The protein transition, a shift towards a more balanced consumption of animal and alternative proteins, is a growing concern in scientific and policy discussions regarding food system transformation. High-income countries, characterized by high meat consumption, are central to this debate due to the environmental, health, and ethical implications of current protein production and consumption patterns. This paper addresses the lack of a unified understanding of the protein transition by systematically reviewing existing literature. The review explores existing definitions of the protein transition, identifies the key challenges it aims to address, and categorizes the diverse narratives shaping proposed solutions. The importance of this study lies in clarifying the often-conflicting views on the concept, bridging the gap between different perspectives, and providing insights into more effective strategies for achieving a sustainable protein transition. The study focuses specifically on Organisation for Economic Co-operation and Development (OECD) countries, acknowledging that the protein transition is not universally applicable, particularly in regions with nutritional inadequacy and low animal protein intake.

Existing research on protein transitions approaches the topic from different angles. Some studies focus on the future of protein consumption in general, including all sources. Others concentrate specifically on alternative proteins (insects, algae, plant-based proteins, fungi), examining their production, consumption, acceptance, and environmental impact. A third strand of research investigates the future of animal proteins and their role in food systems. Previous studies have touched upon sustainability issues related to protein sources, but lacked a fully systematic approach due to the scattered nature of the literature. This systematic review addresses this gap by employing a comprehensive approach to literature selection and analysis, focusing on the protein shift as a transition process rather than on specific protein sources.

This systematic review followed the PRISMA guidelines for rigorous and transparent reporting. The literature search, conducted in September 2022 on Scopus, used keywords such as 'protein transition', 'protein shift', 'sustainable protein consumption', and 'sustainable protein production'. The search encompassed titles, abstracts, and keywords. After initial screening, articles not directly addressing the protein transition were excluded. A snowballing method was employed, screening the most-cited references from already included articles to identify additional relevant studies. A total of 52 articles were assessed for eligibility based on predefined inclusion and exclusion criteria (e.g., publication language, geographical focus, definition of protein transition). Thirty-three articles ultimately met the inclusion criteria. Data coding and synthesis were conducted using NVivo 20.1 software, employing an iterative coding process to refine codes and ensure consistent application across all articles. Qualitative methods were predominantly used in the selected studies, with a smaller number employing quantitative approaches or a combination of both.

The review identified 33 relevant articles. Of these, 20 provided explicit or implicit definitions of the protein transition. Most (16) defined the transition from a consumption perspective, focusing on shifting from animal- to alternative-protein-rich diets; only one mentioned reducing total protein intake. A production dimension was explicitly included in only two definitions. Three main challenges were identified: 1) reducing the environmental impacts of protein production and consumption (all articles), 2) providing healthy diets for a growing population (nearly half of the articles), and 3) preventing ethical issues associated with industrial livestock production systems (about a third). Three narratives emerged based on the solutions proposed: 1) The consumer narrative (13 articles) focuses on consumer-led dietary shifts, utilizing strategies such as information campaigns, incentives, and promoting meat reduction. 2) The techno-centric narrative (10 articles) emphasizes developing resource-efficient protein production systems, focusing on research and development of alternative protein sources and associated technologies. 3) The socio-technological transition narrative (8 articles) aims for a system-wide transition of the agri-food system, advocating for policy changes, regulatory frameworks, and multi-stakeholder collaborations. Each narrative prioritizes different solutions and policy approaches (Table 2). A key finding was the lack of a consistent definition of the protein transition and a tendency to reduce the complexities of food systems to the single macronutrient of protein, neglecting the multiple roles of animals in agriculture and the nutritional diversity of protein sources.

The findings highlight a significant gap in the literature regarding a clear and consistent definition of the protein transition. The diversity of interpretations reflects the multi-faceted nature of the challenge. The three identified narratives—consumer, techno-centric, and socio-technological—each offer valuable but partial perspectives on the problem. The lack of alignment between proposed solutions and specific challenges, as well as the disconnect between the broad scale of challenges and the frequently localized nature of solutions, pose significant obstacles to the effectiveness of the protein transition. While the narratives aim to address the identified challenges, effectively linking solutions to impacts and measuring the extent of their contribution to overarching goals remain critical.

This systematic review identified three key narratives guiding the protein transition: consumer-driven dietary changes, techno-centric innovations, and socio-technological system transformation. However, a lack of consistent definition and a tendency to oversimplify the issue hinder progress. Future research should focus on developing a comprehensive definition that considers all facets of food systems, establishing clear links between solutions and their impact on the three identified challenges, and promoting collaboration between diverse stakeholders to facilitate a more effective and holistic protein transition.

The review's scope was limited to articles published in English and focusing on OECD countries. The reliance on existing literature may have introduced publication bias. The qualitative nature of the narrative analysis could be complemented by quantitative approaches in future studies to strengthen the generalizability of findings. The focus on high-income countries limits the transferability of conclusions to contexts with different nutritional needs and food system structures.