Effect of tree nuts on features of the metabolic syndrome: A systematic review and meta‐analysis of randomized controlled dietary trials

Objective To assess the effect of tree nuts on features of the metabolic syndrome (MetS), we conducted a systematic review and meta‐analysis of randomized dietary trials. Methods We searched MEDLINE, EMBASE, CINAHL, and the Cochrane Library (through May 25, 2012). We included relevant randomized dietary trials of ≥ 3 weeks reporting all 5 features of MetS (waist circumference, fasting glucose, triglycerides, HDL‐cholesterol [HDL‐C], blood pressure [BP]). Two independent reviewers extracted all relevant data. Data were pooled using the generic inverse variance method and expressed as mean differences (MD) with 95% CI. Heterogeneity was assessed by Cochran's Q and quantified by I2. Study quality was assessed by the Heyland score. Results 7 trials (n=1018) met the eligibility criteria. Diets high in tree nuts lowered triglycerides compared with control diets low in tree nuts (MD = −0.09 mmol/L [95% CI, −0.17, −0.01]). There was no effect on waist circumference, HDL‐C, BP, and fasting glucose, with evidence of heterogeneity in all analyses. Limitations Most of the trials were of short duration (<12 months) and of poor quality. Conclusion Pooled analyses show that diets high in tree nuts lower triglycerides. Longer and higher quality trials are warranted. Clinicaltrials.gov identifier: NCT01630980 Funding source: International Nut Council