Background: Adequate nutrition knowledge is important for healthy food choices. Objectives: The aim of this study is to determine the relationship between nutritional knowledge of adults and body mass index of nutritional preferences. Methods: The population of the study, which was carried out with a cross-sectional design between December 2019 and March 2020, consisted of adult individuals registered in Family Health Centers in two different districts of Istanbul. The sample was determined by non-proportional stratified sampling method. A sample of 444 individuals, one male and one female, were systematically recruited from adults who applied to Family Health Centers. The power of the study was found to be 0.89 for the Basic Nutrition section and 0.99 for the “Food Preference” section. The data were collected by using the questionnaire form, ‘Nutrition Knowledge Level Scale For Adults’ by measuring the height and weight of individuals. Descriptive statistics, Pearson correlation and Chi-square analysis were used. Results: Of the adults participating in the study, 49.5% were female and 50.5% were male, with an average age of 41.01 ± 13.67. The majority of the study group, such as 56.1% were overweight and obese and their mean body mass index was found to be 25.81 ± 4.37. It was found that 45.9% of individuals had medium nutritional information level, 36.5% were good, 45.3% of individuals had medium nutritional preferences and 30.2% were good. The difference between the marital status, income and education level variables of adults and Body Mass Index was found statistically significant (p<.05). There was no statistically significant relationship between Body Mass Index and Nutrition Knowledge and Food Preference mean scores (p>.05). Conclusion: Although the nutritional information and preferences of adults are sufficient, it was thought that the majority of them may be related to being overweight/ obese, consuming more than necessary or being inactive.