That study is quite funny as its pretty silly. Of all the inaccuracies and complete misconceptions, it doesn't take into consideration the fact that many people already eat way more than they actually need to, so walking to the shops shouldn't result in the need to grow more food to provide the extra calories. However, I can of course think of a better way to reduce emissions, simply don't buy 'How to Live a Low-Carbon Life' and you will save some trees from being cut down to make paper