My nana once said: “You can never be too rich or too thin.” I don’t think she’ll mind me saying that she’s never been too much of either. Nevertheless, her sage words have become something of a family motto, so we decided to have them written in Latin beneath our heraldic crest (a pair of hair-straighteners mantling a brimming ashtray, leopard-skin shield). Unfortunately none of us can read Latin, so the translation turns out to be something like: “The rich man is either too thin or too much, nor are you able to, so there isn’t.”

The reason my family ain’t so au fait with classical Latin is that, like more than 45% of the country, we are all werkin’ clahss. Classified somewhere charming between grades C2 and E, the social stratum my lot comes from has meant that, for many reasons, being thin (in a healthy way at least) is highly improbable.

The first and most obvious of these reasons for predestined podge is situational. Obesity and opulence once went hand in hand, anything but emaciated being the hardest state to achieve. Increasingly, “fat” has become synonymous with “poor”. Food that’s bad for you is cheap and requires little time, effort or energy to prepare. Anyone who grew up working class in the 90s will recognise my diet as a kid: it mainly resembled a budget cartoon – turkey dinosaurs, smiley potato faces, tinned spaghetti shapes and ambiguous cold meat products shaped like a teddy bear’s face.

The culture around eating was loud and messy and territorial, as it tends to be when everyone’s working hard and crammed in together. The food my nana served, and that we would all dive on, was almost always something (pork chops, corned beef hash, fish fingers) and chips (that she would chip herself, mind), and on Sundays, we would have vegetables (all colour stolen by the cooking water, with extra salt for flavour). The best was her Irish stew: thick as custard and so salty it corroded the top of your mouth. It was a post-war diet riddled with misunderstandings about nutrition, based on false information published decades earlier, and compounded by a half-century’s bad habits. Food was fuel, not something to be savoured; and if it was just fuel, then why not have the most easily savoured fuel going?

For a long time, I had assumed it was a genetic thing, too, that I was the recipient of a sorry strand of DNA that said: “Will struggle with weight.” While I’ll keep telling myself that, the fact that my recent predecessors had a nutritionally narrow diet has almost certainly had a physical effect upon me, and indeed my children, through the mysterious phenomenon of epigenetics.

It goes something like this: if you take a bunch of healthy Smurfs (say) and fed them a diet of high-in-fat Smurfberry pie for their whole lives, their Smurf babies (assuming they procreate sexually) will be much more likely to be SmurFat. As Prof Bill Sullivan at Indiana University put it: “If you consider DNA to be a book of life, the book handed down to the child is not necessarily a pristine copy – some passages may be highlighted, a page or two may be missing, or notes may be scribbled in the margins.”

That’s not to say that someone with unhealthy parents can’t live a healthy lifestyle, but it makes it harder. It also means that if you plan on having children at some point in the future, best to try and change your bad habits now. We can rewrite our methylation profile (the “witness marks” of our DNA’s epigenetics) through interventions such as exercise, diet and even weight-loss surgery (not that I would ever advocate surrendering to the scalpel’s blade, unless, of course, medically necessary).

The fact is, however, that the developed world needs to go on a diet. Not an apple-juice colon cleanse or “keto”: for us to sustain our planet so it can sustain us, we need to stop eating meat, processed foods, foods with totally unnecessary packaging and foods flown in from the other side of the world. Next time you go to the supermarket, take note of the variety of countries your groceries come from – then swallow that carbon footprint because, honey, it’s yours.

The arguments for dietary revolution have got a lot of oxygen in recent months, but regardless of the best intentions of columnists and activists on the subject, the going-vegan-for-the-planet virtue is one that only really belongs to the middle classes and the under-30s. In order for changes in diet to make a real difference, those who hold cultural or economic capital need to get a grip on why the message isn’t translating, why the language that progressives find so emotive is proving to be nothing but antagonistic to those on a tight budget with a load of hungry mouths to feed.

Like everything else in the human world, it all ultimately comes down to economics. If the poorest in society weren’t so impoverished they would have more time, money and head space to engage with the issues that are going to affect them the most. With our national distraction having retreated behind closed doors in Whitehall, perhaps it’s time we started discussing again higher taxes for higher earners, making sure corporations pay tax, even universal income, because only with truly egalitarian fiscal programmes can we invite everyone into the conversation and change our habits of consumption for good.