With the diminishing availability of farmland, climate change and the threat of declining water resources, livestock needs to meet the growing demand for food and feed by using fewer resources. The reuse of food losses as sustainable ingredients for feed formulations could represent a promising alternative to cereal grains for both monogastrics and ruminants, increasing livestock sustainability and reducing the competition between animal and human nutrition. The acceptance of food leftover for feeding animals it is still far to be completely welcomed in several countries, where the outdated stereotypical image of the ex-food used as feed is still existing. To implement this practice, a renewed image of food leftover as feed is needed, mainly disseminating the most recent findings about their properties, the new technologies applied for their production and their impact on the environment. In this scenario our projects (SUSFEED, SAN, ASSO) in southern Europe are exploring and addressing the potential benefits of using food leftovers as alternative feed ingredients in pig and ruminant nutrition. Several characteristics of these materials are examined and compared to a standard diet, such as nutritional-related properties, safety, efficiency and environmental implications. The literature shows that both categories of food leftovers hold a significant nutritional value and are a sustainable alternative to traditional feed ingredients. They resulted as a low risk category for animal health. In addition, when used in complete feed to replace traditional feed ingredients, ex-foods do not decrease animal’s growth performances, digestibility, metabolic and GIT health. Once approved the use of these food leftovers and the replacement of some conventional cereals with them, it is also possible to estimate the environmental benefit of this new strategy. This substitution can lead to saving in agricultural lands and water resources currently used for the production of feed crops, making them available for the production of food crops or other purposes. These savings could also potentially entail a reduction in the international animal feed trade, which is often the driver of environmental issues such as land-use change, biodiversity losses, food insecurity, and water scarcity.These findings valorize food losses into animal feed as a well-suited strategy to contribute to a reduced environmental and climate footprint of animal products and food waste prevention. However, greater participation by feed/food processors and stakeholders is crucial to allow the sector to increase its contribution to the entire EU food and feed chain.