This study will determine whether lactobacillus GG (LGG), a beneficial bacterium, when given in yogurt, will reduce growth faltering in babies living in a poor area of Pakistan who are being weaned from breastfeeding.

Study hypothesis: Use of the probiotic bacteria LGG at the time of weaning will lessen the impact of faltering growth in babies living in the slums of Pakistan.

Faltering growth due to malnutrition and recurrent diarrhea is a serious public health concern in developing nations, particularly among infants who are being weaned from breastfeeding. Evidence suggests that the use of the probiotic bacterium LGG reduces the risk of diarrhea, shortens episodes of diarrhea, and enhances the immune system. Babies who are being weaned from breastfeeding will be given LGG-containing yogurt in this study to determine whether LGG will reduce faltering growth caused by diarrhea and malnutrition.

Infant participants will be enrolled at or within 5 weeks of birth and followed throughout the weaning period. During the weaning period, participants will be randomly assigned to either receive LGG-containing yogurt or placebo yogurt everyday for 3 months. All participants will have height and weight measurements taken at study entry and at Month 3 (study completion). The number of diarrhea episodes experienced by participants during the study will be assessed at study completion to determine participants' health.

Inclusion Criteria:

• Born and reside in Bilal Colony, Karachi Pakistan during the study
• Parent or guardian willing to provide informed consent
• Parent or guardian willing to permit home visits
• Predominantly breastfed at study start

Exclusion Criteria:

• Malnutrition at time of weaning
• Medical condition that would affect response to LGG