The objective of this study was to evaluate the effect of increasing the dietary inclusion of a rumen-protected (RP) Met product (RPMet™, Actus Nutrition, Eden Prairie, MN) on milk, milk components, milk fatty acids (FA), and feed efficiency in lactating dairy cows. One hundred and forty-four lactating Holstein dairy cows were randomly assigned, based on milk yield, parity, and DIM, to nine pens containing 16 cows per pen in an 84-d longitudinal study with a 14-d covariate period and 70-d experimental period. Three pens were stratified to one of three treatment diets based on the yields of milk and milk components and BW collected during the covariate period. The treatment diets were formulated to supply, on a metabolizable basis, 0.86g Met/Mcal of metabolizable energy (ME) (0.86-Met), 1.05g Met/Mcal ME (1.05-Met), and 1.19g Met/Mcal ME (1.19-Met). All diets were formulated to supply, on a metabolizable basis, 1.19g His/Mcal ME and 3.20g Lys/Mcal ME using the Cornell Net Carbohydrate and Protein System (v6.5.5). The statistical model included the fixed effects of treatment, week, and their interaction, and the random effect of pen nested within treatment. The treatment diets did not affect DMI or milk yield, whereas 1.05-Met and 1.19-Met increased ECM yield compared to 0.86-Met. The 1.19-Met treatment increased milk fat content compared to 0.86-Met. The 1.19-Met treatment increased milk protein content and yield compared to 0.86-Met and 1.05-Met, whereas 1.05-Met increased milk protein content and yield compared to 0.86-Met. Compared to 0.86-Met, 1.05-Met and 1.19-Met increased de novo FA content (g/100g milk), and 1.19-Met tended to increase mixed FA content. These data suggest that optimizing the supply of metabolizable Met to 1.19g/Mcal ME improved energetic use efficiency by increasing the synthesis of milk components with no effect on DMI, and that evaluations of AA should consider changes in ECM to capture all energetic and protein-synthetic pathways involved in milk component synthesis.