Lactate Metabolism: Separating Correlation From Causation.

Lactate is among the most frequently measured metabolites in physiology and medicine, yet it remains one of the most persistently misunderstood. Long regarded as a metabolic waste product, a marker of anaerobic metabolism, or a direct cause of acidosis and fatigue, lactate remains burdened by misconceptions that obscure its true biological roles. Recent advances in metabolic flux analysis, isotope tracing, hyperpolarized magnetic resonance spectroscopy, and cellular imaging have revised this view and established lactate as a central intermediary in energy metabolism, redox homeostasis, and interorgan metabolic communication. Here, we re-examine common myths surrounding lactate biology and clarify the distinction between correlation and causation in its interpretation. By reframing lactate as a dynamic indicator and, in some contexts, a regulator, of metabolic state rather than a toxic by-product, this review improves experimental reasoning and clinical interpretation across diverse physiological and pathological contexts.