Background: This study aimed to determine the relationship between diet quality and nutrition knowledge (CN) and nutrition practices (NP) of people who perform physical activity (PA) regularly. Methods: Two hundred healthy individuals who attended the gym at least three times a week were studied. The quality of the diet is calculated using the Healthy Eating Index-2015 (HEI-2015). Linear regression models were used multiplex to assess associations between NC and PN scores and dietary variables. Results: Of the participants, 47.0% had poor NC and 48.0% had poor NP. It was determined that the PN scores were significantly associated with whole grain, seafood, and herbal protein and quality total diet (p < 0.05), while CN scores were not associated with the quality of the diet or its components (p > 0.05). A one-unit increase in CN score resulted in a 26.7% increase in snack consu...