Background: The prevalence of obesity has recently stabilized in some developed countries. Some studies show this stabilization in Spain, but they do not analyse its evolution by cohort.

Objective: This paper analyses the transformation of the Spanish population over time and between quasi-cohorts of weight change by age and sex.

Methods: Data was taken from seven waves of the National Health Survey of Spain between 1995 and 2017, with a sample of 100,206 individuals aged 20–79 years old. Adjusted prevalence of being overweight and obesity were calculated. The changes in body mass index (BMI) by sex and age, by and between quasi-birth cohorts, and over time were analysed using test of proportions, ANOVA, and the t-test.

Results: The prevalence of excessive body weight has stabilized or decreased in men since 2017 and in women since 1997. Among men, the prevalence of obesity stabilized recently and weight gain with age decreased after the 1950s cohort. Among women, mean BMI and excessive body weight decreased after the 1940s cohort.

Conclusions: Our findings showed a stabilization and subsequent decrease in excessive body weight that is recent among men but took place more than two decades ago among women.

Contribution: This is the first study that analyses the evolution of obesity by comparing the age-related weight gains between quasi-cohorts. This is also the first study that analyses the stabilization of excessive body weight in Spain by quasi-cohort, age, and sex, and that shows that this stabilization is due to a bigger weight control among the older cohorts in the older ages.