Background. Data from a longitudinal study of 153 low-income Peruvian infants were used to assess the relationship between internationally-recommended definitions of feeding practices and infants' monthly weight gain and weight status at 12 months. methods. infants were classified into feeding categories using monthly reported data. Analysis of variance was used to assess the relationship between reported usual feeding practices and growth. Reported breastfeeding practices were compared to observed breastfeeding practices and to weighed breast milk intakes to determine the validity of recommended breastfeeding definitions. Results. Breastfed infants who consumed non-human milks during the first month of life gained less weight during that month (P < 0.002) than exclusively and predominantly breastfed infants. Reported daily nursing frequency was associated with observed nursing frequency and breast milk energy intake (P < 0.05) for infants < 9 months old. Patterns of growth varied according to early diets, Infants who consumed breast milk and non-human milks and those who were fully weaned by 4 months were more likely to be underweight at 12 months than other infants. infants classified as token breastfeeders (≤ 3 times/24 hours) from 0 to 120 days had monthly gains that were similar to those of fully weaned infants. Conclusions. Infant feeding definitions should 1) continue to differentiate exclusively breastfed infants from other infants who are almost exclusively or predominantly breastfed; 2) distinguish partially breastfed infants who consume only nonhuman milks from those who also consume solid foods; and 3) distinguish partially breastfed infants according to their breastfeeding frequency or the % of their total daily energy that comes from breast milk.