It has more sugar than a 50g bar of Dairy Milk chocolate or a can of Coke, but Powerade has still managed to secure a spot as the "official sports" drink of the Olympics.

That has prompted advocacy group Consumer NZ to call for tighter advertising standards, to tackle the issue of unhealthy food being marketed to children.

It cited other examples, such as Gatorade, which has a relationship with the New Zealand Rugby Union, KFC, which sponsors rugby teams, serial sport sponsor Burger King and McDonalds, another Olympic partner.

Consumer NZ chief executive Sue Chetwin said there was evidence that food marketing, such as sponsorship, made unhealthy food more appealing to children and was contributing to New Zealand's problem with obesity.

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"We think it would be a good idea if all major sports starts weren't allowed to be associated with drinks that are very high in sugar. Gatorade and Powerade are really good for high-performance athletes but they are largely water and sugar, they are no good for ordinary people," she said.

"They're promoting these drinks while we have the third highest rate of childhood obesity in the OECD."

More than 40 per cent of kids have some level of tooth decay by the time they are five.

Marketing expert Bodo Lang, of the University of Auckland, said more regulation of sponsorship would be a good thing.

"Sponsorship of sportspeople has a huge impact on the perception of the product. At the end of the day, that's why they do it. They know the target group they are after, young people, look up to sports heroes."

He said sponsorship was particularly insidious because it was in the background rather than blatant advertising.

Last year, the Ministry of Health released a Childhood Obesity Plan that acknowledged restrictions on sponsorship from low-nutrient, high-energy foods had a role to play in tackling obesity.

But the industry is mostly self-regulated by the Advertising Standards Authority, which has voluntary codes of practice.

It is reviewing its code for advertising food and code for advertising to children. One of the questions being asked is whether there should be a specific sponsorship guideline

Chetwin said change was needed. "We want advertising standards strengthened to protect children and independent monitoring and evaluation of the codes. We think young people need clear and consistent messages about healthy food choices."

She said the Government could consider a rule whereby athletes would not qualify for taxpayer funding if they were sponsored by a junk food brand.

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