The FSA urges people not to over-cook starchy foods, such as toast, cakes and potatoes. In its 'Go for Gold' campaign, it warns that over-cooking the foods produces high levels of acrylamide, a process that happens in any starchy foods that have been cooked to temperatures above 120 C. The darker the toast, the more acrylamides it contains.
Acrylamide is certainly very nasty stuff. It's used as an industrial sealant, and workers who've been exposed to very high doses have suffered nerve damage, and the International Agency for Research on Cancer has listed it "a probable human carcinogen".
Studies on mice have shown that acrylamide damages DNA and causes cancer—but a similar link has never been found when the chemical has been tested on humans, and it's been researched numerous times.
And it's all down to the exposure. Even burnt toast lovers would need to eat 160 times their usual levels—so 320 slices if they eat two slices at the moment—before they run the risk of developing cancer, says Cambridge University's David Spiegelhalter.