Obesity Clinical Trial
Official title:
Relation of the Nordic Dietary Pattern With Cardiometabolic Risk Factors and Incident Cardiovascular Outcomes: A Systematic Review and Meta-analysis of Randomized Controlled Trials and Prospective Cohort Studies
The Nordic Diet is a dietary pattern rich in traditional Nordic foods, including berries, grains, and fatty fish common in northern Europe. Studies have shown a protective effect of the Nordic Diet on cardiometabolic risk factors, however only select clinical practice guidelines for the management of diabetes (i.e. Diabetes Canada) recommend this dietary pattern. To support the update of the EASD clinical practice guidelines for nutrition therapy, the investigators propose to conduct a systematic review and meta-analysis of prospective cohort studies and clinical trials to investigate the association between the Nordic Diet, cardiometabolic outcomes and cardiovascular disease incidence and mortality. The findings generated by this proposed knowledge synthesis will help improve the health of consumers through informing evidence-based guidelines and improving health outcomes by educating healthcare providers and patients, stimulating industry innovation, and guiding future research design.
Background: Greater adherence to the Mediterranean diet, a traditional dietary pattern of the
wider region of the Mediterranean sea, has been associated with favourable cardiometabolic
outcomes, including the prevention of type 2 diabetes and cardiovascular diseases (CVD).
However, limited local food availability, increased cost or unfamiliar culture and tradition
render the Mediterranean diet difficult to follow in the northern European environment. The
Nordic Diet or those of other traditional diets of the Nordic countries (Sweden, Norway,
Finland, Denmark, Iceland, Faeroe islands) are dietary patterns rich in traditional Nordic
foods, including berries, grains, and fatty fish common in northern Europe. The Nordic Diet
has been associated with favorable cardiometabolic outcomes including improved lipid profile
and insulin sensitivity. These benefits have been recognized in the most recent updates of
the clinical practice guidelines for diabetes in Canada. The European Association for the
Study of Diabetes (EASD) has not included the Nordic dietary pattern in their guidelines.
Need for proposed research: High quality systematic reviews and meta-analyses of randomized
controlled trials and prospective cohorts represent high-quality evidence to support dietary
guidelines and public health policy. As dietary guidelines and public health policy have
shifted towards food and dietary-pattern based recommendations, there is a need for
systematic reviews and meta-analyses comparing the role of the Nordic diet in the prevention
and management of cardiometabolic outcomes and cardiovascular diseases.
Objectives: To support the update of the European Association for the Study of Diabetes
(EASD) clinical practice guidelines for nutrition therapy, the investigators will conduct a
systematic review and meta-analysis of randomized controlled trials and prospective cohorts
using the GRADE approach on the Nordic dietary pattern on cardiometabolic risk factors and
cardiovascular disease outcomes.
Design: The systematic review and meta-analysis of clinical trials and prospective cohort
studies will be conducted according to the Cochrane Handbook for Systematic Reviews of
interventions and reported according to the Preferred Reporting Items for Systematic Reviews
and Meta-Analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE)
guidelines.
Data sources: MEDLINE, EMBASE, and The Cochrane Central Register of Controlled Trials
(Clinical Trials; CENTRAL) will be searched using appropriate search terms supplemented by
hand searches of references of included studies.
Study selection: Randomized controlled trials conducted in humans with a follow-duration ≥ 3
week investigating the effect of a Nordic diet on cardiometabolic outcomes will be included.
Studies that are not conducted in humans, not randomized, have an acute feeding design (<3
weeks), lack a suitable control (non-isocaloric) and/or do not report viable endpoint data
will not be included. Prospective cohort studies with greater than 1-year of follow-up will
be included.
Data extraction: Two or more investigators will independently extract relevant data and
assess risk of bias using the Cochrane Risk of Bias Tool for randomized clinical trials and
the Newcastle Ottawa Scale for prospective cohorts. All disagreements will be resolved by
consensus. Standard computations and imputations will be used to derive missing variance data
for the randomized clinical. Risk ratios, odds ratios and hazard ratios for clinical outcomes
in the prospective cohort studies will be extracted or derived from clinical event data
across exposure to a Nordic diet.
Outcomes: For the randomized clinical trials, the primary outcome will be LDL-cholesterol.
Secondary outcomes will include markers of glycemic control (HbA1c, fasting glucose, fasting
insulin); other blood lipids (non-HDL-C, apo B, HDL-C, triglycerides); adiposity (body
weight, BMI, waist circumference), blood pressure (systolic and diastolic blood pressure) and
inflammation (C-reactive protein [CRP]).
For prospective cohorts, the primary outcome will be incident CVD Secondary outcomes include
incident coronary heart disease (CHD) and incident stroke.
Data synthesis:
Trials: Data will be pooled by the generic inverse-variance method with DerSimonian and Laird
random-effects models and expressed as mean differences (MDs) with 95% confidence intervals
(95% CIs). Random-effects models were used as they account for residual heterogeneity and
yield more conservative estimates. Fixed-effects models will be used for <5 trials. Paired
analyses will be applied to all crossover trials. Heterogeneity will be tested by Cochran's Q
statistic and quantified by the I2 statistic. To explore sources of heterogeneity, we will
conduct sensitivity analyses, in which each study is systematically removed. If there are ≥10
trials, we will explore sources of heterogeneity by a priori subgroup analyses by study
design (parallel or crossover), follow-up duration (<12 weeks or ≥12 weeks), comparator diet,
baseline measurements, risk of bias, disease duration, and funding source. Significant
unexplained heterogeneity will be investigated by additional post hoc subgroup analyses (e.g.
age, sex, diet quality index, composition of the background diet [total % energy from fat,
carbohydrate, protein]). Meta-regression analyses will assess the significance of categorical
and continuous subgroups analyses. When ≥10 studies are available, publication bias will be
investigated by inspection of funnel plots and formal testing using the Egger and Begg tests.
If publication bias is suspected, we will attempt to adjust for funnel plot asymmetry by
imputing the missing study data using the Duval and Tweedie trim and fill method.
Prospective cohort studies: Natural log-transformed relative risks (RRs) or hazard ratios
(HRs) of clinical outcomes, comparing extreme quantiles (the highest exposure versus the
lowest exposure or reference group), will be pooled separately using the generic inverse
variance method with random effects models and expressed as RRs with 95% confidence intervals
(CIs). Heterogeneity will be tested by Cochran's Q statistic and quantified by the I2
statistic. To explore sources of heterogeneity, we will conduct sensitivity analyses, in
which each study is systematically removed. If ≥10 cohort comparisons were available, then we
will perform an a-priori subgroup analyses by meta-regression for follow-up (<10 years vs.
≥10 years), sex (males vs. females, males vs. mixed, females vs. mixed), study quality (NOS
<6 vs. ≥6) and funding source. Significant unexplained heterogeneity will be investigated by
additional post hoc subgroup analyses. Linear and non-linear dose-response relations will be
explored with the use of random-effects generalised least-squares trend estimation (GLST)
models and spline curve modeling (MKSPLINE procedure), respectively. When ≥10 studies are
available, publication bias will be investigated by inspection of funnel plots and formal
testing using the Egger and Begg tests. If publication bias is suspected, we will attempt to
adjust for funnel plot asymmetry by imputing the missing study data using the Duval and
Tweedie trim and fill method.
Evidence assessment: The certainty of the evidence for each outcome will be assessed using
the Grading of Recommendations Assessment, Development and Evaluation (GRADE).
Knowledge translation plan: The results will be disseminated through interactive
presentations at local, national, and international scientific meetings and publication in
high impact factor journals. Target audiences will include the public health and scientific
communities with interest in nutrition, diabetes, obesity, and cardiovascular disease.
Feedback will be incorporated and used to improve the public health message and key areas for
future research will be defined. Applicant/Co-applicant Decision Makers will network among
opinion leaders to increase awareness and participate directly as committee members in the
development of future guidelines.
Significance: The proposed project will aid in knowledge translation to the role of the
Nordic Diet in cardiovascular disease prevention and management, strengthening the
evidence-base for guidelines and improving health outcomes by educating healthcare providers
and patients, stimulating industry innovation, and guiding future research design.
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