"They didn't go to a hotel," she says. "They hired the entire ship and then sailed off into the ocean. That's what I call big business. It's scary."
Given that the industry has such resources to hand, it's hardly surprising that money is no object when it comes to marketing its products - products that all too often contain high levels of fat, sugar and salt.
"They claim that their marketing doesn't have any impact on children," says Rosie. "So why do they spend pound;500 million on advertising to them?"
Now for the first time, she says, there is a concerted effort to counter the barrage of food industry propaganda. "As a nutritionist, I've been frustrated over the years thinking: 'Where is the political will?' This is the first time that ministers have made a commitment to doing some marketing themselves."
The Government's 5 A DAY logo, launched last year , will appear as an endorsement on products such as cartons of pure fruit juice, so that parents will no longer be in any doubt as to what qualifies as a portion of fruit or vegetables. The campaign slogan, "Just eat more (fruit and veg)" will eventually appear without the words in brackets, a reduction technique developed by sportswear advertising.
Research into ways of playing the food industry at its own game has been under way at the University of Wales Bangor since 1992. Psychologists, led by Professor Fergus Lowe at the Bangor food research unit, have devised Food Dudes, a programme that uses cartoon characters and video adventures to make children feel better about eating fruit and vegetables, much as Popeye was used during the Second World War to persuade people to eat spinach.
The Food Dudes are young superheroes who are involved in saving the Life Force from a gang of baddies hellbent on taking away the world's energy by depriving it of fruit and veg. Children who watch the video are urged to keep the Life Force strong by eating fruit and vegetables. Small rewards are offered, and by encouraging them to taste these foods repeatedly, they develop a liking for them and come to see themselves as "fruit and vegetable eaters".
In one nursery study, the Food Dudes programme was shown,15 months later, to have raised lunchtime vegetable consumption from 20 per cent to 89 per cent and fruit intake from an initial 17 per cent to 76 per cent.
But while the Dudes have shown that the devil doesn't necessarily have all the best tunes, and that marketing techniques can be used to sell good things as well as bad, there is evidence that the food industry may itself have woken up to the possibilities of the "healthy-eating" message.
When Rosie Denison attended that convention on the cruise liner, she was trying to advise food producers that healthy products could make money, and that nutrition could be a powerful selling point. And she believes the tide might be turning. There is, she says, a groundswell of opinion in favour of healthier eating. Firms, under pressure from parents and the Government, are beginning to latch on to this.
Whether this means that the Food Dudes will soon be out of a job remains to be seen. But nobody involved with the 5 A DAY campaign is taking any chances. Just in case.