Vegans and others who buy milk substitutes made from soya are harming the planet and would be better off switching to cows' milk, according to the UK’s Sustainable Food Trust.The authors of the research calculate that about 85l of milk are produced in the UK for every kilo of soya bean meal consumed by dairy cows. This is in contrast to no more than 7.5l of soya drink being produced from a kilo of whole soya beans.