'There is something special about today," said Oprah this week. "Today is the day you move out of your fat zone!" I considered that, over my late-afternoon ice-cream and hot fudge sauce.

Where is my fat zone? I wondered. Is it just that narrow band between my waist and my ribs, or does it mysteriously envelop my apartment, thrumming subsonically like the force-field from some glowing kernel of nuclear fatness? Does it perhaps move around with me wherever I go, like a small and personalised raincloud, raining not water but small hourly increments of pudge?

Yes! That makes sense! The quality of my increasing weight is not strained from the things I eat and drink - it droppeth upon me as the gentle dew from heaven. When I feel the buttons begin to strain and the seams begin to sigh, it is not my doing - it is because I am still living inside my fat zone.

Curse that fat zone. It's playing havoc on the property values.

Only fat people need consoling metaphors

The fat zone is the latest metaphor dreamed up by Americans to explain why nothing is our fault. Oprah dedicated her show on Tuesday to stirring stories of weight loss. While Oprah stood on stage, as hearty as a "before" picture, enormous photographs of suburban whales were projected onto screens. One by one the whales appeared on stage to stand before their photographs - but lo! They were whales no longer! They had moved out of their fat zone! "I went from a size 22 to a size 6 in nine months!" enthused one young lady.

"You quit your fat zone, huh?" said Oprah encouragingly.

"No, I started eating less and exercising more," said the young lady. She was having no truck with fat zones. Only fat people need consoling metaphors, she seemed to be saying. Look at me - I'm thin.

We met a former whale named David Caruso. David Caruso (or "The Great Big Caruso", as he should have been called,) used to weigh 238kg. Now he weighs 99kg. David came bounding from the wings, frisky as a young narwhal, pumping his fists and yelling: "Yes! Yes! Yes!" It was as though they had been keeping him blindfolded for the past year, and he had only just seen himself in the mirror.

"The best thing is that you did it for yourself, and you feel better about yourself," said Oprah.

David nodded his agreement. "Eating was just a way of filling a spiritual void," opined David. Oprah was so pleased with David's new-found spirituality that she gave him a Porsche.

"You deserve that car, David," said Oprah.

"I love you, Oprah," said David.

"I love you too, David," said Oprah. David ran off to sit in the driver's seat of his new Porsche. There was so much spirituality in the room it felt as though someone were pushing their fingers down my throat. But that's a different episode of Oprah entirely.

Tuesday must have been Fat Day, because that night Special Assignment (SABC3; 9.30pm) featured another new-fangled weight-loss technique. Not perhaps as efficient as having Oprah bribe you with a sports car, but still effective. Evidently the San of the Kalahari safeguard the secrets of the hoodia cactus, a spiky succulent containing a "miracle molecule" that instantly quells all sensations of hunger. It must work - you seldom see a portly San tracker, and not often do you find a gemsbok loincloth on the rack marked "large". Then again, you rarely see the San lolling about on their sofas in the Kalahari, ordering another large pizza with extra cheese and scorpion.

Special Assignment was all about the exploitation of traditional San knowledge by western pharmaceutical companies, but I couldn't help thinking that no matter what the West does to other markets, it exploits its own far more. The programme derived much of its aesthetic and moral force from the contrast between the lean San, walking across the clean contours and stark wastes of the desert, cross-cut with enormous westerners waddling the malls of America.

We visited the Morbid Obesity Support Group in Atlanta. Fortunately we were spared the spectacle of a parade of porkers winching themselves vertical to proclaim: "My name is David and I am morbidly obese". What would be the appropriate response to such a greeting? "Yes, I can see that," perhaps. Or maybe: "Cheer up, fatty." Still, we did manage to catch words of wisdom from the group's leader.

"Don't forget," said the group's leader, "obesity is a disease, like any other."

I thought about that. I have old-fashioned ideas about disease. A disease, I always thought, is something you contract that is outside the influence of your simple act of will. Tuberculosis is a disease, say, because you carry on coughing even after you have decided that you will not cough anymore. I am sure there are subtler and more inclusive ways of defining disease, but for me the word only has meaning if it implies something beyond a quirk of the personality. To tell someone who eats three large hams and a bucket of fried chicken for breakfast that their obesity is a disease is something like telling them that they are fat because they live in the fat zone.

Whatever causes us to over-eat - whatever vacancies and voids and sublimated miseries drive us to grow outward as we inwardly contract - it will not be solved by a pill. To call obesity a disease is to make it impersonal - a disease can happen to anyone; it has little to do with your choices; it can be cured by ingesting this chemical, or that capsule of powdered cactus. We are growing more fat because of the way we lead our lives, and the way we turn increasingly to external things to soothe our inner aches. Selling fat people pills or giving them Porsches is just encouraging more of the same. Being obese is not a disease. It is a symptom.