High-protein diet, known in Poland as Protal or Dukan’s diet, mainly assumes consuming protein food as the only source of energy. After period of particular popularity in the U.S., this diet has become fashionable in Poland as well. High-protein diet offers significant weight reduction without necessity of making crucial changes in a lifestyle. Unfortunately this unbalanced diet might be followed by considerable implications. There haven’t been many clinical trials done until now, especially long-term observations. However, it’s possible to draw first conclusions concerning safety aspects, based on a few already finished clinical trials. This article constitutes analysis of conducted studies and risk assessment of long-term use of high-protein diet.