Prof Rosenzweig, who directs the Economic Growth Centre at Yale University, has studied links between educational achievement and obesity, including among twins in the city of Kunming, in southwest China.
A striking feature of poor people in many countries was that their height was somewhat stunted, but they were also obese, he said.
In many cases, people who were eating attractive but unhealthy convenience foods were clearly enjoying the experience.
Many people in the United States also did not realise that being overweight increased their risk of developing adult-onset diabetes, which would badly damage their health.
Health education messages aimed at countering obesity among poor people needed to be pitched at explaining why, in their own circumstances, their health could be harmed, and what specifically this could mean for them.
There was no point simply lecturing people about eating healthier foods.
More enjoyable physical activities could be promoted effectively by encouraging people to band together to form a local sporting team - "something to motivate them".
"It has to be fun," he said.
This kind of activity would give them a reason to increase the amount of exercise they did and eat healthier food, he said.
Dr Michelle Rendall, an economist at Monash University in Melbourne also gave a talk, titled "Income Polarisation and Gender Gaps: the Last Decades", in which she argued that increased work opportunities for women had contributed strongly to an overall trend towards both more high-income and low-income work since 1980.
Income gaps between men and women had narrowed in some cases, but persisted in others.
"That's something I really struggle with - `How do we change social norms?'," she said.
However, some more policy measures to encourage women to remain at work- including by countering the high cost of child care in New Zealand - would help, she said.