Australia has experienced an unprecedented collective weight gain over the last three decades and it could lead to the first modern decline in life expectancy.
A new mega-study on four million adults proved for the first time that an unhealthy Body Mass Index had a direct correlation with premature death.
The study published in British medical journal The Lancet found that for every increase in BMI unit after the overweight range, there was an increase in the risk of premature death by around one third.
This increased risk related to coronary heart disease, stroke, respiratory disease, diabetes complications and cancer.
Obesity may lead to the first decrease in life expectancy seen in decades.
Deakin University's World Health Organisation Collaborating Centre for Obesity Prevention professor Anna Peeters said the study pointed to a population-wide catastrophe in Australia.
"With two thirds of Australian adults overweight or obese this underscores the seriousness of current obesity rates for future life expectancy in Australia," Peeters said.
"Obesity may lead to the first decrease in life expectancy seen in decades.
"If we needed yet another reason to step up our efforts to prevent obesity, this is it."
Cancer Council Australia chief executive Sanchia Aranda said cancer was one of the ways morbidity increased the risk of mortality.
"Given the unprecedented population weight gain in Australia over the last 30 years, we can expect to see the number of cancers and cancer deaths related to obesity and overweight increase in the future unless we take action," Aranda said.
What is the Body Mass Index?
The BMI is a measure used to determine if you are a healthy weight for your height. It is calculated by dividing your weight in kilograms by your height in metres squared, to place you in a category of underweight, healthy weight, overweight or obese.
"Cancer Council estimates show around 4000 cancers diagnosed in Australia each year are related to obesity or overweight alone. Even more cancer cases are linked to poor nutrition and inadequate physical activity."
Flinders Medical Centre Diabetes and Endocrinology director Nikolai Petrovsky said the study set up the great challenge facing Australia.
"The question is not whether obesity is associated with excess mortality, which it clearly is, but what do we do about it as a society?" Petrovsky said.
National Health and Medical Research Centre doctor Lauren Ball said we needed population-level solutions instead of focusing on the individual.
"This research comes at a time where we cannot ignore the role of lifestyle behaviours on our health," Ball said.
"Governments need to place much higher priority on supporting healthy lifestyles, including changes to health care system structures, regulating food supply and incentivising physical activity opportunities.
"We need to take innovative action if we are to have an innovative outcome, and this cannot be ignored any more."