Some are analyzing cooking methods and calculating the ''carbon life cycles'' of food.

A holiday all about seasonal food presents a real opportunity to eat sustainably. But making the right choices is more complicated than you might think. Should you buy local or organic? Or is what you eat — and how much — more important?

Researchers are racing to find an answer. Some are analyzing cooking methods and calculating the "carbon life cycles" of food. The Bon Appetit Company Management Foundation, a nonprofit organization that educates consumers about the impact of food choices, assigns carbon points to a variety of ingredients. (Each point is equal to one gram of gases that contribute to global warming.) Other economists have tallied food production and transportation emissions.

There isn't yet a definitive answer to what makes a green Thanksgiving. But knowing some basic strategies can help you make informed choices.

Calories

Holiday splurges are understandable (sometimes even encouraged), but keep in mind: The more you eat, the larger your carbon footprint.

Average daily requirements

Women: 1,600 calories

Men: 2,200 calories

Typical Thanksgiving intake: 4,500 calories

Carbon points per serving

Grams of gases that contribute to global warming emitted during production, transportation and cooking, as figured by the Bon Appetit Company Management Foundation.

Turkey

If you're going to eat meat, turkey is a good choice. On average, a pound of poultry generates one-quarter the amount of greenhouse gases that a pound of meat from a ruminant animal (beef, lamb, buffalo, venison) generates. Buying a local turkey could help, but most of meat's environmental impact comes from production, not transportation. That said, cooking and eating a whole turkey instead of using individual cuts will make the meal more sustainable.

Turkey or chicken: 941 carbon points

Beef: 2,319 points

Pork: 1,247 points

Stuffing

When it comes to carbon points, vegetarian stuffings (or dressings) score the lowest.

With chestnuts and mushrooms: 88 points

With oysters: 105 carbon points

With sausage: 331 points

Vegetables

Buying local — easy to do at Thanksgiving because traditional ingredients are seasonal — can make a difference. Transportation accounts for 11 percent of fruit and vegetables' carbon emissions, vs. just 1 percent for red meat, according to a report from Carnegie Mellon University. Agricultural practices are important. But for produce, local matters.

Local spinach or kale: 0 carbon points

String beans from California: 17 points

Asparagus from South America: 22 points

Pies

A la mode is not environmentally correct. Dairy, which comes from those environmentally unfriendly ruminants, is second to red meat in the amount of greenhouse gases produced per ounce. Three tablespoons of whipped cream add 14 percent to the carbon points of a slice of apple pie. Ice cream adds 41 percent.

One slice of apple pie: 395 carbon points

... with whipped cream: 450 points

... with ice cream: 557 points

Wine

Organic wines don't generate significantly fewer greenhouse gases than conventional wines, in part because grapes require relatively little fertilizer and fewer pesticides compared with other crops. But where the wine comes from matters. Buying larger bottles also helps reduce carbon emissions.

According to a 2007 study by the American Association of Wine Economists, it is more green for a Washingtonian to drink a bottle that arrives by ship from Bordeaux, which generates 1.8 kilograms of greenhouse gases, than one from California's Napa Valley, which because of the long truck trip generates 2.6 kg. The efficiencies of shipping apply to the entire East and Gulf coasts.

Leftovers

On average, American households waste about $590 worth of food annually per family of four. Though families produce enormous quantities at Thanksgiving, leftovers are valued, which reduces the meal's environmental impact.