Dr. William Li opens by presenting research showing that specific food choices directly affect the body's own natural defense systems — angiogenesis, regeneration, microbiome, DNA protection, and immunity — that help prevent and fight disease.

Why this framing reorients how readers think about diet:

• Rather than framing food choices purely around weight management or general 'healthy eating,' Li connects specific foods to specific biological defense mechanisms
• This provides a more mechanistically grounded rationale for particular food choices, beyond general dietary guidelines
• Understanding these specific mechanisms allows more targeted dietary choices aimed at supporting particular aspects of the body's disease-fighting capability

This opening establishes the book's distinctive five-systems framework, providing scientific grounding for its subsequent specific food recommendations.