When Americans think about cutting their carbon footprint, they change their light bulbs, turn down their thermostats and maybe leave their cars in the garage. But a new study says there’s another energy-gobbling gremlin on the domestic front and it’s probably scarfing down a junk-food cheeseburger right now. It’s the meat-rich, over-caloried, highly processed American diet.

By eating less, and eating less food that takes lots of energy to produce, people in the United States could cut climate-warming fossil fuel use in the food system by as much as 50 percent, Cornell University scientists reported in the journal Human Ecology.

The average American eats 3,747 calories a day, the scientists said, some 1,200 to 1,700 calories over what’s recommended. Many of those calories come from meat and processed foods, which use more energy getting to the table than lower-calorie staples like potatoes, rice, fruit and vegetables. So the first step is, eat less. And if you have to keep eating all those calories, veggies may be the way to go — a vegetarian diet uses about 33 percent less fossil fuel.

The researchers also suggested energy savings could come from using more traditional organic farming methods, and getting away from energy-intensive conventional meat and dairy production. In farm fields, cutting back on pesticides, increasing the use of manure as fertilizer, planting cover crops and rotating crops would also improve energy efficiency, the authors wrote.

Changes to food processing, packaging and distribution could also reduce fuel consumption, but the researchers said individual responsibility would have the biggest impact. The most dramatic reduction in energy used in food processing would happen if consumers cut their demand for highly processed foods. This would also cut down on so-called the food miles, the distance food travels from where it’s produced to where it’s eaten — a major consideration, since U.S. food travels an average of 1,090 miles (2,400 km) on its way to American stomachs.

But come on: if you’re already bicycling to work, turning off your electronic gear, sweltering through a hot summer without air conditioning, would you be willing to do without junk food — or at least stop eating so much of it — in the name of the environment? What do you think?