Associations of nutrition knowledge and healthy lifestyle with body mass index status among medical students: a cross-sectional study.

OBJECTIVES: To examine the associations of nutrition knowledge and healthy lifestyle score (HLS) with body mass index (BMI) status among medical students. METHODS: This cross-sectional study included 1,040 medical students from Yangzhou University, China. Participants were recruited using convenience sampling and completed an online questionnaire. BMI was calculated using self-reported height and weight and classified as underweight, normal weight, or overweight/obesity. Lifestyle factors included smoking status, alcohol consumption, physical activity, sedentary time, and sleep duration. HLS was constructed based on five healthy lifestyle factors and categorized as 0-1, 2, 3, and 4-5. Nutrition knowledge was classified as inadequate or adequate according to the questionnaire score. Multinomial logistic regression was used to examine the associations of individual lifestyle factors, nutrition knowledge, and HLS with BMI status, using normal weight as the reference category. Exploratory indirect association analysis and random forest analysis were further conducted. RESULTS: Among the 1,040 participants, 240 (23.1%) were classified as underweight, 540 (51.9%) as normal weight, and 260 (25.0%) as overweight/obesity. After adjustment for sex and age group, adequate nutrition knowledge was associated with lower odds of both underweight (OR = 0.145, 95% CI: 0.103-0.204) and overweight/obesity (OR = 0.087, 95% CI: 0.060-0.126). Higher HLS categories were also associated with lower odds of both underweight and overweight/obesity. Compared with participants with an HLS score of 0-1, those with an HLS score of 4-5 had lower odds of underweight (OR = 0.116, 95% CI: 0.061-0.222) and overweight/obesity (OR = 0.040, 95% CI: 0.019-0.088). Exploratory indirect association analysis suggested that HLS accounted for part of the statistical association between nutrition knowledge and BMI status. Random forest analysis further identified nutrition knowledge and lifestyle-related variables as important contributors to BMI classification. CONCLUSION: Nutrition knowledge and healthy lifestyle patterns were associated with BMI status among medical students. Higher HLS and adequate nutrition knowledge were associated with lower odds of both underweight and overweight/obesity. Given the cross-sectional design, these findings should be interpreted as associations rather than evidence of causality. Future longitudinal studies are needed to clarify the temporal relationships among nutrition knowledge, lifestyle behaviors, and BMI status.