A new campaign asking people to reduce their sugar intake highlights the link between obesity and 13 different types of cancer.

That's the message from the Cancer Council Victoria which launched a new awareness campaign on Tuesday in a bid to highlight the link between obesity and the devastating disease.

A third of Victorians admit drinking more than a litre of sugary drink a week, experts say, which could lead to the build up of dangerous toxic fat around internal organs.

Almost 4000 cancer cases in Australia in 2010 were linked to unhealthy weight, while figures show children in Victoria are the most overweight and obese in the country.

Melbourne surgeon Ahmed Aly, who features in the campaign, said obesity is "the single most critical health issue of our time".

"We want people to realise they could be drinking their way towards weight gain, obesity and toxic fat, increasing their risk of 13 types of cancer," he said.

The campaign includes a graphic advert showing what toxic fat looks like inside a patient's body.

Todd Harper, chief executive of Cancer Council Victoria, said the images "tell it as it is".

"People deserve to know the truth, they deserve to understand the impact of unhealthy weight and its relationship with cancer," he said.

Sugary drinks are the largest source of added sugar in the Australian diet, with each can of cola containing up to 10 teaspoons.

Fiona Humphreys, from Melbourne, used to drink two cans of sugary drinks every day but feels calmer and more productive since giving up seven years ago.

"I had no idea that they could give me cancer, I knew that sugary drinks were a big factor in obesity," the 50-year-old said.

"By ditching them I lost 7kg in one year, obviously seeing those benefits made it easier to kick that habit."

The campaign will run for five weeks and be broadcast on TV and radio in Victoria.