Automatic is not the enemy. An out of date automatic is. The aim is to practise the calmer response until it runs on its own, the way the old one already does.

What the research says

In a randomised controlled trial, five weeks of daily breathing practice was associated with measurable changes in prefrontal structure. What such changes mean clinically is not established, and five weeks is a short window. It sits reasonably alongside the ordinary experience that a practice kept up daily starts to ask less of you.

Strength of evidence: one line of research. A single study, or a theoretical account.