Jamie Oliver today criticised Education Secretary Michael Gove for "eroding" healthy school meal standards.
The TV chef raised concerns that academy schools are not obliged to sign up to food standards introduced by the previous government.
He called on parents to tell Mr Gove not to touch the rules, warning that a move away from them would be a disaster.
Oliver told BBC News: "The bit of work that we did which is law was a good bit of work for any government.
"So to erode it, which is essentially what Mr Gove is doing - his view is we let schools do what they want.
"I think that's a wonderful ambition, that everyone's going to be brilliant, but headteachers are more pushed than ever, expected to do more than ever, now they have to be entrepreneurial caterers as well as everything else they have to do.
"The standards are there to really keep everyone on their game. It's not a large amount of paperwork, it really isn't, and for what it's for, which is essentially the future of our country, it's really important."
More than two-fifths of primary school children and a third of secondary school pupils are now opting for school meals, according to the latest official figures.
Take-up has been growing since the school meals revolution was kick-started by Oliver six years ago when he began a campaign for better quality school dinners.
It won widespread public support and led to strict nutritional guidelines for meals introduced to primary schools in 2008 and secondaries in 2009.
But academies, which are semi-independent state schools, do not have to sign up, and since last year, the coalition Government has allowed any school to apply for academy status.
Oliver told BBC News: "I think parents need to tell Mr Gove that the standards are there for good reason, and actually not everything that the last government did was wrong. They did a lot of good stuff and he shouldn't touch them.
"It could be a disaster."
The chef warned that for 190 days of the year, from the age of four, often for both breakfast and lunch, "the government is in control of ... half of your child's childhood nutrition".
He accused the Conservatives of "cleverly" eroding the standards by allowing academies to opt out.
Oliver told BBC Breakfast: "I think the Conservatives have been very clever, because if they just came out and said 'we're taking away the standards' ... what they've done is they're actively, aggressively pushing academies, which is already one-third of all our secondary schools, and they don't have any requirements at all."
He said he had met Mr Gove, written to him and created a manifesto explaining the worth of healthy food standards.
And he raised concerns that examples Mr Gove had given him of academies providing good meals were "flawed".
"He gave me an example of, 'Jamie, there's an amazing school that I just came from in Hackney Marsh and they did great food' - and I'm sure they do - but he didn't know that I opened it, I opened that kitchen."
Oliver said that the school had originally only had a kitchen that could reheat food.
"Now it has great food, but my point is, his example was flawed and I think many of his examples will be flawed and I think that he's going to let down the next generation of kids."
He warned that Britain is "in the middle of the darkest health moment in British history as far as kids' health is concerned".
A quarter of under-10s are obese, along with a third of teenagers, he said.
Mr Gove has said that giving academies the choice to opt out of nutritional standards gives them the freedom to do what is best for their students.
In a letter to Oliver, following a meeting in June, he wrote: "I noted your concerns about academies not being required to comply with the nutritional standards for school food.
"I would like to reassure you that we have no reason to believe that academies will not provide healthy, balanced meals that meet the current nutritional standards.
"As part of the broader freedoms available to academies, I trust the professionals to act in the best interests of their pupils.
"I understand from the School Food Trust that some of the best schools in terms of attitudes to food and meals are the academies."
He added that he had asked the Trust to carry out a study of established academies looking at their approach to healthy school food.
Christine Haigh, co-ordinator of the Children's Food Campaign said: "Today's expose certainly backs up reports we have been hearing from people on the ground. It's clear that the loophole created by this Government is going to reverse years of hard work to improve food in schools."
She added: "It's ridiculous that the Government is spending precious public money on a survey of food in academies, when healthy food could be maintained at no extra cost simply by requiring them to meet existing school food standards."