Eating more fruit and vegetables and cutting back on red and processed meat will make you healthier. That’s obvious enough. But as chickens and cows themselves eat food and burn off their own energy, meat is a also major driver of climate change. Going veggie can drastically reduce your carbon footprint.

This is all at a personal level. What about when you multiply such changes by 7 billion people, and factor in a growing population?

In our latest research, colleagues and I estimate that changes towards more plant-based diets in line with the WHO’s global dietary guidelines could avert 5m-8m deaths per year by 2050. This represents a 6-10% reduction in global mortality.

Food-related greenhouse gas emissions would also be cut by more than two thirds. In all, these dietary changes would have a value to society of more than US$1 trillion – even as much as US$30 trillion. That’s up to a tenth of the likely global GDP in 2050. Our results are published in the journal PNAS.

Future projections of diets paint a grim picture. Fruit and vegetable consumption is expected to increase, but so is red meat consumption and the amount of calories eaten in general. Of the 105 world regions included in our study, fewer than a third are on course to meet dietary recommendations.

A bigger population, eating a worse diet, means that by 2050 food-related GHG emissions will take up half of the “emissions budget” the world has for limiting global warming to less than 2℃.

To see how dietary changes could avert such a doom and gloom scenario, we constructed four alternative diets and analysed their health and environmental impacts: one reference scenario based on projections of diets in 2050; a scenario based on global dietary guidelines which includes minimum amounts of fruits and vegetables, and limits to the amount of red meat, sugar, and total calories; and two vegetarian scenarios, one including eggs and dairy (lacto-ovo vegetarian), and the other completely plant-based (vegan).