This is the central therapeutic claim of the Hay System, stated in Health via Food (1929) and restated in A New Health Era (1935): that simply separating concentrated starches from concentrated proteins at meals, and favouring “base-forming” foods, protects the body’s alkaline reserve and thereby prevents disease and prolongs life. The claim rests on a proposed mechanism (excess acid formation from mixed concentrated foods) rather than on any controlled outcome, so it is classified mechanism_only. It is refuted on two strands recorded in the archive: the enabling autointoxication/acidosis framework was discredited in the early twentieth century (Bested, Logan and Selhub, 2013), and a controlled metabolic study found that food separation confers no advantage in body weight or composition over an energy-matched mixed diet (Wutzke et al, 2001). The longevity reading is Hay’s own (“longevity would increase notably,” A New Health Era); no lifespan evidence was ever produced.