Here's one easy way to help avoid conflict and strife in your interactions with others: When you eat your three square meals a day, don't skimp on the meats and cheeses. Those foods contain high levels of the amino acid tryptophan, which the body needs to produce the neurotransmitter serotonin, a chemical in the brain that plays a role in regulating mood, aggression and social behavior. In a new study, test subjects with high serotonin levels responded less aggressively while making emotionally charged financial decisions in a test known as the ultimatum game. A research team from the University of Cambridge had the study volunteers fast overnight, and gave them a protein drink in the morning. One day the drink was fortified with tryptophan, while the other day it didn't contain the substance. On both days the subjects played 48 rounds of a so-called ultimatum game in which they and another person were offered a share of money, ranging from "fair" offers of 45 percent of the cash to "most unfair" stakes of 18 percent. If they accepted the offer, both parties got paid. If they rejected it, neither was paid.