An Australian actor who set out to expose hidden sugar in health foods said he gained 8.5 kilograms and a paunch after going on a 60-day low-fat diet that included yogurt, cereal, muesli bars and juices.

Damon Gameau's documentary, That Sugar Film, studies the effect of consuming what it says is the average daily sugar intake for Australian adults - the equivalent of 40 teaspoons - on the human body.

"I think you can't not be shocked by learning the average Australian consumes 40 spoonfuls of sugar per day, " Gameau said.

The film's website explains how Gameau came to the "40 teaspoons" figure, with the first stop the Australian Bureau of Agriculture Resource Economics.

"Sugar is now hidden in so many foods that it is difficult to get a precise measurement. As a result there are lots of different figures flying around," it says.

That Sugar Film, featuring cameos by actors Hugh Jackman and Stephen Fry, opened in Australian cinemas this month and will be released in Britain in March.

In an experiment under medical supervision, the actor-turned-director increased his sugar intake while maintaining his exercise routine, but stayed away from soft drinks, chocolate and ice cream - traditional villains in anti-obesity campaigns.

Gameau's film makes him the guinea pig, just like Morgan Spurlock's award-winning 2004 documentary Super Size Me, in which the US filmmaker stuck to a McDonald's-only diet.

A bowl of cereal with yogurt and a glass of apple juice used up half of Gameau's sugar quota for the day, bringing modern-day breakfast habits under increased scrutiny.

"It especially made me think of kids who are having breakfast in the morning," he said. "Their blood sugars are just going up and down like a yo-yo."

Doctors said the sugar experiment put the actor at risk of fatty liver disease, while his body fat rose by 7 percent.

The film also shows Gameau visiting an Aboriginal community in the desert, where people had lived off the land for decades. But a Western diet has become an insidious threat, ushering in deaths from liver disease and diabetes.

"Their sugar levels are astronomical," Gameau said. "It can't go on because they are going to die out and they are the oldest culture in the world."