The pet food industry is undergoing significant transformation as sustainability concerns, ethical considerations, and nutritional advancements necessitate the transition to alternative protein sources. Traditional protein ingredients such as beef, poultry, and fish contribute to environmental degradation and resource depletion, necessitating the exploration of novel, eco-friendly alternatives. The potential of alternative protein sources in pet nutrition as a response to the dual challenge of meeting high dietary protein requirements and reducing the environmental impact of traditional pet feeds seems promising. Protein is a critical component in pet diets, with requirements ranging from 18% to 22% for dogs and 26% to 30% for cats on a dry basis. However, conventional dry pet food production contributes 56–151 Mt of CO₂-equivalent emissions annually, utilizes 41–58 Mha of agricultural land, and consumes 5–11 km³ of freshwater, accounting for up to 2.9%, 1.2%, and 0.4% of global agricultural resource use, respectively.
Insect-based proteins offer high protein (25–70%) and lipid (10–50%) contents with a lower water, land, and carbon footprint. Single-cell proteins derived from yeast, fungi, or algae can be cultivated using a variety of substrates, including agricultural waste and industrial by-products. The potential of these alternative protein sources is promising in terms of resource-efficient solutions. While these alternatives offer comparable nutritional value and digestibility to conventional protein sources, safety and regulatory challenges remain, particularly concerning allergenicity and anti-nutritional factors, potential contaminants, and strict standards imposed on single-cell proteins. Future research should focus on mitigating potential risks while establishing robust regulatory frameworks to facilitate widespread adoption of sustainable protein alternatives in pet nutrition.