Current dietary patterns are negatively affecting both the environment and people's health. Healthy diets are generally more environmentally friendly. However, few studies have focused on the health consequences of diets with low environmental impact. We analyzed differences in the dietary composition (types of food, macro- and micro-nutrients) of those diets with high and low environmental impact, according to greenhouse gas emission and resources use (water, land and energy) using data from a Spanish cohort (17,387 participants), collected by means of a validated food frequency questionnaire. Cox analyses were used to assess the association of dietary environmental impact with total mortality risk. At a given level of energy intake, diets with lower environmental impact contained higher amounts of plant-based foods and lower levels of animal-derived products. Less polluting diets involved higher amounts of polyunsaturated fats and dietary fiber and lower amounts of saturated fats and sodium. However, diets associated with less environmental damage also contained more added sugars, but lower levels of vitamin B12, zinc and calcium. We did not detect any association between dietary environmental impact and risk of mortality. Diets should not only produce minimal environmental impact, but the maximum overall benefits for all key dimensions encompassed in sustainable diets.