London School of Hygiene & Tropical Medicine

Most types of so-called ‘sustainable diets’, including flexitarian, pescatarian, vegetarian and vegan, are likely to improve your health and have a positive impact on the environment, according to new research, published in Environmental Research Letters.

The study, led by the London School of Hygiene & Tropical Medicine and funded by the Children’s Investment Fund Foundation and the Wellcome Trust, is the first systematic review addressing the effects on both health and the environment of shifting from current diets to various forms of sustainable diets.

The exact composition of sustainable diets varies greatly but they are typically low in animal-sourced food and high in plant-based food.

The team scanned more than 3,200 papers from eight different databases to find studies measuring the shift from current diets to diets designed to have a lower environmental footprint. They identified 18 articles that reported both health outcomes associated with the diets, including cancer, cardiovascular disease and diabetes, and environmental footprints associated with producing the diets, including greenhouse gas emissions, land use and water footprints.

Despite large differences in the composition of the reported sustainable diets, they were associated with improved outcomes in 87% of reported health metrics. For example, sustainable diets were associated with on average 19% reduction in risk of diabetes in adults.  Shifts to vegan diets and diets in which plant-sourced foods replaced all animal-sourced foods had the largest positive effects on health.

Sustainable diets were associated with 25% on average reductions in greenhouse gas emissions as well as reductions in land and nitrogen use. Shifts to vegan diets were estimated to reduce greenhouse gas emissions on average by 81% when compared to current diets. Shifts to vegetarian diets reduced greenhouse gas emissions by 75% and shifts to flexitarian and pescatarian diets reduced emissions by 47%.

In contrast, the study found that the production of some sustainable diets required more water in their production than the diets currently being consumed, an important trade-off to consider at a time when water shortages are an increasing concern in some regions.

Dr Pauline Scheelbeek, Assistant Professor in nutritional and environmental epidemiology and author in the study, said: “Even small dietary shifts can have a great impact on our health and on the environment. There are many ways people can reduce the environmental footprint of diets and improve their health: veganism is not the only option and may not be achievable for everyone.

Finding ways to gradually replace red meat and other animal-sourced foods with vegetables, legumes, fruit or nuts and seed typically improves health, especially for those in countries where red meat consumption is high. These smaller dietary changes can vastly contribute to environmental sustainability, especially if they were adopted by populations on a wider scale.”

The researchers highlight that there could be other trade-offs with large scale shifts to sustainable diets. For example, global food prices may change, and the livelihoods of livestock farmers could be affected.

Professor Alan Dangour, Director for the Centre on Climate Change & Planetary Health, said: “This detailed systematic review gives us important evidence that sustainable diets are not only less harmful for our planet but are also broadly beneficial for our health.  In this dark time, the world desperately needs positive stories and examples of win-win solutions to the devastating climate and health crises we are facing.  Ahead of the forthcoming UN conference on climate change later this year we must use these positive examples to shape potential pathways for a healthy and sustainable future for all.”

Limitations of the study include challenges in the labelling of sustainable diet groups and reporting bias from the literature databases of published papers. 3 of the 18 studies directly measured health outcomes resulting from dietary shifts, and 15 of the 18 studies modelled the impacts of dietary change on health outcomes.

Publication

Stephanie Jarmul, Alan D Dangour, Rosemary Green, Zara Liew, Andy Haines and Pauline FD Scheelbeek. Climate change mitigation through dietary change: a systematic review of empirical and modelling studies on the environmental footprints and health effects of 'sustainable diets'. Environmental Research Letters. DOI: 10.1088/1748-9326/abc2f7