Every claim, every source.

Seyfried and Shelton restate and develop the metabolic theory of cancer first proposed by Otto Warburg, arguing that the origin and progression of cancer is best understood as a mitochondrial-respiratory dysfunction that drives the cellular dependence on glycolysis — the Warburg effect — observed in the majority of tumors. The review compiles evidence from cancer cell biology, tumor metabolism, and animal models suggesting that interventions which restrict glucose availability (caloric restriction, ketogenic diets, multi-day fasting) or that pressure tumor cells through mitochondrial dysfunction may slow tumor growth or sensitize tumors to conventional therapy. The authors propose specific therapeutic implications and discuss the evidence base for ketogenic and caloric-restriction interventions as adjunctive cancer therapy. The review has been influential among researchers exploring metabolic approaches to cancer and is cited heavily in popular content connecting fasting and ketogenic eating to cancer outcomes — sometimes carefully, often less so.

Fred Hatfield (also known as "Dr. Squat" in the 1980s–1990s strength-and-conditioning community) is widely cited in sardine-fasting popular content as the originator of the modern sardine-only protocol. Hatfield publicly reported, in writings and interviews from the 1990s, that he undertook a sardine-only fasting protocol during a personal cancer episode and credited it as part of his recovery. The exact medical details (cancer type, stage, concurrent conventional treatment, follow-up duration) are inconsistent across the secondary sources reporting the claim. Hatfield's account is the historical seed of the contemporary sardine-fasting community's awareness — it predates the modern academic interest in ketogenic and metabolic interventions in oncology by roughly a decade. As a Tier 4 source, it is included for historical context and intellectual honesty, not as evidence of any therapeutic claim.