Can Keto and Cardio Mix?

We get lots of questions about how a ketogenic diet works in the context of exercise: Is it possible to maintain one’s fitness (strength, endurance, performance) and also drop one’s carb intake to ketogenic levels? Is it advisable? Will it help me lose weight faster?

Mark already addressed some of these topics, but it’s clear that many people still feel uncertain about how to pair a keto diet with their current workout routine.

Rather than write a single behemoth post, I’m going to tackle this in two parts. For today, let me talk keto and cardio, specifically how keto works for the average fitness enthusiast who thinks more in terms of general exercise. In a couple weeks I’ll follow up with a post on keto for runners and other endurance types who tend to focus on training programs and racing.

So, keto and cardio… This is for people who like to attend group fitness classes, or go out for jogs or spins on the bike, or do a mix of low heart rate exercise with occasional bouts of HIIT. (This is a problem with the term “cardio”—it can mean so many things.)

You probably already know Mark’s stance on cardio: avoid chronic cardio exercise patterns. The Primal Blueprint approach to exercise comprises lots of everyday movement, lifting heavy things, and occasionally going all out. If you simply must do cardio, most of these sessions should be conducted at an aerobic heart rate not higher than 180-age, as detailed in the Primal Endurance book. So, with the caveat that cardio exercise in the traditional sense of slogging away on an elliptical machine or treadmill doesn’t jibe with the Primal Blueprint approach, let’s get to some frequently asked questions.

Will My Workouts Suffer When I Go Keto?

This is a common concern because some people do report that they feel sluggish when they first go keto. And yes, you might feel like your performance in the gym (cardio, strength, HIIT—all of it) takes a hit in the first few weeks of keto. Rest assured that this is a temporary dip as your body becomes efficient at using fat and ketones for energy in the absence of incoming carbs (glucose). It’s a learning process for your body, so to speak.

The more glycolytic your workouts, the more you are going to notice this. Prolonged, difficult workouts that fall into the category of chronic cardio or “black hole” sessions are especially likely to suffer.

To help mitigate temporary performance decrements during the transition to keto:

  • Dial back the intensity and/or frequency of your workouts for a few weeks. Trade some of your more intense cardio (and strength) sessions for walks, yoga or Pilates, or other gentle forms of movement.
  • Mind your electrolytes. If you are feeling weak or lightheaded, if you get a headache, or you just feel “off,” this is likely due to electrolyte imbalance. Try adding ¼ – ½ teaspoon of salt to a glass of water with lemon juice and see if that helps. You want to make sure you are getting 4.5 grams of sodium, 300-400 mg of magnesium, and 1-2 grams of potassium each day on top of your normal food.
  • While your body is making the switch, give it plenty of fuel. Consume extra fat and eat plenty of calories. If fat loss is a goal, you can adjust your macros and calories as needed once you are feeling in the groove with keto.
  • Tough it out. Don’t cave and add carbs in the first few weeks (see the next point). Know that this is temporary, and you should be back to normal within three to six weeks.

Do I Need To Add Back Carbs To Fuel My Workouts?

During the first few weeks of starting keto, you should not add back carbs. It is important to create a low-glucose, low-insulin environment to promote ketogenesis and the adaptations that accompany a ketogenic state. If your workouts are too hard right now, the correct answer is to change your workouts, not to increase your carbs.

After you have done a dedicated period of a minimum three weeks of strict keto—six or more is even better—you should be feeling better during your workouts if you are not engaging in prolonged, chronic cardio activities. (It might take longer to adapt to longer endurance training, as we will discuss in the next installment.) At this point you have some options:

One, you can continue in strict ketosis (less than 50 grams of carb per day) as long as you are feeling good.

Two, you can start experimenting with eating carbs strategically before your workouts. This is known as a targeted keto approach. There are various ways of implementing this, but the basic formula is that you would ingest 25-30 grams of glucose or dextrose (not fructose) about half an hour before high-intensity workouts to replenish muscle glycogen.

There are a few caveats here. First, most sources of glucose/dextrose are not Primal (think hard candy, gels). Probably the closest is pure maple syrup, but that also delivers a hit of fructose. If you are a Primal purist, you will have to decide if this is a compromise you want to make. Second, people tend to overestimate the degree to which they are actually low on glycogen and how much it matters. It is a common misconception that once you go keto you have “no glycogen.” While muscle glycogen stores are reduced, your tanks are probably still at least 50% full, and perhaps on par with non-ketogenic folks if you have been keto for a long time. Furthermore, the average low-to-medium intensity cardio session isn’t truly depleting glycogen. Remember, the point of becoming fat- and keto-adapted is that you burn predominantly fat and ketones at these lower intensities, sparing glycogen. You have to go hard and/or long to really burn through your muscle glycogen stores. Thus, you should target pre-workout carbs only before truly high-intensity sessions.

Instead of adding simple carbs before workouts, another option if you feel like you need more carbs is to add back nutrient-dense carbs after workouts, when insulin sensitivity is increased. This might make sense if you feel like your ability to recover between workouts is lagging, or you want to recover quickly because you have back-to-back hard sessions planned. In either case—adding carbs before or after exercise—the amount you add should be proportional to the difficulty (intensity) of the workout. You don’t need to carb up for your yin yoga class, for example.

Lastly, if you are feeling underpowered during exercise, instead of adding back carbs you can experiment with adding more protein and/or fat. Some people report good success with “protein ups” timed around heavier workout days.

Will Adding Keto to My Cardio Routine Help Me Lose Weight?

Maybe. It’s a common refrain that “abs are built in the kitchen,” meaning that your food plays a bigger role in fat loss than does your exercise. This isn’t to say exercise is unimportant; it does matter. A caloric deficit is necessary to lose body fat, and exercise is one way to create a caloric deficit. However, this can also backfire if your exercise routine leaves you hungrier, so you unintentionally overeat calories due to increased hunger and cravings. Ketones have known appetite suppressing effects, so a ketogenic diet might help counteract any increased hunger that comes with exercise.  

That said, I think the root of this question is the fact that ketosis is a fat-burning state, and so the logic goes that if you are metabolizing fat for energy, you will automatically shrink your body fat stores. Moreover, if you add keto and cardio together, especially if you are exercising in the so-called “fat-burning zone,” you will lose more fat than either alone. Right? Not necessarily. The fat you burn can come from your adipose tissue or from your plate. If you are eating an excess of fat calories relative to your daily caloric needs, you still won’t lose body fat.

We know that for body recomposition, the best bang for your buck comes from a combo of resistance training and HIIT. Cardio exercise still has many benefits for physical and mental health, and of course a lot of people simply enjoy their cardio; but you shouldn’t be putting all your eggs in the cardio basket if fat loss is your goal. All else being equal, though, it certainly can’t hurt to upregulate your body’s ability to use fat for energy.

Summary Recommendations:

  • When first starting out with keto, follow the recommendations laid out in The Keto Reset Diet, and be strict for at least three weeks.
  • If you are struggling in your cardio workouts during this period, don’t add back carbs! Dial back your workouts, add calories (via fat or protein), or both.
  • Once you believe you are keto-adapted, then you can start to experiment with targeted carbs and/or carb ups if you so choose.
  • No matter your diet, avoid chronic cardio exercise patterns that increase stress and your body’s demand for glucose.
  • Check out this post for additional tips for exercising while keto.

Thanks, everyone. Questions, comments? Share them below, and have a good week.


Koeslag T, Noakes T, Sloan A. Post-exercise ketosis. J Physiol 1980;301;79-90.

Malhotra A, Noakes T, Phinney S. It is time to bust the myth of physical inactivity and obesity: you cannot outrun a bad diet. Br J Sports Med 2015;49:967-968.

Matoulek M, Svobodova S, Vetrovska R, Stranska Z, Svacina S. Post-exercise changes of beta hydroxybutyrate as a predictor of weight changes. Physiol Res. 2014;63 Suppl 2:S321-5.

Newman JC, Verdin E. ?-hydroxybutyrate: much more than a metabolite. Diabetes Res Clin Pract. 2014;106(2):173-81.

Sleiman SF, Henry J, Al-Haddad R, et al. Exercise promotes the expression of brain derived neurotrophic factor (BDNF) through the action of the ketone body ?-hydroxybutyrate. Elife. 2016;5:e15092.

TAGS:  Keto, keto-popular

About the Author

Lindsay Taylor, Ph.D., is a senior writer and community manager for Primal Nutrition, a certified Primal Health Coach, and the co-author of three keto cookbooks.

As a writer for Mark’s Daily Apple and the leader of the thriving Keto Reset and Primal Endurance communities, Lindsay’s job is to help people learn the whats, whys, and hows of leading a health-focused life. Before joining the Primal team, she earned her master’s and Ph.D. in Social and Personality Psychology from the University of California, Berkeley, where she also worked as a researcher and instructor.

Lindsay lives in Northern California with her husband and two sports-obsessed sons. In her free time, she enjoys ultra running, triathlon, camping, and game nights. Follow along on Instagram @theusefuldish as Lindsay attempts to juggle work, family, and endurance training, all while maintaining a healthy balance and, most of all, having fun in life. For more info, visit

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14 thoughts on “Can Keto and Cardio Mix?”

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  1. So for this situation we should call it Kardio I suppose …

  2. I agree that chronic cardio patterns should be avoided. However, this principle has not been accepted by military and law enforcement agencies. All U.S. military branches and law enforcement academies require extensive chronic cardio training and testing. This is true even though their own studies have concluded that being able to run five miles in less than forty minutes has no direct correlation to combat performance. But that is another issue. The point here is that those of us who subscribe to the primal philosophy and that are members of the military and law enforcement are REQUIRED to engage in chronic cardio as a part of our initial and ongoing training and testing. We need a plan for meeting this requirement and minimizing its negative effects within our primal approach to training.

    1. That’s a tough one – although I heard the military is now investigating the benefits of a keto diet, and effects of IF.

  3. Ask yourself why you’re doing keto. It’s not necessary to lose weight. I enjoy 200g or more carbs per day and lift weights. I’m not getting fat.

    1. Big deal. Losing weight is only about 1/10 of the benefits keto can deliver. Also, I ate 200-300g a day or more from carbs until 55 years old and was very slender and weighed 140lbs. Again, big deal. I was skinny/fat and had fatty liver and all sorts of other things. I stayed skinny because I was a jock and was very active. I could be wrong, but my guess is that you are in your 30’s.

    2. There is a guy who consumes 5000 calories a day, was on the Dr Oz, but follows a one meal a day intermittent fast, and is very active – he eats nothing but processed food, donuts, chips, complete junk food – all his blood numbers came up perfect – but its a matter of time until his luck runs out…

  4. Hi Mark, I do much better on keto than carbs, as far as exercise performance. Both from a cardio standpoint and weight training. I have the “athlete gene” (though my body doesn’t show it) for more fast twitch muscle fibers. So maybe my experience is different from those of others. But when I returned to keto a few days ago (after a year away, for reasons), I immediately felt better and more capable of exercise.

    My genetics does hint that I probably process carbs less well than fats, and I have a high percentage of Neanderthal genes. Rather than see that as a negative, I see it as just a way to understand my needs. So I can’t say this is true for everyone on earth. But it’s something people should consider and try, especially if what they’re doing isn’t helping them much. I only wish I could convince more of my family to try it.

    Thanks for all you do to keep us updated on ketogenic subjects. I consider keto to be a vital part of my health.

  5. I’ve been keto for over two years now. I participate in gravel grinders which for those who don’t know are bike races on gravel roads where we race somewhere between 25 to over 200 miles in 1 day. Last year I experimented with carbs because these races can last from a couple hours to 20 hours at times. My thought was that I am probably depleting my glycogen stores when you add up all the time of high intense racing. Every event I tried to incorporate carbs I failed to finish. Every event I began fasted and consuming little if any carbs during the race I successfully completed. Everyone just has to experiment for themselves and find something that works. I can tell you that when I had carbs I could feel the lactic acid building up in my legs and when I am strictly keto and fasted that doesn’t seem to happen. Each time I had carbs I suffered from severe cramping as well. I failed to complete a 64 mile race with carbs one weekend then crushed a 200 mile race the next with no carbs. My advice is to find something that works for you and race day is not the time to experiment.

    1. I, too, have found that now that I am keto, I do not get the muscle soreness that I expected from unaccustomed heavy workouts. I, too, wonder about whether the ketone-burning process dodges the lactic acid buildup. I think Mark’s team should research this!

      1. It has been proved scientifically that keytones produce less lactic acid side effects. If you relied more on glucose, you would have to top up your blood sugar every 2 hours, and your balance of lactic acid would build up faster – on keytones you can just cruise through the race, and it forces the body to burn fat, it has no choice (although its not really cruising, heart rate would be high and constant for a long time, putting it in the chronic cardio zone, so stress factors would go high suppressing the immune system and skyrocketing inflammation, and putting the body into fat storage mode, etc, but that’s another story). A race now and then is good though to shock the body, I wouldn’t be training like that every day, but that’s just me.

  6. I am a professional athlete/circus artist; I don’t participate on long-term cardio endurance sports but rather endurance strength (think gymnastics-style performance, 4-7 minute routines). I have a massive amount of strength for my size (female, 5 feet tall, between 105-110 lbs), and I’ve been Primal/Paleo for the past few years. I dip in and out of being strict about it and being 70/30. I’ve considered going keto just to give it a try, see if energy/performance improves, etc. However, I’m currently the strongest I’ve ever been. I’m worried about losing some of the strength-based skills that I can do if I mess around with my diet too much. Thoughts?

    1. Because you are a pro athlete (that’s rad!), of course yes, you don’t want to lose strength or endurance. I’m not too worried about the strength overall, but you definitely might feel a dip in energy for a few weeks. My first advice would be to time it wisely–i.e., at a time where you can afford to rest a bit more than usual, or when it wouldn’t matter if you weren’t at the absolute peak of your game.

      My next rec is to focus on protein first. You don’t want to slash your protein intake because you might have heard that it interferes with keto. As active as you are, you should be fine to maintain your current level of protein intake. Once you are adapted to keto, you can experiment to see if you do better with a little more or less protein while keto.

      If you’re keeping protein about the same, that means you’ll just swap your carb calories for fat calories. I recommend tracking your food for a while to make sure you are getting at least as many calories as you are now, maybe even a little more during the transition.

      Lastly, check out this article for some specific recs:

      Hope that helps!

    2. Zou, my advice would be to make the shift to keto only gradually. As a pro athlete, I expect you eat plenty of protein? (If not, you want to fix that…) Take a look at the carbs in your diet, and drop them bit by bit. For example, if you drink fruit juice, change that to just water. Once you are no longer finding that odd, limit your fruit to one piece a day. Make up the calories by eating more protein and above-ground vegetables. Take your time making changes, and you won’t shock your body!

  7. I actually started keto to avoid all of those processed sugar refueling products aimed at athletes. People are amazed when I tell them that not only do I not eat during races but also do all of my training runs fasted. I’m not particularly athletically gifted either, just middle of the pack. I do used targeted carbs but I find that a banana before a race is more than enough extra carbs.

    Thanks for putting all of this info out there so people know there are other options out there. I always send my friends who are interested in keto right over to MDA.