Lifting on an empty stomach isn't going to hurt your gains, as long as you aren’t eating two breakfasts’ worth of food for lunch and generally eating healthy otherwise, says Melody L. Schoenfeld, a nutrition specialist and owner of the personal training company Flawless Fitness.
Schoenfeld, who confesses to "almost always lifting in a fasted state" because of her schedule, says she hasn’t seen any drop off. "If it works for you, keep doing what you’re doing."
In terms of research, she points to a 2013 study by the Journal of the International Society of Sports Nutrition on bodybuilders who were fasting for Ramadan and found that fasted training did not affect body mass or composition. And another study noted that heavy lifting in a fasted state seems to increase the muscle-building response to a post-training meal including carbs, protein, and leucine.
“These studies do provide some insight that fasted training is probably not going to hurt you and might actually have some benefit,” says Schoenfeld.