SPARE a thought this weekend for the trans double-bonded unsaturated triglyceride. It was cheap to assemble. It felt great on the human tongue. It lasted for years, whatever type of cake you baked with it, and it ruled the food industry for half a century.

Now it is being abandoned faster than the perky shopper with the Bakewell tart can say: “Sorry, but does this have trans fat in it?” An innocent-looking molecular oddity is the killer component (literally, campaigners say) in the partially hydrogenated vegetable oil that Kentucky Fried Chicken declared this week would no longer be used in most of its recipes throughout the US. The decision by KFC, one of the world’s biggest deep fat-fryers, has been greeted as a turning point by activists seeking to rid the world of a tasteless, odourless, yellowish goo that they claim contributes to 20,000 deaths a year in Britain alone.

“Colonel Sanders deserves a bucket full of praise,” said the director of the Centre for Science in the Public Interest, which had been suing KFC in the US. “This is definitely significant,” one British campaigner added. “Now even McDonald’s will be under pressure to follow suit.”

Marks & Spencer, Asda, Sainsbury’s and Tesco have already removed trans fats from their product ranges, or announced that they intend to. Other large British brands have been quietly replacing trans fats in their products over the past two years in the hope that customers will never know that they had been eating them.

The British Medical Journal has called on the Government to legislate against trans fats. Denmark has already done so. New York City and Chicago, restaurant capitals of the Western world, are likely to ban the commercial use of trans fats within the next few months.

It is almost as if science had shown trans fats and the processed vegetable oils that contain them to be the next great public health menace after tobacco, and policy-makers were finally catching up. Yet this is not quite true.

Compelling studies, including continuing research by the Harvard School of Public Health, have linked trans fat consumption to steep rises in heart disease and obesity. It may also help to trigger diabetes, Alzheimer’s disease and a range of neurological conditions.

“The harder you look at the science, the more conclusive it looks,” says Oliver Tickell, who runs a website dedicated to exposing the evil that trans fats do. But at the molecular level, that evil remains a mystery.

Partially hydrogenated vegetable oils — PHVOs to those who produce them, Franken-fat or devil’s spunk to their detractors — contain fatty acid molecules with hydrogen atoms arranged diagonally rather than symmetrically around pairs of double-bonded carbon atoms.

This “trans” shape baffles the human body, either by fooling the metabolic system into absorbing it as if it were a useful fat, or inhibiting the uptake of essential fats, or both.

Chemically, trans fats are identical to naturally-occurring unsaturated fats. Structurally, they behave like saturated fats. They appear to be masters of molecular disguise, intercepting hormone signals by stiffening cell membranes that should stay fluid and permeable, and blocking messages to and from the brain by sticking to nerve sheathings.

No causal links have been proved between trans fats and their alleged effects, which include strokes, cardiac arhythmia and heart attacks. But the latest statistical research is damning.

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