Aim: To analyze the concept of diet adherence in type 2 diabetes mellitus (T2DM). Background: Different healthcare providers widely use the concept of adherence. In the 1970s, the term compliance was commonly used as the patients' views on treatment decisions were neglected. With consideration of patients' perspectives in treatment choices and treatment management, the concept of "compliance" has been increasingly replaced by "adherence." Adhering to a healthy diet is very challenging among patients with T2DM, and empirical studies show a low adherence rate to a healthy diet. Methods: The Walker and Avant (2011) method of concept analysis was implemented. Scientific databases were probed for research articles in the English language published between 2010-2020 using the search terms: compliance, adherence, treatment adherence, diet adherence, T2DM, and concept analysis. Results: Diet adherence as a concept includes, following diet recommendations, self-monitoring, maintenance, and relapse prevention. Antecedents include motivation, understanding of diet recommendations, health beliefs, self-efficacy, goal setting, and social support. Consequences include overall health promotion, health-related quality of life, and improved disease-specific parameters such as lower body mass index, HbA1c, a better level of triglycerides, LDL-cholesterol, non-HDL-cholesterol, and lower diastolic blood pressure. Diet adherence is frequently measured using the Perceived Dietary Adherence Questionnaire, Patient Diet Adherence in Diabetes Scale, the Compliance Praxis Survey-Diet, multiday food diaries, 24-hour recalls, and food frequency questionnaires. Conclusion: Adherence to a healthy diet for patients with T2DM is a primary determinant of management, but diet adherence is frequently inadequate. Poor diet adherence attenuates optimum expected outcomes; hence more research is needed to promote diet adherence.