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10 Things You Need to Know Before Running a Marathon on a Keto Diet

Michael Graw
A female long distance runner during a race.
Ketogenic diets have exploded in popularity in recent years, and it’s easy to see why. Research suggests that going keto can improve your energy levels, help you sleep better, and make it easier to lose weight.

However, keto diets are often looked down on by long-distance runners, coaches, and sports nutritionists. As a result, it’s hard to find reliable information about how to run long distances while doing keto.

Endurance running while eating ketogenic isn’t easy, but it can be very rewarding. Today, we’ll share 10 tips for running a marathon on a keto diet.

1. Full Ketosis Can Take Months

Getting into the rhythm of ketosis isn’t easy, especially if you’re new to this type of diet. In the beginning, you’re likely to feel tired and hungry. Forcing your body to make the switch to ketosis can take weeks or even months.

It’s important to factor in that transition period ahead of time. Many runners try moving onto a keto diet during the off-season when running intensity and volume are lower than average. That way, experiencing some low-energy days won’t have a big impact on training.

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2. Take in Electrolytes

One common mistake that runners new to keto dieting make is to forget about electrolytes. Carbohydrate-rich foods are often sodium-rich as well, so you need to find another way to get salt into your body after cutting your carb intake.

There are several easy ways to get more electrolytes throughout the day and especially during long runs. For example, you can take salt pills, which are packed with the electrolytes needed for athletic performance. Alternatively, you can make your own salty drink mix by dissolving a bouillon cube in hot water.

3. Make Your Own Snacks

Another helpful thing you can do is to make your own snacks for running. Most gels, bars, and chews designed for runners are packed with simple sugars, which can throw you out of ketosis. You can find some ready-to-eat snacks that are keto, but even these have more carbs than you might expect.

Some good keto snack options for running include frozen peanut butter balls, dark chocolate, and cheese sticks. All of these will keep relatively well and are easy to carry during long runs. Just don’t forget to bring these same snacks with you on your marathon—aid stations are more likely to offer carb-filled gels than cheese sticks!

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4. Drink Protein Shakes

Recovering quickly after each run is critical when you’re training for a marathon on a keto diet. One of the best things you can do to fuel your recovery is to eat protein. This enables your body to rebuild muscle fibers that break down when you run.

A fast and easy way to get enough protein after every run is to make your own protein shakes. Whey and soy protein powder is typically carb-free and can be mixed with keto-friendly almond or coconut milk for a tasty drink. It’s also a good idea to add electrolytes to your shake or take a salt pill along with it, so your body’s salt balance recovers after your run as well.

5. Stick to the Same Foods

Eating keto can be tricky for the simple reason that it takes a lot of time. It’s hard to find ready-to-eat keto meals and snacks at the store, so you need to make a lot of your own food from scratch. At the same time, training for a marathon can take 10 or more hours a week. For many athletes, running long distances while eating a keto diet feels like a full-time job.

One of the simplest ways to save time every day is to stick to just a few foods that work for you. Keep them around the house so that they’re easy to take with you to work or on runs as grab-and-go snacks. The more consistent you can be in what you eat, the less likely you are to fall out of ketosis or miss a run because you’re hungry.

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6. Eat a Big Breakfast

Breakfast is one of the most important meals of the day when you’re training for a marathon on a keto diet. For most runners, the bigger that breakfast can be, the better. Your body will burn the fat and protein from this meal for the rest of the day, helping keep your energy levels high.

If you plan to run in the morning, it’s a good idea to eat breakfast beforehand if you can. Some runners get cramps from running on a full stomach, which makes this much less appealing. If that happens to you, try bringing a few calorie-dense snacks like peanut butter balls along on your run, and then eat a big breakfast afterward.

7. Low-energy Days Happen

Even if you’re perfect about sticking to your fueling and recovery routine, low-energy days still happen once in a while. This isn’t unique to those on a keto diet—almost every marathon runner faces fatigue during training. However, those low-energy days can hit harder and more unexpectedly when your body is in ketosis.

It’s important to take these days in your stride and focus on the bigger picture of your training. Adjust your workout to make it easier, or consider going for a walk instead of trying to run. Pushing through tired legs is an important part of marathon training, but forcing yourself to run when your whole body feels exhausted will only make it harder to stick to your training for the rest of the week.

8. Use Interval Training Sparingly

One of the downsides to running on a keto diet is that without quick-burning carbs, your body simply can’t kick into high gear on demand. As a result, interval training can be much more difficult on a keto diet than on a carb-rich diet.

Interval training is still an important part of preparing for a marathon on a keto diet. However, interval runs should be few and far between—no more than once a week at the maximum. Plan ahead for harder interval workouts by running easy and short the day before.

9. Small Amounts of Carbs are Okay

Even when you’re on a keto diet, you can still eat small amounts of carbs. Use that to your advantage by planning your carb intake around your runs.

For example, if you have an interval workout planned, try eating a bar or mixing some sugar into your drink to give you a boost of energy. You can also try taking a sugar-rich gel with you on long runs to get a jolt of energy midway through your workout. Occasionally eating carbs during runs will also help prepare you for race day, when you’ll probably want to have a bit more sugar than usual to boost your performance.

10. Don’t Expect to Set a PR for Speed

In fairness to coaches and nutrition experts, there’s a reason they’re not big on keto diets for marathon runners: eating keto can negatively impact your performance.

Simply put, carbs are better than fats when it comes to fueling your body for long-distance sports. Carbs are easier for your body to burn on-demand, so you can easily crank your running intensity up and down. When you’re eating a keto diet, running slow and steady might feel fine, but you’re likely to start feeling shaky if you try to run fast.

This might not be a problem as long as you set your expectations appropriately. Don’t plan to run your fastest-ever marathon on a keto diet. Instead, take your time and reap the other potential benefits that ketosis can offer your body, such as increased stamina.


Running a marathon on a keto diet can be tough but rewarding. Training your body to burn fat for fuel makes it easier to run long and steady while also improving your energy levels throughout the day. Just be sure to leave plenty of time to adapt to a keto diet before your race since it can take several weeks or months for your body to reach full ketosis.

If you're interested in trying out a keto diet for your next training cycle you might also consider using a keto meal delivery service to eliminate the hassle of having to plan and cook your own meals.

Michael Graw
Michael Graw is a freelance writer specializing in finance, business, and tech who writes for Top10.com. His work has appeared in numerous well-known online and print publications, including Techradar, BestMoney, Business2Community, Day Trade Reviews, Pacific Standard, Fortune, Business Insider, and more.

*The information on this site is based on research, but should not be treated as medical advice. Before beginning any new diet plan, we recommend consulting with a physician or other professional healthcare provider. Results may vary based on various health factors, individual weight loss plans and adherence to the meal plan.