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Philip James writes: Here is my challenge – and having contributed this month's World Nutrition commentary, finished a couple of days before going on-line, forgive me for being brief.

I have been asked to welcome our Rio2012 conference. This I gladly do. It has a number of features well advertised elsewhere. These include nutrition being part of public health, with its social, political, economic and environmental dimensions. I have been fighting for this since – well, a long time ago, ever since as a young physician I practiced medicine in Jamaica and had the privilege of being able to think about what I was doing.

Our world now is in crisis. When I was young the crisis was the threat of a third and nuclear world war, that would destroy much or all of the planet. Now the crisis is one that involves us as professionals as well as citizens. This is the threat of over-population, over-production, over-consumption, which at current rates will also turn the planet into a world within which any future generations would have reasons to curse us. We have a responsibility here.

These are reasons why I support the vision and mission of the Association. But now is the time for the new leaders to step forward. Do not wait until you are 50 years old – start in your 20s and 30s. As long as I and my elder colleagues have puff we are glad to help and if need be advise. Just be prepared for our advice from our own experience, to expand the horizon and present challenges which at first may seem completely unrealistic. But pioneers are always being accused of being unrealistic.

In my commentary this month I also advocate – insist – that our Association must now get off being spectators or on the sidelines. To be a real force for good, let us now set up working parties or groups of which you yourself reading this right now, can be a member. We need to invent a new world of public health nutrition and we could not be in a better place than Rio, famous for setting a new agenda on the environment and pressing the need for a more equitable world.

Now is the time for you to engage in helping to develop new approaches, vividly set out, for a new world order where for once society is seen as a community living in a mutually supportive, equitable frame where good food and health are fundamental rights and not simply determined by one's inherited wealth, privileged education and position or genetically acquired ability.

How can we set the agenda for change? We can start by pointing out that by far the most effective societies are those that seek such an outcome. That's the vision. We need you to start transforming the vision into reality..