Australian households are spending half their food budget on discretionary or 'junk' items and soft drinks, according to research.

Analysis of the Australian Health Survey found of the 58 per cent spent on 'unhealthy' foods, 14 per cent was used to buy takeaways and four per cent sugar-sweetened beverages.

Public health expert and dietitian Professor Amanda Lee from the Sax Institute, who will present her research at the Dietitians Association of Australia's National Conference in Hobart, says the findings are worrying given poor diet is a leading cause of preventable illness.

"Less than four per cent of Australians eat adequate quantities of healthy foods, yet more than 35 per cent of their energy intake comes from discretionary foods and drinks, which provide little nutrition," said Professor Lee.

Australian households are spending big on junk food and takeaway. Photo: Fairfax

The research also found that, although healthy diets cost 15 per cent less than current 'unhealthy' diets, people in low incomes still need to spend around a third of their disposable income to eat a healthy diet.

Professor Lee says food security is a real problem and will only worsen if healthy foods are made more expensive.

The former chair of the National Health and Medical Research Council's Dietary Guidelines Working Committee has called for a co-ordinated approach to nutrition policy.

"At the moment, basic healthy foods like fresh vegetables and fruit are exempt from the GST but there's been talk of extending this to all foods. If this were to happen, the cost of a healthy diet would become unaffordable for low-income families."

AAP