Dietary protein and protein-containing food groups in relation to menarche: A longitudinal study
Abstract Background Inconsistent findings have been reported for associations between protein intakes and age at menarche. We aimed to investigate the longitudinal associations between intakes of protein and protein-containing food groups with the occurrence of menarche and early menarche in a cohort of Iranian girls.Methods Girls aged 6–14 years in the third or fourth examination cycles of the Tehran Lipid and Glucose Study were selected and were followed to the fifth examination cycle. Daily intakes of protein from different animal/plant sources and ten protein-containing food groups were assessed using a food frequency questionnaire collected at baseline. Attaining menarche and age at menarche were asked during each examination cycle. Cox proportional hazards regression was used to estimating hazard ratios (HRs) and 95% confidence interval (95%CI) for the occurrence of menarche per one standard deviation (SD) of dietary intakes. Logistic regression was also used to estimate the odds of reaching menarche ≤ 12 years.Results During the study, 147(61%) of girls reached menarche, the median age at menarche was 12 years. The HRs (95% CI) for the occurrence of menarche per one-SD of dietary intakes were 0.68(0.48, 0.98) for plant protein and 1.36(1.01, 1.84) for animal protein after adjusting for confounders. Substituting 10-g animal protein with plant protein was associated with a 16% (95%CI: 5–25%) lower risk of menarche. Dietary intakes of poultry (HR: 1.35; 95%CIs: 1.00-1.82) and low-fat dairy (HR: 1.20; 95%CIs: 0.99–1.46) were marginally associated with the increased risk of occurrence of menarche. However, the odds of early menarche was significant only for plant protein (odds ratio = 0.39; 95% CI: 0.16–0.96).Conclusions Our findings indicate that animal and plant protein intake was positively and negatively associated with the risk of menarche, respectively. Some protein-containing foods such as poultry and low-fat dairy were also related to menarche occurrence, but neither animal protein nor protein-containing food groups were associated with menarche occurrence ≤ 12 years.