Lactose-Free Milk or Soy-Based Formulas Do Not Improve Caregivers' Distress or Perceptions of Difficult Infant Behavior.

Objectives: The aim of the study was to test the hypothesis that caregiver-reported difficulties in infant behavior and caregivers' distress will significantly improve on lactose-free (LF) milk-based or LF soy-based formulas compared with a milk-based, lactose-containing formula.

Methods: In this double-blind randomized controlled trial, infants (mean age: 4.97 weeks) with caregiver-reported feeding problems on a milk-based lactose-containing formula were randomized to receive either LF milk-based (n = 96), LF soy-based (n = 97), or milk-based, lactose-containing (n = 103) formula. Study formula was infants' sole item of diet for 14 days. Infants' caregivers completed measures of infant behavior and caregivers' distress for the week preceding baseline and again for the week preceding the 14-day follow-up.

Results: Infants who received LF milk or LF soy-based formulas did not significantly differ from those who received milk-based, lactose-containing formula on follow-up caregiver-reported measures of infant difficultness from the Infant Characteristics Questionnaire, F(2, 277) = 0.83, nor on measures of caregivers' distress, assessed with measures of caregivers' mental health and parenting efficacy, F(2, 285) = 0.73-1.07. Across the 3 formula groups, scores on outcome measures significantly improved from baseline to follow-up (P < 0.001).

Conclusions: Our study does not support LF milk or LF soy-based formulas to alleviate common infant behaviors such as fussiness, crying, or need for attention. Moreover, the data suggest that some difficulties in infant behaviors, as well as caregivers' distress and perceived efficacy in parenting difficult infants, may improve within a couple weeks of reporting difficulties to the pediatrician.