On any given day, 20% of Americans account for nearly half of U.S. diet-related greenhouse gas emissions, with high levels of beef consumption being a large factor, according to a new study released by researchers at Tulane University, New Orleans, La., and the University of Michigan, Ann Arbor, Mich.

To estimate the impact of diet on emissions, researchers determined the environmental impacts involved in producing more than 300 types of foods. They then linked this database to results of a 1-day dietary survey involving more than 16,000 American adults.

They ranked the diets by their associated greenhouse gas emissions, from lowest to highest, then divided them into five equal groups. The researchers found that the 20% of U.S. diets with the highest carbon footprint accounted for 46% of total diet-related greenhouse emissions.

If Americans in the highest impact group shifted their diets to align with the average U.S. diet, the 1-day greenhouse gas emissions reduction would be equivalent to eliminating 661 million passenger vehicle miles.

The highest impact group was responsible for about eight times more emissions than the lowest impact of diets. And, beef consumption accounted for 72% of the emissions difference between the highest and lowest groups.  

If implemented every day and accompanied by equivalent shifts in domestic food production, such diet changes would achieve nearly 10% of the emissions reductions needed for the United States to meet its targets under the Paris climate accord.

“This study is the first in the United States to look at self-reported dietary choices of a nationally representative sample of thousands of Americans,” says Diego Rose, principal investigator on the project and a professor of nutrition and food security at Tulane University School of Public Health and Tropical Medicine.

Emissions related to the processing, packaging, distribution, refrigeration and cooking of foods were not part of the study, but would likely increase total emissions by 30% or more, says Martin Heller, first author and the co-principal investigator from the University of Michigan. 

“Reducing the impact of our diets—by eating fewer calories and less animal-based foods—could achieve significant reductions in greenhouse gas emissions in the United States. It’s climate action that is accessible to everyone because we all decide on a daily basis what we eat,” Heller says.