OK, I Take It Back -- We Don't All Have to Eat Vegan to Save the Planet

This will not be an easy column to write. I am about to put down 1,200 words in support of a book that starts by attacking me and often returns to this sport. But it has persuaded me that I was wrong. More to the point, it has opened my eyes to some fascinating complexities in what seemed to be a black and white case.

In the Guardian in 2002 I discussed the sharp rise in the number of the world's livestock, and the connection between their consumption of grain and human malnutrition. After reviewing the figures, I concluded that veganism "is the only ethical response to what is arguably the world's most urgent social justice issue". I still believe that the diversion of ever wider tracts of arable land from feeding people to feeding livestock is iniquitous and grotesque. So does the book I'm about to discuss. I no longer believe that the only ethical response is to stop eating meat.

In Meat: A Benign Extravagance, Simon Fairlie pays handsome tribute to vegans for opening up the debate. He then subjects their case to the first treatment I've read that is both objective and forensic. His book is an abattoir for misleading claims and dodgy figures, on both sides of the argument.

There's no doubt that the livestock system has gone horribly wrong. Fairlie describes the feedlot beef industry (in which animals are kept in pens) in the US as "one of the biggest ecological cock-ups in modern history". It pumps grain and forage from irrigated pastures into the farm animal species least able to process them efficiently, to produce beef fatty enough for hamburger production. Cattle are excellent converters of grass but terrible converters of concentrated feed. The feed would have been much better used to make pork.

Pigs, in the meantime, have been forbidden in many parts of the rich world from doing what they do best: converting waste into meat. Until the early 1990s, only 33% of compound pig feed in the UK consisted of grains fit for human consumption: the rest was made up of crop residues and food waste. Since then the proportion of sound grain in pig feed has doubled. There are several reasons: the rules set by supermarkets; the domination of the feed industry by large corporations, which can't handle waste from many different sources; but most important the panicked over-reaction to the BSE and foot-and-mouth crises.

Feeding meat and bone meal to cows was insane. Feeding it to pigs, whose natural diet incorporates a fair bit of meat, makes sense, as long as it is rendered properly. The same goes for swill. Giving sterilized scraps to pigs solves two problems at once: waste disposal and the diversion of grain. Instead we now dump or incinerate millions of tons of possible pig food and replace it with soya whose production trashes the Amazon. Waste food in the UK, Fairlie calculates, could make 800,000 tonnes of pork, or one sixth of our total meat consumption.

But these idiocies, Fairlie shows, are not arguments against all meat eating, but arguments against the current farming model. He demonstrates that we've been using the wrong comparison to judge the efficiency of meat production. Instead of citing a simple conversion rate of feed into meat, we should be comparing the amount of land required to grow meat with the land needed to grow plant products of the same nutritional value to humans. The results are radically different.

If pigs are fed on residues and waste, and cattle on straw, stovers and grass from fallows and rangelands – food for which humans don't compete – meat becomes a very efficient means of food production. Even though it is tilted by the profligate use of grain in rich countries, the global average conversion ratio of useful plant food to useful meat is not the 5:1 or 10:1 cited by almost everyone, but less than 2:1. If we stopped feeding edible grain to animals, we could still produce around half the current global meat supply with no loss to human nutrition: in fact it's a significant net gain.