Praise the lard!

Our ideal of beauty may be absurdly thin now, but history shows fat will become absolutely flabulous again

Try this regime for six weeks: eat fat, as much of it whenever, wherever you please, in any form or flavour you choose. Eat well, for six weeks, eat fatly, to your heart's content, if only to see what you allow yourself to eat once you give yourself permission to eat whatever you want.

Would you eat only fat? Would you never once eat vegetables or salad? If you stopped watching what you eat - if you interrupted the repeated cycles of dieting and bingeing, you might actually lose weight. There is a lot of anecdotal evidence suggesting that people who stop dieting stop their compulsive obsessing about fat, which leads to over-eating, secret snacking and irresistible cravings. It is estimated that 95 per cent of all people who diet put back on the weight they lose in four to five years, usually in spades. The more you diet the more likely you are to be fatter in the long run.

It is well known that when the body is confronted with the shock of severe weight-loss diets, it begins to manufacture fat more efficiently; faced with what it perceives to be starvation, the body also loses fat more slowly. Modern diets, which aim to make you thin, make you fat. If you try the postmodern diet suggested above for six weeks you might get thin. But there are no guarantees. The only thing that seems sure is that you will not get any fatter than most of us are getting anyway. The latest statistics released by the United States government indicate for the first time that more than 50 per cent of Americans, already the fattest people in the world, are statistically obese. Obesity is measured as 20lb above some ideal or standard weight devised by actuaries. Of course, American butts have already been the butt of jokes around the world - in every country but my own: Americans are getting fatter, faster, as we approach the millennium.

Exactly the same tendency can be observed in the United Kingdom, as well as in most industrial societies - everywhere, in fact, except where there are a few famines. We are getting fatter in America despite the existence of a $40-billion diet industry, not to mention the fitness business, or the whole new generation of diet drugs that have recently come to market. Our supermarkets are full of less -products advertising their virtue of being low in fat or fat free, yet despite them, perhaps because of them, we eat more and are getting fatter.

At the same time, our ideal of beauty grows excessively, absurdly thin. One need only examine Miss America contestant measurements in the past 15 years, or take the measure of Playboy centrefolds. Open any fashion magazine and you will observe how skeletal our current idea of beauty has become. Protesters in Britain recently objected to the anorexic chic of some particularly gaunt top models. Not everyone is getting fatter; eating disorders abound. At the university, I observe how anorexia and bulimia appear to have exploded among the young, not only among women but among men. It is not uncommon for nine- or ten-year-old girls to be dieting. People feel fat with only a few added pounds of flesh.

In America, the obsession with thin has led many people to find unscrupulous doctors who prescribe the new diet drugs, so they might succeed at last in losing the 8-12lb that seem, in their minds, to stand between themselves and happiness, health and, doubtless, riches. These drugs are powerful metabolic substances that one must take daily for long periods of time, at considerable expense, with risks not well understood. They are estimated to produce a weight loss of 8-14 per cent, in most people; when you stop taking them, as you must, you often quickly regain all the weight you lost, and then some. Since Redux, the most advanced form of these new serotonin-enhancing drugs, was introduced in May, over a million prescriptions have already been filled, many for people who did not need to lose fat for medical reasons, but only to conform with the impossibly thin ideal that has come to seem desirable.

There is no reason to think that thin in itself is inherently erotic. It is well known that when a woman's weight falls below a certain level, she ceases to menstruate, she becomes infertile and frequently loses her sexual drive. Conversely, recent studies surprised investigators at the University of Texas when they revealed that fat people tend to be more sexually appetitive than thin people. They are sometimes harder to get started but, as if by inertia, they are much more persistent and enduring - harder in short to stop. It is not surprising, after all, when one thinks how closely fat is linked to fertility. In the womb and out, a healthy layer of fat is good for mothers and their babies. Even today, when fat is hateful, we still find fat babies beautiful. In the last century, P. T. Barnum, wherever he put up his circus, would sponsor a beautiful baby contest; children were brought from miles around; the fattest always won.

The most surprising result of my research was discovering how rarely thin has been thought to be beautiful. Ninety years ago, fat was not only tolerated but celebrated for its virtues, for the health, and beauty, and erotic desirability it bestowed. Look again at Victorian pornography; the women on those post-cards are frequently (not always) huge, with prominent cellulite they seemed delighted to expose. In America, Lillian Russel, the greatest beauty of her day, was re-nowned for her gargantuan appetite. The Prince of Wales, who became Edward VII, was similarly famous and seemingly all the more gallant and admired as he acquired the prestige and dignity of his enormous fat. Women were squeezed into corsets, not to make them thin, but to pinch their waist to balloon their flesh more voluminously out at the top of their decolletage, cascading fat over fronts of dresses while spreading it more abundantly across the hips. T. C. Duncan wrote a famous book, How to Become Plump.

What was true less than 90 years ago, has been the rule rather than the exception in human history. Rare are the times when people have thought that thin was beautiful. There was to be sure the moment of the Gothic Middle Ages, when the only naked bodies one sees are pitifully thin representations of Adam and Eve leaving the Garden in shame. One understands that for those artists, fat was sinful. Another moment of thin beauty came in the 16th century with French mannerism. The bodies of many Dianas of Fontainebleau have extravagantly elongated proportions anticipating the perverse allure of contemporary chic. The 17th and 18th centuries, conversely, were moments of exuberant, luxuriating fat, starting with the royal courts. Louis XVI at his wedding embarrassed his grandfather, Louis XV, by eating and drinking so much he passed out, snoring loudly. The nudes of Rubens are like sheaves of wheat, says Sir Kenneth Clark in his great study, The Nude. Those women have weight - the beauty and dignity of what imposes itself with serene solidity and confident girth, promising abundance. The babes of Boucher are like bubbles of flesh that invite the spectator to dream over buttocks and breasts pink and white and round as clouds.

Not until the 19th century, with Romanticism, does thin return to fashion. The Romantics, seeking the beyond, admired ethereal beauty, flesh that most closely embodied the lightness of spirit. But at the end of the 19th century, taste changed once more and, as the centennial approached, people became excessively fat. During what has been called "the banquet years," every pretext was found to eat, drink, and make copious speeches. Perhaps there is something about the social anxiety occasioned by the imminence of fateful transitions, like century's end. We of course are facing a new millennium, a new order we hope - and fear. What better to do than what people did a century ago? There are already indications that the next four years will see an explosion of feasting as we all get fatter.

I locate the sudden, abrupt reversal of fashion around 1907 when designers in Paris, Poiret and Furth and then Chanel, liberated women from their whalebone and stays, and imposed a new longer straighter look. Women began to want to look like young boys. I identify that sudden shift with the advent of modernism: the aesthetic movement or moment when artists began finding beauty and seeing themselves in machines. For most of the 20th century we have aspired in our bodies to imitate the sleek, slim, speedy lines of our automobiles, to embody the straight-line geometries of cubism and art deco.

But all that may be about to change, just as abruptly. Remember how suddenly the Beatles made long hair chic, after decades of thinking that men's hair should be short. The same sudden shift may be about to occur, as we leave the modernist century and enter a postmodern millennium that calls for a new evaluation, a transvaluation of fat. Our machines, in the age of po-mo, are neural, rather than mechanical. A child born today in America will spend nine years of its life sitting in front of a television screen - not to mention the time spent at the video screens of computers. More and more the only reality we get is a virtual, digital one; our work and leisure take place in an increasingly contemplative mode, sitting in front of a screen. Remember Buddha too was fat.

Richard Klein is professor of French at Cornell University. Eat Fat is published by Picador, Pounds 15.99. He is also the author ofCigarettes are Sublime.