The government needs to do more to protect South Africans from the lure of junk food by making healthier food cheaper and more readily available, say researchers from the University of the Western Cape.

A diet containing too much processed food which is laden with fat, sugar and salt has been linked to obesity and an increased risk of non-communicable diseases such as hypertension and diabetes. But in SA, healthier food is generally more expensive than calorie-dense packaged food, limiting the choices available to poor people, said the researchers. Writing in PLoS Medicine, Prof David Sanders and colleagues said the government had allowed the quality of food available to South Africans to deteriorate dramatically in the past decade.

Sales of snack bars, ready meals and noodles all rose by more than 40% between 2005 and 2010 as large commercial entities, dubbed Big Food by the journal, successfully pushed the sales of pre-packaged food. Big Food has rapidly replaced smaller food retailers, as supermarkets forged into areas formerly serviced by convenience stores, public markets and spaza shops.

"Today food prices are lower in supermarkets than in traditional retail outlets, which makes both staple foods and packaged foods produced by large manufacturers more affordable to local populations. However, healthier foods typically cost between 10% and 60% more in supermarkets when compared on a weight basis, and between 30% and 110% more when compared on the cost of food energy," said the researchers.

Refined cereals and foods with added sugar and fat were among the cheapest energy sources in rural supermarkets, making biscuits, margarine and oil-rich snacks much more affordable than nutrient dense-foods like fish and fruit, said Prof Sanders. Making processed food more expensive, for example by taxing sugar, would hit poor people hard unless healthy alternatives were readily available, he said.

While Prof Sanders acknowledged the Department of Health was taking steps to regulate the ingredients in processed food, including lowering the salt content and limiting the levels of trans-fats, he said the rest of the government needed to do more to promote healthy food.

"We don't link the programmes (run by the different government departments)," he said.

The national school nutrition programme was a prime example of a lost opportunity for providing children with healthy food. Much of the food provided under this programme was "obesogenic" processed food, made by big companies, he said. A better approach would be to create jobs for people from the local community and prepare the food in school kitchens, he said.

The department 's head of noncommunicable diseases, Prof Melvyn Freeman, said health officials were aware of the issue and wanted to work with their counterparts in other government departments to promote healthier food.

"We have put it in our strategic plan for noncommunicable diseases. It's not something the health department can deal with on its own. Of course they (other departments) have their own priorities, so we have to find a way (to get them to agree to promote healthier food). We have said we are going to deal with this and we will," he said.