Having spent the festive season in the company of my 18-month-old grandson, I am delighted by plumpness; he looks like a Renaissance cherub fallen from the ceiling, even though those cherubim were rarely dressed in a Cameron of Erracht tartan kilt. No doubt he will slim down over the years, but for the moment he is happily plump, as healthy infants should be.

Now older plumpies, also, who may have been disturbed by the cult of the slender and by the propaganda that recommends this diet or that one, have reason to relax. According to an extensive survey conducted by the US National Centre for Health Statistics, being a bit overweight is good for you. Those with a BMI (body mass index) of between 30 and 35 have 5 per cent less chance of dying at a given age than their skinny contemporaries. Of course, it all depends on your definition of overweight – what is considered overweight in Islington might be thought scrawny in Tonga – but this survey examined 2.88 million people in the United States, Canada, Europe, Australia, China, Japan, Brazil, India, Israel and Mexico. You can’t say it isn’t thorough – and its conclusion is a happy one.

Plumpness is not obesity. It means simply being well-covered, sufficiently so to turn down the central heating. The survey offers no suggestion that it is all right to be grossly obese; obesity remains bad, and those with a higher than 35 BMI should still try to slim down. But the plump have no cause to be anxious. Those of us with a bit of a belly can sit happy; we’ve nothing to worry about. It may even be fine to be as podgy as Mr Pickwick. The plump have no call to take up jogging or subject themselves to the gym. Moderate exercise – a two-mile walk or so – will keep the plump in good health throughout the middle years of life, and indeed well into old age. This is just the cheerful news we need after the excesses of the winter Saturnalia.

For most of history, being well-covered was thought a good thing. It was a sign of prosperity. A friend recently told me of a German politician in the 1950s who pointed at his wife and said, admiringly, “Isn’t she fat?” After the rigours of the Second World War and the post-war years, fatness was a sign of good health as well as evidence of economic recovery. It is indeed only in modern times – recently and again in the 1920s – that girls and women have been obsessed with being slim, or indeed that men have admired the thin or boyish figure. Think of the ample charms of the women painted by Rubens or indeed Titian, rolling in embonpoint. If these seem just a bit much, then think of Renoir’s delicious girls with their plump pink thighs.

Plumpness has been associated with good humour and a relaxed attitude to life; and this may indeed explain the findings in this survey, even though its authors suggest that one reason for the greater longevity of the well-covered may be that they have made an earlier call on the services of their doctor, and so have taken whatever measures are appropriate to maintain their health and prolong their life. No doubt this is so, but it seems just as likely that the plump live longer because they worry less and take life as it comes.

Shakespeare’s Julius Caesar recognised that the plump are contented: “Let me have men about me that are fat; / Sleek-headed men and such as sleep o’ nights. / Yon Cassius has a lean and hungry look; /He thinks too much: such men are dangerous.” This is good sense. Has there ever been a fat revolutionary? Robespierre, Trotsky, Hitler were all scrawny – all had that lean and dangerous look. Would Osama bin Laden have turned fanatical terrorist if, instead of being thin as a rake and consequently sour as vinegar, he had been as plump as a well-fed partridge? It seems unlikely.

Forget the diet sheets unless you are what is termed clinically obese. Eat, drink and be merry; that is the message from the wisdom of ages. Horace, the great poet of good sense and contentment, says, in one of his Epistles, “If you want a good laugh, you will come and find me fat and sleek, in excellent condition, one of Epicurus’ herd of pigs.” He was inviting his friends, one should add, to laugh with him, not at him. The survey from the United States offers the same message; the well-covered are healthy, and, being so, are happy as any of the Greek philosopher’s pigs. On the other hand, people who worry about their health lose weight and wither. This is a very comforting thought.

Finally, consider Winston Churchill, usually voted the greatest Briton of modern times. What did he look like? We all know the answer: no lean and hungry man, Winnie looked just like a well-fed baby. He resembled, indeed, an elderly, if mischievous, cherub – plump as my grandson, Luca.