吃素也会危害到健康?

It has often been claimed that avoiding red meat is beneficial to the environment, because it lowers emissions and less land is used to produce alternatives.

But a study by Cranfield University, commissioned by WWF, the environmental group, found a substantial number of meat substitutes – such as soy, chickpeas and lentils – were more harmful to the environment because they were imported into Britain from overseas.

The study concluded: "A switch from beef and milk to highly refined livestock product analogues such as tofu could actually increase the quantity of arable land needed to supply the UK."

The results showed that the amount of foreign land required to produce the substitute products – and the potential destruction of forests to make way for farmland – outweighed the negatives of rearing beef and lamb in the UK.

An increase in vegetarianism could result in the collapse of British farming, the study warned, causing meat production to move overseas where there may be less legal protection of forests and uncultivated land.

Meat substitutes were also found to be highly processed, often requiring large amounts of energy to produce. The study recognised that the environmental merits of vegetarianism depended largely on which types of foods were consumed as an alternative to meat.

Donal Murphy-Bokern, one of the authors of the study and former farming and science coordinator at the Department for Environment, Food and Rural Affairs, told a newspaper: "For some people, tofu and other meat substitutes symbolise environmental friendliness but they are not necessarily the badge of merit people claim.

"Simply eating more bread, pasta and potatoes instead of meat is more environmentally friendly."

Lord Stern of Bradford, the climate change economist, claimed last October that a vegetarian diet was beneficial to the planet.

He told a newspaper: "Meat is a wasteful use of water and creates a lot of greenhouse gases. It puts enormous pressure on the world's resources. A vegetarian diet is better."

Liz O'Neill, spokeswoman for the Vegetarian Society, told The Times: "The figures used in the report are based on a number of questionable assumptions about how vegetarians balance their diet and how the food industry might respond to increased demand.

"If you're aiming to reduce your environmental impact by going vegetarian then it's obviously not a good idea to rely on highly processed products, but that doesn't undermine the fact that the livestock industry causes enormous damage."

The National Farmers' Union said the study shower that general arguments about vegetarianism being beneficial to the environment were too simplistic.