Image copyright AP Image caption Data on people's diet is "abominable", say experts

Global food policy needs to shift way from focusing on feeding people calories to nourishing people with healthy diets, say leading experts.

They state that poor diets were responsible for more of the global health burden than sex, drugs, alcohol and tobacco combined.

While almost 800 million people are hungry, they say two billion people are either overweight or obese.

Their comments have been published in the journal Nature.

One of the experts, Lawrence Haddad, executive director of the Global Alliance for Improved Nutrition (Gain), said the need to address the problem of global hungry remained but poor diets was a much bigger problem.

"It is one that we are blind to," explained Mr Haddad.

"We estimate that on-in-three people have really poor diets," he told BBC News.

"This is causing a whole host of malnutrition problems that has massive health consequences as well as economic consequences.

"We are saying to people, especially policymakers and research funders, we now need to move away from a world thinking about malnutrition as hunger but to think of it as hunger and poor quality of diet.

"Instead of feeding the world, we need to think about nourishing the world."

Mr Haddad and colleagues, including former UK government's chief scientific adviser Prof Sir John Beddington, used the commentary in Nature to call for "urgent interdisciplinary research is needed to support concerted policy action".

Eating the planet

In another commentary in Nature, UN goodwill ambassador Pavan Sukhdev and fellow authors highlighted how current production and consumption patterns were not sustainable.

"Food systems are now the source of 60% of terrestrial biodiversity loss, 24% of greenhouse emissions, 33% of soil degradation and 61% of the depletion of commercial fish stocks," they wrote.

"And the increasing homogenisation of food sources worldwide is narrowing the genetic diversity in animals and plants that is crucial to secure human nutritional needs against climatic and other changes."

They add that the agriculture sector was a globally significant player economically, employing about 1.3 billion people.

"Small-scale agriculture provides subsistence, employment and most of the food directly consumed by urban residents throughout the developing world," they observed.

They warned that current metrics for agriculture did not take into account the sector's costs and benefits.

"The emphasis on yields or profits per hectare is as reductive and distorting as is gross domestic product, with its disregard for social and natural capital," they wrote.

"Food metrics must be urgently overhauled or the UN's Sustainable Development Goals (SDGs) will never be achieved."

Adopted in September 2015, the UN SDGs replaced the international Millennium Development Goals and included targets to end world hunger, and improve wellbeing and health of the global population.

Diet data

Mr Haddad said that improving "food metrics" would be one of the first things he would look to improve in order to shift global food policy on to a sustainable footing.

"Diet data is abominable," he said.

"We only have a clue that our diets are so terrible is because of the outcomes, because there is so much micronutrient malnutrition and calorie deficiency, and obesity.

"We have some diet data and it does not tell us a great story."

He added: "If policymakers are really going to figure out what is going to be the first, second or third thing they are going to do then they are going to need some good data to carry out some diagnostic work."

Writing in Nature, Mr Haddad and his colleagues said: "Policymakers urgently need to recognise that diets are compromising economic productivity and well-being as never before. Delegates to the upcoming G20 and G7 meetings in 2017 should take collective responsbility for fixing our failing food system."