Keto diets are hot right now, and it’s clear why. Dozens of weight-loss studies have shown this method of eating—which emphasizes a very low amount of carbs, a moderate amount of protein, and a relatively high amount of dietary fat—can lead to significant and rapid weight loss, as well as health benefits such as improved blood sugar and insulin levels. 

“The scientific community is finally coming around to the idea that all fat isn’t bad and that excessive consumption of carbohydrates like sugar is actually what is behind the growing obesity crisis,” says Kristen Mancinelli, R.D., author of The Ketogenic Diet. In a keto diet, about 75 to 80% of your calories come from fat, 10 to 15% from protein, and just 5 to 10% from carbs. The premise: Severely limiting carbs forces your body to burn fat for fuel, a process called ketosis. “Ketosis is the gateway to rapid fat loss,” Mancinelli notes. By keeping your carb intake low, your body will continue to keep burning fat for energy.

The high fat content of your meals (which comes from both animal and plant sources) also helps suppress your appetite and keeps you feeling fuller longer, so you naturally eat less throughout the day. Since it requires more energy to burn stored fat, you’ll also increase resting energy expenditure, while stabilizing blood sugar and lowering insulin levels. This, in turn, reduces fat storage, explains Mancinelli. Ready to get started?

What follows are a few guidelines to keep in mind as you kick off your plan. One big caveat is that you should try to begin your keto diet at least one to two weeks before you undertake a comprehensive new workout program. That’s because, for the first couple of weeks on a keto diet, you’re apt to develop what some call “the keto flu,” a feeling that can leave you lethargic and a little foggy.

“There is definitely a transition period as your body makes the switch into ketosis,” Mancinelli says. “Your workout performance may suffer until you are keto adapted, so it makes sense to take it a little easy at first.”

Don’t worry, this keto flu won’t last too long, and by the time your body is fully fired up on fat, you’ll be able to take on new workout challenges with ease.

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