This year I spent a couple of nights in hospital. In the bed next to me was sparrowlike Freda, born at an undisclosed date in the 1930s, who remembered her mum running to help when the neighbour unexpectedly had twins and no clothes or cot for the second one (they used a drawer). Opposite was the much younger, huge and serially crisp-eating Dawn, bed ridden with multiple chronic conditions. I felt as if I had strayed into a Daily Mail lifestyle feature.

It is so inviting to see fat as a personal choice, especially if you’re thin. Thin people, mostly, like being thin, probably put a bit of effort into it, and secretly think that fat – determined by wearing a dress size one up from their own – signifies a regrettable character flaw. This is a pattern of thought with delicious calorie-free moral superiority.

Simon Stevens, the newish boss of NHS England, looks thin and I’d guess he’s fit, and he is a smart bloke, possibly even smart enough to save the health service. But to do that, he is counting on making us, the potential patients, play a part too.

His plan for the next five years is less than 80 pages long, as lean and fit as a hot yoga fanatic, and fat is top of the list of things not to be, well ahead of smoking and drinking, top of the list of childhood problems, and in the form of diabetes and bariatric services, top of the list of avoidable costs.

When, according to Diabetes UK, treating diabetes soaks up £10bn a year from the NHS budget, and type 2 diabetes is associated with being overweight or obese, it’s the obvious place to start. Greater personal responsibility, lower spending on avoidable health costs – bingo!

For some people – Stevens admits that he himself is one – it only takes the jolting realisation that the pounds have mysteriously piled on to reform one’s eating habits, adjust one’s lifestyle and get back to a healthy weight. When he was working for United Healthcare in the US, he shed three stone on an incentive scheme run by his employers. As he points out, in the UK in contrast to most western countries, most employers don’t pay a direct contribution for their employees’ healthcare. So why not rope them in?

But why all the focus on fat. Stevens knows he has to tackle something much more profound than that. Smoking is still the number one killer, the biggest cause of premature death. And it is linked to half – HALF – the inequality in life expectancy between social classes. That’s about two years between south-west and north-west England. That is, the poorer you are, the less likely you are to hear, or perhaps just to act on, the anti-smoking message. Then there’s alcohol abuse, which is directly responsible for more than 100,000 hospital visits, and costs about £3.5bn.

Yet easily the most eye-catching cause of preventable illness, the one everyone wants to hear about, is fat.

This is a territory with many well-trodden paths. Bad food is cheap food, fatty, sugary, easy to eat, always available. It is fast, not just to get hold of, but also to consume. It gives you a lift. What normal child would choose meat and two veg over a burger and chips, and how often would a normal, busy parent choose a fight rather than peace. Particularly if they like burgers too.

But here’s a really striking statistic that Stevens quotes: one in 10 children starting primary school are obese. By the time they leave, that’s almost one in five. Is this a dereliction of personal responsibility by the kids themselves, or by their parents? Or is it the food available in school, or in the streets around the school, or the way the school day is structured, or the absence of sports facilities, or the lack of the sports club tradition?

Or is it because some time between five and 11 you grow up enough to realise that in this world you are what you look like, and if you look wrong then the quickest way to feeling better about it is to grab a burger?

In the next bed in my local hospital back in March, Freda never had a chance to be fat. Across the ward, maybe Dawn never had a chance to be thin.