Almost a fifth of food available to consumers worldwide is lost through either overeating or waste, according to a new study.

The researchers from York University and Edinburgh University analysed the global food system using data from the UN's Food and Agriculture Organisation.

It found that the world's population consumes around 10% more food than it needs and almost 9% is thrown away or left to spoil.

The researchers looked at losses at different stages in the production process and found that almost half of all harvested crops - or 2.1 billion tonnes - are lost, taking into account inefficiencies in production processes as well as consumer waste and over-consumption.

The study again stressed the inefficiency of livestock production, which it said produced losses of 78% on harvested crops.

They found that around 1.08 billion tonnes of harvested crops are used to produce 240 million tonnes of edible animal products including meat, milk and eggs.

The research, published in the journal Agricultural Systems, said reducing waste in food production and consumption could improve global food security, although increased demand for some foods, particularly meat and dairy products, will decrease the efficiency of the food system further.

It said encouraging people to eat fewer animal products, reduce waste and not exceed their nutritional needs could help to reverse these trends and a failure to address the situation could see an increase greenhouse gas emissions, deplete water supplies and cause a loss of biodiversity.

Professor Dominic Moran, of The York Management School and Department of Environment, University of York, said: "This study highlights that food security can only be sustainably achieved through holistic approaches because consumer behaviours, as well as the actions of food producers and processors, all influence the sustainability of the food system. To date, much of the focus has been overly dominated by improving production efficiency."

Dr Peter Alexander, of the University of Edinburgh's School of GeoSciences and Scotland's Rural College, said: "Reducing losses from the global food system would improve food security and help prevent environmental harm. Until now, it was not known how overeating impacts on the system.

"Not only is it harmful to health, we found that overeating is bad for the environment and impairs food security.

The researchers from Edinburgh and York worked in collaboration with Scotland's Rural College, Karlsruhe Institute of Technology and the Centre for Australian Weather and Climate Research.

The research was funded through a Global Food Security Programme supported by the Biotechnology and Biological Sciences Research Council, Economic and Social Research Council, Natural Environment Research Council and the Scottish Government.