Finally, an expert on human nutrition brave enough to tell us what we don't want to hear - it's our fault if we're fat.

Obesity, we're told by those well-meaning groups formed to fight it, is a complex issue caused by environmental or hormonal or psychological issues. Individuals are not to blame and should not be discriminated against, they opine. More money should be poured into DHBs to help them. They mustn't be persecuted. It's not their fault they can't walk past a patisserie without wolfing down pies and doughnuts.

Then along came John Birkbeck of Massey University, adjunct professor in human nutrition, who told journalist Geraldine Johns in this newspaper: "You can't get over-fat without eating more calories than you expend."

And this: "You do not see fat people in concentration camps. Why? Because they get hardly anything to eat and they have to do a lot of work."

National MP Maurice Williamson must be muttering into his whiskers. Two years ago he was pilloried for saying virtually the same thing: "If some people can't lose weight no matter what, how come there were no fat people in Nazi concentration camps?"

Williamson was correct then, and Birkbeck's correct now, but of course he's already angered the Eating Difficulties Education Network. Spokeswoman Maree Burns called Birkbeck's comments "flagrant, inappropriate, intolerant and offensive", adding "shaming and blaming people has never been effective".

But actually it has. Look what we do to smokers. We treat them like lepers, forcing them out into the street, away from bars and restaurants. Two decades ago it was acceptable to smoke on planes, in offices and pubs. Now everywhere is proudly a smokefree environment.

If it's acceptable to shame and sin tax anyone addicted to nicotine and alcohol, why not do the same to those addicted to food? "This is a pizza/pie/burger/fizzy-drink free zone". I doubt it - remember the outcry when Air New Zealand did away with meals on its one-hour flights? I watch fat people in the Koru lounge piling up their plates with "free" food, then going back for more and I wonder if they are really starving, or just plain greedy.

Over-fat people eat too much for numerous reasons. They're unhappy, unloved, lazy, don't care, love food, are weak-willed, can't cook properly, but they're not obese for cultural reasons, or because they're big-boned, have hormone problems, or other "it's not my fault" excuses. Thankfully, we all come in different sizes - large, petite, slim, solid - but basically obesity is caused by eating too much food.

As Birkbeck stated, our society is in danger of accepting over-fatness as the norm. These days, it's the skinny, flat-chested girls who are shamed on television modelling competitions. She must be anorexic, we gasp, if we see a hip bone or a rib.