Background and Purpose L-type amino acid (AA) transporters LAT1 (SLC7A5) and LAT2 (SLC7A8) facilitate the bidirectional transport of branched and aromatic AA across the plasma membrane. While LAT1 is overexpressed in different tumour cells and it is dedicated to deliver AA into growing cells, LAT2 facilitates the transcellular AA transport at biological barriers. Data on dynamic AA transport by LAT1/2 in physiological media are widely lacking and the impact of LAT1-selective inhibitors and mutations on the cellular metabolome is unknown. Experimental Approach The human MDST8 cell line lacking LAT1/2 expression was employed to generate transiently and stably expressing MDST8-LAT1 and MDST8-LAT2 cells. Together with the HT-29 cell line, we depicted metabolic signatures mediated by LAT1 and LAT2 using LC-ESI-MS/MS and characterized potent LAT1/2 inhibitors for their selectivity and mode of action. Moreover, LAT1 mutations associated with autism spectrum disorder (ASD) were functionally evaluated. Key Results LAT1 and LAT2 expression induced the expression of 4F2hc and facilitated differential cellular metabolomic signatures in MDST8 cells. The LAT1(A246V) mutation showed overall reduced aromatic AA uptake and profound alterations of intracellular metabolites and biochemical processes. The equipotent LAT1 inhibitors JPH203 and JX-078 showed intriguing differences on metabolomic effects, uncovering their distinct mode of action. Conclusion and Implications Our study demonstrates that SLC7A transporters mediate differential dynamic cellular AA changes under physiological conditions and reports the broad effects of one human LAT1 mutation associated with ADS. Moreover, the characterization of biased LAT1 inhibitors challenges current concepts about transporter pharmacology and has implications for drug discovery.