Methodology

Stress, Cortisol and Belly Fat, What's Real

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

Why cortisol gets blamed for everything

Cortisol has become a catch-all excuse, and a catch-all sales pitch, in fitness content. The truth is narrower than either version: cortisol makes everything less efficient. It drives water retention, softens the look of muscle, and reduces metabolic function across the board.

"Cortisol is not an enemy. It's a physiological defence mechanism telling you to reduce stress and improve recovery."

What it actually does, and doesn't do

Cortisol cannot manufacture a belly that wasn't there. What it can do is amplify the visible and felt effect of one that already exists, through water retention and reduced muscle tone, making the same amount of fat look and feel like more than it is. Treating cortisol as the enemy misses the point. It's a signal worth listening to, not a problem to fight directly.

He built Mr Z, an AI coach trained on his methodology to bring the same approach to a wider audience.