Reversal of the Upward Trend of Obesity in Boys, but Not in Girls, in Spain

(1) Background: To compare the prevalence of overweight and obesity in boys and girls and to estimate socioeconomic differences associated with obesity in Spain in 1997, 2007, and 2017. (2) Methods: Data were drawn from national health interview surveys. For each year of study, the prevalence of overweight and obesity was measured, and these results were compared by gender (boy/girl) and socioeconomic status (low/high education). (3) Results: The prevalence of overweight and obesity rose from 1997 to 2007 but then fell in 2017 in all subgroups except in girls aged 10 to 15 years. In this group, there was a steady increase in the prevalence of both overweight (1997, 14.6%; 2007, 17.7%; 2017, 19.6%) and obesity (1.1, 3.2, and 3.7%, respectively). The decrease in prevalence of overweight in both sexes and of obesity in boys, along with the increase in prevalence of obesity in girls, was of a higher magnitude in children whose parents had a lower educational level. (4) Conclusions: The apparent turnaround in the obesity epidemic in Spain should be interpreted with caution. Children’s body weight is influenced by both gender and socioeconomic status—considerations that should be kept in mind when designing health promotion interventions.