Working Out on the Keto Diet Can Be Weird—Here’s What Works

Oh, the keto diet. Everyone’s buzzing about it—my friends, their friends, random Facebook friends I don’t actually know but have somehow appeared in my feed. People simply won’t shut up about how the keto diet has been yielding all these amazing results, like super-fast weight loss and increased energy. At first, I found this profoundly annoying, but eventually, I decided that if you can’t beat ’em, well… I went ahead and tried it for myself.

Make fun of me for being the sort of person who would throw herself off a bridge if all of her friends were doing it all you want—at least I did my research going in: I learned early on that this diet is different, and I couldn’t just try keto out for a quick week or two like most fad diets. Clinical nutrition coach Ariane Hundt, M.S., told me that, depending on your usual eating habits, it could take 1-2 weeks to drop into ketosis—a state in which your body turns to fat instead of glucose as a main energy source—and that it’s best to go an additional two weeks to see significant results.

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That put me at a month of counting my macros like crazy, making sure that 75 percent of my caloric intake came from healthy fats, 15 percent came from protein, and a mere 10 percent came from carbs. To put that into perspective, on my 2,000 calorie-a-day diet, I’d have about 25-50 grams of carbs allotted per day, and one New York City bagel (which I am very, very fond of) has about 67 grams of carbs.

Once I realized my usual eating strategy (that focused mostly on protein and a healthy hit of fats and carbs) was about to fly out the window, I started to wonder how my workouts would fare.

At first, I didn’t feel so hot.

Like any good dieter, I started keto on a Monday after a weekend of enjoying the f*ck out of some pizza and a few beers. More often than not, my calendar has a sweat session scheduled Monday through Friday, but I figured it’d be smart to take the day off from a hard workout in case I felt funky on day one.

That day came and went and I felt… fine. So I returned to my regularly scheduled programming on day two, starting with one of my favorite running-and-strength treadmill classes at Mile High Run Club. I know it’s not a genius idea to try a brand new workout and a brand new diet (the fewer variables you have, the better) so I thought it was a safe choice.

I felt OK during most of the class—I didn’t pass out or fly off the back of my treadmill—but whenever I kicked up the speed to my usual interval paces, I was quickly hit with fatigue. I rode the struggle-bus during the kettlebell portion of class too. Using the same weights I typically choose, I couldn’t bust out as many reps as I normally do in the time allotted.

Menacham Brodie, C.S.C.S., C.N.C., head coach of Human Vortex Training, tells me this is normal. “Your body is using a different pathway to unlock the energy it needs to meet exercise demands,” he says. “Plus, as a general rule, high-intensity workouts with repeated hard efforts tend not to go well with the keto diet, as your body is using fat for its fuel source. In order to get the energy it needs, the body has to break down fats as opposed to pulling from carbs, and that takes more time.”

Which is why, for the rest of the week, I scaled back on the intensity of my workouts. “Understand that what you ‘should’ be able to do will be different, as you’re asking the body to run in a different fashion, and on an energy system that can’t keep up with demands in the way that you’re used to,” Brodie says.

I also wasn’t fueling my workouts well enough, and I learned the hard way.

Toward the end of my first week, I was slammed with the keto flu, a series of nasty, flu-like symptoms that often crop up as your body adjusts to a new energy source and decreased electrolyte levels. I had a boxing class at Rumble scheduled but decided it was better for my body to rest—interval workouts needed to take a backseat as my body balanced itself out.

“For the sake of easing into ketosis, in the first week or two, it’s best to focus on workouts that ensure appetite, cravings, and energy are balanced—like weight lifting two to three times a week, followed by low-intensity cardio,” Hundt says. “Lower-intensity cardio burns more fat as fuel, while higher-intensity burns more sugar as fuel. That’s why lower-intensity workouts allow you to move into ketosis with more ease.”

What wasn’t easy? Eating.

Another change I needed to make? Eating more. Because I was consuming such a high percentage of fats—which Hundt says can be very filling—I felt full a lot of the time. But I wasn’t hitting my calorie goals. Brodie explained that if I was in too much of a caloric deficit, my body would kick into starvation mode, and that can lead to muscle breakdown and even more energy shortage than what I was already experiencing. It could also increase my odds of injury, he says, and there was no way in hell I was about to take myself out of the workout game entirely.

I thought I was doing enough, tracking every morsel on my Fitbit app and constantly Googling, “How many carbs does fill-in-the-blank have?” But I was still eating on the fly. Brodie explained that planning my meals in advance would make life on keto a lot easier.

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“Take a look at your energy demands for your sport, your daily energy demands outside of your workouts, and know with more certainty how much you actually need to eat,” he says. “Then plan your nutrition throughout each day, breaking meals and snacks down into what you need to meet those goals.”

Steady-state workouts were my jam.

Every so often, I have days when I totally draw a blank about what workout to do. When that happened during this month-long experiment, Brodie suggested I fall back on steady-state, endurance-style workouts.

“It’s the fluctuation of effort that can kill you,” Brodie explained. “When you start having these variations in intensity, that’s when the carbohydrates are called upon to fill a quick need.”

This actually ended up working out perfectly: I was signed up for a 62-mile charity bike ride right as my month of keto dieting was wrapping up. Rather than get bogged down with my normally interval-heavy workout schedule, Brodie gave me permission to hop on the saddle for exploration rides around the city. To stave off boredom, he suggested increasing my intensity once a week to see how I fared.

“Plan mini-experiments with increasing intensities in 1-2 workouts every 5-7 days,” he says. “This will help you find your body’s limits and continue to kick ass and take names while hitting your goals.”

And strength training saved me.

While I did a lot of bike riding on the weekends, I focused more on strength training during the workweek. “Increasing dense, lean muscle mass helps the body burn more fat at rest and can supercharge you on your body-transformation journey,” Brodie says.

Hundt agrees. “Strength-training workouts provide a much better metabolic effect than cardio workouts, whether you’re in ketosis or not,” she explains. So long as I busted out a routine that made me hot and sweaty, increased my heart rate, and reached muscle fatigue, I’d cash in on the coveted afterburn effect for up to 48 hours post sweat, she says.

Plus, strength workouts provide a boost in testosterone and growth hormone, which Hundt says shifts the body into fat-burning and muscle-building mode—two things I definitely wanted to experience on keto.

And there’s at least some research to back her up: A recent study in the Journal of Strength and Conditioning Research recorded the results of 25 men following a resistance training program. Some were on the keto diet, and others were on a standard Western diet. While lean body mass increased and fat mass decreased in both groups during the first 10 weeks, only the keto group showed more of an increase in lean body mass during the final week, when carbs were reintroduced. Of course, a study of 25 people is hardly proof, but it is a good start to supporting evidence.

That’s why Brodie suggested I incorporate 3-4 days a week of strength training. But seeing how much I love the tread, he said I didn’t have to ignore the machine completely. “After your strength training, hit the cardio equipment for 20 minutes of low-endurance work based on heart rate,” he suggests. My go-to? Audio-guided outdoor running and treadmill classes on the Peloton app.

At the end of the day, sure, I had to scale back on the HIIT classes I usually sign up for…

but that freed up time for activities I know I love but rarely make time for, like riding outside and lifting. And after that first week, so long as I fueled correctly, I could still work my body in an endorphin-producing, sweat-inducing, fat-burning way.

And now that I’m done? I have a hot date—with an everything bagel.

Samantha Lefave is a freelance writer who is living, eating, and sweating her way around the world. You can find her Instagramming her favorite destinations, squeezing a Friends quote into every conversation she can or—when there’s downtime—eating peanut butter straight from the jar.

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