Again, Capper said, the intuitively environmentally friendly option has a far higher resource and environmental cost.

Capper said in comparing pasture- or grass-fed beef to conventionally produced beef, all growth-promoting technology was excluded. A corn-fed example included no growth hormones or implants at all, she said.

Capper is working to assess the influence of those technologies in beef production from an environmental standpoint and hopes to have the results within the next six months.

In Europe, where growth-promoting technology has been removed from beef production, a 10pc drop in efficiency has been documented. Capper's calculation will have to take into account the energy expended to manufacture the implants and growth hormones.

Another emerging trend among American consumers is the desire to purchase food grown locally.

"Often, 'locally grown' food is thought to have a lower environmental impact than food transported over long distances due to carbon emissions from fuel," explained Capper.

The phrase "food miles" has become a popular buzzword, defined simply as the distance food travels from its place of origin to its place of final consumption.

"Although well intentioned, it is incorrect to assume that the distance food travels from point of origin to point of consumption is an accurate reflection of environmental impact," Capper said. "This simplistic approach fails to consider the productivity of the transportation system, which has tremendous impact on the energy expended per unit of food."

For example, buying one dozen eggs that was transported several-hundred miles to a grocery store in a tractor-trailer that can carry 23,400 dozen eggs is a more fuel-efficient, eco-friendly option than purchasing one dozen eggs at a farmers' market, as that uses 4.5 times more fuel, or at a local farm, as that uses 17.2 times more fuel.

In the comparison, total mileage came to about 807 miles for the grocery store eggs, 93.2 miles for the farmers market example and 27.34 miles in the local farm example. The tractor-trailer transported 23,400 doz. eggs, the farmers market calculation was based on 1074 eggs in a pickup truck and the local farm calculation was based on a consumer picking up one container of a dozen eggs in a single trip.

"The high-capacity vehicles used in modern transportation systems improve productivity, allowing food moved over long distances to be highly fuel efficient and environmentally friendly compared to locally grown food," Capper explained.

She noted that the study found that the greatest fuel usage resulted from the consumer's car.

The desire to protect the environment and to do so, in part, by altering personal behaviors is admirable, said Capper. However, she emphasised that those personal decisions must be based on logic rather than intuition.

"Consumers might think they are making the responsible, virtuous food choices when, in truth, they are supporting production practices that consume more natural resources, cause greater pollution and create a larger carbon footprint than more-efficient, technology-driven, conventional methods," she concluded.

Co-authors on this work included Dr Roger Cady, senior technical consultant at Elanco, and Dr Dale Bauman, Liberty Hyde Bailey professor at Cornell University.

Here's the point

AS a source of global warming, the food we eat - and how we eat it - is no more significant than the way we make clothes or travel or heat our homes and offices, Michael Specter of The New Yorker magazine pointed out in a Feb. 25, 2008, article titled "Big foot". According to Specter, "food miles" have become a focal point in the climate discussion because of the enormous symbolic power of food.

In his article, Specter interviewed chief scientific adviser to the Carbon Neutral Co. John Murlis, who expressed his concern about how, in our collective rush to make choices that display personal virtue, we may be losing sight of the larger problem.

So, would a carbon label on every food product have a benefit to consumers? Murlis said he thinks not. "You can feel very good about the organic potatoes you buy from a farm near your home, but half the emissions - and half the footprint - from those potatoes could come from the energy you use to cook them. If you leave the lid off, boil them at a high heat and then mash your potatoes, from a carbon standpoint, you might as well drive to McDonald's and spend your money buying an order of French fries."

Adrian Williams, an agricultural researcher at Cranfield University in England, has called food miles a foolish concept that is provincial, damaging and simplistic. "The idea that a product travels a certain distance and is, therefore, worse than one you raised nearby - well, it's just idiotic," Williams said.

A well-known critic of modern agricultural practices, Michael Pollan of the University of California-Berkley, said eco-friendliness is not the only reason consumers patronise farmers markets and buy locally. Consumers go to farmers markets to support local farmers, to keep local farmlands in business, to partake of the community spirit and to enjoy food that is unusually fresh and of high quality, he said. Pollan, a journalism professor, has written several books on the topic of how the current food production system is too energy intensive and how more local, organic food production would make more sense from an overall efficiency standpoint.

The basic premise of Specter's article - as well as work by other researchers - boils down to the fact that reducing carbon emissions is really much more complex than "buying locally".