What the Keto Diet Will Do to Your Workout

If you’ve decided to try out the ketogenic (“keto” for short) diet, you probably hope to reap some of the myriad health benefits it claims to bring. The keto diet is designed to put the body in a state of ketosis. When your body is in ketosis, it is burning fat as a fuel source, as opposed to running on carbohydrates. The touted advantages of keto include weight loss, boosted energy, and fewer blood sugar swings.

1. It May Be Tougher to Boost Performance When It Comes to High-Intensity Exercise While on the Keto Diet

The majority of high intensity exercise — activity that requires short, intense bursts of energy — is powered by the carbohydrates you eat. The human body stores carbohydrates in the muscle cells as muscle glycogen. That muscle glycogen becomes an immediate fuel source for your body when you do any sort of activity that periodically requires intense movement, including strength training, sprinting, and other sports.If you’re on the keto diet, your body is burning fat for energy rather than carbohydrates (if you’re doing keto right). As a fuel source, that fat isn’t as easily burned as carbohydrates, so the process is overall less efficient, Galpin explains.

2. Keto May Boost Fat Burn

While keto may not be best for things that require short bursts of energy such as weightlifting or Spinning, it does seem to work well in burning more fat in people who like to do steady state aerobic exercise, like distance running or cycling at a steady pace.In the May 2017 issue of the Journal of Physiology, a study of elite competitive walkers showed that the athletes who were on ketogenic diets were able to significantly increase fat burning in their bodies during training compared with walkers on a more standard diet that included carbohydrates. But despite burning more fat during training while on the keto diet, those athletes also experienced worse athletic performance than the athletes on the more standard diet. The race walkers on the keto diet complained that they felt it took greater exertion to complete the same workouts as the athletes on a more standard diet, and they were less likely to complete the assigned workouts compared with the athletes on the more standard diet.

3. You May Feel Like Your Gas Pedal Doesn’t Work as Well, Especially at First

As your body becomes “keto-adapted,” it begins to train itself to burn fat for energy instead of carbohydrates. Initially, that process may leave you feeling less energized than usual when it comes to working out.Some research findings suggest that athletes have been successful in increasing their ability to use fat as a fuel source, according to Nitin K. Sethi, MD, an associate professor of neurology at Weill Cornell Medical Center in New York City, who began studying the effects of the keto diet on human performance because one of its original purposes was to treat epilepsy.

4. Your Body May Burn Calories Quicker on Keto

A study published in the BMJ in November 2018 found that when overweight adults replaced carbohydrates in their diet with fat for a period of five months, their bodies were able to burn approximately 250 more calories per day than people who ate high-carbohydrate and low-fat diets. Keep in mind though that gram per gram, fat is more calorie-dense than carbohydrates: each gram of fat has nine calories, while a gram of protein or carbohydrate has four calories (according to the U.S. Department of Agriculture).That difference in caloric burn over the course of a day can add up when it comes to weight loss. Remember, to lose weight the body needs to burn more calories than it takes in. “Calories are not the only thing that’s relevant, but they still matter,” Galpin says.

5. Keto Is Better for Maintaining Muscle Mass Than Adding Muscle

Maintaining and growing muscle mass helps slow down the aging process and protect against the risk of age-related bone loss. Muscle mass helps you to burn more calories each day, even when you aren’t exercising.RELATED: What You Should Know About Exercise at 40 and BeyondIf you are in the gym to keep the muscle mass you have, a ketogenic diet could work for you. But if you are looking to add muscle mass, the lower amounts of calories and protein you take in each day while you are on keto could make it tougher for you. “The average person is going to have a much harder time adding muscle on keto,” Galpin says.

6. Just Because You Are Burning Fat, That Doesn’t Mean You Are Losing Fat

While the ketogenic diet can be a good way to train your body to use fat as a fuel source, it doesn’t mean that when you exercise, the body will use up all that fat. You still need to be burning more calories overall than you’re consuming to actually lose fat (and lose weight).“Burning fat doesn’t always mean fat loss,” Galpin says. When you are on keto, you burn more fat, but you also store more fat, because more of your calories are coming from fats than they otherwise would, he explains. “You still have to have a calorie deficit to see weight loss results.”