The Advertising Standards Authority (ASA) has upheld a complaint against a supermarket advertisement for A2 milk, saying the beneficial claims are not backed up by scientific evidence.

Progressive Enterprises said its television advertisement, for Countdown, ran three times over one night in September and was on the company's website before it was pulled.

In the advert a celebrity chef described A2 milk as "a protein rich milk that's been shown to help those with heart disease and type 2 diabetes".

However, it prompted a complaint from one viewer, who said the claim was a medical one which had not been supported by research - and such claims should only be made for approved medicines.

A2 milk is rich in A2 beta-casein rather than A1 beta-casein, and the a2 Corporation said its more expensive milk "may assist with digestive wellbeing".

The New Zealand Food Safety Authority said further research was needed before it could be claimed the A1/A2 composition of milk was important in human health.

Progressive did not believe the advert breached codes, and said it was not an absolute health claim but "merely an observation that studies have shown a positive correlation".

Progressive relied on evidence supplied by the a2 Corporation, and took it in good faith, believing it to be true.

The Commercial Approvals Bureau also believed the claim was OK as it was a generalised nutritional claim.

However, in a majority decision, the ASA said it saw the chef's statement as an absolute claim, and as such it required a high level of substantiation.

The ASA said the evidence did not include scientific studies but articles promoting A2 benefits, and one was written by the chief executive of the a2 Corporation.

The advert was not prepared with a high standard of social responsibility, required when nutritional claims were made, the ASA ruled.