5 Ways Going Keto Could Affect Your Workouts

Julia Malacoff
by Julia Malacoff
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5 Ways Going Keto Could Affect Your Workouts

The low-carb, high-fat ketogenic diet is majorly trending right now. In fact, you probably know a few people who have tried it. Just like any other eating style, it works well for some people, while others find it impossible to stick with. And if you’re spending a lot of time in the gym, it’s natural to wonder: will it help or hurt your workout efforts?

If you choose to try the eating style (or are considering it), you should know about how the keto diet changes your body’s source of energy. When that happens, your workout performance and how you feel during exercise can change, too.

Here, nutrition pros explain how going keto can affect your workouts:



The keto diet involves eating a very small amount of carbs and very high amounts of fat. “While those following the keto diet may cut out processed sweets and starches, they are also eliminating or severely restricting nutrient-dense simple carbohydrates found in fruit and low-fat dairy products as well as whole grains and legumes,” explains Mindy Haar, PhD, RDN, a registered dietitian and associate dean of undergraduate affairs at NYIT School of Health Professions. For this reason, among others, Haar does not recommend the keto diet for anyone.

For those who are active in particular, missing out on high-quality carbohydrates can have some less-than-ideal repercussions. “As carbohydrates are the best fuel for the body, following a ketogenic diet can result in low energy levels,” Haar says. That might be less energy during your workouts, and possibly even less motivation to get to the gym in the first place.



“Starting a ketogenic diet is a major adjustment for your body, especially if you are used to eating a moderate to high carbohydrate diet,” notes Chelsea Amengual, MS, RD Manager of Fitness Programming & Nutrition at Virtual Health Partners.

“If you are following this low-carb, high-fat diet properly, then in the first few weeks, your body will be switching over from using glucose as the primary source of fuel to using ketones produced from the breakdown of fats,” she explains. This switch has a major impact on your power and endurance.

“Be sure not to try any new or very intense workouts during this time,” Amengual suggests. Stick what you’re used to, and possibly consider dialing back the intensity a bit. “For example, if you normally take four indoor cycling classes a week, maybe try two or three classes instead, or go a little easier on those sprints during class.”



Another downside of keto in terms of exercise is that you need to be very on top of how much water you’re drinking. “Excreting the waste products from this diet requires abundant fluids, putting people at a higher risk for dehydration,” Haar explains. This is one of the reasons she doesn’t recommend the diet in general.

Dehydration is also part of the reason people experience what’s known as “keto flu” when they first start the ketogenic diet. So if you do choose to go keto, be sure to drink plenty of water — especially around your workouts.



For those who are concerned about personal bests or are training for a race, it’s important to note that a true ketogenic diet is not usually associated with better athletic performance. Some studies have suggested that endurance athletes may perform well on the keto diet, but not all sports nutrition pros are convinced, especially since other research has found the opposite. When it comes to power sports like weightlifting or sprinting, most research has found that the diet does not benefit performance in any way.

In addition to lacking sufficient carbs, strict ketogenic diets are low to moderate on protein. “Protein is required for muscle strength and recovery, along with a multitude of other tissue and enzyme functions in the body,” Amengual explains. When strength gains and recovery are impaired, fitness gains will happen at a slower rate.

On a positive note, weight and body composition may improve when on the ketogenic diet, Amengual says, which is why some competitive athletes choose to follow keto in the off-season.



Here’s the good news: “After a few weeks on a strict ketogenic diet (75% fat, less than 5% carbs), you will have likely transitioned into ketosis, meaning your brain and body are burning ketones (from fat) as fuel,” Amengual explains. This means you’ll probably be better adjusted to having fewer carbs available for fuel, and therefore will likely have improved energy levels, mood and concentration compared to the first few weeks on the diet.

“That said, you still want to focus on workouts that are less dependent on carbohydrate, like yoga, lower-intensity walking/jogging or light weightlifting,” she adds. “You’ll want to avoid endurance exercise (over 1 hour) or very intense workouts like HIIT, CrossFit and boxing unless you are supplementing with additional carbs before and after these types of workouts.” In other words, if you’re a bootcamp pro, keto is probably a no-go.

About the Author

Julia Malacoff
Julia Malacoff

Julia (@jmalacoff) is a seasoned writer and editor who focuses on fitness, nutrition, and health. She’s also a certified personal trainer and Precision Nutrition Level 1 coach. Based in Amsterdam, she bikes every day and travels around the world in search of tough sweat sessions and the best vegetarian fare.


9 responses to “5 Ways Going Keto Could Affect Your Workouts”

  1. Avatar marlonluna says:

    This article is wrong according to my life.

    I do CrossFit hiit and have been Ketogenic for 10 months.

    If you know CrossFit, it’s HIGH INTENSITY and has lots of weight lifting.

  2. Avatar Matt. says:

    This article is completely speculative and lacks imperical evidence to support the hypothesis. As someone who has been in nutritional ketosis for 18 months and plays competitive rugby now, and works out 5-6 days a week at 25 Net carbs a day can tell you from my own experience and the mountain of scientific studies I have read that it’s just the opposite. I have more energy, my endurance has significantly increased, mental focus has improved. I was obese 18 months ago with 36% body fat, today I am at 14% body fat. Carb eaters are junk eaters and thrive off sugar, our bodies are very capable of generating glucose from proteins when it’s needed, flooding your body with high levels of glucose is horribly bad for you. Don’t believe this hype in the article, ketones for fuel last longer and sustains you through more physical demands than carbs.

  3. Avatar DesertWarrior77 says:

    Just another anti-ketosis article probably funded by Gatorade or Lucazade. I am lifting the heaviest weights I have ever done in my life at the moment, also competing in martial arts competitions so don’t believe the negativity going around people. Keto is real and is positively changing lives of many people from all walks of life. Keep on ketoing on

  4. Avatar Bo Grimes says:

    “After a few weeks on a strict ketogenic diet (75% fat, less than 5% carbs)”

    I don’t do keto (or any diet); I think they’re all distortions of healthy eating, but surely this is a misrepresentation. It’s almost impossible to get pure fat without protein (e.g. meat) or carbs (e.g avocado). People on keto aren’t eating butter sticks and lard and drinking olive oil. 75% fat is nonsense.

  5. Avatar MNKetoFitness says:

    I hope people think critically and DYOR. This is a terribly misleading article. The interviewers are not current with the most current literature that studies the effect of the ketogenic diet. If you have time, listen to Joe Rogan’s podcast with Layne Norton and Dom D’Agostino. Two people actively researching/participating in research behind not only keto but other diets.

  6. Avatar bb says:

    “As carbohydrates are the best fuel for the body…” Vegetable carbs are good, but not processed ones like pasta, rice, sugar and bread. These things didn’t exist when the human body evolved, but fat did, which is why we store it so well, and burn it efficiently. You don’t get energy spikes and slumps from fat, you don’t eat fat and feel like you could eat more 20 minutes later; you feel satiated on less food (important when you are trying to eat less) and I don’t hit the wall after 3-4 hours cycling.

  7. Avatar Meghan T says:

    So Mindy Haar would rather see my husband have Diabetes type 2, high cholesterol and high blood pressure rather than recommend the keto diet? I have been on every diet there is out there from the time my mother started taking me to “diet doctors” at 12 years old. This is the only eating plan I have tried on which I do not feel miserable and deprived. We have been keto for 6 months. He has lost about 60 pounds and I have lost about 40. He is off of his cholesterol meds and diabetes meds. We eat vegetables everyday and both of our doctors are ecstatic. Yes, we have had to scale back on some types of exercise, but we have replaced it with longer walks. We will stick with what our medical doctors recommend rather with something a PHD in “health sciences” says she wouldn’t recommend.

  8. Avatar Noelle says:

    This article is a train wreck. Clearly the “experts” have never tried keto or done their research into ketosis and low carb athletes. I’ve been keto for 3 years and I do cross fit and endurance workouts many times a week. I’m a totally unmedicated diabetic and my blood glucose is close to that of a “normal” person. I have friends that do marathons in ketosis. Your panel needs to get a clue and stop putting a negative spin on something they clearly know very little about.

  9. Avatar John Calvert says:

    This ending statement sums up all that is wrong with the writers POV: “You’ll want to avoid endurance exercise (over 1 hour)” The diet is tailor made for endurance athletes that keep a lower constant heart rate going as they use fat for fuel. Glycogen is depleted very quickly and very difficult to replenish over long periods of time. The soluability of the fat stores is very close to the water in our body and readily released. I have found difficulty with high intensity efforts such as while mountain biking and hitting my max heart rate. I started to use UCANN before and after rides to help with that.

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