“If the whole world, which continues to grow, eats more like us, the impacts are staggering, and the planet simply can’t withstand it,” said Sharon Palmer, a registered dietitian nutritionist and plant-based food and sustainability expert in Los Angeles who was not involved in the new research.
Sustaining a healthier planet will require halving the amount of food loss and waste, and improving farming practices and technologies. But it will also require a shift toward more plant-based diets, according to Springmann.
As Palmer noted, “research consistently shows that drastically reducing animal food intake and mostly eating plant foods is one of the most powerful things you can do to reduce your impact on the planet over your lifetime, in terms of energy required, land used, greenhouse gas emissions, water used and pollutants produced.”
How a meat-based diet negatively affects the environment
It might come as a surprise, but Springmann’s study found that the production of animal products generates the majority of food-related greenhouse-gas emissions — specifically, up to 78% of total agricultural emissions.
This, he explained, is due to manure-related emissions, to their “low feed-conversion efficiencies” (meaning cows and other animals are not efficient in converting what they eat into body weight) and to enteric fermentation in ruminants, a process that takes place in a cow’s stomach when it digests food that leads to methane emissions.
The feed-related impacts of animal products also contribute to freshwater use and pressures on cropland, as well as nitrogen and phosphorus application, which over time could lead to dead zones in oceans, low-oxygen areas where few organisms can survive, according to Springmann.
For an example of how animal foods compare with plant-based foods in terms of environmental effects, consider that “beef is more than 100 times as emissions-intensive as legumes,” Springmann said. “This is because a cow needs, on average, 10 kilograms of feed, often from grains, to grow 1 kilogram of body weight, and that feed will have required water, land and fertilizer inputs to grow.”
In addition, cows emit the potent greenhouse gas methane during digestion, which makes cows and other ruminants such as sheep especially high-emitting.
Other animal foods have lower impacts because they don’t produce methane in their stomachs and require less feed than cows, Springmann explained. For example, cows emit about 10 times more greenhouse gases per kilogram of meat than pigs and chickens, which themselves emit about 10 times more than legumes.
Like animals, plants also require inputs from the environment in order to grow, but the magnitude is significantly less, Springmann explained.
“In today’s agricultural system, we grow plants to feed animals, which require all of those resources and inputs: land, water, fossil fuels, pesticides, herbicides and fertilizer to grow. And then we feed plants to animals and care for them over their lifetime, while they produce methane and manure,” Palmer said.
Adopting more plant-based diets for ourselves could reduce the greenhouse gas emissions of the food system by more than half, according to the Nature study. A mainly plant-based diet could also reduce other environmental impacts, such as those from fertilizers, and save up to quarter use of both farmland and fresh water, according to Springmann.
Palmer explained that “legumes [or pulses], such as beans, lentils and peas are the most sustainable protein source on the planet. They require very small amounts of water to grow, they can grow in harsh, dry climates, they grow in poor nations, providing food security, and they act like a natural fertilizer, capturing nitrogen from the air and fixing it in the soil. Thus, there is less need for synthetic fertilizers. These are the types of protein sources we need to rely upon more often.”
(For the balance of this article, including a rather lengthy discussion of the “Flexitarian” option, please see: https://www.cnn.com/2018/10/18/health/plant-based-diet-climate-change-food-drayer/index.html)