Welsh Health Survey: A quarter of adults are obese
Around one in four adults in Wales is obese, and almost 60% are overweight, according to the Welsh Health Survey 2015.
Doctors and politicians said the annual figures reflect a "public health time bomb".
But numbers of adult smokers have dropped to a record low of 19%, and binge drinking has also decreased.
The Welsh Government said the survey showed "signs of encouragement" but there was "work to be done."
Less than a third of all adults, 32%, reported eating five or more portions of fruit and vegetables a day.
Around a third did less than half-an-hour moderate physical activity a week.
More than half of all adults are being treated for an illness; a fifth suffer from high blood pressure and 13% have a mental illness.
A total of 13,700 adults and 2,600 children took part in the survey.
Dr Charlotte Jones, chair of the British Medical Association's (BMA) Welsh GPs' committee, called the reduction in smoking "pleasing".
But, she said, "soaring rates of obesity" have led to an increase in type II diabetes, with 7% of adults in Wales now suffering from the disease, as well as more heart disease and cancer.
She added that the cost of the NHS would increase, unless the problem was tackled.
"We need to start with children, to prevent children from becoming overweight in the first place and to equip them with good habits for the future.
"Parents, schools, health professionals, the media, food manufacturers and the government all have an important role to play."
Fast food restrictions
Although 94% of children were reported as having good health, around only half eat fruit and vegetables every day.
Dr Mair Parry, officer for Wales at the Royal College of Paediatrics and Child Health, said Wales still has the worst rate of child obesity in the UK.
"It's clear that more needs to be done to address these shortfalls. Concerns still remain over the number of children who eat fruit and vegetables every day and those who do exercise."
She said there should be more restrictions on fast food outlets opening near schools and colleges, as well as 20 mph speed limits to encourage children to "scoot, walk and cycle" to school.
'A bleak picture'
Welsh Conservative health spokesman Darren Millar said the report "paints a bleak picture for the health of our nation".
He said it is a "very real indicator of the Welsh Government's failure to get a handle on what is fast becoming a public health time bomb".
"It is vital to health of our nation and the future of our health service that the new deputy minister for public health uses her post to drive forward preventative initiatives, which have to date simply not worked, as this report glaringly demonstrates."
Public health minister Rebecca Evans said the Welsh Government was close to achieving a 2020 target to reducing smoking to 16%.
"While the results of the survey show signs of improvement - especially in regards to smoking - there are still areas where there is work to be done.
"We need to make more progress on obesity and activity levels, and I am confident our decision to integrate grassroots sport and health policy will help us do this."