The role of diet in the treatment of gastroesophageal reflux disease (GERD) is still under discussion. Some studies support the evidence that specific components of food plays a role in triggering symptoms or may have an impact on reflux oesophagitis. Still, only limited data are present on the long-term real-life effects of diet and behaviour on the disease manifestations and outcomes. This specific study aims to investigate the role of diet in real-life cohort of patients in whom diagnosis of GERD is initially confirmed with the use of modern techniques (questionnaires, endoscopy, oesophageal pH-impedance recordings). To make the study possible, it is planned to form a cohort of patients with different manifestations of gastroesophageal reflux disease: non-erosive GERD (NERD), reflux-oesophagitis (EE), hypersensitive oesophagus. Each form of GERD is to be established in accordance to modern concept of GERD (i.e. Lyon consensus). In addition to standard-of-care examinations, diet assessment will be performed with the use of computer-based food frequency questionnaire (FFQ), which allows to analyse frequently used foods, food products in terms of frequency of consumption and sizes of the portions. Assessment of diet will be performed at the enrolment and than with a period of three months during three years. Based on the results, it would be possible to assess the effect of long-term adherence to diet, change of the composition of it, and perform a multifactorial statistical analysis with the consideration of other confounders: change in BMI, physical activity, smoking, concomitant medications, etc.