Saddled with a middle-aged spread, I am about to abandon my car

When my son began referring to 'Big Fat Dad', I knew something had to be done. So I am about to become a cyclist

Whatever about having the face you deserve by middle age, I have become obsessed with the belly I don't deserve. I made the mistake of appearing near a mirror in a state of nakedness last week. Bounding out of the shower and searching for a suitable shirt I glimpsed a vision of tubbiness that set the conscience clacking. James Joyce began Ulysses by describing "stately, plump Buck Mulligan" as he shaved. I am such a man. But I have no wish, at the age of 42, to be either stately or plump. Look at the photograph adorning this column and you will see a man who aspires to the haggard and poetic. But the photograph, concealing as much as it reveals, does not do me justice. The reality is bigger and quite unlovely.

Whatever about having the face you deserve by middle age, I have become obsessed with the belly I don't deserve. I made the mistake of appearing near a mirror in a state of nakedness last week. Bounding out of the shower and searching for a suitable shirt I glimpsed a vision of tubbiness that set the conscience clacking. James Joyce began Ulysses by describing "stately, plump Buck Mulligan" as he shaved. I am such a man. But I have no wish, at the age of 42, to be either stately or plump. Look at the photograph adorning this column and you will see a man who aspires to the haggard and poetic. But the photograph, concealing as much as it reveals, does not do me justice. The reality is bigger and quite unlovely.

This is all by way of explaining why I have decided to abandon my car and take up cycling. But more of that in a while. The problem of weight came upon me in my late teens and began as a result of a long summer spent working in my uncle's public house. Under the expert tuition of my cousin Conor Keane, already a distinguished associate of J Arthur Guinness and Company, I learned the gross arts of porter guzzling. How many gallons flowed down my boyish throat as I caroused the dancehalls of Ballybunnion with Conor? As Paddy Kavanagh wrote: "Lost the long hours/all the women that loved young men." The hours were lost and the pounds gained. By the end of the summer 1979 I returned to Cork with a porter belly out of all proportion to my slender arms and legs. I had the beginnings of several chins as well. Had I followed my mother's advice and gone into the law matters might have been arrested then.

But I went into journalism. I was just in time to experience the last days of the golden age of free drink. On my small salary there was little scope for merriment. But the PR companies of Limerick understood the quickest route to a journalist's heart: keep the liquor flowing. I first got drunk at somebody else's expense at a reception organised by the Limerick Harbour Commissioners. After that I gadded from reception to reception, eating and drinking and promising to write stories that I knew would never see the light of day. The belly grew and the chins accumulated. The more unkind of my friends began to call me Bunter, an appellation that has survived down the years.

I left that drinking world a good few years ago and got into the habit of paying for my own dinner. But the belly stayed. It consolidated and then expanded, a part of my persona that refused to apologise for itself, a belligerent customer you might say. Food replaced drink as the cause of expansion. You now you are in deep trouble when the black and navy blue shirts in your wardrobe (they conceal the weight) outnumber the lighter colours, or when you take to wearing a T-shirt on the beach in the middle of the hottest day of the year.

I have given up counting the number of doctors who've advised me to exercise, just as I can longer recall the number of efforts I've made at dieting. In my 20s, I tried jogging but gave up quickly. I thought it then, and my view hasn't changed, the most tedious way to spend time. Physical exercise bores me. I know few athletes and those I've met have rarely thrilled me with their conversation. As for diets, they have come and gone but the only times I've ever lost weight have been when war has disrupted my feeding patterns.

Once in Angola I contracted amoebic dysentery and over a period of several weeks shed two stone. I emerged a shaken but trimmer man. In Afghanistan and Iraq the limited supplies of food - and the regrettable necessity to share it with colleagues - took me down a few pounds.

But once back in London I eat to make up. When my son began referring to "Big Fat Dad" I knew something had to be done. It roughly coincided with the shock of revelation in front of the mirror last week. So I am about to become a cyclist.

Exercise needs a point beyond the distant goal of getting fit and less fat. So cycling seems to me the only choice. If I get on a bike I am going somewhere for a purpose. That was where jogging defeated me. So utterly bloody pointless. And the statistics are reassuring. If I cycle I am assured I will have the fitness level of a man 10 years younger, which opens up all kinds of interesting possibilities. At the least the nagging fear of heart attacks and strokes will be banished.

There is also the element of danger. Now that I am cutting back on going to war zones (admittedly an incremental retreat from life-threatening situations, it may take some years yet) I need an edge. Given the behaviour of most London motorists towards cyclists I can't believe my days on the saddle will pass without many hair-raising diversions. As a driver I have often cursed at cyclists. I have also seen them respond like snarling brutes, bashing the doors of cars and then vanishing into the traffic.

Yet according to the London Cyclists Network a cyclist is seriously injured only once every 185,000 cycling miles. That is one of those statistics whose measurement must have demanded extraordinary ingenuity. How on earth do calculate such a figure? What is a cycling mile compared to an ordinary mile? I will soon know. Give me a week and I will bore for Britain on the topic.

But health isn't the sole motivating force. Part of the decision has to do with the hell of London traffic. It is a city choking to death. The congestion charge has made a difference in the city centre but beyond it things are going from bad to worse. Every day brings an encounter with some slavering oaf in a white van, cutting across me in traffic or screaming because of some imagined misdemeanour on my part.

Now the Mayor wants to extend the congestion charge to Chelsea and even Hammersmith. If so there seems little point to me continuing to drive. It is becoming too costly and stressful. Far better to scoot down to Television Centre on two wheels or freewheel into Piccadilly to surprise my literary agent in his West End lair. Again the statistics give cause for celebration. The London Cyclists Network (I will be reading their website avidly) says any journey shorter than five miles is quicker by bike.

The car we will keep for the longer excursions. For example, I cannot see myself or my loved ones taking to the road for a cycling holiday to Ireland. We would, I fear, be badly received by the locals. They might take it as evidence of mental instability or a sign of some fall in our economic and social standing back in Britain. "Sure God help us, he can't afford the car any more you know."

Today I go to the bike shop on the high road. I have already spotted my charger. It goes by the name of "Storm" and is cheap and rather functional looking. My instinct is to buy something much flashier but my wife demurs. "You won't last," she says. "I've seen this before." I am an optimist. Not only will it last but I can already feel the weight getting ready to depart. Forget the hyped-up promises of the Atkins diet - the calorie inferno is about to begin.

The writer is a BBC Special Correspondent