Presumably you're already totally sickened by the excesses of Christmas as a gift-giving ceremony, and your goodwill to others has been leached out of you by the size of the queue outside Jo Malone (10 minutes of your life, scorched, in the quest for a candle that smells).

I've now got two excellent phrases to spoil your Christmas dinner, and turn the marshmallow-topped sweet potato to ash in your mouth: "obesity crisis" and "food bank". They're actually related, you know. But not in the way Richard Littlejohn would have us believe, that people who go to food banks only eat chips.

In the new year the Overseas Development Institute is to publish Future Diets: Implications for Agriculture and Food Prices, behind which rather dry title lie some eye-popping figures about global obesity. One interesting line of inquiry, though, is what successfully combats obesity. The UK is a rare country for running the full gamut, from a government initiative that did work, to one that doesn't at all. That is, rationing in the second world war, and the Change for Life campaign, which has been running since 2009, addressing a knowledge deficit that doesn't exist (obesity specialists are pretty well united on the fact that there are very few people who don't know a high-calorie foodstuff from a low one).

It's always presented as a happy accident, one of those cute paradoxes in which the second world war specialised, that rationing, in a bid to stop us starving, also stopped us getting fat. In fact, while obesity may not have featured in the planning, this isn't an accident: in order to be the kind of government that can effect that kind of public health improvement, you have to start by being the kind of government that cares whether or not your people are hungry. You have to be the kind of government that takes what people are putting on their tables every night as its most urgent and pressing business.

At the end of rationing (which was incredibly unpopular, let's not forget – nobody enjoys being told how much bacon they're allowed) not only was there much less obesity, but other indicators of a nation's health – birth weight, infant mortality – also improved. At a recent Women's Institute history night, I saw for the first time a full list of what the rations actually were.

I concluded ruefully that they were so meagre (one egg a week, 50g of butter) that I don't think I'd bother eating, I'd just live on protein powder and alcohol. But that's not the point; when one discusses rationing, it's in the context of national circumstances so straitened that everybody simply had to eat less, because there wasn't enough. But the next stage of that logical process is never discussed – which is that it was a fear, really, for the poor not having enough that led to a policy for everyone. Circumstances weren't so dire that rich people would have starved, or even people in the middle: the concern was a) that scarcity would falsely inflate prices, so people who could previously afford to eat would be priced out; and b) that people would hoard. The hoarding point is interesting as it gives the lie to a narrative often tacitly peddled, that human nature during the war was better than it is now, more self-sacrificing, less demanding, more generous.

But more important is that point about prices – all markets favour the rich. In times of scarcity, though, the poor are disadvantaged by an amount so stark that you can't count it. Whatever the price is, the entire point is that it will be too much for that group, so that demand is reduced and supply at the top can remain at normal levels. It's like a bully holding a boy's satchel 5cm higher than he can jump. That much was obvious in the 1940s, and you would hope it would be again today, unless 30 years of neoliberalism has totally hollowed out our sense of reason.

In that era, food was a manifestation – perhaps the central manifestation – of solidarity. Rather than deal with the threat of starvation as it happened, with emergency food parcels and people slipping through the net, that government dealt with it pre-emptively, and it worked. People didn't starve, and they ended up healthier, and our parents were born slightly bigger, which accounts for why they need their ginormous baby-boomer houses.

Contrast that with food banks today: obviously the situation is slightly different, since the scarcity is not of food but of money, and it has been wilfully created by the government by unjust benefit sanctions and maladministration. Nevertheless, people are hungry, and rather than answer that with a call to act collectively, to sacrifice collectively, we are asked to maybe give a tin of kidney beans as we pass through Tesco, reflecting as we go on the tendency of the poor to mismanage their finances (pace Michael Gove), or people's limitless desire for things that are free (and Lord Freud).

However, while the hungry are, of course, hit hardest by the modern solipsism, it makes change impossible all the way through society so that it hits us all. We all get fatter, and there are no public health levers, because the levers that work are the ones wherein we're all in it together as a demonstrable fact, and not just nauseating rhetorical guff.

Across the world there are other things that work; in Denmark, a solid resistance to corporate interests has led to the healthiest McDonald's and KFC recipes of any country. In South Korea, a mass education programme has led to the consumption of insane amounts of vegetables.

You don't have to ration people to one egg a week to be a big government; but you do have to be a big government to make a big difference.

Twitter: @zoesqwilliams