Abstract Aims To determine what dietary interventions have been tested in heart failure with preserved ejection fraction (HFpEF), the modulation method, and outcomes employed and to summarize any evidence for benefit. Methods and results We performed key word searches in five bibliographic databases from 2001 to 2021, to identify randomized or experimental dietary interventions tested in HFpEF or mixed heart failure (HF) samples. Study characteristics were summarized according to population, intervention, comparator, outcome categories and intervention complexity was assessed. Twenty-five clinical investigations were retrieved; only 10 (40%) were conducted exclusively in HFpEF; the remainder enrolled mixed HF samples. Most studies employed either highly tailored prescribed diets (n = 12, 48%) or dietary supplementation (n = 10, 40%) modalities. Dietary pattern interventions (n = 3, 12%) are less well represented in the literature. Conclusion Heterogeneity made pooling studies challenging. Better reporting of baseline characteristics and the use of standardized HF lexicon would ensure greater confidence in interpretation of studies involving mixed HF populations. The field would benefit greatly from explicit reporting of the biological mechanism of action (e.g. the causal pathway) that an intervention is designed to modulate so that studies can be synthesized via their underlying mechanism of action by which diet may affect HF. An extension of the current set of core outcomes proposed by the European Society of Cardiology Heart Failure Association would ensure dietary clinical endpoints are more consistently defined and measured. Registration PROSPERO: CRD42019145388.