Chances are if you cook carrots you slice them first. Cooking them whole takes longer, but it turns out to have both health and flavour benefits.
BBC News reports that a new study shows that cooking carrots whole means that they have a much higher level of falcarinol, a compound which earlier studies have linked to reduced levels of cancer:
The latest findings show that when carrots are heated, the heat kills the cells, so they lose the ability to hold on to the water inside them, increasing the concentration of falcarinol as the carrots lose water. However, the heat also softens the cell walls, allowing water-soluble compounds such as sugar and vitamin C to be lost via the surface of the tissue, leading to the leaching out of other compounds such as falcarinol. If the carrot is cut before being boiled, the surface area becomes much greater - and so the loss of nutrients is increased.
While no single food is going to prevent cancer, there's a second benefit as well: carrots cooked whole taste better, since they lose less of the sugars that give them their flavour. As the BBC points out, the only real sacrifices involved are a slightly longer cooking time and having to use a slightly larger saucepan. Picture from Wikimedia Commons
Cancer boost from whole carrots [BBC News]