A new study shows significant levels of discrimination towards fat people at work. No surprise, perhaps, when we live in a fat-phobic world. Today fat has become not a description of size but a moral category tainted with criticism and contempt.

Fat shaming is a new and vicious sport. Fat youngsters in Georgia have their photos pasted on billboards like mug shots. Children and their parents are being shamed for looking different than the thousands of Photoshopped pictures we see weekly on our screens, phone, computers, laptops and magazines. No wonder society has a thing about fat. Fat people are so rarely included in visual culture that fat is perceived as a blot on the landscape of sleek and slim.

Today our idea of fat is imbued with disease, indulgence, poverty, disregard for personal dignity and sloppiness. In recent characterisations, fat is a signal of determined self-abuse and the cause of preventable diseases such as cancer, heart attacks and strokes.

But is it true? Part of what drives this prejudice is a denial of the evidence that demonstrates that it is not fat per se that is a health problem. Indeed, a 2005 study led by Katherine Flegal of the Centres for Disease Control in the US found that people in the "overweight" category of 25-30 BMI (where Brad Pitt and George Clooney sit) demonstrate a lower death rate than their peers who are of "normal" weight.

Thin isn't good and fat bad. Stable weight, for example, causes far less stress to the heart than going up and down the scales in weight. Thin people with health issues don't get demonised for their size. Thank goodness. But then neither should fat people.

When it comes to looking for a job, there is, as this study shows, serious discrimination. Our idea of a healthy body is so destabilised that insecure people have come to bolster their own bodies by deeming others – those with fat bodies – less worthy, less capable and less employable.

Fat people are regarded as less successful at restraint. The paradox of consumer culture is that we should and must consume – our economy depends on it – but we should at the same time do so discreetly and expensively. Fat challenges this idea. Fat dares to show. Fat is disdained because it is read as greed and an inability to choose or say no.

Of course fat doesn't really say or imply such things, but surrounded by images of perfected bodies, invitingly displaying the hugely expensive and lavishly marketed goodies that we are roused to desire, fat becomes the vehicle on to which we project all the ugly aspects of our over-consumption and hunger for objects. Consumer society tantalises us. We then try within ourselves to control the needs that are being constantly stimulated. We value holding back and then assign to fat people the contempt we can feel for our own longings. It's not unlike other forms of discrimination. Things we don't like or discipline in ourselves we choose to see in others, and in another group. In this case, people who have nothing in common except for their size.

Fat looks on the surface as though it is about a failure of restraint. It isn't actually any more an issue of restraint than it is for many thin or medium-sized people. Most eating problems don't show. Fat, which may or may not mean an eating problem, does. That doesn't make it immoral or contemptible. It doesn't mean the fat individual has faulty judgment or inferior leadership skills. It certainly doesn't sanction discrimination. What it does demonstrate is that cruelty and stupidity arises when we are pressed to make our bodies into uniform shapes. This creates widespread body anxiety, and makes us search for a scapegoat to feel secure. We know from other forms of discrimination what a fruitless and lousy deal that is.

• This article was amended on 4 May 2012. The original photo caption implied that the Venus of Willendorf is permanently housed in Dresden. Its permanent home is in fact the the Museum of Natural History in Vienna.