The environmental burden of meat and dairy has drawn attention to alternatives, although their capacity to fulfil similar dietary roles remains uncertain. Here, we evaluate the effects of replacing meat and jointly replacing meat and dairy with alternatives on the environmental impacts and nutrient profiles of current and recommended diets. We consolidate environmental inventory and food composition databases in a product- and diet-level analysis to evaluate various impact categories and nutrients. The results show that replacing meat with alternatives can lower environmental impacts by up to 52%, though adequate intake of some critical nutrients, particularly vitamin B12, needs to be ensured. Compared to dairy products, dairy alternatives more frequently lack nutrients, such as calcium and iodine, and certain ingredients, such as almond and coconut, may increase specific environmental impacts. Our findings highlight the challenges of reducing environmental impacts without compromising nutrition, with implications for high-income countries pursuing sustainable dietary transitions.