A review study in ISRN Nutrition suggests that eating a high protein diet for a long time can result in serious diseases or disorders.  The study based on data from 32 studies including 21 experimental humans studies and 11 reviews shows that long term consumption of a high protein diet or high meat diet can increase risk of disorders of bone and calcium homeostasis, renal dysfunction, increased risk of cancer, liver diseases, and progression of coronary artery disease.  

The recommended dietary allowance for adults was 0.8 grams of protein per kg body weight per day.  Dr. T. Colin Campbell, a nutrition professor of Cornell University suggests that for most people protein should count for 11% of the total calories while most Americans eat more than 15% calories from proteins.

Delimaris I.  Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults.   ISRN Nutr. 2013 Jul 18;2013:126929. doi: 10.5402/2013/126929.