This Reprint brings together current research addressing the major clinical, epidemiological, and mechanistic dimensions of nutrition and obesity. The collected contributions examine obesity across the life course and in diverse settings, from adolescents and children with specific clinical conditions to adult population based cohorts. The articles address the relationship between nutritional status, body composition, inflammation, emotional eating, and cardiometabolic risk. They highlight the value of refined body composition assessment beyond body mass index, including bioelectrical impedance based approaches, and examine sociodemographic and sex related differences in the prevalence and distribution of excess adiposity. This Reprint also explores biological mechanisms linking dietary exposures with obesity related complications. These include the effects of high fat diets and microbiota related interventions on host metabolism, the potential role of bioactive compounds in metabolic dysfunction, hepatic steatosis, and muscle health, and cellular pathways through which saturated fatty acids may contribute to oxidative stress, neuroinflammation, and obesity related cardiovascular risk. Together, these studies provide multidisciplinary evidence relevant to obesity prevention, assessment, and management. They underline the need for personalized and life course approaches that integrate nutritional, behavioral, body composition, inflammatory, and metabolic factors to improve obesity care and reduce its associated health burden.