association between formula feeding and acute diarrhea in infants under two years: a case–control study

Background: acute diarrhea is a major cause of morbidity in infants under two years, often leading to dehydration and healthcare use. while breastfeeding is protective, the association between formula feeding and acute diarrhea remains insufficiently studied, particularly in middle eastern populations with distinct feeding practices.objectives: this study aimed to examine the association between formula feeding and acute diarrhea among infants in rafsanjan, iran.methods: we conducted a hospital-based case–control study between april 2024 and january 2025 at ali ibn abi talib hospital and affiliated health centers in rafsanjan, iran. the study included 100 infants under two years of age with clinically diagnosed acute diarrhea (defined as ≥3 watery stools within the preceding three days) and 100 age- and sex-matched controls without a history of diarrhea in the past month. data on infant feeding practices (categorized as breastfeeding, formula feeding, or mixed feeding), demographic characteristics, recent antibiotic exposure (within the past 14 days), and parental factors (age, education, employment status, residence, and ethnicity) were collected using a structured, researcher-designed questionnaire. associations were evaluated using logistic regression models. multivariable analyses adjusted for selected covariates, including birth weight, feeding practices, antibiotic use, and parental characteristics.results: formula feeding was associated with higher odds of acute diarrhea in the adjusted analysis (adjusted odds ratio [aor]=3.88, 95% confidence interval [ci]: 1.21–12.40, p=0.022). breastfeeding was associated with lower odds of acute diarrhea (aor=0.44, 95% ci: 0.25–0.78, p=0.005). recent antibiotic use was also associated with increased odds (aor=4.46, 95% ci: 1.59–12.47, p=0.004). associations were observed between acute diarrhea and lower parental education, rural residence, and non-iranian ethnicity.conclusion: formula feeding was associated with increased odds of acute diarrhea in infants under two years, whereas breastfeeding was associated with lower odds. these findings should be interpreted cautiously given the case–control design, potential selection bias, and residual confounding. further prospective, multicenter studies are needed to clarify causal relationships and to explore the role of environmental and behavioral factors, including feeding practices and hygiene conditions.