Major brands Sanitarium and Heinz Watties supported the move, which would see the nutrients in packaged food assessed and given a health rating out of five stars.
Heinz Watties said it would wait to see the conditions and the labelling requirements before adding the rankings to its packaging, while Sanitarium said it would use the ratings for all its products including Weet-Bix and Up 'n' Go.
Sanitarium's corporate food, environment and science manager Greg Gambrill said the ratings could prompt the company to change the ingredients in its foods to make them healthier.
He said Marmite was likely to rank poorly on the rating scale because of its high salt content, and because the system measured nutrients per 100g.
"Marmite may achieve a low score because of the sodium in it. Obviously we'll look at how they score and some may be able to be tweaked. If it's feasible ... it's certainly something we would do before we used the system on our products."
The rating system would not be compulsory and companies could back out if their food or beverages received a bad rating.
"Short-term it's better to start voluntarily," Mr Key said. "Companies are usually pretty good at responding to consumer demands and consumer wishes."
But consumers would be able to check the healthiness of all packaged foods by entering their ingredients into a calculator on a website which will be launched by the Ministry for Primary Industries next week.
Powerful lobby group Food and Grocery Council, which represents $26 billion in exports, came out in support of the change.
The council successfully lobbied for the logo size to be flexible, and for a calculating method which did not penalise dairy products.
Auckland nutritionist and Nutrition Society of New Zealand member Lynda Smith said the new system was simplistic and likely to mislead consumers.
"It's the whole lifestyle and the whole day's food, not just one thing they're buying at a time at the supermarket," she said. She was "dismayed" to see orange juice got a rating of 4.5 out of 5 stars.
Research by the ministry showed the Healthy Star Rating system was effective at helping Maori and Pacific Islanders make healthy choices. These communities were at the greatest risk of chronic illnesses related to unhealthy eating.
- Additional reporting APNZ