Linked to liver cancer: Peanuts actually grow underground, where they acquire a pervasive fungus called Aspergillus, a source of aflatoxins, which are toxic and highly carcinogenic. Some studies concluded that too much aflatoxin exposure is linked to developing liver cancer.
Hard for humans to digest: Peanuts contain an anti-nutrients known as lectins. Lectins serve as a primitive pest-resisting strategy in the peanut plant. However, the structure of lectins, makes them almost impossible for humans to digest.