STICKY fingers don't do it any more; now you need a sticky face, too.

Last December a photograph of Nigella Lawson with salted caramel running down her fizzog for the cover of Stylist magazine had Twitter hyperventilating. Nigella archly denied that there was anything sexualised about the image – "it is simply rapturous joy in caramel" – though a sceptic might point out that the joy most people take in caramel results from gobbling it rather than tipping it over their heads for the watching cameras.

Nigella herself boldly denied that she trafficked in "double entendre", which in a way is true: the sex-chat of her TV food-cabaret is not really subtle enough to count as double entendre. It's more like entendre et demi. ("Ah, look at these gorgeous golden globules"; "My mouth can handle it all".) But Nigella is just the most knowing, vampish performer in a ubiquitous passion play. Everyone revels in the "filthiness" of what they are naughtily pleased to call "gastroporn", congratulating themselves on their own delicious sinfulness while at the same time denying that there is anything wrong with it.

Modern foodists have not invented the link between food and sex – but they don't half go on about it.

Certain foods have long had a reputation for being aphrodisiac. But, it seems, "post-coital tristesse" applies as much to sexualised eating as to sex itself. Indeed, American celebrity chef Anthony Bourdain informs us that, after a "pantagruelian" tasting-menu dinner at a foodist Mecca such as The French Laundry in California, no-one wants to have sex; instead the happy foodist will be "belching like a medieval friar". Well, indeed: if music be the food of love, it follows that food itself be not.

It is one thing to point out that food is a more reliable and safer pleasure (occasional bouts of E-coli or shellfish poisoning notwithstanding) than sex: it occurs more often for most people, and according to modern mores it is more normal to enjoy it in large groups. Furthermore, you need to eat (but not to have sex) in order to stay alive. So why not enjoy it?

But it is another thing overtly to sexualise one's gluttony, a practice that quickly comes to look like a desperate kind of compensation. Nigel Slater's Toast, an over-buttered crumpet of a memoir of childhood food, takes pains to assure the reader near the end that, working as a young hotel cook, he was having sex every night; yet Slater nevertheless reserves the swellings of eroticised language for a description of the first time he ate gratin dauphinois: "Warm, soft and creamy - this was food that was pure sex."

"Is every aspect of the oral system assimilated in the kiss?" wondered Jacques Derrida, in his 1990 seminar Manger L'autre (Eating The Other). Foodists are not so philosophical. "Oral sex is the foodies' favourite kind – good practice," the Official Foodie Handbook squeaks, though if you are practising oral sex like you are eating, you are probably doing at least one of them wrong.

But even as a joke, the idea that sex is merely good "practice" for eating is revealing. The prevailing idea is that eating is better sex than sex is.

Anthony Bourdain gleefully describes a secret New York foodist seance in which the assembled luminaries are served the notorious "ne plus ultra" of the gourmet, ortolan. The ortolan bunting is a very small songbird – "about the size of a young girl's fist", says Le Figaro's restaurant critic, in a perhaps too-revealing choice of comparison – which traditionally is captured, held in a dark box and force-fed with millet over several days, and then drowned alive in armagnac before being roasted.

The lucky diner eats it whole, crunching down on the tiny bones with a napkin placed over his head and face so that God does not witness his disgusting gluttony. (François Mitterrand ate one for his last meal; the dish is now illegal in France.) Bourdain reports that at the secret New York tasting, the eaters, after crunching and swallowing their baby fowls and removing the napkins from their heads, all have "glazed, blissed-out expressions, the beginnings of guilty smiles, an identical just-f***ed look on every face".

Sexual metaphors are pandemic in restaurant reviewing, one of the more ingenious having been dreamed up by John Walsh, whose fantasy seems to be a cannibalistic version of one of the diarist-politician Alan Clark's conquests: a dish of rump and shoulder "offered a brilliant contrast, as if you were eating both mother and daughter in the same dish". To be fair, restaurant criticism is the kind of challenging exercise that encourages such flights of fancy, if only to fill up the column inches. As the novelist Sebastian Faulks wrote of his own brief stint as a restaurant critic: "Of course, I couldn't actually write down what it had been like. You can't make 'fine' run to 1000 words."

The best restaurant reviewer I have encountered is the dashing Lieutenant-Colonel Newnham-Davis, who wrote about London restaurants for the Pall Mall Gazette in the late 19th century. He approached the discipline by writing simply about the food ("The quails were a trifle over-cooked"), and with vivid wit about his pseudonymous dinner companions.

Newnham-Davis is never so ungallant as to call a dish "sexy", but Jamie Oliver calls his food little else ("a beautiful sexy little pasta"), as though unsure whether he would like to sleep with it or eat it. (Perhaps the same indecision haunts devoted fans of open-mouthed "goddess" Nigella Lawson.) And Marco Pierre White makes the interesting admission: "A lobster is more beautiful to me than most women are." It doesn't stop him boiling them.

If food and eating are sex, then depictions of food are pornography. Hence the term "gastroporn", which might have been coined by the journalist Alexander Cockburn in a 1977 review-essay on cookbooks in the New York Review Of Books. Reading a book by the French chef Paul Bocuse, Cockburn calls it a "costly - exercise in gastro-porn", and traces structural parallels between the cookbook and the sex manual: "The same studious emphasis on leisurely technique, the same apostrophes to the ultimate, heavenly delights".

Today, there is also the quasi-pornography of domestic contentment, spiced with the subliminal promise of sex: the cookbooks by Gwyneth Paltrow and Sophie Dahl feature innumerable shots of these women with eyes demurely downcast while they subserviently chop or pour.

Paltrow's Notes From My Kitchen shows her thoughtfully shelling peas, a teatowel artfully slung over one shoulder, or tastefully slumming it in jovial knitwear, while the text offers seductive glimpses of the celebrity-foodist lifestyle: one dish Gwyneth discovered "at Nora Ephron's house"; another is what she likes to serve "when my favourite vegetarian friend, Stella McCartney, brings her family over".

Miss Dahl's Voluptuous Delights, for its part, does not neglect finally to reward the patient reader with a subliminal analogue to the pornographic money shot: through the book, Dahl has been looking down or away from what she is doing – in a little summer cardigan smashing a crab's claw with a mallet, or spooning something out of a measuring jug to make "peasant soup", looking nothing like a peasant – until in the last photograph she is pictured sitting at the kitchen table with her hands coquettishly clasped at an angle, looking directly into the camera with an enormous, satisfied smile.

Gastroporn need not be visual: like pornography, it may be written, too. Anthony Bourdain is an enthusiastic practitioner and sharp diagnostician of the art. "Writing about sights and sounds and flavours that might otherwise be described as orgiastic – and doing it in a way that is calculated to inspire prurient interest, lust, and envy in others - that raises more questions in my mind as to - I don't know - the moral dimension," he muses, ellipses straining to maintain the casual-hip pose (for Bourdain is fundamentally a serious, and seriously good, writer).

A similar ambivalence between celebrating sensual delights and worrying about the decorum of such celebration has long been evident in the literary evocation of all kinds of physical pleasure. Bourdain makes a passing reference to "Zola, the greatest of food pornographers", and indeed Zola's description of charcuterie in The Belly Of Paris is a classic instance of almost literally having one's cake and eating it.

Our hero Florent stares gobsmacked at the window display: "There were vast quantities of rich, succulent things, things that melted in the mouth - boned hams, nicely rounded, golden with breadcrumbs - stuffed Strasbourg tongues, with their red, varnished look - strings of black pudding coiled like harmless snakes - There, on the highest tier of this temple of gluttony - the altar display was crowned by a small, square fish tank - in which two goldfish swam in endless circles."

The order in which these things are revealed is one of dastardly literary and moralising craft: first the author employs all his gastropornic art in order to tempt the reader into sharing the salivating fascination of his hero; and only then, once we are helplessly dazed with imaginary tastes, does he hand down the editorialising judgement that this is a "temple of gluttony", whose poignant crowning goldfish are, perhaps, meant to represent the pointless bestial circling of those interested in food above all else.

The linkage of such gourmandist fascination with sex itself, meanwhile, is immediate: in the very next paragraph Florent gazes on "a handsome woman" with "glossy hair" and a "swelling bosom", who "had the fine skin and pinky-white complexion of those who spend their lives surrounded by fat and raw meat". Florent's long visual appreciation of her figure is interrupted by Gavard informing him that she is his sister-in-law. So the erotic reverie is retrospectively perverted as incest, just as the food reverie is retrospectively denounced as gluttony.

A certain strand of foodism rejoices in the exotic: celebrating outlandish food becomes, instead of mainstream gastroporn, a kind of high-class fetish erotica. A great part of the appeal of The Fat Duck Cookbook's recipes is the sheer novelty of apparently disgusting combinations (egg-and-bacon ice-cream; olive and leather purée), as though we found ourselves suddenly transfixed by some outré flavour of bestial porn; yet we are simultaneously reassured that they are delicious and sanctioned by the latest science. (The horse really wants it.)

Heston Blumenthal's perverse concepts (bee-egg omelettes!) are only the latest exercises of a seam of jolly shock-foodism that reaches back to Roman times. Certainly the anti-foodist Roman moralists conflated their disgust at overeating with their disgust at sex, as in Horace's dour warning: "The brothel and the greasy cookshop stir your longing." Plato's Republic, meanwhile, had already compared the desire for a wider variety of food than necessary for "fitness" with an immoderate sexual appetite, both tending to lead to the disaster of democracy. Nonetheless, it is possible to denounce a preoccupation with food without also disapproving of sex; indeed, it might be precisely because one approves of sex that one wants to resist the ambition to reduce it to an aspect of, or subsume it completely into, the mundane and consumerist practice of eating fancy victuals.

Bourdain has a theory as to why food in our mass-cultural times might have become "the new porn": perhaps it offers "a less dangerous alternative to the anonymous and unprotected shag of decades past". Or maybe it is just that, even in the accelerating pornification of everything in today's culture, it remains more respectable to display cookbooks than framed stills from sex movies in one's home. And the heavy-stomached, sluggish foodist, with all available blood diverted to his digestive organs, likely has rather more use for one than the other anyway.