Obesity is linked to an increased risk of many cancers and can impair the anti-tumour immune response. This project examined the effect of different sources of dietary fats on tumour immunity using a syngeneic model of melanoma in mice fed high fat diets (HFD) derived from different sources. HFD based on beef tallow, lard and butter increased tumour growth in this model, while HFD derived from coconut oil, palm oil or olive oil did not. Further experiments focusing on butter and palm oil based HFD found differential regulation of natural killer (NK) cells and CD8 T-cell infiltration and function in the tumour microenvironment, and identified enrichment in immunosuppressive long chain acylcarnitine species in mice fed a HFD based on butter compared to palm oil. This dataset contains proteomic data from NK cells from mice fed a standard fat diet (SFD), NK cells from mice fed a HFD based on butter and from mice fed a HFD based on palm oil.