Matís (Matvælarannsóknir Íslands) has opened a database on the chemical content of food. The database, called ÍSGEM, contains information on substances in about 900 foods in Iceland.
Among other things, you can get information on proteins, fats, carbohydrates, water, energy, vitamins, minerals and undesirable substances such as mercury, lead, cadmium and arsenic.
You can view the ÍSGEM database here.