This study will use a 2 x 2 factorial design to test impact of two intervention strategies (bottle size and bottle opacity) on infant weight gain.

Infants who gain weight rapidly have over 4 times higher odds of developing obesity as a child or adult; infants who are predominantly bottle-fed are at higher risk for excessive infancy weight gain and childhood obesity, yet there are not effective interventions to reduce excessive weight gain among infants who are bottle-fed. The investigators' preliminary work suggest that two novel intervention strategies are feasible and may reduce excessive infancy weight gain: reducing bottle size; and increasing bottle opacity. The investigators aim to test the independent and joint efficacy of these two intervention components among exclusively bottle-fed infants in a randomized, full factorial clinical trial. The investigators' primary objective is to measure the change in conditional weight gain z-score (CWGz) from birth to four months by study group. 4 groups are composed of two conditions: smaller bottles and opaque bottles, independently and in combination, via a 2x2 factorial trial design.

Inclusion Criteria:

• Child is 3 days old to 1 month old
• Greater than 37 weeks gestational age at birth
• Birth weight greater than 3% for sex-specific WHO growth standard
• Caregiver must plan to use local clinic as infant's primary medical home for first 6 months of life
• Caregiver must speak English or Spanish as primary preferred language
• Caregiver age 18 years or older
• Caregiver must agree to use intervention bottles assigned during randomization and agree to stop using their existing bottles during the study period

Exclusion Criteria:

• Multiple gestation
• Significant congenital anomaly or acquired or inherited condition directly affecting feeding, physiology, metabolism, or growth
• Feeding with soy-based, hydrolyzed, lactose-reduced, or elemental formula
• Weight loss greater than 95% for population reference in the first two weeks of life