He did it quietly, and the decision is the better for that: Al Gore, according to reports in the US press, has gone vegan.

Certain things could be said about other aspects of his lifestyle: his enormous houses and occasional use of private jets, for example. While we can't demand that everyone who espouses green causes should live like a Jain monk, I think we can ask that they don't live like Al Gore. He's a brilliant campaigner, but I find the disjunction between the restraint he advocates and the size of his ecological footprint disorienting.

So saying, if he is managing to sustain his vegan diet, in this respect he puts most of us to shame. I tried it for 18 months and almost faded away. I lost two stone, went as white as a washbasin and could scarcely concentrate. I think I managed the diet badly; some people appear to thrive on it. Once, after I had been unnecessarily rude about vegans and their state of health (prompted no doubt by my own failure), I was invited to test my views in an unconventional debate with a vegan cage fighter. It was a kind invitation, but unfortunately I had a subsequent engagement.

In 2010, after reading a fascinating book by Simon Fairlie, a fair part of which was devoted to attacking my views, I wrote a column in which I maintained that I'd been wrong to claim that veganism is the only ethical response to what is arguably the world's most urgent social justice issue. Diverting to livestock grain that could have fed human beings, I'd argued, is grotesque when 800 million go hungry.

Fairlie does not dispute this, and provides plenty of examples of the madness of the current livestock production system. But he points out that plenty of meat can be produced from feed that humans cannot eat, by sustaining pigs on waste and grazing cattle and sheep where crops can't grow. I was swayed by his argument. But now I find myself becoming unswayed. In the spirit of unceasing self-flagellation I think I might have been wrong about being wrong.

Part of the problem is that while livestock could be fed on waste and rangelands, ever less of the meat we eat in the rich nations is produced this way. Over the past week, a row has erupted between chefs and pig farmers over the issue of swill. Feeding pigs on swill has been forbidden since the foot and mouth outbreak of 2001. The chefs point out – as Fairlie does – that it is ridiculous to feed pigs on soya grown at vast environmental cost in the Amazon instead of allowing them to dispose of our mountain of waste food.

The farmers respond that the risks of spreading disease are too great and that pigs fed on waste grow more slowly than pigs fed on soya. I side with the chefs: I believe that a society capable of identifying the Higgs boson should be able to sterilise waste food. But I suspect that they're not going to win: the industry and its regulators are firmly against them.

I should have seen it coming, but I watched in horror as the meat industry used my article to justify the consumption of all meat, however it was produced, rather than just the meat raised on food that humans can't eat. A potential for good is used to justify harm.

While researching my book Feral, I also came to see extensive livestock rearing as a lot less benign than I – or Fairlie – had assumed. The damage done to biodiversity, to water catchments and carbon stores by sheep and cattle grazing in places unsuitable for arable farming (which means, by and large, the hills) is out of all proportion to the amount of meat produced. Wasteful and destructive as feeding grain to livestock is, ranching appears to be even worse.

The belief that there is no conflict between this farming and arable production also seems to be unfounded: by preventing the growth of trees and other deep vegetation in the hills and by compacting the soil, grazing animals cause a cycle of flash floods and drought, sporadically drowning good land downstream and reducing the supply of irrigation water.

So can I follow Al Gore, and do it better than I did before? Well, I intend at least to keep cutting my consumption of animal products, and to see how far I can go. It's not easy, especially for a person as greedy and impetuous as I am, but there has to be a way.