Obesity is a personal failing caused by lack of willpower

Quality and quantity of direct evidence for or against the claim — RCTs, systematic reviews, natural experiments, large cohort studies.

Drewnowski's energy-cost gradient research shows food environment and price structure predict obesity risk independent of individual willpower, directly contradicting a pure-discipline explanation.

Whether the proposed mechanism is valid and established — does the how make sense, or are there fundamental flaws in the causal logic?

The willpower mechanism cannot explain systematic exposure differences to ultra-processed food marketing and stress/sleep disruption across income groups that independently predict obesity risk.

Degree of agreement among domain experts and relevant scientific or policy bodies — depth and quality of consensus, not just majority opinion.

Obesity researchers broadly reject a pure-discipline framing given the well-documented role of food environment, stress physiology, and healthcare access.

Whether findings hold across independent studies, populations, and contexts — resistance to p-hacking and publication bias.

The environment-over-willpower finding replicates across multiple population studies examining food access, marketing exposure, and obesity prevalence.