They found Aldi had the highest proportion of discretionary foods on the shelves and its own-brand products were the most «ultra-processed», relying heavily on sugar, oils, fats, salt, anti-oxidants, stabilisers and preservatives.
The researchers analysed tens of thousands of products by the 33 major food and beverage brands.
The new report, FoodSwitch: The State of the Food Supply, shows that, between 2017 and 2018, Woolworths maintained its ranking as the healthiest supermarket, while IGA’s ranking slipped from second to fourth.
«We’re talking about differences in salt, saturated fat and sugar content,» Associate Professor Gary Sacks from Deakin University said. «On average, if you were to buy home brands products from Woolworths, those products are likely to be quite a bit healthier than those from IGA.»
The largest movers in the rankings were Bega Cheese, which dropped nine places to 24th, and IGA, which fell seven places to 19th.
«The fall in the ranking of Bega Cheese principally reflects its acquisition of the Vegemite and Zoosh brands, which score poorly because of high levels of salt, sugar and saturated fat,» the report said.
About 63 per cent of Australian adults and 27 per cent of children aged five to 17 are overweight or obese, which increases the risk of developing heart disease and type 2 diabetes.
The authors urged the government to make health star ratings mandatory, companies to improve the healthiness of products and supermarkets to play a more active role in tackling obesity.
Metcash, which supports more than 1400 independently owned IGA stores, said the researchers overlooked key factors that «unfairly» impacted its ranking, such as the fact it has a much smaller own-brand range.
It said it chose to use the Recommended Daily Intake system over the «significantly flawed» health star rating system because RDI provided «more detailed and useful» nutritional information.
«There is an incorrect finding that we had less fresh own-brand products in 2018 compared to 2017. In fact, we only introduced fresh items into our Community Co own-brand range in 2018, therefore the number of fresh products increased,» Metcash’s spokesman said.
«More broadly, our Community Co range has a strong focus on healthy eating, including ensuring products are responsibly sourced and do not include artificial colours, flavours or genetically modified ingredients.»
A Mondelez spokeswoman said the company was unsurprised by the results because it specialises in confectionery, which could be enjoyed as part of a healthy and balanced diet.
«We recognise the complex issue of obesity and … and we’re investing significant time, energy and resources into being part of the solution,» she said.
«For example, we have internal nutrition standards to guide product developments, we’ve increased wholegrains and reduced saturated fat and sodium across all of our products globally.»
Australian Beverages Council’s chief executive Geoff Parker said its members, which include Bundaberg, Frucor and Red Bull, had pledged to cut sugar in drinks by 20 per cent by 2025.
«This initiative complements the work of our member companies, many of which have invested in significant portfolio renovation programs such as new recipes, more reformulation and smaller pack sizes.»
Esther Han is the state politics and health reporter at The Sydney Morning Herald