Seven years in the planning and a few weeks in execution, the Olympics is a strange affair. Supporters argue the £9bn investment will generate bigger long-term returns. Tourism, goodwill and economic branding are all cited.

Critics say the Games usually leave host cities and countries with public debt. 38 Degrees, the internet campaign, did a fine job exposing and reversing some sponsors’ less-than-desirable tax arrangements. And a British Medical Journal study of big sporting events found little solid evidence of any positive effects across a wide range of indicators.

I declare an interest. As a member of the London Food Board, the Mayor’s advisory group, I’ve been nervous about hyping future gains. But I’ve also witnessed real advances from London’s Olympics in the case of sustainable fish. Painstaking, patient work by Kath Dalmeny, Rosie Boycott and others achieved a high-level agreement on selling only sustainably sourced fish. Providers signed up, creating a new sector benchmark. A country whose national dish is arguably fish and chips really must eat sustainable fish. It currently doesn’t.

“The £9bn should be spent on building exercise into daily life”

We ought to seek systemic advantages from big investments. Offsetting carbon as people jet in is weak policy. The £9bn should be spent on building exercise into daily life for the mass population. Ancient Greeks moved a lot and ate within environmental limits! It’s a shame we don’t. We are all sub-Olympians now.

Modern Olympics are festivals of the superfat watching the superfit. A handful of élite competitors is not the same thing as populations being encouraged to move. That’d be a real nudge!

£9bn could help create segregated bicycle tracks in cities, towns and villages, and walk-to-school schemes. It’d kick-start unstoppable cultural change. A country daring to narrow the gap between sporting superheroes and the mass population could really claim to be civilised.

If the purveyors of excess calories really believed we needed more physical activity, avoiding co-responsibility for diet, they’d stop sponsoring spectator sports and join us in planning how to transform conditions for everyday good health. Now that would be a lasting legacy.