Fitness pros have long hypothesized that strength training + a low-carb diet is a combo made in get-lean heaven.
"Eating high-fat foods and no more than 50 grams of carbs per day, plus moderate protein—a ketogenic diet—can help increase your body's reliance on fat for energy, so you burn more of it," explains Carwyn Sharp, Ph.D., chief science officer for the National Strength and Conditioning Association.
But for some, going too low on Cs can backfire. If any of these red flags persist for more than two weeks, slowly add the starchy stuff back in (up to 150 total grams daily) to find your sweet spot.
If you feel beat leaving the gym—even after slow-lifting sets—you may need more fuel. About an hour before your sesh, nosh on an apple or banana (both have 25-ish grams).
When your body burns fat for energy, it produces molecules called ketones. You pee them out, along with sodium, which can cause dehydration and headbangers. Sip a little extra water during the day, or drink a sodium-enhanced supplement pre-workout, like Nuun Vitamins ($7, nuunlife.com).
Carbs aid in the production of illness-fighting antibodies. So if you're over-skimping—for many, that's under 100 grams per day—you may get sick more often. Unrefined carbs like sweet potatoes can help keep you healthy and on track.