The healthiest, five-star products, include trim milk and plain yoghurt.
Auckland nutritionist and Nutrition Society of New Zealand member Lynda Smith said the 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.
"Not everyone should be drinking blue milk, it's not the best thing for everyone."
Ms Smith was "dismayed" to see orange juice got a 4.5 out of 5.
"I wouldn't want people to think it was a good thing to have a lot of."
The cost of manufacturers labelling their products would outweigh the message, which wasn't hugely effective.
"Who doesn't know that fizzy drink is bad? Do we really need a number one on it to tell us that?"
The types of people who bought soft drinks were unlikely to take any notice of a one star rating, she said.
Heinz Wattie's nutrition manager Julie North said the star ratings would be a move in the right direction.
"We're positive about the system, we think it's a sensible move forward for consumers and for everyone in the field."
Any moves to help consumers understand more about food was a good thing, and the system had been "well considered" in its development, she said.
For the ratings to be a success, companies would have to get on board.
New Zealand food manufacturers had been providing good information on products since the Food Standards Code changed in 2002.
But a five-star rating was "one further tool", she said.
Reader opinions
Would you like to know more about the food you are buying? Should a star-rating system be compulsory?
Ross Burnett, 58, Manawatu
I'm a diabetic so sugar content is what I look for when I buy our food. At the moment, I'm trying to grow my own food. I'm a farmer so I eat my own beef. I know where that's come from and what's in it and I'd like to see that for the food I buy from the supermarket.
I think a compulsory scheme for all foods would be a really good idea.
William Ko, 22, Avondale
If I can't read the ingredients then I won't buy it. I'm a personal trainer so what I eat is really important to me. I eat a lot of organic stuff.
Tyler Chiplin, 20, Mangere Bridge
I sometimes look at things but I usually don't. I just buy the same foods every day and I know that they're fatty - energy drinks and fast foods.
But it would be helpful to have something that let people see exactly how good or not good something was. I'd definitely read it then, I think.
Chyenne Carroll, 27, Mt Eden
I'm not fussy about labels because I tend to buy fresh foods. I think it would be a good idea to help people see what's in the food they're buying.
