When it comes to greenhouse gas emissions and diet, some changes pack a bigger punch than others.

“We looked at the thousands and thousands of different food items that individuals reported eating in the previous 24 hours, and ranked them,” says Diego Rose, professor of nutrition and food security at Tulane University.

Using that data—on 16,800 participants in the National Health and Nutrition Examination Survey—Rose estimated their individual carbon footprints.

“The 20 percent of diets with the highest carbon footprints accounted for well over 40 percent of the impact,” says Rose. “So our first question was: What’s going on with those top 20 percent?”

The answer was hard to miss

“Over and over again, we saw that one food item could turn one person’s diet from an average diet to a really high-impact diet,” says Rose. That food: beef.

Rose looked at specific foods, not categories like “beef” or “pork.”

“The top 10 were all beef items,” he explains. “I’m talking about a hamburger or a beef steak or a beef roast.”

What makes beef so harmful?

“Cattle are ruminants, so they expel a lot of methane as burps as they digest food,” says Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health. More comes from their manure.

As a heat-trapping gas, methane is about 30 times more potent than carbon dioxide. And cattle live longer than other livestock.

“Chickens come to market in about six weeks, and pigs come to market in about six months,” says Willett.

“In contrast, cattle take about 1 to 1½ years to come to market if they’re grain fed and 2 to 2½ years if they’re grass fed. And every day, they’re burping out methane and breathing out carbon dioxide.”

What’s more, the fertilizers used to grow cattle feed release nitrous oxide, a greenhouse gas that’s 300 times more potent than carbon dioxide.

And it takes enormous quantities of fossil fuels to process and transport that feed.

So it’s no surprise that Rose’s top 10 emitters were all beef dishes.

Rose's main takeaway

“For people who eat beef—and that is about 20 percent of the U.S. population on any given day—they could cut their dietary carbon footprint in half by replacing beef with chicken or pork,” says Rose.

They could switch from beef ribs to pork ribs, for example, or go from a hamburger to a turkey or chicken or, better yet, plant-based burger.

“Substituting soy milk for dairy milk also has a good-sized impact,” notes Rose. But it still falls short of a beef swap.

“You don’t have to become a vegetarian to lower your impact,” he adds. “But replacing beef is the biggest bang for your buck.”

Beef is also a big loser when it comes to water

“We characterized water usage by where the product was grown,” explains Rose. “So a tomato grown in a drought-stricken area like California would have more of a footprint than a tomato grown in, say, Louisiana.”

Again, some easy swaps showed up.

“Some foods, like almonds, are water hogs,” says Rose. “So peanuts would be a good swap if you’re not allergic.”

Other water savers: replacing grapes with apples, asparagus with peas, and white rice with bulgur.

One more tip

Whatever you buy, don’t let it go to waste.

“A quarter to a third of food is wasted,” says Rose. “When restaurants give you huge portions, take home the excess in a recyclable container.”

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