A new study by UK scientists showed that cooking carrots whole preserves their anti-cancer properties better than cooking them sliced or diced.

The study was the work Dr Kirsten Brandt and researcher Ahlam Rashed at the University of Newcastle Upon Tyne and is being presented today at the NutrEvent nutrition and health conference that is taking place in Lille, France.

Brandt and colleagues found that carrots boiled before cutting had 25 per cent more of the anti-cancer chemical falcarinol than those that were cut up before boiling.

They also found uncut cooked carrots had higher concentrations of the naturally occurring sugars that give them their distinctive flavour.

Brandt, who is based at the School of Agriculture, Food and Rural Development and the Human Nutrition Research Centre at Newcastle University said that:

"Chopping up your carrots increases the surface area so more of the nutrients leach out into the water while they are being cooked."

"By cooking them whole and chopping them up afterwards you are locking in both taste and nutrients so the carrot is better for you all round," she added.

Working with colleagues at the University of Southern Denmark, Brandt and her team at Newcastle discovered the health properites of falcarinol in carrots four years ago.

They showed that feeding rats a diet containing either raw carrots or isolated falcarinol reduced their risk of developing tumors by one third compared with rats in a control group.

Since then the researchers have been looking at the health benefits of raw and cooked carrots, comparing different varieties of the vegetable, and how their properties change with heat.

They found that cooking a carrot kills its cells so they can't hold water and this increases the concentration of falcarinol. But heat also softens the walls of the cells so sugar, vitamin C and other compounds such as falcarinol leach out more readily.

Cutting the carrot into pieces before boiling increases the surface area which allows more of the nutrients to leach out of the cell walls into the boiling water.

The scientists also asked 100 people to wear a blindfold and compare the taste of carrots that had been cut before cooking and carrots that had been cut after cooking. More than 80 per cent said the carrots that were cut after cooking tasted better.