Earth Day got you thinking about how your diet impacts the planet?

The World Resources Institute has news to ease a meat-lover's conscience: In a new report, it says you don't have to bid burgers bye-bye in order to reduce the environmental footprint of what you eat. Cutting back could go a long way, it says.

In the report, the nonprofit calculates the planetary effect of various possible changes in how the world eats.

According to the WRI, the planetary impact of Americans' meat and dairy habit accounts for nearly 90 percent of all the land used to feed us — and 85 percent of the greenhouse gas emissions resulting from our diet.

The average American man eats almost 100 grams of protein a day – and a lot of that protein comes from meat and dairy. As we've reported, many American teen boys and men consume even more.

According to Janet Ranganathan and her colleagues at WRI, if Americans slashed their intake of proteins from all animals – beef, dairy, lamb, poultry and pork – by 50 percent, it would have a dramatic impact. The amount of land required to feed us, and the resulting greenhouse gas emissions, are only a little more than if the whole country went vegetarian, says Ranganathan.

"I was surprised at that – and I'm a vegetarian," she tells me. In part, that's because most vegetarians substitute dairy for meat in their diet.

"So instead of having two slices of ham, you have one slice of ham or beef," says Ranganathan, the institute's vice president for science and research. Or you could switch to chicken, "which [is a] much more efficient source of protein."

In a statement, the American Meat Institute called the WRI's report "riddled with factual flaws about protein consumption and, in turn, the environmental impact of balanced diets that include meat." (Full statement is here.) Update: Ranganathan says the American Meat Institute's facts "don't stand up on several fronts" and WRI plans to issue a statement in response.

Despite such criticisms, the WRI says according to its models, if everyone in heavy meat-eating countries – that's folks in U.S., Canada, Europe and Brazil – cut back on animal protein, so that their total intake of protein (from plants and animals) was 60 grams a day, that could potentially save up to 1.6 billion acres of land from going into agricultural use. As Ranganathan notes, that's "an area of land roughly twice the size of India."

This kind of global cutback on meat and dairy sounds like an incredibly ambitious scenario. But according to WRI's modeling, a less dramatic shift in diet — just cutting back on beef — could still have a planetary impact.

That's because, per unit of edible protein, beef production requires a lot more land, and results in lots more greenhouse gas emissions, than plant protein sources like beans and lentils. (In part, it's because the need for pastureland drives deforestation in places like the Brazilian Amazon.)

So if Americans ate about one-third less beef in their diet, and either replaced it with chicken or pork or with more beans and other legumes, that would still shrink their diet's environmental footprint, according to WRI's models: Both the amount of land used to feed us and the greenhouse gas emissions generated by our diet would go down by about 15 percent.

While cutting back meat consumption by 33 percent sounds very ambitious, it's not unprecedented. Between 1976 to and 1993, American's per capita beef consumption dropped by 30 percent, according to data from the U.S. Department of Agriculture's Economic Research Service.

But American habits can be hard to budge. In December 2015, our polling found many Americans are eating no less meat than they were three years earlier. And according to a report from the USDA on long-term projections, beef consumption is expected to rise slightly, but steadily over the next several years.

Plant-based foods can take a toll on the environment, too. Almonds have been linked to a lot of water use. And last year, researchers from Carnegie Mellon University found that, on a per calorie basis, eating lettuce can produce more greenhouse gases than eating bacon. Of course, you'd have to eat a lot of lettuce to match the calories in bacon, and the researchers also found that plenty of other vegetables, from kale to broccoli to spinach and more, have much lower greenhouse gas emissions than pork.

As Carnegie Mellon's Paul Fischbeck, one of that study's authors, told The Huffington Post last December, "There are no simple answers to complex problems. Diet and the environmental impact of agriculture ... is not a simple problem."

Copyright 2021 NPR. To see more, visit https://www.npr.org.