An extreme diet that has come under fire in Australia is under investigation in New Zealand.

An Australian watchdog has blasted the Lemon Detox Diet, popularised by superstar singer Beyonce, for promoting dangerous weight loss.

The fad recommends drinking a lemon-juice-based liquid and not eating solids for up to 10 days. Around 40,000 Lemon Detox products were sold in New Zealand last year, a spokesman said.

The New South Wales Food Authority has placed it on a "name and shame" list and fined and the company behind it for making false nutritional claims.

The New Zealand Food Safety Authority has launched "preliminary inquiries" to see whether it has breached regulations here. "The NZFSA assessment of this product will consider labelling and advertising statements," said spokesman Gary Bowering.

In NSW, Pure Natural Health, the company behind the products, was fined $1710.88 for misleading claims on packaging and in advertising material.

"Trying to lose weight is a serious issue for many people and there is absolutely no room for companies or individuals who try and take advantage of this situation," said NSW Cabinet minister Steve Whan.

The diet is sold at more than 100 pharmacies and health shops around New Zealand. Australian managing director Endree Saade said the website had been approved by the Association of New Zealand Advertisers' Therapeutic Advertising Pre-vetting System.

He said the company was "shocked and horrified" by the NSW Food Authority's allegations and was seeking legal advice. "We believe that we have been made a scapegoat for all similar products."

Dietitian Nikki Hart welcomed NSW Food Authority's move. "These diets are setting you up to fail, because they're eliminating real food."