The effect of population norms on self-reported weight perception and weight control behaviour: evidence from Spain

The research employs eight waves of the Spanish National Health Survey—1987 to 2011—to investigate whether self-reported weight perception (SWP) and weight control decisions are affected by the population weight norm. We find that the percentage of overweight or obese have changed from 37.82% to 50.68% in the survey period. Surprisingly, SWP, weight loss medication intake and dieting have not increased as expected. Similarly, people in the most overweight regions do not seem to perceive their weight or behave differently than those in the territories with the lowest body mass index (BMI) values. We argue that this pattern could be explained by a mechanism of adaptation to the norm. We find evidence that weight perception and behaviour are affected negatively by BMI norm—measured as average BMI in a region-year-sex group—after controlling for individual BMI. We argue that these results could be relevant for designing health policies and could provide an economic argument for public interventions based on the effect of social norms on decisions.