Sustainable diets reduce diet-related greenhouse gas emissions and improve diet quality: results from the MyPlanetDiet randomized controlled trial
Katie P. Davies, Eileen R. Gibney, Ursula M. Leonard, Leona Lindberg, Jayne V. Woodside, Máiréad Kiely, Anne P. Nugent, Elena Arranz, Marie C. Conway, Sinéad N. McCarthy, Aifric O’Sullivan
Abstract
Background Diet-related environmental impacts must be reduced to mitigate climate change. Although many sustainable diets have been proposed, the human and planetary impacts of following such diets have not been tested. Objective The aim of this study was to assess health and environmental outcomes related to following whole-diet sustainable dietary advice. Methods The MyPlanetDiet RCT was a 12-week single-blinded, parallel study testing the impacts of a more sustainable diet. Participants were randomly assigned to receive personalized advice based on a sustainable diet (intervention) or based on current healthy eating guidelines (control). Dietary assessments, fasted anthropometry, and fasted serum samples were collected at baseline and end point. The primary outcome was change in diet-related greenhouse gas emissions (GHGE) measured in kilograms carbon dioxide equivalents per day (kgCO 2 -eq/d). Secondary outcomes included changes in diet quality, macronutrient and food group intakes, diet-related water footprint, and health biomarkers. Data were analyzed using 2-way mixed analysis of covariance. Results Study participants ( n = 292) decreased diet-related GHGE over time ( P < 0.001) with a significant time × group interaction between control (from 6.5 ± 0.2 to 5.7 ± 0.2 kgCO 2 -eq/d) and intervention groups (7.1 ± 0.2 to 4.8 ± 0.1 kgCO 2 -eq/d; P < 0.001). Diet quality increased in control (from 44.2 ± 0.8 to 52.9 ± 0.9) and intervention (from 44.7 ± 0.8 to 53.0 ± 0.9) groups ( P < 0.001). Participants decreased red meat intakes (control: from 34.2 ± 2.9 to 25.7 ± 2.4 g/d; intervention: from 42.7 ± 3.4 to 12.8 ± 1.9 g/d; P < 0.001) and increased plant-based food intakes including beans, peas, and lentils (control: from 15.4 ± 1.9 to 18.3 ± 2.1 g/d; intervention: from 18.4 ± 2.1 to 49.2 ± 4.3 g/d; P < 0.001), fruit (control: from 164.8 ± 12.3 to 264.5 ± 13.9 g/d; intervention: from 188.5 ± 14.2 to 233.7 ± 13.5 g/d; P < 0.001), and vegetables (control: from 148.1 ± 6.5 to 163.1 ± 7.3 g/d; intervention: from 161.3 ± 5.9 to 201.9 ± 8.0 g/d; P < 0.001). No changes in anthropometry, serum biochemistry, or diet-related water footprint were observed. Conclusions Personalized sustainable dietary advice led to healthier diets and lower diet-related GHGE with no short-term negative health effects. This trial was registered with clinicaltrials.gov as NCT05253547 ( https://clinicaltrials.gov/study/NCT05253547 ).