Unhealthy habits ... the study found a tax on sugary drinks would be most succesful.

Unhealthy habits ... the study found a tax on sugary drinks would be most succesful. Photo: Janie Barrett

Increasing the price of unhealthy food and drinks through a tax of at least 20 per cent could improve people's health and have an impact on diet-related diseases, a new study shows.

The study by BMJ (formerly the British Medical Journal) suggested fat and sugar taxes needed to be at least 20 per cent to have a significant effect on obesity and cardiovascular disease.

A tax on sugary drinks would be most successful, the study showed.

It also revealed that taxes on unhealthy foods should be combined with subsidies on healthy foods such as fruit and vegetables.

''Price is an important determinant of food choices and diet,'' the study said.

''As the price of an item rises the consumption of that item will typically fall.

''Increasing the price of unhealthy foods, by taxation, should reduce consumption of the taxed foods.''

Denmark has introduced a fat tax and Hungary a junk food tax. France has introduced a tax on sweetened drinks and Peru is planning to implement a junk food tax. Some public health experts in Australia have called for a tax on junk food.

Adjunct professor at the Australian National University's Medical School, Dick Telford, said there needed to be subsidies in Australia which encouraged people to buy healthy foods.

He didn't think unhealthy food and drink taxes were the answer to improving people's health.

''We should be encouraging, not penalising,'' Professor Telford said.

''Most people, no matter where they're from and what their background is, know that certain foods, such as highly fatty, sugary foods, aren't good for your health.

''If people are eating these foods with unhealthy regularity, I don't think that any tax is going to stop that.''

Heart Foundation clinical issues director Robert Grenfell said taxation had a role in influencing health behaviours.

But he said a fat tax was not a top priority, because of the difficulty involved in implementing it.

The foundation's priority is to have healthier fats and oils in foods and to decrease salt content by at least 25 per cent.

Dr Grenfell said cutting Australians' average salt intake by three grams a day would prevent about 6000 deaths a year from heart disease and stroke.

The average Australian consumes about nine grams of salt a day; three grams more than the recommended maximum.

''As about three-quarters of the salt eaten by Australians comes from processed foods rather than salt added at the table, the most effective way to cut salt is to change the ways foods are manufactured,'' Dr Grenfell said.

''There's a lot of hidden salt out there in our diet - breakfast cereals and breads are two of the big ones.

''Two slices of average processed bread contains one gram of salt, which is a substantial amount.''

Dr Grenfell said the Heart Foundation had been challenging food companies to make their foods healthier. The foundation is also part of the federal government's Food Health Dialogue, which aims to reduce salt content in many foods.