How Not to Die hinges on the idea that nutrition plays a vital role in both the prevention and reversal of chronic diseases. Greger presents evidence to support the claim that lifestyle-related diseases, such as heart disease, diabetes, and certain cancers, are largely preventable through dietary changes. The book argues that many of the leading causes of premature death in Western societies are linked to unhealthy eating habits and that these conditions can often be managed or even reversed by adopting a whole-food, plant-based diet.

Greger backs up his assertions with a plethora of studies and research that highlight the correlation between diet and health outcomes. For example, he discusses the work of Dean Ornish, who demonstrated that a low-fat, plant-based diet, combined with lifestyle changes, could reverse heart disease. Ornish’s studies showed that patients with severe coronary artery disease experienced significant improvement and, in some cases, even complete reversal of their condition, without the need for invasive procedures or medications. This evidence underscores the idea that food can act as medicine, providing not only sustenance but also therapeutic benefits.

The book further explores how specific foods can target and reduce the risk of particular diseases.