LETTUCES have their use but it is hard to explain in dietary terms why so much money is spent on them. If a restaurant owner is concerned about the cost of the meal and portion size, the meagreness of the dish can be disguised with a thick carpet of lettuce. With any luck the diner, having waded through a pile of sprayed and preserved but nevertheless limp and lifeless salad, may fail to notice that the size of the lamb chops would disappoint one of Gulliver’s little people. Even if the tomatoes, peppers and other salad vegetables that dilute the lettuce are fresh and so provide significant food value, the amount offered would dismay even those who weren’t starving.

Such is the misconception that lettuce is health-giving that it is also assumed to be free of pathological organisms. If multiresistant Salmonella typhimurium DT104, resistant to ampicillin, tetracycline and sulphonamides as well as to the less commonly used chloramphenicol, streptomycin and spectinomycin, had been found in a steak or an egg (ask Edwina Currie), the uproar would have made it a major story.

Recently in the Scottish Borders 23 cases of food poisoning from this highly resistant, potentially lethal organism were traced back to lettuce, but little about the outbreak was reported.

Such optimism about lettuce’s nutritional value takes no account of its growth in circumstances where it may have been exposed to every aspect of nature, and thereafter washed inadequately or handled by people with grubby hands.

A portion of lettuce contains only a twentieth of the fibre in a helping of broad beans, and a fraction of that found in peas or parsnips. The amount of vitamins that lettuces contain is trivial. There is a little bit of beta carotene in the darkest lettuce leaves, and a trace of folate, but compared with that found in peppers, tomatoes, spinach, red cabbage or baked beans, it is insignificant. Lettuce is an expensive way to buy water.

Tomatoes are a valuable source of beta carotene, vitamins C and E and potassium and are particularly rich in lycopene, a potent antioxidant that is known to be a preventative shield, to some extent, against cancer of the prostate and breast. A recent study published in the journal Cancer Research has shown that this applies especially to men with a particular genetic make-up.

The same genetic make-up that improves a person’s response to the protective power of lycopene is also a significant factor in determining the protection provided by selenium and vitamin E. The lycopene in tomatoes is more effective when the tomatoes have been cooked, processed, puréed or juiced, but even when added raw to a salad they have great nutritional value. Lycopene can also be obtained from other foods such as red and green peppers, and from the chemist as Lyc-O-Mato.

A return to something more akin to old-fashioned cooking and greater reliance on good quality ingredients together with wholesome vegetables and fruits, as advocated by Jamie Oliver, Rick Stein and a host of doctors at the Royal Society of Medicine last week, would do much for the health of this country.

I first encountered pre-cooked, reheated food when travelling to Edinburgh more than 30 years ago for a medical meeting. I called en route for lunch with some old colleagues who had been junior doctors with me. As they were brilliantly academic but otherwise unworldly, it seemed unlikely that we would be having anything other than shepherd’s pie or fish and chips. Over our initial drink my hostess offered a choice from a menu that could have been cribbed from Le Caprice. The food was a just passable imitation of haute cuisine.

Before I left, my old friends let me into the secret: their deep freeze was stacked with pre-prepared meals that needed only warming. Jamie Oliver has now exposed, in his television series on school dinners, the horrific result of institutional bulk buying, distant cooking and reheating when the original ingredients are not of the best quality. Rather than being derived from locally grown or raised produce, the food served to school pupils was either made from reconstituted recovered poultry, or worse, and then reheated.

The message is that if we are to have a healthier generation, institutional cooks should be emulating the best of old-fashioned home cooking, not attempting to imitate the menu of multi-starred restaurant food. Keep food simple and fresh. You could even include firm lettuce — so long as it has a heart and is freshly gathered from the garden.