It’s a curious fact about medical check-ups that you always leave shorter and heavier than when you arrived. “If I go on losing inches this fast,” I told the doctor the last time he measured me, “I will soon have disappeared altogether.” “That’s unlikely to happen,” he said, “so long as you go on gaining pounds at the same rate.”

The vanishing inches I ascribe to faulty equipment, but the accumulated pounds I acknowledge, though what’s making them accumulate I have no idea. I understand dieting and occasionally practise it. I get the science of nutrition. Yes, I eat bread and drink wine, but I have cut down on cheese, can take or leave champagne, only eat biscuits on trains, only eat cake at birthdays and no more like chocolates than I like carrots, consumption of which I have also reduced. “It could be,” the doctor told me, “that you’re happy.”

That was such an astonishing suggestion that I forgot to ask him to explain what the one had to do with the other. Happy? Me! I have been miserable – and have prided myself on being miserable – for as long as I can remember. I was a prodigy of misery when I was small. Strangers commented on it. “Why the long face?” “Cheer up, sunshine, it may never happen.” “Smiles are free, you know, you sour-faced little bastard.”

Sour

That last remark was my father’s. He hated having a surly son. I think my mother persuaded him it was early-onset adolescence. “What, in his pram?” But he left me to it and hoped my temperament would lighten by itself. Which it partly did once real adolescence came and went. But I still remained more sullen than sunny, didn’t like the feel of my face from the inside, or indeed the look of my face from the outside, when I smiled, and found an echo of my feelings only in sardonic literature and heartbreaking music.

And now, suddenly, according to my doctor, I’m happy. He’s right, as it happens, though I’m embarrassed that it shows. I seem to have reversed the normal order of things which is to gurgle away cheerfully when you’re an infant and decline into despondency as you start hitting the big numbers. Here is not the place to discuss how this reversal has come about. More interesting is my doctor’s contention that happiness puts on weight.

Having pondered it for a while, I think this has a physiological rather than a psychological explanation. When you’re happy, you dispense with exercise. I have not spent a great deal of time in gyms or health clubs. Having loathed PE as a boy, it makes no sense to me to embrace it as a man. But whenever I’ve been in a gym I’ve been struck by the angry sadness of everyone I see there. The received wisdom has it that running on a treadmill or pressing weights releases endorphins that make us happy, but that’s only relative to how unhappy we were to start with. A man with a loving bed-warmed wife to stay wrapped around does not leave the house at seven in the morning to sweat in the company of other men. Unless... But that’s something else again. Ditto a man with a job he cannot be torn away from. The gym is a place we go to find a simulacrum of happiness, not to compound the happiness we already feel. We are not fools. We can distinguished endorphin-induced bliss from the real thing. No genuinely happy man ever saw the need to exercise.

Don't walk

And walking the same. I have walked a lot in my life. Aged eight, I left home with a Dick Whittington bundle on my shoulder and walked to my grandmother’s a mile away. Unhappiness was the cause. My parents had refused to go on paying the fines on my library books. I’d taken out Goethe’s The Sorrows of Young Werther and André Maurois’ Call No Man Happy months before and hadn’t wanted to return them. I hoped my grandmother would pay the fines for me, though, as I trudged along, I knew in my heart she wouldn’t. And once I very nearly walked from Manchester to Cambridge having failed to hitch a single ride. Drivers don’t like picking up hikers with sour faces. Since then, I have found it helps to walk off a bout of depression, a severe disappointment, a sudden loss of self-belief, or simply a marriage. More than once, and by more than one wife, I have been accused of “flouncing” out, but it wasn’t a flounce, it was just an irresistible compulsion to walk away from the anguish of conflict, and suffer it on my own. There are Walter Sickert paintings and Thomas Hardy poems that evoke the walled-in suffocation of couples no longer in love; in every case, all parties would have benefited from a walk. I don’t say they would have been happier, but walking suits and even explains unhappiness, and so makes for a sort of private harmony of wretchedness.

Some will no doubt maintain that a bracing walk can express high spirits but the fact that they’ve slipped in the word “bracing” proves that a walk for them is not a walk for me. There was a popular German song we all made fun of in the 1950s called “The Happy Wanderer” or “Der Fröhliche Wanderer”. “I love to go a wandering,” it began, and then we’d all join in with Val-deri, Val-dera, Val-deri, Val-dera-ha-ha-ha-ha-ha, the false Germanic ha-has giving the lie to the idea that shlepping a knapsack through the Tyrol made you happy.

In fact, all the great wanderers – Cain, Werther, the rejected lover in Schubert’s Winterreise – were miserable as sin. Walking is motion to feel bad to. Stumble on felicity and you’ll never walk again. And that’s why the happy put on weight. Why they also lose inches is a question I’m working on.