Associate Professor Rachael Taylor summarised weight-loss research to answer the question of how early in life obesity prevention should begin - partly because the Government is redirecting nutrition funding into the maternal and newborn area.
She said some programmes found no reduction while others, such as the Sydney-based Healthy Beginnings trial (which has similarities to an Otago baby and toddler programme being evaluated), were effective.
The Sydney intervention produced a significant reduction in average BMI (body-mass index) of 2-year-olds which equated to being about half a kg lighter than children in the non-intervention group.
Dr Taylor asked if it might be better to intervene in pregnancy, but said the big problem there was that nearly half of pregnancies were unplanned.
Targeting teenage girls might be ideal, "but unfortunately teenagers aren't that receptive" to nutritional and physical activity interventions.
So the population-wide measures, like taxes on sugary drinks, were most likely to make a difference.
Several other researchers threw in traffic-light labelling - to mark foods as healthy or unhealthy - as an important part of combating a food "environment" which promotes obesity.
Professor Robert Beaglehole called for a national strategy on obesity reduction - which National MP Paul Hutchison said the Government would release in months - and for a social movement, as with tobacco control, to create the climate for controls on the food industry.
"Obesity (here) is a public health disaster ... It is a tragedy at the personal, family and social levels. It's a pandemic."
Overweight kids
Obesity rates in children aged 2-14 in 2012
• 10% of all children
• 19% of children in poorest 20% of homes
• 3% of children in richest 20% of homes
• 6% of European/other children
• 17% of Maori children
• 23% of Pacific children
• 7% of Asian children
Source: Ministry of Health