Supermarket food prices will rise 4 per cent this year, the Centre for Economics and Business Research predicts in a report published today. The consultancy says heavy price discounting has cut net profit margins by an average of 13 per cent during the past three years. The discounts generated no identifiable change in total sales, the research found. Volumes did not rise enough to recoup the revenue lost from lower prices. Other marketing efforts, such as advertising, were far more likely to boost sales.