Is Exercise Harder on the Keto Diet?

Research shows you might need to change up your workout routine if you're doing keto.

December 04, 2019

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In short, the ketogenic diet (more commonly known as the keto diet) is a low carb and super high fat diet plan that mandates a daily intake of carbs in the neighborhood of 20 to 50 total grams per day — a far cry from the typical recommendation of upwards of 300 grams. This carb restrictions forces the body to convert fat to fuel. This process isn’t only a less efficient way to produce energy, it promotes the production of ketone bodies, which in large amounts can be life threatening. Since excessive ketones can be so dangerous, dieters must strike a delicate balance to get enough calories, eat ample fat and limit carbs and protein just enough to be in ketosis, without entering into a more dangerous condition known as ketoacidosis.

Forcing your body into ketosis is no picnic. It often causes symptoms like extreme fatigue, body aches and other flu-like symptoms. Once over the initial hump of going keto, some folks report improved energy levels, but some of these energy boosts may be the result of eating excess carbs on an intentional or accidental modified keto plan.

At the recent Food and Nutrition Conference and Expo, experts presented on the ever-popular keto diet and the effects it can have on competitive athletes and exercise enthusiasts alike. Here's what you need to know about exercising on the keto diet.

Bottom Line: Keto Can Make Your Workouts Feel Harder

In the knuckle-dragging early stages of keto, exercise can be beyond tough. The initial phases of cutting carbs also drives a swift shift in water weight, which sounds better than it feels. This lack of fluids sets the stage for utterly exhausting dehydration, especially when exercising.

Here's Why It Feels Tougher

Under normal carb-eating circumstances, exercise does use some fat for fuel, especially during moderate intensity workouts. On a normal diet, your stores of carbs (aka glycogen) are at the ready the kick in whenever there is a need for energy. When those sources aren’t there the body has to work harder to seek out glucose elsewhere or, in the case of keto, reply solely on fat for fuel. The detrimental effects will be felt in your workouts. Many new to keto may also cut calories too low while making the switch, which can lead to even less energy for exercise. Symptoms may include fatigue, headaches, dizziness.

Keto Can Result In Satisfactory Performance — Sometimes

Small studies have showed some successful outcomes on 12-week keto regimens in well-trained athletes and ultra-endurance, but this doesn’t mean just anyone could or should hop in the keto train. Even the hard core athletes in these studies reported fatigue during the early stages of going keto.

How to Exercise on Keto

If you really want to maintain a workout regimen while on keto, here are some highly recommended tips. Those with medical conditions such as insulin resistance or diabetes should check with their doctor before going keto and certainly before exercising on keto.

  • Hydrate: Offset shifts in water loss by drinking plenty of water before, during and after exercise.
  • Eat Before Exercise: Pre-workout fueling is essential. Get some calories in before you exercise.
  • Consider Cheating: Long term and hard core keto can be very dangerous; don’t give up on carbs completely.
  • Modify Your Exercise: High intensity exercising like HIIT training and sprinting may be more difficult due the intense demand for glucose; consider lower intensity training for a safer exercise routine.
  • Salt Your Food: Yup, you’ll need more of this important electrolyte! The body processes ketones and loses more sodium than usual on the keto diet. Tack on the fact that you’ve cut out most processed foods (keto diet demands that) and take into account sweating during exercise, which adds even more sodium loss.

Dana Angelo White, MS, RD, ATC, is a registered dietitian, certified athletic trainer and owner of Dana White Nutrition, Inc., which specializes in culinary and sports nutrition. She is the author of four cookbooks First Bites: Superfoods for Babies and Toddlers, The Healthy Air Fryer Cookbook, The Healthy Instant Pot Cookbook and Healthy Quick and Easy Smoothies.

*This article was written and/or reviewed by an independent registered dietitian nutritionist.

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