Mr Z

Is ChatGPT Good for Fitness Advice?

Francesco Zen, founder of ZTraining · Last updated June 19, 2026

A real example: more than double the protein needed

What happened

What happened A client doing strength training and CrossFit — where protein should be set for performance, not pure muscle growth — used ChatGPT to build a diet. Because body fat was never asked about or factored in, he ended up at 280g of protein a day. When he came to us for help, we recalibrated him to around 130g — less than half. The result of the over-correction wasn't extra muscle. It was bloating, increased body fat, higher food spend, and unnecessary load on his liver and kidneys.

This is the pattern worth understanding: the advice wasn't wrong because ChatGPT made an error in its reasoning. It was wrong because nobody asked the one question that would have changed the entire calculation — what's your actual body composition, and what is this protein target for?

Why this keeps happening

A generic model answers the question you asked, not the question you should have been asked. "Help me build a diet" gets a diet. It doesn't get a follow-up about body fat percentage, training goal, or recovery capacity — the inputs that determine whether 280g or 130g is the right number for a specific person.

What changes with a method-based AI

Mr Z is built specifically to ask the questions a generic prompt skips — body fat, training goal, and recovery state — before it sets a number, because those are the inputs Francesco Zen's 18-year coaching method is built around.

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.

Is ChatGPT Good for Fitness Advice?

A real example: more than double the protein needed

Why this keeps happening

What changes with a method-based AI

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