This cross-sectional study, conducted in Bavaria, southern Germany, aimed to assess the impact of breast feeding on the risk of obesity and overweight in children at the time of school entry. The study collected data from 134,577 children participating in the obligatory health examination, with a subsample of 13,345 children assessed using a questionnaire about early feeding, diet, and lifestyle factors. The main outcomes were defined as being overweight (body mass index above the 90th centile) and obesity (body mass index above the 97th centile). Key findings included: - The prevalence of obesity was 4.3% in children who had never been breastfed compared to 2.8% in breastfed children. - A dose-response effect was observed, with the prevalence of obesity decreasing as the duration of exclusive breast feeding increased: 3.8% for 2 months, 2.3% for 3-5 months, 1.7% for 6-12 months, and 0.8% for more than 12 months. - Similar trends were seen for being overweight. - The protective effect of breast feeding was not attributed to differences in social class or lifestyle. - After adjusting for potential confounding factors, breast feeding remained a significant protective factor against obesity (odds ratio 0.75, 95% CI 0.57 to 0.98) and being overweight (odds ratio 0.79, 0.68 to 0.93). The study concluded that promoting prolonged breast feeding in industrialized countries may help reduce the prevalence of childhood obesity, which could eventually lead to a reduction in cardiovascular diseases and other obesity-related health issues.This cross-sectional study, conducted in Bavaria, southern Germany, aimed to assess the impact of breast feeding on the risk of obesity and overweight in children at the time of school entry. The study collected data from 134,577 children participating in the obligatory health examination, with a subsample of 13,345 children assessed using a questionnaire about early feeding, diet, and lifestyle factors. The main outcomes were defined as being overweight (body mass index above the 90th centile) and obesity (body mass index above the 97th centile). Key findings included: - The prevalence of obesity was 4.3% in children who had never been breastfed compared to 2.8% in breastfed children. - A dose-response effect was observed, with the prevalence of obesity decreasing as the duration of exclusive breast feeding increased: 3.8% for 2 months, 2.3% for 3-5 months, 1.7% for 6-12 months, and 0.8% for more than 12 months. - Similar trends were seen for being overweight. - The protective effect of breast feeding was not attributed to differences in social class or lifestyle. - After adjusting for potential confounding factors, breast feeding remained a significant protective factor against obesity (odds ratio 0.75, 95% CI 0.57 to 0.98) and being overweight (odds ratio 0.79, 0.68 to 0.93). The study concluded that promoting prolonged breast feeding in industrialized countries may help reduce the prevalence of childhood obesity, which could eventually lead to a reduction in cardiovascular diseases and other obesity-related health issues.