What Factors Influence Obesity in Spain? A Multivariate Analysis of Sociodemographic, Nutritional, and Lifestyle Factors Affecting Body Mass Index in the Spanish Population

Aim: This cross-sectional study examines sociodemographic, nutritional, and lifestyle factors affecting Body Mass Index (BMI) in the Spanish population, with a particular emphasis on obesity. Methods: A sample of 22,181 Spanish residents aged 18 years and older was recruited through digital and physical channels from August 2020 to November 2021. Data were collected using the validated NutSo-HH questionnaire, which includes sections on sociodemographic information, health perceptions, eating habits, and lifestyle factors. Results: Among respondents, 661 (3%) were underweight (BMI < 18.5 kg/m(2)), 14,562 (65.7%) were normal weight (18.5 kg/m(2) <= BMI <= 25 kg/m(2)), 4825 respondents (21.8%) were overweight (25 kg/m(2) < BMI <= 30 kg/m(2)), and 2133 (9.6%) were obese (BMI > 30 kg/m(2)), with significant differences across these groups in relation to diet and lifestyle behaviors. Principal Component Analysis (PCA) was employed to identify the primary variables influencing obesity, revealing that poor dietary habits (frequent consumption of fast food, fried foods, and ultra-processed items) were negatively correlated with healthy behaviors such as regular fish consumption and physical activity. The PCA plot indicated notable distinctions based on educational attainment and age, with individuals with lower educational levels displaying poorer nutritional patterns and younger participants exhibiting higher fast food consumption and poorer sleep quality. Statistical analyses confirmed that sociodemographic factors, including age, education, and income level, significantly influenced BMI. Some differences were also found according to the place of residence. Conclusions: These findings underscore the need for targeted interventions that address both sociodemographic and lifestyle factors to mitigate obesity risk in Spain.