No previous research has looked at the impacts of infant formula feeding with added sugars although it has been linked to the establishment of a different infant gut microbiome when compared to human milk. The gut microbiota of 91 Hispanic newborns who ingested human milk [at breast (BB) vs. pumped in a bottle (BP)] and two types of infant formula [(traditional lactose-based (TF) vs. lactose-reduced with added sugar (ASF)] were studied by researchers. Infant stool was collected at 1 and 6 months to define gut flora. Mothers conducted 24-hour meal recalls and questionnaires at 6 months to assess whether their infants consumed human milk (BB vs. BP) or formula (TF vs. ASF). At 6 months, linear regression models were employed to find relationships between milk consumption type and microbiological characteristics. Infants in the formula groups had a considerably more mature microbiome than infants in the human milk groups, with the ASF vs. BB groups showing the most obvious differences. Bifidobacteriaceae log-normalized abundance was reduced in the ASF group (TF-BB Mean Difference = 0.71, ASF-BB Mean Difference = 1.10), but Lachnospiraceae log-normalized abundance was raised (TF-BB Mean Difference = +0.89, ASF-BB Mean Difference = +1.20). The ASF group also had a higher Community Phenotype Index of propionate (TF-BB Mean Difference = +0.27, ASF-BB Mean Difference = +0.36), which is most likely produced by Lachnospiraceae. The study conducted by the researchers is the first study to show that infant formula in addition to added sugar has more impact on the infant’s microbiome at 6 months of age than birth delivery mode, infant caloric intake, or maternal BMI.