Abstract Aims Dietary modification is essential for the secondary prevention of cardiovascular disease. However, there are limited published evidence syntheses to guide practice in the cardiac rehabilitation (CR) setting. This systematic review’s objective was to assess effectiveness and reporting of nutrition interventions to optimize dietary intake in adults attending CR. Methods and results Randomized controlled trials (RCTs) of nutrition interventions within CR were eligible for inclusion and had to have measured change in dietary intake. MEDLINE, Embase, Emcare, PsycINFO, CINAHL, Scopus, and The Cochrane Library were searched from 2000 to June 2020, limited to publications in English. Evidence from included RCTs was synthesized descriptively. The risk of bias was assessed using the Cochrane Risk of Bias 2 tool. This review is registered on PROSPERO; CRD42020188723. Of 13 048 unique articles identified, 11 were eligible. Randomized controlled trials were conducted in 10 different countries, included 1542 participants, and evaluated 29 distinct dietary intake outcomes. Five studies reported statistically significant changes in diet across 13 outcomes. Most nutrition interventions were not reported in a manner that allowed replication in clinical practice or future research. Conclusion There is a gap in research testing high-quality nutrition interventions in CR settings. Findings should be interpreted in the light of limitations, given the overall body of evidence was heterogenous across outcomes and study quality; 6 of 11 studies were conducted more than 10 years old. Future research should investigate strategies to optimize and maintain nutrition improvements for patients attending CR. Registration PROSPERO; CRD42020188723.