What effect do attempts to lose weight have on the observed relationship between nutrition behaviors and body mass index among adolescents?

BACKGROUND Little research has given consideration to how people's weight control behaviors may moderate the relationships between nutrition and body mass index (BMI) in large cross-sectional studies. The objective of the current study is to determine how attempts to lose weight confound the relationships between nutrition behaviors and BMI among a population of predominately overweight adolescents. METHODS Data were drawn from the baseline measurements of the Pacific OPIC (Obesity Prevention In Communities). Participants included approximately 3500 high school students in New Zealand. Students in the sample primarily identified as a Pacific Island ethnicity (57%) and the mean age for participants was 14.8 years. Participants completed a questionnaire about nutrition and physical activity patterns and were weighed and measured for height. RESULTS In our sample, 57% of students were overweight/obese, with the highest prevalence among Pacific Island students (71%). Approximately 50% of students were currently trying to lose weight, and this was more common among females, Pacific Island students and overweight/obese students. Examination of the nutritional correlates of BMI in the total population found inverse relationships between BMI and consumption of high-fat/high-sugar foods and positive relationships between BMI and eating 5 or more fruits and vegetables a day (all significant after controlling for age, sex, and ethnicity). For example, students who drank the most soft drinks or ate fruit and vegetables infrequently had the lowest mean BMI. Students' attempts to change their weight significantly moderated the relationships between most nutritional behaviors and BMI. In most cases, among students not trying to change their weight, expected relationships were observed; among students trying to lose weight, unexpected or no relationships were observed. CONCLUSION Our findings suggest that among this population of predominately overweight students, solely relying on cross-sectional findings between nutrition behaviours and BMI would misinform intervention strategies. It appears that many students are already taking appropriate steps to reduce their weight. Intervention efforts should now move beyond education-based strategies to environmental changes that support students in adopting healthier nutrition practices.