The common belief that local is better than imported when it comes to assessing the environmental impact of our food has been recently called into question by a new research of the British Department for Environment, Food and Rural Affairs (Defra).

The "food miles" philosophy that decrees anything transported over distance is worse for the environment than something closer to home is frequently flawed, according to researchers, as the environmental impact when growing tomatoes or strawberries in Britain, for example, is higher than when we import the same products from Spain. Much more energy is needed to heat greenhouses in cold Britain than in Spain's warm temperatures, so there is a trade-off between the increased use of gas and electricity, and the longer transport distance and greater demands on water in Spain.

"The global-warming potential arising from production of tomatoes and strawberries in Spain, poultry in Brazil and lamb in New Zealand remained less than from those foods produced in the UK despite the greenhouse gas emissions that took place during transport," says the Comparative Life Cycle Assessment of Food Commodities report.

As a matter of fact, while the production systems used by Brazilian and British poultry farmers were largely similar, the report says 25% less energy was used in producing Brazilian poultry meat. The reason? "A main feed, soya, has much lower transport burdens in Brazil, Brazilian poultry houses are essentially naturally ventilated and structures are simpler so that the housing burdens are smaller," the report says.

The study, which was published last year but not made public by Defra, also says lamb from New Zealand was more sustainable than British-produced lamb if transport was taken out of the equation.

So, the best way to help reduce our impact on the environment when buying our food is paying much more attention to seasonality. In other words, unless consumers radically changed their lifestyles by becoming vegan or eating more seasonal foods, it may be better to import staple foods and avoid the emissions caused by refrigerating British produce for long periods, the report concludes.