Your next burger might be heavy on the stomach, but not on the environment.

Burger King is putting its cows on a special diet to trim their carbon footprint and make Whoopers greener.

The fast-food chain announced Tuesday it has tailored a feed formula with the help of scientists to cut down its herd's methane emissions, a potent greenhouse gas and a significant contributor to global warming.

Puffs of methane floating in the atmosphere trap the Sun's heat and bring temperatures up. Grazing cows are key culprits.

Cattle are walking methane factories, pumping the gas into the air, mostly through burps, but also flatulence, as bacteria in their digestive tract break down the tough grass they consume. An average cow belches out anywhere between 250 and 500 liters of methane a day. Globally, that's 50 percent more greenhouse gas emissions than one billion cars on the road per year, according to Barclays.

Data from the United Nations' Food and Agriculture Organization (FAO) shows that livestock is behind up to 14 percent of all greenhouse emissions from human activities, and around 44 percent of that comes in the form of the dreaded methane.

But Burger King may have stumbled upon a solution. It added 100 grams of lemongrass to the meals of cows during their last four months on Earth, with initial results showing that the new diet lessened daily methane emissions by up to 33 percent.

"We believe that delicious, affordable, and convenient meals can also be sustainable," said Fernando Machado, global chief marketing officer at Restaurant Brands International, which owns Burger King, in a statement.

The formula is "fairly simple to implement," and will be made part of the public domain for anyone to access, the company said.

"If the whole industry, from farmers, meat suppliers, and other brands join us, we can increase scale and collectively help reduce methane emissions that affect climate change," Machado added.

The smelly emissions have earned cows a bad rap as environmental offenders – and therein lies the beef. A new crop of climate-conscious consumers is cutting back on burgers, steaks, and chops or swearing off eating meat altogether because of the impact of livestock farming on the environment.

These choices are fueling a rise in plant-based meat alternatives, whose makers proudly parade their green credentials, and pushing big names in the F&B industry to commit to sustainable practices. Starbucks has promised to be more "resource positive" and introduced animal-free meat menus, while McDonald's is doing away with plastic straws in its restaurants around the world, including in China.

Farmers and scientists have tried in recent years to switch up the diets of belching bovines to tame their gut bacteria and make them less gassy. They've tried giving them onions, experimented with seaweed in the feedbag, and even spritzed a probiotic on the grass. Earlier this year, a UK startup unveiled a prototype for nose masks that vacuum cows' burps and filter their methane content. It claimed the wearable device can suck up to 60 percent of methane emissions.

The burger chain is rolling out its low-methane sandwiches in select stores in Miami, New York, Austin, Portland, and Los Angeles.

(Cover: Cow grazes in a field in Croatia. /CFP)