A diet high in fructose diet may lead to liver damage, according to a study published in "The American Journal of Clinical Nutrition" in 2013. In a controlled trial, monkeys developed significant liver damage after taking in large amounts of fructose for only six weeks. According to the research, the excessive fructose caused bacteria to migrate from the monkeys' intestines and attack their livers. A six-week period in monkeys is equivalent to about three months in humans.