but for all subgroups most people became heavier at about the same time. This simple observation indicates something important about factors that did not precipitate the US obesity epidemic. We believe it is implausible that each age, sex and ethnic group, with massive differences in life experience and attitudes, had a simultaneous decline in willpower related to healthy nutrition or exercise.Rodgers A, Woodward A, Swinburn B, Dietz WH. Prevalence trends tell us what did not precipitate the US obesity epidemic. Lancet Public Heal [Internet]. 2018 Mar; Available from: linkinghub.elsevier.com/retrieve/pii/S2468266718300215
Changes in food supply are mentioned as key drivers, including portion sizes.
There’s also this