There might be a Darwinian explanation. According to Meninger clinic researchers, lower blood LDL cholesterol may be a signal for famine, which led to an adaptation of a response of more aggressive behavior.(1) Of course I think this is a pretty far-reaching hypothesis, but it's interesting.
Reference
Erickson, MT. Lowered serum cholesterol, famine and aggression : a Darwinian hypothesis. Available at: http://cat.inist.fr/?aModele=afficheN&cpsidt=2872688. Accessed on November 2, 2008.
