Objectives: the aim of the study is to determine whether there is a difference in the improvement of lung functions and the reduction of abdominal fat tissue in people with obesity who are on a restrictive diet program and are involved in regular trainings and people who are also on a reduced diet program, but do not exercise. Subjects and methods: this prospective study included 50 patients of the Obesity Outpatient Clinic of the Internal Medicine Clinic of KBC Rijeka with a diagnosis of obesity and lasted from October 2023 until May 2024. All patients were included in the restrictive diet program and were offered the option of joining organized training sessions. Patients were divided into two groups, those who participated in training (n=25) and those who did not participate in training (n=25). At the beginning and at the end of the intervention, data related to gender, age, weight, height, BMI, waist circumference, abdominal fat tissue thickness and pulmonary function parameters: FVC, FEV1 and VC were measured for all patients. The patients who participated in the trainings exercised twice a week for 60 min. Inclusion criteria were: BMI higher than 27 kg/m2, patients registered in the Obesity Clinic during 2023 with a recommendation for organized exercise by a doctor and physiotherapist. Exclusion criteria were the presence of any chronic lung disease, history of pulmonary embolism, angina pectoris, history of myocardial infarction, loss of consciousness for any reason in the last 6 months, irregular exercise. Results: the obtained results do not indicate the existence of statistically significant differences in the final measurements of BMI (p = 0.154), waist circumference (p = 0.382), abdominal fat tissue thickness (p = 0.435), FVC (p = 0.741), FEV1 (p = 0.676) and VC (p = 0.892) between subjects of the experimental and control groups. The data analysis showed that in all tested parameters there is a statistically significant difference between the first and second measurements (p < 0.001). Conclusion: the research confirmed the positive effect of a restrictive diet on certain pulmonary functional parameters and anthropological characteristics of patients, while the effect of physical activity on improving those parameters was not proven.