Curling tranches of streaky bacon; bulging sausages; wedges of fried bread, sinking inside their crusts under the weight of fat. The doctor was aghast: “What about the diet I prescribed for you, Mrs Jones?”

“Oh, doctor,” the patient replied. “I had that earlier this morning. Now I’m having breakfast.”

Some learned opinion is on Mrs Jones’s side. San hunter-gatherers, who derive a third of their calories from meat, have levels of cholesterol and blood pressure similar to other foragers. In suitably disposed individuals, low-fat diets reduce coronary and circulatory afflictions, but most victims of heart disease register normal cholesterol readings. Animal fat is an unrivalled source of calories: among its beneficent effects is the opportunity to work it off. If you treat food as medicine, it will taste bad, turning eating into a dreary routine. Well-marbled, Burgundy-irrigated steak and chips feed the soul. Sad salads starve it.

And the body? “The body knows,” Isaiah Berlin used to bellow across the table, whenever he heard fellow-diners exchange dietary advice. Every metabolism is unique. Cravings can be responses to imbalance, like the gustatory caprice that makes a pregnant body demand outlandish delicacies: crayfish with marmalade, in one case I recall, and curried custard in another. Hugh Trevor-Roper used to eat pinches of salt straight from the nautilus: I believe he needed them, not because he was an addict but because his innards processed salt faster than normal.

Roy Porter, unexcelled historian of medicine, despised physicians’ advice and made a point of demanding whatever experts proscribed. At the height of the BSE scare, he insisted that we order roast beef at the Athenaeum. The immediate consequences were agreeable, and when Roy died young it was from overwork, not alimentary imprudence.

At the start of a new year, when resolutions retreat and dieters abandon the good intentions that followed yuletide excess, backsliders can take comfort from facts: professional dietetics has been a disaster, and the world would have been better-off ignoring most of the self-appointed nutrition gurus’ advice. With occasional excursions into prohibitionist madness and crazes for vitamin-counting, the conflict between proteins and carbohydrates has dominated the modern history of diet-mongering.

With every swing of fashion, eaters foolish enough to pay heed have unbalanced their intake. Obsession with fibre and demonisation of fat caused a boom in proprietary carbohydrates. An epidemic of obesity was among the results. Reaction in favour of low-carbohydrate regimens condemned susceptible individuals to unsuitable reliance on heart-stopping proteins.

With the collapse of medical arguments, the foes of meat are about to launch a campaign on equally spurious environmental grounds, blaming climate change on innocently eructating livestock. Demonologists who decry wine as a witches’ brew deprive their victims of a glorious aid to digestion. I can give my undergraduates in Indiana any amount of industrially engineered, chemically contrived soda-pop (out of the discretion that is the better part of valour, I don’t mention Coca-Cola in this regard); but I may not proffer a health-giving glass of sherry.

Warriors in the nutrition wars might forgo some of their ardour if they knew the relevant history. Protein-aversion began as food-magic: an irrational attempt to affect character by sacrifice. Pythagoras outlawed beans to promote chastity. Jacobin vegetarians, indifferent to the waste of human blood, denounced meat-rich diets as inducing cruelty.

Frankenstein’s monster abjured meat on moral grounds. Protein’s most effective nineteenth-century enemy was the Rev Sylvester Graham, “prophet of whole grains”, who in the 1830s devised the first universally appealing American doctrine since the Declaration of Independence. In repugnance from the lax sexual mores of the Enlightenment, he proposed to replace proteins with carbohydrates to eliminate “despotism, violence and impatience” and, most particularly, to “reduce emissions of sperm”. He likened sex to paroxysm and orgasm to an attack of diarrhoea. I doubt whether breakfast cereal — the abomination he invented — or the “Graham cracker” that honours his memory would be popular if consumers knew his purpose.

The equally fanatical Baron Justus von Liebig opposed Graham. Just as the cleric sought to control his own urges, the baron was obsessed with his own dyspepsia. He was the author of the modern taxonomy of foods — proteins and fats, which he valued, and carbohydrates, which he condemned.

With an alchemist’s zeal, he boiled, squeezed, infused and titrated meat juices in search of pure protein, inventing the meat-extract cube along the way. He worshipped fat as comestible fuel, superior to wood and coal because “soluble in the human body”.

So dietetics became pseudo-science, while Comte called for a science of society, Constable claimed that painting was science and Darwin reduced morality and aesthetics to side-effects of biology. In menu-planning, I prefer sybaritism to pseudo-science. Proprietary diets have little more nutritional value than the paper they’re written on. I commend the unpatented “Felipe Diet”: eat well and eat less.