Despite the popularity of books such as
The 100-Mile Diet and an increasing awareness among consumers of how far their food has travelled from paddock to plate, studies have found that transport makes up only a small part of food's environmental impact.
British consumers would be better off buying dairy products from New Zealand than from their own country, a report from Lincoln University, New Zealand, concluded last year.
British dairy produces 35pc more greenhouse gas emissions than New Zealand dairy, even including transport from New Zealand to Britain, the report found.
This is because New Zealand agriculture uses fewer fertilisers and its dairy cows graze outside on grass, whereas British cows are housed in barns where they eat bought-in, concentrated feed.
More efficient farming methods also make New Zealand lamb and apples better options in Britain than local produce, the researchers found.
In Australia, promoting a product as environmentally friendly because it is local may even be illegal under the Trade Practices Act.
"It can break the law to mislead people by suggesting a food has environmentally superior qualities if it has travelled a shorter distance," says Joe Lederman, a principal of food law firm FoodLegal and an adjunct professor of law at Deakin University.
A study published at Iowa State University this year found that transport was responsible for just 4pc of greenhouse gases produced during the life cycle of food. Production accounted for 83pc.
What people eat is more important than where it comes from, the researchers found.
Giving up red meat one day a week would be more effective in reducing climate change than shopping locally for everything.
Rather than concentrating on food miles, we would be better looking for labels that recognise genuinely environmentally friendly practices, Lederman says, such as sustainable seafood accreditation or certified organics.
Should we forget about shopping locally altogether?
Corey Watts, the sustainable rural landscapes co-ordinator for the Australian Conservation Foundation, says it is still important.
"Food miles is not the whole story," he says. "However, it can be significant and shouldn't be ignored."
He points to a study conducted by the Centre for Education and Research in Environmental Strategies, in Melbourne, last year. It found that the food in a typical supermarket shopping basket had travelled more than 70,000 kilometres to get there. That is a lot of greenhouse gases.
"It's not just the distance but how it got there that determines the environmental impact," Watts says.
Transporting food by air is worse than road, which is worse than sea, which is worse than rail.
Most of Australia's food travels by road. The need to tackle climate change and the impact of peak oil will mean that Australia's food supply chain is going to have to change.
Watts calls on government to invest in rail infrastructure, both nationally for transporting from farm to shop or market, and in cities, so consumers can get to those shops and markets more efficiently.
Once they are there, they should have the ability to make informed choices.
"We need to ensure everyone has access to healthy, sustainable food. We should demand that governments and retailers step up to the plate and ensure food is labelled so its environmental impact is taken into account."
Britain, where the food miles idea originated, is moving on. For several years some food labels have featured aircraft symbols that show how many miles the food has travelled.
Now, carbon labels are beginning to be used on food items, showing the product's total environmental impact.
A label on a packet of chips, for example, shows that the product took 75 grams of greenhouse gases to produce.
"If I were an Australian supermarket boss I'd be looking very carefully at what's happening in the UK," says Cam Walker, campaigns co-ordinator for Friends of the Earth.
The group wants labels to show not only carbon emissions but water use.
"The real food movement is much more advanced in the UK," Walker says. "Here we've concentrated too much on local food.
"However, when you're trying to get a message across to the public and you've only got seven seconds it's easy to say 'Low food miles is good because it means low carbon'."
The confused ethical consumer should be guided by a few basic rules, Watts says.
"Eat a plant-based diet, eat seasonally, eat locally as much as you can, don't waste food, choose organic and grow some of your own."
Faced with a certified organic product from overseas versus a conventionally grown product from down the road, which would he choose?
"That's hard to answer. Buying locally you can interact with the producer and ask them challenging questions.
"But if I buy a tin of organic tomatoes from Italy at least I'm sending a message to the supermarket that I like organic food. Hopefully that will make local industry improve."
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