Through a video link to about 170 people attending the University of Otago Foreign Policy School in Dunedin yesterday, Prof Lang, of the University of London's Centre for Food Policy, said some people in New Zealand had been fighting his idea of food miles as if it were the only issue around future food production.
He suggested that as a country with a lot of land space, few people and a lot of fresh water, New Zealand could consider using land for aquaculture.
New Zealand, along with other countries, would have to define what constituted a sustainable diet.
Such a diet would have a low carbon and water impact and meet nutrition guidelines.
It was an issue that needed to be addressed rapidly, and although it transcended current foreign policy concerns, it needed to be central to them, he said.
Both domestically and internationally, there was a lack of coherence in leadership over food issues, where different groups were providing contradictory information and not looking at the whole picture.
The neo-liberal approach, where governments did not want to direct the food system, was a problem.
States were addressing climate change issues "a bit", but did not want to reduce the number of goods on supermarket shelves from 30,000 to 5000.
Many governments provided nutritional guidelines which addressed public health issues without taking the environment into consideration.
In Britain, for instance, the eating of fish was promoted.
If he listened to both nutritional and environmental advice, he could eat sardines, herring and mackerel.
But if nine billion people did that, the fish would be gone in a year.
All governments should be asking whether the food system was changing fast enough to become sustainable, and they should do something to"kick-start" the process.
He praised the lead of Sweden, which last week became the first country to announce environmentally friendly nutritional guidelines.
They advocated not eating meat on two days a week and reducing rice intake.
One of the directors of the Foreign Policy School, Prof Hugh Campbell, said the school had been a huge success and a "very productive" academic meeting for those interested in New Zealand foreign policy.
Trade policy had been centred on getting rid of subsidies in Europe and the United States, and the school had asked what else needed to be done.
