Baseline Participant Characteristics.

An unresolved debate persists in public health, concerning a distinction between communicable diseases that are causally linked to microbes or viruses and “non-communicable diseases” that are not. We offer evidence in support of the view that public health categories need rethinking; that more precise and granular ones are needed; and that “non-communicable” and “non-infectious” can be tautological misnomers. The scientific literature suggests an underlying socially “infectious” phenomenon and we put forth a fundamental Social Contagion Hypothesis: that social networks constitute a propagating force; that this force can be quantified in socio-biological terms; and that it can be leveraged for public health. Yet a major question still remains unanswered: if weight loss, like biological pathogens, cascades through host populations, and can be mitigated through interventions targeting risky social behaviors, then can a social reproductive number (Social R0) for metabolic and cardiovascular disease be estimated and modulated? We present the first known evidence from a randomized trial, demonstrating the epidemiological dynamics of socially infectious diseases. We find that health propagation can achieve epidemic proportions (including changes in weight, 1R0 = 1.3, pR0 value thereby potentially managing, preventing, or reversing social infections at epidemic scale (yielding population-averaged comparative R0 ratios, 244Rcp