Supermarkets should concentrate their price promotions on healthy food to assist in the battle against obesity, according to consumer group Which?
Analysis of 77,165 promotions across the major UK supermarkets found 53% of them were put on less healthy products.
Confectionery was much more likely to be on special offer than fresh fruit and vegetables, Which? said.
The supermarkets' trade body said a balanced diet was now more affordable than ever.
Andrew Opie, director of food and sustainability policy at the British Retail Consortium, said: "Supermarkets offer great value in all the products they sell and it has never been easier or more affordable to choose a balanced diet."
The Which? analysis covered deals found in six major retailers - Asda, Morrisons, Ocado, Sainsbury's, Tesco and Waitrose - between April and June.
It classed less healthy food as any product with a red traffic light label for fat, saturates, sugars or salt - unless an item scored a red for fat and a green for saturated fat - and automatically counted fresh, unprocessed fruit and vegetables as healthier.
It found that 52% of confectionery was on special offer, compared to 30% of fresh fruit and 34% of vegetables.
Also on promotion, the results suggested, were 69% of soft drinks that would fall under the higher sugar band category, with more than 8% sugar, of the government's proposed sugar tax.
Alex Neill, director of campaigns and policy at Which?, said: "Everybody has to play their part in the fight against obesity and people want supermarkets to offer more promotions on healthier foods and yet our research found the opposite.
"It is time for supermarkets to shift the balance of products they include in price promotions and for all retailers to get rid of temptation at the till by taking sweets off the checkout."
Supermarkets suggest there are high levels of competition, and promotions, along all the supermarket shelves.
They also suggest that with a relatively even mix of promotions across all types of food, it did not follow that people would choose unhealthy food based on the promotions offered by supermarkets.
Paul Mills-Hicks, Sainsbury's food commercial director, said: "Since 2014, we have been working hard to remove promotions and invest money in regular lower prices. In doing so, we have made hundreds of fresh and healthy products affordable all of the time and our fresh produce sales are growing as a result.
"We have also taken a big step by calling on the industry to remove multi-buys, which we believe will lead to healthier diets and reduce household waste."