Being morbidly obese is a choice. There, I’ve said it. I know it won’t make me popular, that many will accuse me of ‘‘fat-shaming’’ , while others will argue that being grossly overweight is a disability, and who chooses to be disabled?

But to be honest I am still reeling in shock from having seen Plus Sized Wars on Channel 4 this week. I watched the documentary with a mounting sense of horror, as the so-called P lus Size Bloggers - young, obese women who flaunt their excess weight on Instagram and Twitter and have thousands of online followers - together with a host of fashionistas, retailers and shoppers lined up to insist that “fat is fabulous” .

But here is just one less than fabulous consequence of the obesity epidemic in this country that I encounter daily in my work as a doctor. I’m a radiologist and some of the men and women who come to see me (in the new, extra large wheelchairs the NHS now has to purchase) are so large that they can’t fit in a standard MRI scanner so we can't diagnose what is going on underneath all those layers of fat. There are open-sided scanners we can use instead but the images they produce are of a much poorer quality.

Far from fat being fabulous, it is a public health time bomb. Forget the problems that the health system faces face with an ageing population - a recurring theme in this election campaign. Statistics show that 60 per cent of teenage girls in this country are overweight, and 20 per cent of young mothers are obese. Britain is home to the fattest women in Western Europe and our menfolk are fifth in the league table, according to a 2011 study published in The Lancet. I can’t believe that things have improved.

The harsh truth is these people are simply not going to reach old age. Complications associated with their obesity will get them first – after having cost the rest of us a fortune along the way in treating them just because they eat too much, and no-one seems prepared to tell them. To tell them that they need to stop, that it will be hard but they can - with help - do something about it. Efforts to ‘‘normalise’’ gargantuan appetites and bodies, as high street retailers are so cynically doing with aggressive marketing of high fashion plus sizes promoted by beautiful, but morbidly obese models, is utterly wrong.

Perhaps we need to define our terms here. I am not talking about those women who are size 14 or 16. I am all for initiatives, such as the Dove campaign for Real Beauty, that celebrate real women rather than air-brushed stick insects. For the record, as a 52-year-old mother of two, I am a size 14 and I could probably do with losing a few pounds for health reasons rather than vanity.

Interestingly, not one of the talking heads from the fashion industry, PR companies and, with a few exceptions, the model agencies who featured in the Channel 4 documentary was very overweight. Here was a buch of folk who would never want to be fat themselves seeking to make money out of those who are by lying to them they looked great. It was akin to fat pornography for them. (And, by the way, that exploitation extended to the broadcaster interspersing the documentary with pizza commercials. That was downright irresponsible.)

I don’t have a heart of stone, so I can’t to be too critical of the morbidly obese young women in their late teens and early twenties who appeared. Like many other viewers, I suspect, I could see the pain that lay just below their brittle exteriors as they assured the interviewer that they were happy and at ease with being a size 24, and how inspired they were by the likes of American super (plus-sized) model, Tess Munster, 29, who at 5ft 4in is a size 18/20 (and possibly then some). They are deluding themselves and it is desperately sad. What I do know is that if any of these girls were my daughter, I would be telling them the truth about what lies ahead.

• Why we should embrace plus-size, not seek to ban the term, by Bethany Rutter

Some of the contributors had undeniably had pretty faces, great skin and hair and they dressed with style and panache. At the moment, they have youth on their side, but I will not be surprised if, by the age of 40, some of them are using mobility scooters. Indeed, some of them already appeared to be having problems with their knees as they struggled to stand up without support.

In terms of life expectancy, the morbidly obese face a similar scenario to the lifelong smoker. Research shows that could cost them at least 10 years of life. With those youngsters already morbidly obese in their teens, I’d say 20 years would be more realistic.

And what will happen in the intervening years? Well, to start at the lower end of the scale, there will be the annoying niggles – backache and joint issues, chaffing etc, from carrying all that extra flesh. They will be especially prone to being knock-kneed, as the joint space is eroded by the weight bearing down on it.

I see plenty of women who come for scans because they have lower limb problems that I know would be eased if they weren’t so overweight, but no-one seems willing to confront them with that simple remedy. Instead, we treat the limb problems, and often end up listing the women as medically disabled.

Another issue obese young women may face is impaired fertility, as their size impacts their hormones and periods become irregular. And let’s be brutally frank – their partners may not be quite so willing to have sex with them. Being morbidly obese causes personal hygiene problems. I don’t call that fabulous.

If these women then need infertility treatment, they will find most consultants demand that the first thing they do is lose weight. Even if they can get past this obstacle, morbidly obese mothers have higher than usual levels of foetal deaths and of complications when giving birth, not to mention the damage their over-eating does to their unborn child’s metabolism.

Tess Munster (also know as Tess Holliday)

As the years pass, they will face a much higher risk than the general population of diabetes, cardiovascular problems, strokes and heart attacks. There are also strong links with being morbidly obese and breast and endometrial cancer.

I am sorry if this litany of pain and suffering sounds extreme, but someone has to say it. Someone needs to tell these young women, bedazzled by the bloggers, big models and the high fashion advertisements, that they are killing themselves. If we allowed our pets to over-eat to this extent, the RSPCA would remove them from our homes.

I am well aware that by speaking out I will face a backlash. When the singer Jamelia, a panellist on ITV’s Loose Women, suggested this week, in the wake of the documentary, that shops shouldn’t stock clothes for obese women (or, for that matter “size zeros”) because they need to “feel uncomfortable” about their unhealthy size, she was hounded online and forced to apologise.

How wrong-headed is that? She was simply and correctly challenging those who are set – out of conviction or in order to make a profit – on enabling youngsters to make choices that ultimately, despite all the fat-is-fabulous rhetoric, will be disastrous for them.

The young women featured in the documentary may be in utter denial now, but what they are doing to themselves will overshadow their lives. And the rest of us, who fund the NHS.