OBJECTIVE:To conduct a systematic review and meta-analysis examining the effects of carnosine and histidine containing dipeptides (HCDs) on anthropometric and glycaemic outcomes.
METHODS:Electronic databases (MEDLINE, Medline in process, EMBASE, CINAHL, and All EBM) were searched from inception until 25 January 2019 for randomized controlled trials (RCTs) investigating the effects of carnosine/HCD supplementation on anthropometric and glycaemic outcomes. Two independent reviewers screened all titles and abstracts and eligible articles were screened in full text. Relevant data were extracted, and meta-analyses were performed using random-effects models to calculate the weighted mean difference (WMD) and 95% confidence interval (CI) for each outcome. Risk of bias was assessed for each of the included articles and quality of the evidence for each outcome was assessed using theGrading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.
RESULTS:Thirty RCTs were included in qualitative synthesis, of which 23 were pooled for meta-analysis (n=986).HCD-supplemented groups had a lower waist circumference (3 RCTs, n=162; WMD [95% CI]= -3.53cm [-5.65, -1.41], p=0.001) and HbA1c level (5 RCTs, n=365; WMD [95% CI]= -0.76% [-1.29, -0.24], p=0.004) at follow up compared with placebo groups. In the sensitivity analyses of low risk of bias studies, the effects on waist circumference and HbA1c remained significant (both p<0.05). In addition, fasting glucose levels were also significantly lower in HCD supplementation groups versus placebo/controls (7 RCTs, n=413; WMD [95% CI]=-0.63mmol/L [-1.09, -0.18], p=0.006). There were no differences in BMI, body fat, fasting insulin, 2-hour glucose, or measures of insulin resistance between groups (all p>0.05).
CONCLUSIONS: This meta-analysis provides evidence that HCDs may improve anthropometric and glycaemic outcomes. Larger clinical trials with longer follow-up periods are essential to strengthen the current evidence regarding the benefits of carnosine/HCD supplementation and to establish whether improvements in anthropometric and glycaemic measures following supplementation would translate into improved health outcomes and disease prevention on a population-wide scale.