The True Food Guide informs shoppers of what they are eating and prompts manufacturers to rethink what they are putting in our foods.

A Greenpeace shoppers' guide naming foods that could contain genetically modified ingredients has prompted some companies to investigate their products and try to eliminate potential GM sources.

Eight months after the guide was released, several companies have contacted Greenpeace to say they have upgraded their policies on GM foods to earn a higher rating in the True Food Guide

The guide, which has been delivered to half a million shoppers around Australia, rates popular supermarket brands as "green", "orange" or "red".

Companies that earned a green rating gave written assurances that they were not using GM ingredients anywhere in the food chain, while orange ratings were given to companies that were committed to removing GM ingredients and were in the process of doing so.

The red rating was given to companies that were unable to show they had policies to remove GM-derived ingredients, or that Greenpeace said had not responded adequately to its inquiries.

Since the guide's launch in May, companies including Weis (sorbets) and Sakata (rice crackers), originally rated red, have confirmed to Greenpeace that their products are GM-free. Other brands, including Sargents (pies), Three Threes (condiments), Murray Goulburn (dairy products) and Spring Gully (pickles), have also been moved from the red category to the green.

The feed given to animals that are the sources for dairy products, meat and eggs must also be GM-free for a company's products to rate in the highest category.

Greenpeace GM campaigner Rebecca Hubbard said companies had responded to the concerns of customers who had contacted them after reading the True Food Guide.

She said many had not been aware that they might be using GM ingredients in their products. "A lot of food companies didn't even know that animals are being fed GE (genetically engineered) stockfeed," she said.

"It's been quite a learning process for a lot of people."

Ms Hubbard said Greenpeace was encouraged by the responses of many companies.

Since the guide was published, some had eliminated ingredients that could have contained GM material.

A new guide is planned for publication mid-year that will include fresh meat and other animal products. In the meantime, updated ratings can be found on the Greenpeace True Food website.

Ms Hubbard said The Pancake Parlour, although not listed in the guide, had eliminated specific ingredients because it could not confirm they were GM-free.

The German supermarket chain, Aldi, was now rated orange after giving a commitment it would eliminate GM ingredients from its "own-brand" products, she said. Other companies, including Sanitarium, Coles, Woolworths and Barilla, had been talking to Greenpeace in a bid to lift their ratings.

Ms Hubbard said the response from consumers and companies was a clear sign that people were concerned about GM products in their food chain.

Ms Hubbard said GE foods came from genetically engineered crops that, she said, were like a "living pollution" if released into the environment, carrying the risk of reproducing with other crops.