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BMJ Open. 2014 Jul 29;4(7):e004660. doi: 10.1136/bmjopen-2013-004660.

Effect of tree nuts on metabolic syndrome criteria: a systematic review and meta-analysis of randomised controlled trials.

Author information

1
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada.
2
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
3
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada Faculty of Health Sciences, School of Medicine, Queen's University, Kingston, Ontario, Ontario, Canada.
4
Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada.
5
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada Division of Endocrinology and Metabolism, St. Michael's Hospital, Toronto, Ontario, Canada Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
6
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada Department of Clinical Epidemiology & Biostatistics, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.
7
Toronto 3D Knowledge Synthesis and Clinical Trials Unit, Clinical Nutrition and Risk Factor Modification Centre, St. Michael's Hospital, Toronto, Ontario, Canada Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada Division of Endocrinology and Metabolism, St. Michael's Hospital, Toronto, Ontario, Canada Department of Pathology and Molecular Medicine, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.

Abstract

OBJECTIVE:

To provide a broader evidence summary to inform dietary guidelines of the effect of tree nuts on criteria of the metabolic syndrome (MetS).

DESIGN:

We conducted a systematic review and meta-analysis of the effect of tree nuts on criteria of the MetS.

DATA SOURCES:

We searched MEDLINE, EMBASE, CINAHL and the Cochrane Library (through 4 April 2014).

ELIGIBILITY CRITERIA FOR SELECTING STUDIES:

We included relevant randomised controlled trials (RCTs) of ≥3 weeks reporting at least one criterion of the MetS.

DATA EXTRACTION:

Two or more independent reviewers extracted all relevant data. Data were pooled using the generic inverse variance method using random effects models and expressed as mean differences (MD) with 95% CIs. Heterogeneity was assessed by the Cochran Q statistic and quantified by the I(2) statistic. Study quality and risk of bias were assessed.

RESULTS:

Eligibility criteria were met by 49 RCTs including 2226 participants who were otherwise healthy or had dyslipidaemia, MetS or type 2 diabetes mellitus. Tree nut interventions lowered triglycerides (MD=-0.06 mmol/L (95% CI -0.09 to -0.03 mmol/L)) and fasting blood glucose (MD=-0.08 mmol/L (95% CI -0.16 to -0.01 mmol/L)) compared with control diet interventions. There was no effect on waist circumference, high-density lipoprotein cholesterol or blood pressure with the direction of effect favouring tree nuts for waist circumference. There was evidence of significant unexplained heterogeneity in all analyses (p<0.05).

CONCLUSIONS:

Pooled analyses show a MetS benefit of tree nuts through modest decreases in triglycerides and fasting blood glucose with no adverse effects on other criteria across nut types. As our conclusions are limited by the short duration and poor quality of the majority of trials, as well as significant unexplained between-study heterogeneity, there remains a need for larger, longer, high-quality trials.

TRIAL REGISTRATION NUMBER:

NCT01630980.

KEYWORDS:

Nutrition & Dietetics

PMID:
25074070
PMCID:
PMC4120343
DOI:
10.1136/bmjopen-2013-004660
[Indexed for MEDLINE]
Free PMC Article

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