The traditional forms of public health law were directed largely toward communicable diseases and other externalities, such as pollution, with negative health impacts. The more modern view treats any health issue that affects large numbers of individuals as one of public health, which would include such problems as obesity and diabetes. This paper examines the constitutional evolution of the public health principle from the narrower to the broader conception. It then argues that the narrower conception better defines the appropriate scope of coercive government intervention than does the broader definition, which could easily authorize interventions in economic affairs whose indirect effects are likely to reduce overall social wealth and freedom, and with it the overall health of the population.