Nearly four in five Australians overindulge in junk food every day, according to research by the CSIRO.

The national agency wants people to change their approach to eating "discretionary items" and has released a free online junk food analyser to help.

"Discretionary or junk foods are the number one issue affecting Australian diets today," CSIRO research scientist Dr Gilly Hendrie said.

Excessive consumption results in poor nutrition, high rates of obesity and an even higher risk of lifestyle diseases, she added.

The CSIRO analysed data from a survey of more than 230,000 Australian adults collected between 2015 and 2020.

It found almost 80 per cent of them consume too much "discretionary food" and that, on average, adults are eating about twice the amount of it recommended by national dietary guidelines.

A whopping 5.1 servings are consumed on average each day, the equivalent of about 3000 kilojoules, or 20 small solid chocolate Easter eggs.

Top "weaknesses" were alcohol (21 per cent of discretionary food intake), cakes and biscuits (19), sugar sweetened beverages (12) and savoury pies and pastries (nine).

"While these types of foods and drinks are often high in sugar, kilojoules and fat, they do bring enjoyment, which means alternative methods must be explored in helping people enjoy their favourite treats in the context of a healthy diet," Dr Hendrie said.

A range of strategies to help people reduce kilojoule intake are modelled in the junk food analyser, not just cutting food altogether, she added.

"That might include choosing to eliminate alcohol, taking a break from cakes and biscuits and halving confectionery consumption."