THE KETO DIET sounds stellar in theory: By optimizing your diet you can reprogram your body so its metabolism burns primarily fat—known as ketosis—rather than sugar.

Even better: The keto diet maximizes fat and protein, and includes as little sugar as possible. But there’s one catch: You have to all but banish carbs—we’re talking less than 5% of your daily calorie intake—to get your body’s fat-burning furnace firing at full capacity.

The bigger problem: Whittling down carbs and sugars takes a gargantuan amount of self-control. And to be honest? In the transition period, you’re gonna feel like crap.

“Carbohydrates provide 90% of the brain’s fuel,” says Jim White, R.D., a certified exercise physiologist and owner of Jim White Fitness and Nutrition Studios in Virginia Beach. And if you’re lifting a ton, the keto diet can backfire. You want to get great workouts in to see results, but most guys start dragging when they drop their carb intake that low. Your workouts can drop in intensity and efficacy, and your willpower often drops as well.

Yet, ardent keto diet supporters argue once you get “over the hump” you’ll feel, look, and perform better. To help you decide whether or not to take the plunge, here’s everything a lifting-focused athlete needs to know about the keto diet.