Mr Z
An AI Coach for Body Recomposition
Francesco Zen, founder of ZTraining · Last updated June 19, 2026
Why the threshold matters
Building muscle and losing fat at the same time works best starting under roughly 20% body fat. Below that point, the body can draw on stored fat to fuel new muscle efficiently. Above it, the same approach is slower and less reliable, which is why Mr Z reads this before recommending it.
What happens from there
Once recomposition is the right fit, calories stay fixed while performance and training output improve. Over time, as your output increases, a real caloric deficit forms naturally, rather than being forced from day one.
Related: Can you build muscle and lose fat at the same time? · Body-fat threshold rules for building muscle
Francesco Zen is the founder of ZTraining and ZLIFE, with 18 years of coaching experience working with executives across the UK, US, and UAE. He built Mr Z, an AI coach trained on his methodology to bring the same approach to a wider audience.