Sweet potato for type 2 diabetes mellitus.

BACKGROUND: Sweet potato (Ipomoea batatas) is among the most nutritious subtropical and tropical vegetables. It is also used in traditional medicine practices for type 2 diabetes mellitus. Research in animal and human models suggests a possible role of sweet potato in glycaemic control. OBJECTIVES: To assess the effects of sweet potato for type 2 diabetes mellitus. SEARCH METHODS: We searched several electronic databases, among these The Cochrane Library (issue 7, 2011), MEDLINE, EMBASE, CINAHL, SIGLE and LILACS (all up to July 2011), combined with handsearches. No language restriction was used. SELECTION CRITERIA: We included randomised controlled trials that compared sweet potato with a placebo or a control intervention with or without pharmacological or non-pharmacological interventions. DATA COLLECTION AND ANALYSIS: Two authors independently selected the trials and extracted the data. We evaluated risk of bias using the items randomisation, allocation concealment, blinding, completeness of outcome data, selective reporting and other potential sources of bias. MAIN RESULTS: Three randomised controlled trials (RCTs) met our inclusion criteria: these investigated a total of 140 participants and ranged from six weeks to five months duration. The studies were contributed by the same author. Overall, the risk of bias of these trials was unclear or high. All RCTs compared the effect of sweet potato preparations with placebo on the glycaemic control in type 2 diabetes mellitus. There was a statistically significant improvement in glycosylated haemoglobin A1c (HbA1c) at three to five months with 4 g/day sweet potato preparations compared to placebo (mean difference (MD) -0.3% (95% CI -0.6 to -0.04), P = 0.02; 122 participants, two trials). No serious adverse effects were reported. Diabetic complications and morbidity, death from any cause, health-related quality of life, well-being, functional outcomes and costs were not investigated. AUTHORS' CONCLUSIONS: There is insufficient evidence to recommend sweet potato for type 2 diabetes mellitus. Improvement in trial methodology as well as addressing the issues of standardization and the quality control of preparations of other varieties of sweet potato are required. For medical nutritional therapy, further observational trials and RCTs evaluating the effects of sweet potato are needed to guide any recommendations in clinical practice.