Sainsbury's chief executive Justin King is to tell the government that its healthy eating message is failing to get through to teenagers.

In a survey commissioned by the retailer 85% of teenagers polled were not eating the recommended five portions of fruit and veg a day, with 40% eating two or fewer portions. Some 37% of teenage girls quizzed were either on a diet or had dieted recently, with nearly half saying they consumed less than 1,200 calories a day - 40% less than the RDA.

"These results show teenagers are struggling to understand what constitutes a balanced diet," said Sainsbury's nutritionist Charlotte Parker.

The research will be unveiled in full next Thursday at a debate on diet led by King and attended by Department for Children, School and Families minister Kevin Brennan.