One in seven people suffer from malnourishment, the head of the UN's food agency said Wednesday in a report released ahead of a summit on sustainable development to be held in Rio de Janeiro June 20-22.

"We cannot call development sustainable while this situation persists, while nearly one out of every seven men, women and children are left behind, victims of undernourishment," said FAO director general Jose Graziano da Silva.

"At the Rio Summit we have the golden opportunity to explore the convergence between the agendas of food security and sustainability," he said, referring to the difficulties in making sure that the poor have sustained access to food.

The report calls on governments to invest in infrastructure and protect the rights of the poor to food resources.

Three quarters of the world's poor live in rural areas and most of them depend on agriculture and related activities for their livelihoods, it said.

Access to natural resources -- such as land, water or forests -- is essential for the 2.5 billion who produce food for their own consumption and income.

"Hunger puts in motion a vicious cycle of reduced productivity, deepening poverty, slow economic development and resource degradation," the report said.

The FAO called for food consumption and production systems to "achieve more with less," and said it was necessary to shift to nutritious diets with a smaller environmental footprint, as well as reducing food losses and waste.

Global food losses and waste amount to 1.3 billion tonnes per year, roughly one-third of the world food production for human consumption, it said, and correspond to over 10 percent of the world's total caloric energy consumption.

"In 2050 there will be an expected global population of 9 billion, with increased incomes and rising food demand. Pressure on the world's agricultural and food systems and the resources they use will grow," the agency said.

"Worse, unless purposeful action is taken, the increase in food production of 60 percent needed to meet effective demand will still leave behind over 300 million people who are expected to suffer from chronic hunger in 2050."

The Rio conference comes 40 years after a Stockholm conference on the environment in 1972, 20 years after a Rio conference on development in 1992 and 10 years after a summit on sustainable development in Johannesburg in 2002.

The themes of the so-called Rio+20 conference next month were laid down in a United Nations General Assembly resolution adopted in December 2009, and aim to renew political engagement in sustainable development.