Food diet choices can have a considerable effect on climate change as around 15-30% of the total greenhouse gas (GHG) emissions correspond to the food sector. Life-cycle assessment has been an effective tool to evaluate the environmental impact of food production, normally using mass as the functional unit (FU). As this is not always able to reproduce the consumption of different foods and their nutritional value, alternative nutrient-related FUs that can do so should be used. The present study assesses, quantifies and compares the nutritional quality and the environmental impact of two different food diets, a Mediterranean diet (MD), which includes meat-source products and fish, and a vegan diet (VD), which only includes plant-based products. The nutritional quality index NRF9.3 and the impact categories of global warming potential (GWP) and regional biodiversity impact (RBI) due to land use (LU) are assessed for both diets. The VD resulted to have a higher nutritional quality than the MD mainly as it contained less disqualifying nutrients like saturated fat, added sugars and sodium and more qualifying nutrients, although some likely micronutrients deficiencies like B12 in the VD are not assessed here. All the environmental impacts were much higher for the MD, mainly due to the presence of livestock products and fish, which on average had the highest GWP and LU values of all products studied. The GWP, mostly dominated by the food production stage compared to cooking and transport, was around twice as high in the MD. The LU, in livestock products dominated by the land requirements of feedcrops in more than a 99%, was around three times higher in the MD. Finally, the RBI of the MD was also around three times higher than the VD's, although this could be underestimated as fish biodiversity has not been assessed. Impact differences between diets increased when impacts were adjusted by the NRF9.3, which demonstrates that the nutritional quality of diets affects the comparison of the environmental impacts. In an attempt to provide a possible solution to the tightly linked diet-environment-health trilemma, it is concluded that a shift towards a mix of these two diets, where all nutrients are consumed in the recommended levels and where only the least environmental impacting livestock products are consumed, would maybe help reducing GHG emissions, deforestation and biodiversity loss, as well as preventing diet-related diseases like diabetes, obesity, cardiovascular diseases and cancer.