I've been on the keto diet for two years now, and the whole time I've been lifting weights in the fasted state. It's really easy to do on keto because your insulin levels are low, and this allows you to access body fat easily. I can go as long as fourteen hours between my last meal and my morning workout. I've noticed no difference in performance over the past two years, and I seem to have made the same progress I would've otherwise. And you can even run a marathon in the fasted state on keto (five pounds of stored body fat has 17,500 calories, more than enough to make it across the finish line). It's all about insulin sensitivity/resistance.