Abstract
High intakes of total protein and animal-sourced protein in infancy have been identified as risk factors for childhood obesity (1). However, it remains unclear whether reducing protein intake in infancy through isocaloric replacement with fat or carbohydrate influences body weight development. Thus, this study examined the association of substituting protein with fat or carbohydrate intake, and the substitution of protein subtypes at 9 months of age with body weight outcomes at 5 years of age. Data of 345 children from the Melbourne InFANT Program (2) who completed the 9-month and 5-year follow-ups were analysed. Dietary intake at 9 months was collected using three 24-hour recalls. Body mass index (BMI) z-score was measured at 9 months and 5 years of age. Multivariable linear and logistic regression models with adjustment for potential confounders examined the associations between macronutrient and protein subtype substitutions at 9 months and changes in BMI z-score or overweight status at 5 years. Substitution of 5%E or 100kJ protein intake with carbohydrate intake at age 9 months was associated with a 0.16-unit (95% CI: -0.29, -0.02) or 0.10-unit (95% CI: -0.18, -0.02) decrease in BMI z-score at 5 years of age. Similarly, replacing 5%E or 100kJ of protein intake with fat intake was associated with a 0.14-unit (95% CI: -0.27, -0.004) or 0.10-unit (95% CI: -0.18, -0.01) decrease in BMI z-score. No evidence of associations was found between substitution of protein with fat or carbohydrate intake and overweight status (P>0.05). Replacement of animal protein with plant or dairy protein was also not significantly associated with BMI z-score or overweight status. The present study supports the need to discourage excessive protein intake during infancy. This information will be valuable for informing the refinement of macronutrient intake recommendations during infancy and infant feeding guidelines.