Peanuts contain aflatoxins (aka Aspergillus flavus and Aspergillus parasiticus) and both protein and carbohydrates, often making them hard to digest. They are also high in fungus and pesticides possibly explaining the disproportionate rate of cancer in peanut farmers. In Australia, they are not regarded as a threat of cancer due to the high level of inspection and testing done by agribusinesses to eliminate the contaminants from the peanuts.

Source: Queensland, Australia Government Dept. of Agriculture