Barbara O'Neill's "Self Heal by Design" argues that many illnesses stem from an imbalance of microorganisms within the body, particularly the overgrowth of fungi and yeast. The book explores the role of microorganisms in the carbon cycle, highlighting how they break down matter and how this process relates to human health. O'Neill challenges conventional medical approaches, emphasizing the body's self-healing capabilities and advocating for a holistic approach that includes dietary changes and lifestyle modifications to restore microbial balance. The text supports this perspective by examining historical perspectives on disease, exploring the link between fungi and cancer, and discussing the importance of genetics and environmental factors. Finally, it provides practical advice, including dietary recommendations and lifestyle habits to support overall health.