SYDNEY - What's good for your wallet is often bad for your health, according to a study which found sugar-packed drinks are more likely to be discounted.

The Dietitians Association of Australia (DAA) is calling for supermarkets to rethink what they put "on special", after a study revealed they were usually not the healthiest products in their aisles.

Researchers looked at about 1500 discounted drinks advertised for sale across four supermarkets, over a month, in New Zealand.

They found just 15 per cent of the discounted drinks were considered to be healthy - water, plain reduced-fat milk or plain reduced-fat soy drinks.

The remaining 85 per cent of unhealthy products included softdrinks, sports beverages, flavoured waters and cordial.

Not only did unhealthy drinks dramatically outnumber healthy ones, they were also sold at larger discounts, according to the study published in the journal Nutrition & Dietetics.

"Our study shows healthy drinks are discounted less often than unhealthy drinks," said author Louise Signal from the University of Otago.

"But there are more unhealthy drinks available in supermarkets and this may explain some of the difference."

DAA chief executive Claire Hewat said family eating and drinking habits were influenced by these discounting practices, and supermarkets should instead be promoting foods with less saturated fat and added sugar.

"This would encourage shoppers to purchase healthier choices at the supermarket and would be an important step in addressing overweight and obesity," Ms Hewat said.

The DAA said a comprehensive response to Australia's mounting obesity problem should also include tighter government regulation of food marketing and clearer nutrition information on food labels.