Healthier school meals are being shunned by many pupils, with figures published showing that 20% fewer meals are being served in secondary schools.
Jamie Oliver says healthier school meals must continue
The Liberal Democrats claimed that the 250,000 drop in meals served in secondary schools meant that the school meal service was in "meltdown".
But celebrity chef, Jamie Oliver, said such an initial decline was not a surprise as "kids don't like change".
Mr Oliver forecast that "we'll see that negative turn into a positive".
The figures, revealed in response to a parliamentary question, show that the drive for healthier food in schools has not been popular with all classroom consumers.
In the past two years there has been a substantial fall in the number of pupils taking school meals - particularly in secondary school.
"The new standards for healthier school meals have been introduced too quickly, too inflexibly, and with too little education of pupils and parents," said Liberal Democrat schools spokesman, David Laws.
School meals have declined in popularity since becoming healthier
But Jamie Oliver, who helped to inspire the campaign to improve school food, said that the tide would change over the next five years.
"We have to keep supporting it. We have to know and do what's best for our kids," he said.
The Schools Minister Lord Adonis, said that a short term drop was to be expected.
"When you are withdrawing the fizzy drinks, the crisps, the sweets, the chocolate bars, then clearly there is going to be an immediate transitional issue," he said.
However there were signs of an improvement in children's diet, in a study of a scheme offering free fruit and vegetables to young school children.
The survey from the National Foundation for Educational Research says it has helped thousands more pupils eat five portions of fruit and vegetable daily.
Under the School Fruit and Vegetable Scheme (SFVS), introduced by the government in 2004, all four to six-year-old children in state infant, primary and special schools are entitled to a free piece of fruit or vegetable each day.
An evaluation of the scheme, carried out across 37 schools in north-east England by the National Foundation of Educational Research, concluded the number of children eating their five-a-day has increased substantially.
They compared food diaries and questionnaires of more than 1,600 children taking part in the scheme in the north-east in March 2004 with nearly 2,000 different children in November 2006.
They found 32% of children eating five portions of fruit and vegetables in 2004, compared with 44% of children in the 2006 study.
The researchers observed: "It should be noted that the largest increase was in vegetable consumption, not fruit, which may indicate that changes in school meals had a greater impact."
Children eating school lunches ate "significantly" more vegetables at lunchtime (0.94 of a portion) compared to those with packed lunches (0.18 of a portion).
Health Minister Ben Bradshaw said: "Children eating more fruit and vegetables each day and reaching their five-a-day target is excellent news.
"The SFVS is important in underpinning the government's commitment to healthy eating in schools.
"It provides an opportunity for children to try out new foods particularly vegetables and for them to become accustomed to eating them as part of their daily diet."
Studies show that eating at least five portions of fruit and vegetables a day could lead to an estimated 20% reduction in overall deaths from chronic diseases such as heart disease, stroke and cancer.
From September 2007, the SFVS is to be extended to add carrots and tomatoes to apples, pears, bananas and easy-peel citrus fruit.