Greenhouse gas emissions higher for non-vegetarian diets than for vegetarian diets

A new analysis adds to evidence that nutritious diets are often more environmentally sustainable, while also demonstrating the feasibility of evaluating diet sustainability at the scale of specific foods-;rather than broader food-group categories. Dr. Holly Rippin of the University of Leeds, U.K., and colleagues present these findings in the open-access journal PLOS ONE on November 24, 2021.

Food production is a major source of greenhouse gas emissions, accounting for about one third of emissions worldwide. Previous research suggests that environmentally sustainable diets are often also less processed, less energy-dense, and more nutritious. However, much of that work has been conducted using measurements of sustainability for broad categories of food instead of specific food items, leaving room for greater accuracy in evaluating the environmental impact of individual diets.

Working towards better accuracy, Rippin and colleagues evaluated existing published research in order to assign greenhouse gas emissions to over 3,233 specific food items listed in the UK Composition Of Foods Integrated Dataset (COFID). COFID already contains nutrition data and is commonly used to evaluate the nutrition of individuals' diets. Then, the researchers used the combined emissions and nutrition information to evaluate the diets of 212 adults who reported all the foods they ate within three 24-hour periods.

Statistical analysis of the reported diets showed that non-vegetarian diets were associated with greenhouse gas emissions that were 59 percent higher than emissions associated with vegetarian diets. Men's diets were linked to emissions that were 41 percent higher than emissions associated with women's diets, primarily due to greater meat intake. And people whose intake of saturated fats, carbohydrates, and sodium met levels recommended by the World Health Organization had lower greenhouse gas emissions than people who exceeded recommended levels of those nutrients.

These findings support a focus on plant-based foods for policies meant to encourage sustainable diets. It also suggests both environmental and nutritional benefits for replacing coffee, tea, and alcohol with more environmentally sustainable substitutes. In the future, similar research efforts could provide further clarity by incorporating such details as food item brand, country of origin, and other indicators of environmental impact, beyond emissions.

The authors add: "We all want to do our bit to help save the planet. Working out how to modify our diets is one way we can do that. There are broad-brush concepts like reducing our meat intake, particularly red meat, but our work also shows that big gains can be made from small changes, like cutting out sweets, or potentially just by switching brands."