The report said food production and fossil fuel use caused pollution, greenhouse gases, diseases and forest destruction.
"How the world is fed and fuelled will in large part define development in the 21st century," said the 112-page report by the International Panel for Sustainable Resource Management.
"Agricultural production accounts for a staggering 70% of the global freshwater consumption, 38% of the total land use and 14% of the world's greenhouse gas emissions," said Achim Steiner, head of the UN Environment Programme.
The report said consumers could help by cutting down on meat consumption and use of fossil fuels in heating or travel. "Animal products are important because more than half of the world's crops are used to feed animals, not people," it said.
"A substantial reduction of impacts would only be possible with a substantial worldwide diet change, away from animal products."
Researchers said it was no surprise fossil fuels were a top concern.
"More surprising was food production - agriculture, fishing and pasture," Edgar Hertwich, lead author at the Norwegian University of Science and Technology, told Reuters.
Reform "will be a titanic task, but one that is essential for our future prosperity and quality of life," Janez Potočnik, the EU environment commissioner, said in a statement.
Increasing wealth in developing nations could mean more damage, such as more demand for meat.
"Meat consumption per capita in China rose by 42% over eight years from 1995 to 2003," said Sangwon Suh of the University of California, Santa Barbara.
The study also said that the world should focus on improving use of materials such as plastics, iron, steel and aluminium.
Janet Salem of UNEP said the report should remind people in urban areas that clearance of distant forests - making way for farmland and destroying habitats of animals and plants - could be traced to their choice of food in supermarkets.
"Faraway environmental impacts are related to people in cities," she said.
(EurActiv with Reuters.)