**Background:** Current global food systems are environmentally unsustainable, contributing 21–37% of anthropogenic greenhouse gas emissions and 70% of global freshwater withdrawals. Overconsumption of animal-derived foods, particularly red and processed meat, is linked to increased risk of cardiovascular diseases, colorectal cancer, and obesity, while also placing significant burden on natural resources. The EAT-Lancet Commission advocates for a 'planetary healthy diet' rich in plant-based foods with limited animal-derived products. Despite growing interest in plant-based diets, evidence on the effectiveness of interventions to shift dietary behaviour toward lower ecological footprint protein sources remains limited. This systematic review aimed to critically evaluate interventions promoting consumption of protein-rich foods from lower ecological footprint sources.
**Methods:** The review followed PRISMA guidelines and was registered on PROSPERO (CRD42020178683). Five electronic databases (Medline, Web of Science, Scopus, Embase, Global Health) were searched for articles published up to January 2021. Quantitative studies reporting actual or intended consumption, purchase, or selection of animal-derived and/or plant-based protein foods in real or virtual environments were eligible. Two researchers independently screened 5,043 studies, assessed 140 full-text articles, and included 51 studies. Data extraction and quality assessment using the Effective Public Health Practice Project (EPHPP) tool were performed independently by two researchers, with disagreements resolved by a third.
**Key Results:** The 51 included studies were categorised into individual-level behaviour change interventions (n=33) and micro-environmental/structural interventions (n=18). Among individual-level studies, 24 were RCTs, 2 were non-randomised controlled trials, and 7 used pre-post designs. Half of individual-level interventions (52%, n=17) targeted people with current or past chronic conditions (cancer, diabetes, cardiovascular disease). Only 3 of 33 individual-level studies considered both health and environmental concerns. Educational interventions (12 studies) showed mixed results: 6 of 8 RCTs found significant reductions in red meat intake in intervention versus control groups, with follow-up ranging from 3 months to 6 years. Counselling interventions (11 studies) were largely positive, with 9 of 9 RCTs showing reduced red/processed meat intake. Self-monitoring via daily SMS (2 studies) significantly reduced processed meat intake after 1 week (F(1,112)=13.09, p<0.001, ηp²=0.11) and red meat intake after 2 weeks (F(1,226)=29.76, p<0.001, η²=0.12). Multicomponent interventions (8 studies) showed mixed results, with 3 of 5 RCTs finding no significant effect. Among micro-environmental studies (18 studies), 9 were RCTs, 2 were controlled trials, 3 were field experiments, 1 was quasi-experimental, and 3 used pre-post designs. Menu manipulation (7 studies) showed mixed results: 2 of 4 RCTs found positive effects on plant-based choices, while 2 found no difference. Choice architecture (3 studies) showed that altering portion sizes significantly reduced meat intake (mean 183.1g vs 211.1g, p<0.001) and increased vegetable intake (mean 115.5g vs 61.7g). Multicomponent environmental interventions (7 studies) generally showed positive results, with 2 of 3 RCTs finding significant reductions in processed or high-fat meat intake. Overall study quality was 'strong' for 12 studies, 'moderate' for 28, and 'weak' for 11.
**Clinical Implications:** Individual-level interventions (education, counselling, self-monitoring) show promise for reducing red/processed meat intake, particularly among motivated clinical populations, but their effectiveness in the general population and long-term sustainability remain unproven. Micro-environmental strategies such as menu manipulation, altering portion sizes, and nudging can effectively shift food choices in dining settings, but most evidence comes from high-income countries. The review identifies a critical need for interventions targeting the general healthy population, incorporating both health and environmental messaging, and evaluating long-term behaviour change. Future research should explore strategies in low- and middle-income countries and investigate motivations for sustainable food purchasing to support the 'Great Food Transformation' needed for planetary and human health.