Of all the myriad new titles published each year, those about golf, knitting and diets are surely the most boring, yet without them the publishers would never be able to afford to print that slim volume of short stories that everyone, unfortunately, thinks he has in him. Diet books are of course nothing new, but the ludicrous nature of their claims often makes the Doctrine of Signatures look perfectly plausible. In effect, they are all saying you are what you eat.

So bizarre is the process of ingesting extraneous organic matter that it is perhaps forgivable that our culture has invested it with ritual, fad, and superstition. In the age of Ignorance when court poisoners and uromancers were at their height, the layman had little choice but to follow whatever mumbo-jumbo was in vogue. What with the cuppings and purgings, stomach-scourers and nostrums, it’s amazing that anyone made it past puberty.

Nutritional advice is as old as culinary literature itself, and several of the early printed books addressed this subject quite intelligently. My own favourite is A Dyetary of Helthe (1522) by Andrew Boorde, a medical monk, full of wit and wisdom about how to combat melancholy and ‘engender good blode’. His researches were sadly curtailed in 1549, when he died in prison under charges of ‘boggery’, the recipe for which seems nonetheless to have survived.

Nowadays, of course, we have nearly all the answers to everything. Following the isolation of vitamins and certain bacteria, the introduction of fluoride into water, and the splendid advances in sanitary engineering, Western man, at least, is now enjoying a greater life expectancy than at any previous era in history. What a piece of work it is, to be sure.

And chief amongst those we should thank are the clever scientists who formulated the ‘diet-disease thesis’ – you know, that brilliant discovery that you get heart disease from eating too much fat, and terrible things happen if you touch sugar or salt. Well, as you push away your plate of carrot-shavings and cress, and prepare to nibble another muesli bar, I’ve got some news for you that is going to send up your blood-pressure quicker than the mere sight of a Tournedos Rossini. The whole thing is a load of cobblers.

Exit the warm-up man, and enter Stage Right James Le Fanu, Medical Correspondent of the Sunday Telegraph. His thesis, which is methodically and snappily expressed, is that ‘as far as present knowledge allows, food is simply not an important or modifiable cause of disease in our society.’ He contends that the evidence upon which the recent diet-disease fallacy is based has been selectively applied to produce an unjustifiable conclusion, and he is concerned at the readiness with which this orthodoxy has taken root. His case makes for salutary reading.

When this book refers to diet, it is not describing subsistence regimens, of course, nor does it include allergies, obesity, adulteration or poisoning. It addresses the notion that diseases such as cancer and heart complaints can have their level of incidence directly linked to the groceries that we consume. After outlining his reasons for doubt, and surveying the past history of nutrition, Dr Le Fanu then proceeds to attack in a certain amount of detail the research on which this ‘scientific truth’ has been based.

In 1982, after a decade in which some $115m were spent, an experiment dubbed MRFIT (Multiple Risk Factor Intervention Trial) concluded that there was just the same rate of heart-disease among thousands of men who had quit smoking and switched to a low fat diet as there was in a control group that continued with its normal lifestyle. Something similar was performed in Europe, and in the following year the superbly named NACNE (British National Advisory Committee on Nutrition Education) responded in kind. The trouble is, the conclusions that were put before the public suggested nothing of the sort. Rather, they insisted that the opposite was true.

You will have to read the book for yourself to appreciate the way in which its author points out the careful massaging of the data. It seems that sufficient confidence had been expressed in the obvious truth of the theory that by the time the evidence came to hand there was no exit clause. Professional reputations were on the line, and public confidence could not be shaken. Besides, Le Fanu demonstrates how the available data could easily be made to fit the desired conclusion without actual falsification , and this was done because the majority of experts on these committees believed that they had still got it right.

The time was ripe, moreover, for the public to be told to clean up its act. In the absence of any funded research to the contrary, the health food boom was soon briskly under way, office parties were serving pulses and fruit punch, ‘healthy’ folk were throwing up their hands in horror at white bread, and scouring the countryside each weekend in their Volvos in search of nut-brown eggs. There was no turning back.

And yet, as the good doctor points out, only fifty years previously the official advice on nutritional requirements was precisely the opposite. More meat, eggs, milk and dairy products were then advocated for the nation’s optimum diet, yet all of a sudden, when most of us are likely to reach our allotted span, we are gravely informed that we shall be dropping like flies. Never before has unadulterated food been considered so lethal, and most experiments that try to prove that a Western diet imposed on subjects from a ‘healthier’ ethnic group induce higher rates of heart disease simply don’t come up with the goods.

So, then, what is the answer? Has there been a mass conspiracy of medical pundits, aiming to prove what they instinctively believe? And if so, what is the real cause for the undoubtedly alarming statistics of such fatal diseases? The author is nothing if not honest; he clearly suspects the former, and argues that a wholesale acceptance of the central fallacy is not only closing the matter to objective investigation but also creating an unwholesome equation between pleasure and death, and a concomitant feeling that the patient himself may be largely to blame for his illness.

I was rather hoping that somewhere along the line a diet of junk-burgers and Scotch might be recommended, with perhaps thirty ciggies a day chucked in for good measure, but it is not that kind of a book. It does not tell you that the road to longevity may be achieved by sticking pineapple segments up your backside or cooking your food by impaling it on a toasting-fork and waving it at the sun, but it does imply that, provided you behave sensibly, you can still enjoy a morning fry-up, make an ancient gesture at Mrs Currie, tell your nanny that all that stuff about fish and spinach is twaddle, and not die of anxiety.

Nor is Dr Le Fanu a crank, for his is by no means a lone voice of protest amongst the experts of his profession. If you are suspicious of diet books and etiolated poltroons who preach over the dinner-table, then Eat Your Heart Out will provide ample arguments to the contrary. Personally, I am inclined to believe every last word of it, and if you don’t agree you can go boil your head.