Authors' contribution Wkład autorów: A. Study design/planning zaplanowanie badań B. Data collection/entry zebranie danych C. Data analysis/statistics dane-analiza i statystyki D. Data interpretation interpretacja danych E. Preparation of manuscript przygotowanie artykułu F. Literature analysis/search wyszukiwanie i analiza literatury G. Funds collection zebranie funduszy Summary Background. The goal of the study was to compare self-reported eating behavior and knowledge of nutrition in cohorts of women with simple obesity, who begin nutritional intervention to treat obesity, and in women who achieved the goal of obesity treatment, i.e. reduction of initial body mass by a minimum of 10%. Material and methods. The study was conducted in a group of 38 women with simple obesity who were starting dietary treatment (aged 18-72, mean 41, SD 14.95) and 49 women with simple obesity, who, as a result of dietary treatment for obesity, achieved a body mass reduction by at least 10% (aged 18-67, mean 41, SD 13.44). The survey also included a control group of 100 women with normal body mass (aged 19-59, mean 33, SD 13.29). The study used the Questionnaire of Eating Behavior. Results. Women with simple obesity starting dietary treatment were characterized by a paradoxically higher intensity of characteristics of a pro-health diet as well as a higher intensity of unhealthy diet characteristics, compared to women with normal body mass. Women starting treatment compared to women who achieved successfully completed treatment, exhibited a significantly lower intensity of pro-health diet characteristics and higher intensity of unhealthy diet characteristics. The level of nutrition knowledge among healthy women was significantly higher compared to obese women starting treatment. The women who achieved the goal of treatment were characterized by a higher level of nutrition knowledge compared to those starting treatment. Conclusions. There are significant differences between the studied cohorts of women in terms of level of nutrition knowledge and eating behaviors associated with dietary treatment for obesity.