Purpose Type 2 diabetes mellitus represents a significant health problem. Many studies have reported that intensive nutritional intervention by itself or in addition to medications is the best method to improve glycaemic control in type 2 diabetes mellitus. However, in clinical practice, dietary education is not implemented as an integral part in the management of type 2 diabetes mellitus. The purpose of this systematic review and meta-analysis is to analyse the scientific evidence concerning the role of nutritional intervention in the glycaemic control of type 2 diabetes mellitus. Methods We searched Pubmed, Scopus, Cochrane Library and Web of Science databases from inception till May 2019 for randomised controlled trials (RCTs) that include dietary interventions in the management of patients with type 2 diabetes mellitus. Results A total of 28 studies were included. Our results demonstrated that lifestyle interventions significantly lowered glycosylated haemoglobin (HbA 1c ) levels compared to the usual care for patients with type 2 diabetes mellitus, overall weighted mean difference, WMD = − 0.51 (− 0.67, − 0.35). Strategies combining individualized and group-based activities were the most effective, WMD = − 0.95 (− 1.24, − 0.66). Most of stratified analyses did not totally resolve heterogeneity, but improvement in HbA 1c levels has been consistently observed. Conclusions The available evidence from RCTs shows that lifestyle intervention is more effective than the standard care regarding the glycaemic control of type 2 diabetic patients, particularly when there is a weight loss. It is time to translate this evidence to the primary health care practice. The protocol of the present systematic review was registered in PROSPERO, registration number CRD42018090469.