Who can afford to eat sustainably?

Climate scientists urge people to eat more plants and less meat to help curb carbon dioxide emissions. And to help achieve that goal, researchers from around the world launched a guide earlier this year on how to eat sustainably.

Under those guidelines, the most affordable green diet would cost $2.84 per day. But that isn’t affordable for 1.68 billion people — more than one-fifth of the world’s population — according to a study published Thursday in the journal The Lancet: Global Health. The researchers also determine who would spend the most on food, and what kinds of food, under the recommendations.

The original guidelines, called EAT-Lancet, call for diets rich in fruits and vegetables. They recommend that protein and fats come mainly from plant-based foods; unsaturated oils from fish; and carbohydrates from whole grains.

EAT-Lancet was exciting, senior researcher at the International Food Policy Research Institute and study lead author Kalle Hirvonen, Ph.D., tells Inverse.

“I think we were all very excited to see this dietary recommendation that first time took into account both health of humans and the planet,” says Hirvonen.

“At the same time, my co-authors and I have rich experience with working in and on lower income countries so we started to wonder whether people in countries like Ethiopia, Nepal or Nicaragua can actually afford these diets.”

That doesn’t mean EAT-Lancet isn’t helpful, Hirvonen says: “On the contrary, he says, “we hope our findings will alert policy makers towards fixing our broken food systems.”