Obesity can 'spread' within social networks, to the point that if a friend becomes obese, your own chances of becoming so increase by 171%.

noli's read

The advice is based on a famous observational study published in the New England Journal of Medicine (Christakis & Fowler, 2007). While the data show a real statistical correlation, the 171% figure is a specific interpretation of that correlation within a given social group, rather than a probability of direct contagion. It is crucial to note that this is an observational study: it demonstrates an association but does not prove a direct causal link (homophily). In other words, friends may simply share similar environments, lifestyle habits, or socioeconomic statuses that promote weight gain, rather than transmitting obesity to one another. Subsequent research has nuanced these results, highlighting that methodological biases and confounding factors can influence these statistics. Thus, while social influence on health behaviors is a well-established concept in social science, presenting this result as a direct 'contagion' simplifies a complex, multifactorial phenomenon.

the sources

No named source held this one up — that absence is part of the verdict.