James Nestor opens Breath with his foundational premise, developed through extensive research and his own direct self-experimentation: modern humans have collectively lost proper breathing technique, particularly through widespread chronic mouth breathing rather than nasal breathing, producing significant, underappreciated negative health consequences that specific breathing technique correction can meaningfully address.

Nestor's foundational argument:

• He presents evidence — drawn from anthropological, evolutionary, and clinical research — that contemporary humans breathe considerably differently than earlier historical populations and other primates, with modern dietary softness and other environmental factors contributing to structural changes in jaw and airway development that predispose toward chronic mouth breathing and shallower, less optimal breathing patterns
• Nestor conducted direct, dramatic self-experimentation, including a period of experimentally blocking his own nasal breathing entirely to directly document mouth breathing's measurable negative physiological effects compared to subsequent nasal breathing recovery, providing vivid, direct personal evidence supporting his broader research-based argument
• This foundational premise, combining extensive research review with striking personal self-experimentation, sets up the book's overall project: examining specific breathing techniques' measurable physiological effects and providing practical guidance for correcting common, health-compromising breathing patterns

This foundational framing establishes Nestor's distinctive investigative approach, combining journalistic research review with direct, sometimes extreme personal self-experimentation to build his case for breathing technique's underappreciated health significance.