Can you build muscle while intermittent fasting?

The problem isn't fasting itself. It's what a long fast takes away. On Ep. 137, Nikkiey explains that extended fasting without adequate protein can impair muscle protein synthesis, the process your body uses to repair and grow muscle after training. If you don't give your body the energy it needs, one of the first places it turns is your muscle. On Ep. 190 she adds that a short eating window makes recovery harder. If you train at 6 a.m. but can't eat until 11 a.m., you're delaying the protein and carbs your muscles need, and she says that gap shouldn't stretch to four hours. On Ep. 187, Merav, co-founder of Lumen, says suddenly jumping into a 16 to 18 hour fast can raise cortisol, put the body into stress mode and lead it to break down muscle for energy.

The episodes land in slightly different places. On Ep. 38 Nikkiey says IF can be compatible with building muscle, but most people do it wrong. On Ep. 190 she's firmer: IF is a tool that works for weight loss and for some health issues, but if muscle is your main goal, she doesn't believe it's the best protocol. That's the distinction she keeps coming back to, weight loss versus fat loss. If the goal is to look toned, you need more muscle and enough fuel to build it. If fasting hasn't gotten you there, it's the plan, not you.