Cited by 1,630Food composition and propertiesNutritional Studies and DietDiet, Metabolism, and Disease

The DOI matches its Crossref record; 47 of the 47 references it cites were found in a registry or an index; 1 of the 31 sources its claims cite were checked for support.

Carbohydrate quality and human health: a series of systematic reviews and meta-analyses

Open access
Reynolds, Andrew, Mann, Jim, Cummings, John, Winter, Nicola, Mete, Evelyn, Te Morenga, Lisa·2019·The Lancet

Abstract

BACKGROUND Previous systematic reviews and meta-analyses explaining the relationship between carbohydrate quality and health have usually examined a single marker and a limited number of clinical outcomes. We aimed to more precisely quantify the predictive potential of several markers, to determine which markers are most useful, and to establish an evidence base for quantitative recommendations for intakes of dietary fibre. METHODS We did a series of systematic reviews and meta-analyses of prospective studies published from database inception to April 30, 2017, and randomised controlled trials published from database inception to Feb 28, 2018, which reported on indicators of carbohydrate quality and non-communicable disease incidence, mortality, and risk factors. Studies were identified by searches in PubMed, Ovid MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials, and by hand searching of previous publications. We excluded prospective studies and trials reporting on participants with a chronic disease, and weight loss trials or trials involving supplements. Searches, data extraction, and bias assessment were duplicated independently. Robustness of pooled estimates from random-effects models was considered with sensitivity analyses, meta-regression, dose-response testing, and subgroup analyses. The GRADE approach was used to assess quality of evidence. FINDINGS Just under 135 million person-years of data from 185 prospective studies and 58 clinical trials with 4635 adult participants were included in the analyses. Observational data suggest a 15-30% decrease in all-cause and cardiovascular related mortality, and incidence of coronary heart disease, stroke incidence and mortality, type 2 diabetes, and colorectal cancer when comparing the highest dietary fibre consumers with the lowest consumers Clinical trials show significantly lower bodyweight, systolic blood pressure, and total cholesterol when comparing higher with lower intakes of dietary fibre. Risk reduction associated with a range of critical outcomes was greatest when daily intake of dietary fibre was between 25 g and 29 g. Dose-response curves suggested that higher intakes of dietary fibre could confer even greater benefit to protect against cardiovascular diseases, type 2 diabetes, and colorectal and breast cancer. Similar findings for whole grain intake were observed. Smaller or no risk reductions were found with the observational data when comparing the effects of diets characterised by low rather than higher glycaemic index or load. The certainty of evidence for relationships between carbohydrate quality and critical outcomes was graded as moderate for dietary fibre, low to moderate for whole grains, and low to very low for dietary glycaemic index and glycaemic load. Data relating to other dietary exposures are scarce. INTERPRETATION Findings from prospective studies and clinical trials associated with relatively high intakes of dietary fibre and whole grains were complementary, and striking dose-response evidence indicates that the relationships to several non-communicable diseases could be causal. Implementation of recommendations to increase dietary fibre intake and to replace refined grains with whole grains is expected to benefit human health. A major strength of the study was the ability to examine key indicators of carbohydrate quality in relation to a range of non-communicable disease outcomes from cohort studies and randomised trials in a single study. Our findings are limited to risk reduction in the population at large rather than those with chronic disease. FUNDING Health Research Council of New Zealand, WHO, Riddet Centre of Research Excellence, Healthier Lives National Science Challenge, University of Otago, and the Otago Southland Diabetes Research Trust.

Overview

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TL;DR

This series of systematic reviews and meta-analyses found that higher intakes of dietary fibre and whole grains are associated with lower risk of non-communicable disease incidence and mortality, with dietary fibre intakes of 25–29 g/day showing greatest benefit. Glycaemic index/load were less useful markers, with low or very-low quality evidence and inconsistent trial effects.

Key findings

  • Across 135 million person-years of prospective data and 58 trials with 4,635 adults, higher versus lowest total dietary fibre was associated with a 15–31% lower risk of critical outcomes; all-cause mortality RR 0.85 (95% CI 0.79–0.91), CHD incidence RR 0.76 (0.69–0.83), type 2 diabetes incidence RR 0.84 (0.78–0.90), and colorectal cancer incidence RR 0.84 (0.78–0.89).
  • Greatest risk reduction for fibre occurred at 25–29 g/day (improvement in 6 of 7 critical outcomes); dose-response curves were often linear with no plateau, suggesting higher intakes may confer additional protection against cardiovascular diseases, type 2 diabetes, and colorectal and breast cancer.
  • Higher whole grain intake was associated with a 13–33% lower risk; per 15 g/day higher intake, RRs were 0.94 (0.92–0.95) for all-cause mortality, 0.93 (0.89–0.98) for CHD incidence, 0.88 (0.81–0.95) for type 2 diabetes, and 0.97 (0.95–0.99) for colorectal cancer.
  • Low glycaemic index diets showed an 11% (95% CI 3–18%) relative risk reduction in type 2 diabetes, attenuated to 5% (13% less to 4% more) in sensitivity analysis; evidence was graded low to very-low, and trials showed no consistent benefits.

Methods

  • Systematic reviews and meta-analyses of prospective studies published before April 2017 and randomised controlled trials published before February 2018, identified via PubMed, Ovid Medline, Embase, Cochrane CENTRAL, and other sources, with duplicate independent searches, extraction, and bias assessment.
  • Included 185 publications of prospective studies involving just under 135 million person-years and 58 clinical trials with 4,635 adult participants; outcomes included NCD incidence, mortality, and cardiometabolic risk factors.
  • Random-effects models for high-versus-low quantile analyses, dose-response testing (linear and spline), sensitivity analyses, meta-regression, subgroup analyses, and GRADE assessment of evidence quality.

Limitations

  • Stated: Evidence was most often graded moderate or low rather than high because GRADE typically requires RCTs with disease endpoints for high quality, and unexplained heterogeneity led to downgrading; data on other dietary exposures and specific fibre sources/subcategories were limited.
  • Stated: High fibre and whole grain intakes may have deleterious effects in populations with borderline iron/mineral status, where very high whole grain intakes may further compromise iron status.
  • Evident from text: Observational associations cannot prove causality, though authors argue consistency and dose-response make causality likely; glycaemic index/load findings were inconsistent and attenuated in sensitivity analyses; trials excluded weight-loss trials, fibre supplement powders, and people with diabetes or marked hyperlipidaemia, limiting generalisability.

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Integrity signals

Registry

Crossref · 10.1016/s0140-6736(18)31809-9

Cites

47 of 47 references verified0 citation errors · 0 not checkable

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  • Probably not a substantial claim. 25
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52 of 52
  • The authors state this as an assumption.

    The dose-response analysis assumes a linear relationship between intake and outcome.

    “assuming linearity with a two-stage dose response random-effects analysis.”
  • The authors state this as an assumption.

    The dose-response relationship between dietary fibre or wholegrain intake and the clinical outcomes is linear.

    “Assuming linearity a reduced risk ratio of 0•93 (0•90 to 0•95) was observed for every 8 grams more fibre consumed per day.”
    “Assuming linearity a reduced risk ratio of 0•94 (0•92 to 0•95) was observed for every 15 grams more whole grains consumed per day.”
    “Assuming linearity a risk ratio of 1•16 (0•90 to 1•49) was observed for every 10 glycaemic index unit increase per day.”
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Research works printed but not linked: 1

  1. Aune, 2011, Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies, BMJ, 343, d6617, 10.1136/bmj.d6617 · DOI · Paper page

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Metadata

Authors
Reynolds, A., Mann, J., Cummings, J., Winter, N., Mete, E., & Te Morenga, L.
Affiliations
  • University of Otago (NZ)
  • Riddet Institute (NZ)
  • University of Dundee (GB)
Corresponding author
Mann, Jim
Venue
The Lancet
Publisher
Elsevier BV
Published
2019-02
Volume
393
Issue
10170
Pages
434-445
ISSN
  • 0099-5355 (ISSN-L)
  • 0140-6736
OpenAlex
W2910727162
Cited by
1,630
References
46
Citations by year
2026: 196 · 2025: 239 · 2024: 227 · 2023: 249 · 2022: 243 · 2021: 206 · 2020: 163 · 2019: 106
FWCI
24.38
Type
journal article
Language
en
Update notices
erratum (2019-02-02)
Open access
Locations
  • The Lancet (publishedVersion)
  • PubMed (publishedVersion)
  • Discovery Research Portal (University of Dundee) (publishedVersion, cc-by-nc-nd)
Funders
  • World Health Organization
  • University of Otago
  • Health Research Council of New Zealand
Topics
  • Health Sciences › Nursing › Nutrition and Dietetics › Food composition and properties
  • Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Nutritional Studies and Diet
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Diet, Metabolism, and Disease
Keywords
carbohydrate quality, dietary fiber, whole grains, glycemic index, glycemic load, non-communicable diseases, cardiovascular disease, type 2 diabetes, colorectal cancer, breast cancer, all-cause mortality, stroke, coronary artery disease, body weight, blood pressure, total cholesterol, dose-response relationship, dietary recommendations, dietary diversity
MeSH terms
Noncommunicable Diseases, Dietary Carbohydrates, Dietary Fiber, Humans, Primary Prevention

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