If food policy is to do its job, it has to be based on hard evidence, not merely reflect vested interests. And politicians must take charge of it

The real world of food policy has a sometimes tortuous relationship with evidence. Cynics abound. "Policy-making inevitably is political," they cry. Optimists agree but argue we must develop better processes for the evidence-policy-practice relationship. Technocrats want self-reinforcing cycles of policy using best evidence and systematically collected data.

In practice, a more fraught relationship exists. We witness policies in search of evidence, without evidence or out-of-date evidence, lagging behind evidence, with partial evidence, denying evidence, with evidence which conflicts, and our friend evidence in search of policy.

No wonder the fashion recently has been to create agencies. Politicians argue it's best to put blue water between political and scientific structures. But this doesn't resolve the difficulty. It just gets it off politicians' desks. But in time the evidence returns.

Last week's publication of the Intergovernmental Panel on Climate Change's latest report on evidence to policy-makers is a reminder of how that happens. The IPCC presented its implications in stark terms: do something now or we reach the point of no return. Even governments in denial buckled. The US went silent. And coincidentally, the Australians voted their government out anyway.

Is this proof that evidence will triumph in the end? Yes and no. Don't forget, evidence about climate change has been around for a long time. What changed is that the scientists got organised, NGOs campaigned, public worries rose, companies realised this affected them and the cauldron of pressure mounted. I find this inspiring but the truth is that not much has actually changed. All that's happened is global agreement that something is happening, not what precisely to do about it. The difficult bit comes now: persuading rich consumers (us) to consume less and differently, while enabling poor consumers to aspire to more but differently, too.

The moral of my tale is not just about climate change. There is lots of evidence of this kind of situation in other topics. The fissure exposed is vested interest and how to get it out into the open. Evidence that colourings are harmful has been contested for years. On alcohol, advertising, nutrition, pesticides, the list could go on. Far from the answer being to send evidence off to agencies or arms-length bodies, the answer lies in making politicians do their job: take decisions, give leadership and let the people ultimately decide. n

Tim Lang, professor of food policy, City University