Ketogenic Diet for Endurance Athletes: The Ultimate Guide
keto for endurance athletes

The Keto Diet for Endurance Sports – The Ultimate Guide

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The conventional wisdom has us believe that you need carbs to keep you going if you’re into endurance sports, especially during longer events, lasting for more than 2-3 hours.

Is this true, though? Do you really need carbs in order to perform well in endurance disciplines, such as marathon running, hiking, trekking, long distance cycling, triathlon, and other endurance sports?

Or can keto diet be an advantageous dietary strategy for people interested in endurance sports, beginners and advanced athletes alike?

If so, what are the results you could expect? How much time will it take you until you reach optimal performance while on keto, and what are the strategies you could adapt to make the process easier?

For the answers to all of these questions, read on.

Can Keto and Endurance Sports be Combined?

In short, yes, keto and endurance sports can be successfully combined. If you’re interested in improving your endurance, especially without needing to refuel every 2-3 hours, keto is an excellent dietary choice to consider.

The widely accepted knowledge paradigm says that during periods of intense exhaustion, you need carbs to refuel, and you need a constant supply of them.

This is why during long endurance events, most people will consume fast-digesting carbs, such as sugary sports drinks, energy bars, gels, and the like, and usually, that’s done at regular intervals.

Your muscles and liver can store up to about 1600-2000 calories in the form of glycogen, and once you use them up, you’d need to refuel, or you risk “bonking”, also known as hitting the wall – a state in which you experience a rapid loss of energy and fatigue, sometimes to the point of being unable to continue even at a slow pace.

If you aren’t restricting carbs, you need to preemptively refill glycogen stores as you go, in order to avoid bonking.

However, if you switch to keto and pull through the adaptation phase, your primary fuel will become fat, and you’ll no longer be dependent on constantly refueling during training or a sports event.

Your body has an enormous amount of energy stored in the form of body fat, and it is readily available to be used as needed. The fat that you’re carrying has thousands and thousands of calories, even if you’re very lean, and this means that it’s a quick and easy resource you can easily tap into during a strenuous event.

The debate around keto and endurance sports is heated. After all, the transition to keto is not necessarily an easy one, and if you’re a very active person, the drop in performance you’ll see might be discouraging.

Additionally, for highly experienced athletes, the advantages of keto might not be so obvious or clear, as their performance is already highly optimized. For them, chasing the last 1 or 2% to peak performance is essential, and the answer might be elsewhere.

Nevertheless, for most people who are interested in pushing their limits with endurance sports (without necessarily doing sports on a professional level), keto can provide them with a number of benefits. More on that in a bit.

Fat Adaptation and Endurance

If you’re already doing endurance sports and want to give keto a try, that’s an excellent choice and will likely help you a lot in the future.

You should keep in mind that your performance will likely take a hit during the adaptation phase. That’s completely normal and is only temporary.

It might take you anywhere from 1 to 6 weeks to get back to your performance level from before keto, so if you have any events scheduled in the near future, you need to account for that. If your next endurance event is less than a month away, we recommend sticking to your usual diet before that and going keto after that.

What To Expect During The Adaptation Phase:

  • Performance will temporarily worsen: most people experience a decrease in performance (both in strength and endurance) as they transition to keto. That’s because your body needs time to adjust to burning fat for fuel instead of carbs, which is a significant metabolic change.
  • More time might be needed for recovery: in the first few weeks, you might feel more tired after training and might need more time for recovery. Again, that’s normal – just be patient with yourself.
  • Your pace will likely be slower: because of the decrease in performance, you’ll probably not be able to keep the same pace as before for the same amounts of time as before. This will improve within a few training sessions.
  • You might experience the keto flu: in the first couple of days, you might feel exceptionally tired, have cramps or headaches, or generally feel weak, irritable and unmotivated. Let it be – it’ll soon be over (don’t worry, this phase only takes a couple of days and not weeks).

All of these symptoms will improve once you become fully fat adapted, so you just need to be patient and trust the process. In order to help your body adjust, you should pay special attention to electrolytes and to hydration.

Reasons Why Keto And Endurance Sports Can Be An Excellent Combination

Now that we’ve covered the side effects that you might experience from going keto, let’s see what the specific advantages are. And they are plenty!

#1. Bonking is No Longer an Issue

Now that you’re not relying on your glycogen stores, but on your fat stores instead, the amount of energy you have available is suddenly much, much bigger. You don’t have to fear “hitting the wall” anymore – there is no wall.

Well, obviously your body still has its physical limits, and there aren’t any magical shortcuts to overcoming these, except for training hard and staying focused. However, as you know, bonking can be extremely unpleasant and detrimental to your success, and on keto it will no longer be an issue.

#2. You don’t need to eat so often during sports events (if at all)

Because of the fact that you no longer need to fear bonking, you won’t need to eat any sugary energy bars, gels and the like (and let’s face it – the fact that they might be necessary under some circumstances doesn’t make them any more healthy or okay to eat).

This also means the following:

#3. An endurance event on keto is much easier in terms of gastric distress

Because of the fact that you won’t need to eat so often during an episode of highly strenuous activity, you will be saving your stomach and GI tract much trouble. Gastric distress is one of the problems many marathon runners experience, together with other endurance athletes, and might significantly hinder performance.  

#4. Weight loss will help you optimize performance and make you faster

Let’s face it – losing a kilogram or two can make a drastic difference in your performance, both in terms of speed and endurance. After all, if your body is lighter, it will be easier for you to move it through space.

The keto diet is one of the best ones out there for weight loss, and will help you regulate your appetite in a natural way. Diet adherence and sticking to your daily calorie limit is usually much easier with keto, so unless you’re already very lean (or trying to gain weight), losing some weight might be very advantageous.

#5. Your energy levels will improve

Many people report having more energy on keto, which is a direct result from having their blood sugar levels stabilize.

While this might not necessarily translate into huge differences in your performance straight away, the increased energy will help you stay focused on your training and will give you the additional motivational boost we all sometimes need.

On top of all those, your general health might also improve significantly, depending on what your previous diet was like. Chances are, if you are fuelling yourself with energy bars and gels each time you are training, even if you’re very lean and fit, you could definitely benefit from stabilizing your blood sugar levels.

How to Achieve Optimal Results with Keto & Endurance Sports

  • Do Not Make Drastic Changes Before An Important Event

If you’re an experienced athlete and are preparing for an event, do not make any drastic changes in your diet or training prior to it. Do not experiment with any new strategies if you’re a few weeks away from it. If you want to go keto, it’s much better to do it afterwards, rather than rush into it and see your performance plummet.

The same would apply if you are doing keto and want to reintroduce more carbs, or do a carb-up – don’t do it if you don’t have the necessary prior experience and are 100% sure you know how your body will react. That’s particularly important for the day of the event – don’t do anything new then – stick to your usual routine instead.

If you’re not preparing for any specific events in the near future, but just want to optimize your performance and eventually lose some weight, then keto is a great option – feel free to begin with your new diet straight away.

  • Lower Your Carbs At Once To Help Your Body Adapt Quicker

There’s no need to slowly lower carbs – you can limit them to 20-25 g per day at once. Your performance might suffer in the beginning, but again, that’s only temporary.

Although some people prefer easing their way into keto (and for some it might even be a better option, for example, if you have had your gallbladder removed), we actually advice going all in and doing it at once.

The first few days might be rough, but by forcing your body to quickly adapt you won’t be stuck in the low-carb limbo of constantly switching between being in ketosis and being kicked out of it. If you’re fairly active on a day-to-day basis, you’ll deplete your glycogen stores in a day or two, after which the adaptation process will begin.

  • Electrolytes Are Essential

If you’re interested in endurance sports, chances are that you’re already well-aware of the importance of electrolytes.

On keto, they’re even more important, because your body will not be retaining as much water and therefore will be flushing out electrolytes, too – so you need to make sure that you’re replenishing them.

That’s even more important if you’re very active and sweating a lot – ever wondered why sweat is salty? It’s because of the electrolytes you’re losing with it (including sodium and potassium). So keep these in check to optimize performance and help your body adapt.

Check out our article on electrolytes, but keep in mind that for active individuals the requirements for sodium might be higher, depending on how hard and how often you’re training.

For beginners, you can try this Perfect Keto’s Electrolytes that has everything you need on a keto diet.

perfect keto electrolytes

If you experience any side effects pointing towards an electrolyte imbalance, such as cramps, headaches, insomnia, and fatigue, try upping your sodium intake.

During an event, make sure to carry your electrolytes with you and to take enough of them throughout the whole duration of it. Think of it as if you were refuelling with carbs.

You need to take them before you experience any side effects, in the same way that you’d be ingesting carbs to prevent bonking, if you weren’t fat adapted. To make it easier, you can just put sodium in your drinking water and make sure your potassium and magnesium are on point that day.

  • Once You Gain Enough Experience With Keto, You Can Experiment With Your Carb Limit

The carb limit for keto that you most often will see quoted, 20 to 25 g net carbs per day, is a safety net, which is to ensure that anyone would be in ketosis if they stick to it.

Nevertheless, if your routine includes heavy endurance training, your carb limit might be higher than that, for example double or, in some cases, triple that amount.

Once you get enough experience with keto (meaning, at least 6 to 8 weeks), you might want to experiment with that and spread your carbs strategically throughout the day, by timing them before or during exercise.

This might give you a boost in energy and endurance, so if you’re an experienced athlete it might be a strategy worth considering. It shouldn’t be an excuse to gorge on carb treats, though. Use food as fuel, not as entertainment.

  • Eat Your Protein

You need protein to sustain yourself, and that’s valid for absolutely everyone.

If you’re very active, your daily protein requirement on keto might be much higher than those of sedentary people, even if you’re not doing any strength training (but really – you should consider adding some sort of strength training to your routine, even if you’re primarily interested in endurance sports, even if it’s just for the sake of preserving your lean body mass).

This translates into eating 0.8 to 1 g of protein per pound of lean body mass (or 2 – 2.5 g per kilogram of LBM), and you can even go as high as 1.2 g per pound of LBM.

Make sure your daily meal plan meets your protein goal. Don’t worry, excess protein doesn’t turn into sugar (a common misconception in the keto community). Instead, it’ll help you with recovery, and consequently will allow you to optimize your output. Which leads us to the next point:  

  • Remember To Give Your Body Enough Fuel To Function And Enough Time To Recover

Going keto means limiting your carbs, consuming adequate protein, and consuming enough fat to sustain yourself. Even though you might notice a significant decrease in hunger and appetite on keto, you should still remember to fuel your body properly.

The energy that you used to consume with carbs still needs to come from somewhere, which will most likely be from fat – after making sure your protein macro is on point.

The more active you are, the more energy you need to sustain yourself – the same thing is valid for keto (or for any other diet, for that matter).

Keep in mind that all online calculators will provide you with an estimation, and there’s no way for them to be 100% precise – in order to find out what your actual caloric needs are, you need to track your food meticulously and observe your body and any weight fluctuations.

In addition to that, with heavy training you also need to make sure that you’re giving your body enough time to recover. While most people are not actually in danger of overtraining, pushing yourself too hard might still hinder your performance. That’s not specific to keto, but once you go keto your body might need a bit more time to recover during the adaptation phase.

  • Fasting Vs. Eating During Heavy, Prolonged Training And/or Sports Events – Which Strategy Is Better?

Some people who have gone keto report feeling best if they fast for the whole duration of a given event (especially for shorter ones, 2-3 hours or less), while others prefer to carry around a keto-friendly snack, such as nuts, nut butters, MCT oil, beef jerky, and fat bombs, and consume them if necessary.

Some athletes also supplement with exogenous ketones for their energy needs.

That’s a matter of personal preference, and there isn’t a universal rule. Experiment with both approaches and see what works better.

For longer training sessions (upwards of 4 hours), it’s a good idea to have a snack at hand – even if you end up not needing it, it might help you pull through a difficult moment.

If you have always done one thing and feel good with it, do not change that during an important event – instead, stick with what your body is used to.

Regardless of the specific strategy you choose, make sure you’re supplementing with enough electrolytes.

Our conclusion

Keto and endurance sports, such as marathon and ultramarathon running, long-distance cycling, triathlons, hiking, trekking and the like, can make an excellent combination, if you give your body enough time to adjust.

Your performance might take a hit during the transition period; nevertheless, the advantages of using fat for fuel instead of carbs during endurance events are plenty.

You’ll no longer be relying on glucose to fuel you, but will be tapping into your body fat resources instead, which also means that you could go for much longer without needing to refuel (and therefore without experiencing any gastric distress) – as a result, your endurance will improve in the long run.

Finally, it’s advised that you cook your own meals instead of buying premade meals. There are many keto meal delivery services out there but chances are the meals won’t help you meet your personal macros goals.

Cooking your own foods from scratch allows you to take 100% control of what you eat and the portion size to better optimize your performance as an athlete. We also have a keto food list on our website that you can use.

Is keto suitable for every person out there who is into endurance sports? Probably not, as some highly active people might still feel and perform better on a moderate to high amount of carbs – we don’t believe in the “one size fits all” approach. We do believe, however, that keto can provide you with a number of definite advantages, and that if you give yourself enough time to adjust, you could further optimize your performance in terms of both strength and endurance.

Up Next: The Ultimate Guide to Keto for Bodybuilding and Weightlifting

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