When starchy foods are cooked to a dark brown, acrylamide is formed. Animal studies suggest there might be a link between acrylamide and cancer risk, but a large, 10 country study across Europe found no significant evidence in humans (Watch Dr. Mitrou discuss this study.) While the jury is still out, you could follow the Food Standards Agency suggestion to lower exposure by aiming for golden yellow when baking, toasting or roasting bread, potatoes or parsnips.
PositiveTip: Strong evidence points to not smoking, avoiding alcohol, physical activity and a healthy weight as significant ways to reduce cancer risk.