Objective: To analyse the influence of habitual protein intake in early childhood on age and body mass index (BMI) at adiposity rebound (AR), a potential critical period for the development of obesity.

Subjects: A total of 313 children (161 boys, 152 girls) participating in the Dortmund Nutritional and Anthropometric Longitudinally Designed Study.

Methods: Weighted summary indices were created reflecting habitual, energy-adjusted protein intake (expressed as % of energy) and protein intake per kg reference body weight per day (g/kg RBW/day) between the age of 12 and 24 months. Body mass index standard deviation scores (BMI-SDS), age at AR and covariates (mother's BMI, gestational age, breastfeeding and siblings) were included in the final models.

Results: After adjusting for potential confounders, girls in the highest tertile (T3) of habitual energy-adjusted protein intake had a significantly higher BMI-SDS at AR than those in T1 (T1: -0.61 (95% CI: -0.90; -0.31), T2: -0.49 (-0.79; -0.20), T3: -0.08 (-0.36; 0.20), P for difference=0.01). A comparable association existed with habitual protein intake expressed as g/kg RBW/day (T1: -0.64 (-0.93; -0.36), T2: -0.22 (-0.52; 0.09), T3: -0.25 (-0.54; 0.04), P=0.04). In boys, there were no differences in BMI-SDS at AR between tertiles of habitual protein intake (% of energy or g/kg RBW/day) (P>0.05). Boys in the lowest tertile of habitual energy-adjusted protein intake tended to experience a later AR (T1: 6.0 (5.6; 6.4), T2: 5.5 (5.1; 5.9), T3: 5.4 (5.0; 5.9) years, P=0.07). But neither in girls nor in boys was age at AR significantly different between tertiles of habitual protein intake (% of energy or g/kg RBW/day) (P>0.05).

Conclusion: A higher habitual protein intake between the age of 12 and 24 months was associated with a higher BMI-SDS at AR in girls, but not in boys. There was no consistent relation between habitual protein intake in early childhood and timing of AR.