Citation: Davies, K. P., Gibney, E. R., Leonard, U. M., Conway, M. C., McCarthy, S. N., & O’Sullivan, A. M., et al. (2025). Sustainable diets reduce diet-related greenhouse gas emissions and improve diet quality: Results from the MyPlanetDiet randomized controlled trial. The American Journal of Clinical Nutrition. Advance online publication. https://ajcn.nutrition.org/article/S0002-9165(25)00268-0/fulltext
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 (kgCO2-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 kgCO2-eq/d) and intervention groups (7.1 ± 0.2 to 4.8 ± 0.1 kgCO2-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: It is clear that the environmental impact of food systems must be reduced to mitigate the effects of climate change and adhere to global climate targets. Meaningful change will require a full-system approach, which means all actors, including consumers, doing their part for a more sustainable food system. Moving individuals toward more sustainable diets is critical, and our findings address an evidence gap to support this transition. We have shown that it is possible at the consumer level to adopt more sustainable diets. Changes to dietary intakes resulted in decreased diet-related GHGE without compromising health status. Further research is warranted in other populations, for longer intervention periods, or with other outcomes measures (ie, nutrient status). However, our findings add to the literature for what the transition to sustainable diets will look like in the real world. It is important for future FBDGs to consider how to appropriately support individuals to make dietary changes. Our findings show that supporting individuals with personalized nutrition led to dietary change for more sustainable and healthy diets without negative health consequences.
updated 2025 November
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