Experiments with middle-aged rats, roughly equivalent in age to a 60-year-old person, showed that after only eight weeks of eating high fat foods, those on a high trans fat diet could not perform simple memory tasks as well as those on a high fat diet of soybean oil.
The study was carried out by scientists at the Medical University of South Carolina (MUSC), including the university's director of the Center on Aging, Anne-Charlotte Granholm, who sees this work as another nail in the coffin for trans fats, one of the new 'evils' of food processing.
The group compared rats on a high fat diet of 12 per cent soybean oil with those on a high fat diet of 10 per cent trans fats and two per cent cholesterol. In one experiment, the rodents, all of a similar weight, had to recall the location of hidden platforms in a water-filled maze - a task the trans fat rats were around five times worse at.
A range of studies have already shown that high fat/ high cholesterol diets could contribute to learning and memory difficulties in the brain, but the MUSC research appears to highlight trans fats as the biggest single offenders.
Granholm said that while "it is always difficult to draw comparisons between animal studies and humans," the study was nevertheless "quite alarming". She believes food companies should show greater responsibility by cutting levels of trans fats in products more quickly.
The MUSC research is another kick in the teeth for trans fats, the common name for hydrogenated fats and oils, which are already thought to significantly increase the risk of heart disease by blocking arteries and have also been linked to a higher risk of Alzheimer's disease.
Hydrogenated fats and oils have been widely used in the food industry for the last 50 years, primarily to extend the shelf life of products because trans fats do not go rancid as quickly as unsaturated fats. The high melting point and solid nature of hydrogenated fat also helps industrial bakers to maintain structure in their breads.
A number of companies have made commitments to reduce trans fats in their products, prompted by governmental and medical concerns. In the US, Kraft foods has launched trans fat free Oreo biscuits and PepsiCo now produces trans fat free Doritos through subsidiary Frito-Lay. In Europe, United Biscuits' unit McVities has removed trans fats from its biscuit dough, though not cream filling, and UK retailer Sainsbury now claims to use low trans fat pastry.
Some alternatives to trans fats have also begun to appear, such as Danish company Danisco's new emulsifier/oil blends and US firm Dow Agrosciences' natural Natreon canola oil, which claim to fill the role of partially hydrogenated fat.
But MUSC study author Granholm said that trans fats should be removed even before alternatives have been perfected: "Trans fats have only been around since the Second World War and before that we obviously did fine without them.
"What will happen is that people will have to adjust their lives a little. For example, buying a loaf of bread and having it last for a month or more without freezing it may no longer be an option. In fact, most European countries live by that."
Granholm said that the next step for herself and her colleagues would be to investigate the exact process by which trans fats affect the brain, and examine further the difference between cholesterol, saturated fats and trans fats in terms of the possible detrimental effects on people. She admitted that the group's studies needed to be followed up by "careful examination of the human body" to gain greater credence.
By January 2006 all manufacturers operating in the US will have to label trans fat content on their products, according to a recent ruling by the country's Food and Drug Administration.
In the UK, the government's Food Standards Agency has been slower to react to a threat from trans fats, warning people to consume less but concentrating its efforts on reducing salt and saturated fat levels in foods. Industry association the Food and Drink Federation said that government figures showed peoples' trans fat intake had halved between 1985 and 2000.