Plant-based diets might not be environmentally friendly, French study finds
NEW YORK — A nutritious diet that includes lots of fruits and vegetables might not be the greenest in its environmental impact, according to a study from France.
After analyzing the eating habits of about 2,000 French adults and the greenhouse gas emissions generated in producing plants, fish, meat, fowl and other ingredients, researchers concluded that widely embraced goals for the health of people and the planet are not necessarily perfectly compatible.
Growing fruit and vegetables doesn't produce as much greenhouse gas as raising cattle or livestock, the study confirms, but people who eat a primarily plant-based diet make up for that by eating more.
“When you eat healthy, you have to eat a lot of food that has a low content of energy. You have to eat a lot of fruits and vegetables,” said Nicole Darmon, the study's senior author from the National Research Institute of Agronomy in Marseille, France.
Greenhouse gases — which include carbon dioxide, methane and nitrous oxide — are produced by machines that burn fossil fuels. That gas is released into the atmosphere, where it contributes to climate change.
Food production — including the use of farming equipment and transportation — is estimated to be responsible for 15 percent to 30 percent of greenhouse gas emissions in developed countries, the authors write in The American Journal of Clinical Nutrition.
Darmon and her colleagues used food diaries from 1,918 French adults to compare the nutritional quality of people's real-world diets and how much greenhouse gas they produced.
About 1,600 grams of carbon dioxide were emitted for every 100 grams of meat produced. That's more than 14 times the amount of greenhouse gas emitted during the production of fruit, vegetables and starches. It's about 2.5 times as much greenhouse gas as that generated by production of fish, pork, poultry and eggs.
That gap narrowed, however, when the researchers looked at how many grams of carbon dioxide were emitted per 100 kilocalories (kcal) — a measure of energy in food.
The most greenhouse gas — 857 grams — was still emitted to produce 100 kcal of meat, about three times the emissions from a comparable amount of energy from fruit and vegetables.
Greens ended up emitting more gas for the calories than starches, sweets, salty snacks, dairy and fats. It was also about as much gas as pork, poultry and eggs.
When Darmon and her colleagues looked at what people actually ate to get a certain amount of energy from food every day, they found that the “highest-quality” diets in health terms — those high in fruit, vegetables and fish — were linked to about as much, if not more, greenhouse gas emissions as low-quality diets that were high in sweets and salts.
“I think to any reader it's surprising. One of the standard things we hear is that meat — particularly red meat — has the greatest greenhouse gas emissions,” said Roni Neff, who studies how food contributes to climate change but was not involved with the new study.
But Neff, the director of research and policy at Johns Hopkins Bloomberg School of Public Health's Center for a Livable Future, cautioned against taking the findings too literally. “It's a lot more complex than that.”