"Local" and "sustainable" are just a couple of the buzzwords thrown around by trendy new restaurants, signifiers of an eatery's commitment to quality and environmental ethics.

But the environmental impact of what's on the plate at a three-star bistro isn't just a matter of distance traveled. There other factors to consider.

Recently, researchers at the Royal Melbourne Institute of Technology did consider the many factors that determines a food's carbon footprint -- the environmental impact of the energy and materials used to raise, harvest and prepare fruits, vegetables and animals for consumption.

They came up with the first comprehensive carbon footprint league for fresh food.

Not surprisingly, fruits, grains and vegetables had the smallest carbon footprints, followed by nuts and beans. Among animal proteins, chicken, pork and fish offer the greenest options, with moderate carbon footprints. But scientists found wide variations among fish species.

The research confirmed what many environmental scientists have already warned: putting lamb and beef on the plate is the least eco-friendly way to consume protein.

But more than offer general guidelines, the new league -- or table -- puts a number on each food item's impact on climate change.

For example, 5.8 kilograms of onions, about 12.7 pounds or 50 medium onions, is the equivalent of a single kilogram of greenhouse gas emissions. On the other end of the spectrum is beef. Just 38 grams of beef, less than 0.08 pounds, is the equivalent of one kilogram of greenhouse gas emissions.

Now, chefs, caterers and consumers can make more accurate approximations of the environmental impact of what they serve and eat.

"We wanted to help people make informed choices, to empower consumers and people working in the food industry who would like to reduce their environmental impact," researcher Karli Verghese said in a news release. "With this full picture of the greenhouse gas impact of different foods, people can reliably work out more sustainable diets and menus for themselves and for their customers."

The new table and the calculations used to compile are detailed in a new paper, published this week in the Journal of Cleaner Production.