Vegans should stop drinking soya milk in order to save the rainforest, the UK Sustainable Food Trust has said.
A report from the trust argues milk from cows - especially cows traditionally grazed on grass - is much better for a sustainable planet.
The global consumption of soya products has been rising, but many are produced on deforested land with the Amazon rainforest suffering great losses due to soya production.
However, the report adds that livestock are frequently fed with soya, and accounts for a large part of the profitability of the "unsustainable" soya industry.
Ireland suffers less from this than other countries because cows are fed on our lush grassland.
The authors calculate about 85 litres of milk is produced for every kilo of soya bean meal consumed by dairy cows.
In contrast, no more than 7.5 litres of soya drink are produced from a kilo of whole soya beans.
As a result, drinking milk produced from cows in Ireland uses far less soya than consuming drinks made from soya.
"Vegans and others who buy milk substitutes made from soya for their latte and cappuccino, or breakfast cereal, are also harming the planet. They would do better to switch to milk from cows, and especially cows traditionally grazed on grass, if they want to help make a more sustainable planet," the report states.
Patrick Holden, the trust's executive, said: "This is an important study. It shows that livestock farmers could reduce their dependence on imported protein, which is produced at such a high environmental cost, and rely more on home-produced feed.
"But it also shows that drinking cows' milk uses far less soya than drinks made from soya, because most of the milk comes from grass. This highlights the importance of grass, a crop ideally suited to our climate."