A conference on obesity has heard adults today weigh 9kg more on average than people 30 years ago.
The symposium on food policy, politics and population health is being held at Otago University's Wellington campus.
The policy director of the London-based International Association for the Study of Obesity, Tom Lobstein, told delegates the extra weight the average person now carries costs them more because they're eating more.
He says it also exposes them to risks, including diabetes, heart disease, stroke and some cancers.
Dr Lobstein says the food industry benefits financially from overweight and obese people, and its efforts to self-regulate have failed.
He says governments need to regulate and control marketing.
"You can't leave it to individuals to make the healthy choices. We need to set a healthy environment, and that means governments stepping in," he says.
"There is a real market failure at the moment, with people being enticed and encouraged to consume high-fat, high-sugar, salty foods, and this is a mistake. The market is failing."
'Traffic light' labelling best - researcher
A visiting expert on food labelling at the symposium says the so-called traffic-light system is the best in the world, and New Zealand should adopt it.
The director of a British Heart Foundation research group, Mike Rayner, says the so-called traffic light system of food labelling is the best in the world and New Zealand should adopt it.
The system is being introduced in Britain this year.
Dr Rayner says the red, orange and green works.
"People can instantly get a feel for the healthiness of the food by how many red lights there are as opposed to green lights."
Dr Rayner believes it works better than an Australian star system that New Zealand has considered.
In Auckland, public health doctors, paediatricians and others will also be considering policy on sugar-sweetened drinks, at a symposium on Wednesday and Thursday.
One of the participants, Dr Tony Blakely, has called for a 20 percent tax on sugary soft drinks, which he estimates would prevent 67 deaths a year from cardiovascular disease, diabetes, and diet-related cancers.
A public health physician, Dr Simon Thornley, told Nine to Noon the evidence linking sugar with cardiovascular disease is stronger than that linking it to saturated fat and salt intake.