He's currently leading a campaign to stop children from being bombarded with junk food adverts on TV.
But some children's meals at one of Jamie Oliver's restaurant chains can contain more calories, fat and sugar than similar dishes at some of the biggest fast food giants, FEMAIL can reveal.
A children's burger served with sweet potato fries and salad at branches of Jamie's Italian contains up to 452 calories, 18g of fat and 18g of sugar.
A Burger King Kids Hamburger in the UK on the other hand - which can come with apple slice 'fries' in the Kids Meal - contains 250 calories, 6g of sugar and 9g of fat.
With his viral #AdEnough campaign, Jamie has been calling for the government to introduce a 9pm watershed for fast food advertising on TV, as well as urging fast food chains to stop promoting before these times too.
But some dishes at his Jamie's Italian chain can be more calorific and fattening than similar meals at the giants he has been targeting with his
A children's Margherita pizza at Jamie's Italian contains 374 calories, and 11g of fat.
Meanwhile, a Little Heroes Thin Pizza Margherita at Pizza Hut contains 327 calories, and 10.3g of fat, with a Pan and Gluten Free containing about 100 more.
Jamie's Italian's children's burgers also come in a large and small size. The large contains 452 calories - 200 more than Burger King's kids burger - and the small contains 370. Both are served with sweet potato fries and salad.
Burger King's values are for its burger alone, but a meal with apple fries, which contain 30 calories and 0g of fat, still comes to less than a burger meal at Jamie's.
However with a small portion of fries, a Burger King Kids Burger meal would come to 470 calories and 19g of fat, making it unhealthier than a burger meal at Jamie's Italian.
It comes after Jamie Oliver called on both Burger King and Pizza Hut to move their adverts to after the watershed in tweets last week.
To Burger King, he wrote: "Burger King! I've #AdEnough of our kids being hit with ads for high salt, fat & sugar foods and I'm on a mission to sort it. Will you guys support me? I think there'd be a lot of love out there for burger giant on the right side of this fight."
He also made the same request of Pizza Hut, and wrote: "I wonder how many retweets it'd take for to move their ads to after the watershed?"
His message received just 139 retweets.
A spokesman for Jamie Oliver said that the restaurant's children's menu has won a Soil Association award for the healthiest on the high street for the last six years.
On its website, Jamie's Italian states that at least "30 per cent" of its menu is made up of "fantastic healthy options".
About its kids meals, it adds: "Every meal is completely balanced, containing all the food groups that growing children need. All meals meet our healthy eating targets for children and contain at least two portions of a child's recommended five portions of fruit and veg a day."
Fast food chains have also been making steps to introduce more healthy options in the last few years.
Children are given a side of apple fries - apple slices shaped like fries - in their Kids Meal at Burger King, and at Pizza Hut, a Little Heroes meal includes salad.
Jamie's #AdEnough campaign has seen stars including Amanda Holden, Claudia Schiffer and Richard Branson sharing pictures of themselves covering their eyes on social media.
The celebrities - who also include Fearne Cotton, Paloma Faith and the cast of Cold Feet - argue the only ad-blocker that children currently have is covering their eyes.
Explaining his campaign on his blog, Jamie said: 'Kids are bombarded, day-in, day-out, with adverts for food and drink products that are high in unhealthy fats, sugar and salt.
"They're online, on TV, on the streets and all over public transport."
He continued: "It's time we put child health first. I'm calling for the government to introduce a 9pm watershed on junk food advertising on TV, and for proper controls on what ads kids see online, in the street and on public transport."
A Jamie Oliver spokesman said: 'Our kid's menu has been won the Soil Association's best children's menu on the high street for the last 6 years. It is a nutritionally balanced meal which includes baked sweet potato chips and salad.
"For adults, 30 per cent of our menu is a healthy option. The comparisons for the BK kids burgers and small fries (470 cals, 19g fat, 6g sat fat) and the large JI kid's burger, sweet potato wedges and salad (452 cals, 18g fat, 6g sat) PLUS we have a small option too (370 cals, 14g fat, 4g sat fat)."