Climate change mitigation through dietary change: a systematic review of empirical and modelling studies on the environmental footprints and health effects of 'sustainable diets'

Abstract

The adoption of healthy diets with low environmental impact has been widely promoted as an important climate change mitigation strategy. Typically, these diets are high in plant-sourced and low in animal-sourced and processed foods. Despite the fact that their environmental impacts vary, they are often referred to as 'sustainable diets'. Here we systematically review the available published evidence on the effect of 'sustainable diets' on environmental footprints and human health. Eight databases (OvidSP-Medline, OvidSP-Embase, EBSCO-GreenFILE, Web of Science Core Collection, Scopus, OvidSP-CAB-Abstracts, OvidSP-AGRIS, and OvidSP-Global Health) were searched to identify literature (published 1999-2019) reporting health effects and environmental footprints of 'sustainable diets'. Available evidence was mapped and pooled analysis was conducted by unique combinations of diet pattern, health and environmental outcome. Eighteen studies (412 measurements) met our inclusion criteria, distinguishing twelve non-mutually exclusive sustainable diet patterns, six environmental outcomes, and seven health outcomes. In 87% of measurements (n = 151) positive health outcomes were reported from 'sustainable diets' (average relative health improvement: 4.09% [95% CI -0.10-8.29]) when comparing 'sustainable diets' to current/baseline consumption patterns. Greenhouse gas emissions associated with 'sustainable diets' were on average 25.8%[95%CI -27.0 to -14.6] lower than current/baseline consumption patterns, with vegan diets reporting the largest reduction in GHG-emissions (-70.3% [95% CI: -90.2 to -50.4]), however, water use was frequently reported to be higher than current/baseline diets. Multiple benefits for both health and the environment were reported in the majority (n = 315[76%]) of measurements. We identified consistent evidence of both positive health effects and reduced environmental footprints accruing from 'sustainable diets'. The notable exception of increased water use associated with 'sustainable diets' identifies that co-benefits are not universal and some trade-offs are likely. When carefully designed, evidence-based, and adapted to contextual factors, dietary change could play a pivotal role in climate change mitigation, sustainable food systems, and future population health.

Keywords: co-benefits; dietary change; greenhouse gas emissions; health impacts; land use; sustainable diets; water use.

Figure 1. ROSES flow chart of searching, screening and inclusion of papers for systematic review on health effects and environmental footprints of ‘sustainable diets’.

Figure 2

Heat map of health and environmental outcome combinations reported in 18 studies included in systematic review (values are number of measurements; (x) = number of studies); CVD = cardiovascular disease; ‘Diet-related Chronic Disease’ = Morbidity and/or mortality of combined nutrition related chronic diseases. GHG = Greenhouse Gas Emissions; LU = Land Use; WU = Water Use; NU = Nitrogen Use; PU = Phosphorus Use; Other includes acidification, biodiversity loss, and environmental footprint index.diets (+13.8% [95% CI: 8.72—18.9] in studies comparing baseline diets with those substituting ASF with PSF). There was generally good concordance in these findings across modelling and empirical studies.

Figure 3

Reductions in (A) greenhouse gas emissions; (B) land use; (C) water use; and (4) nitrogen use; and their associated combined health outcomes for the eight most common dietary category reported in measurements included in systematic review. (GHGe = Greenhouse Gas Emissions; ASF = animal sourced foods; PSF = plant sourced foods.