MELBOURNE (Reuters) -- Fifty-six percent of Australian adults and 27 percent of children are obese because they eat too much and exercise too little, a study found on Sunday.

About 9 million Australians over the age of 18 are overweight and childhood obesity rivals North American levels and exceeds those of Britain, the ***Medical Journal*** of Australia said.

Combined with inactivity and poor nutrition, obesity is responsible for at least 10 percent of health problems, including heart disease, diabetes and cancers, making the health effects as bad as those of tobacco, the journal said.

In a separate study, it said Australian women spent a total of A$414 million each year in their quest to slim, with some women spending more than A$3,000 annually.

Annual expenditure on commercial weight loss programs, gyms, fitness equipment, personal trainers, weight loss pills, slimming products and meal replacements averaged A$441 per woman.

Yet all their efforts seem to be in vain as obesity rates continue to rise, the journal said.

Bigger portions, cheaper processed foods, and heavy marketing of takeaway foods and soft drinks are among the factors driving obesity in Australia.