How do I know if my fat burners are decreasing my muscle gains? As long as my daily caloric intake is way up there, and I'm getting all the protein I need, I shouldn't be in danger of losing lean mass when I'm taking fat burners, should I? Reason I ask is I've heard guys recommend keeping off fat burners until you've reached your size MAX, then using them to help cut. As for me, though, I'm not ready to sacrifice a lean physique today for a huge cut one in 5 years. So I'm wondering if I should still be taking fat burners.