically “trains” the body to switch to burning fat for energy quicker when it is subjected to sustained aerobic exertion levels. I think it should actually be called “The Depletion Run” because the idea is to slowly empty the glycogen tanks, which sensitizes the body to switch to fat burning faster. The extended effect is the body adjusts by increasing glycogen stores in the future… so long as you keep doing depletion, err long runs or something of similar effect. The proportion energy used for the activity will slowly shift more towards burning fat. The amount of time it takes to switch to fat burning is related to how well the runner has trained, accumulation of miles (base), and more than likely some genetic components. The amount of fat a person actually burns on something like a marathon is actually less than conventional wisdom might imply. Fat contains A LOT of stored energy and it takes a lot of ‘miles’ to use them up. So the real answer is, avoid getting fat and if you do get fat, get on a good diet and ‘run’… a lot.

    • Carlos

      Thank you.