Systematic reviews and meta-analysis in nutrition research

A Meta-Analysis of the Effects of Dietary Yeast Mannan-Rich Fraction on Broiler Performance and the Implication for Greenhouse Gas Emissions from Chicken Production

Dietary supplementation of yeast-derived mannan-rich fraction (MRF) could improve the gastrointestinal health and production efficiency of broilers, and, consequently, lower the environmental impacts of chicken production. The objective of this meta-analysis was to quantify the retrospective effects of feeding MRF (Actigen®, Alltech Inc., Nicholasville, KY) on the production performance of broilers. The meta-analysis database included 27 studies and consisted of 66 comparisons of MRF-supplemented diets vs. basal (i.e., negative control) and antibiotic-supplemented (i.e., positive control) diets. A total of 34,596 broilers were involved in the comparisons and the average final age of the birds was 35 days. Additionally, the impact of feeding MRF on the carbon footprint (feed and total emission intensities) of chicken production was evaluated using the meta-analysis results of broiler performance (MRF vs. basal diets) to develop a scenario simulation that was analyzed by a life cycle assessment (LCA) model. A database of all trials (MRF vs. basal and antibiotic diets) indicated that feeding MRF increased (p < 0.01) average daily feed intake (ADFI; +3.7%), final body weight (FBW; +3.5%), and average daily gain (ADG; 4.1%) and improved (p < 0.01) feed conversion ratio (FCR; -1.7%) without affecting (p > 0.05) mortality. A subdatabase of MRF vs. basal diets indicated that dietary MRF increased ADFI (+4.5%), FBW (+4.7%), and ADG (+6.3%) and improved FCR (-2.2%) and mortality (-21.1%). For the subdatabase of MRF vs. antibiotic diets, both treatments exhibited equivalent effects (p > 0.05) on broiler performance parameters, suggesting that MRF could be an effective alternative to in-feed antibiotics. Subgroup analysis revealed that different study factors (year of study, breed/strain, production challenges, and MRF feeding duration) influenced the effect of dietary MRF on broiler performance. Simulated life cycle analysis (LCA) indicated that feeding MRF decreased feed and total emission intensities, on average, by -2.4% and -2.1%, respectively. In conclusion, these results demonstrate that dietary MRF is an effective nutritional solution for improving broiler performance, an effective alternative to in-feed antibiotic growth promoters, and reduces the environmental impact of poultry meat production.

Using meta-analysis to understand the impacts of dietary protein and fat content on the composition of fecal microbiota of domestic dogs (Canis lupus familiaris): A pilot study

The interplay between diet and fecal microbiota composition is garnering increased interest across various host species, including domestic dogs. While the influence of dietary macronutrients and their associated microbial communities have been extensively reviewed, these reviews are descriptive and do not account for differences in microbial community analysis, nor do they standardize macronutrient content across studies. To address this, a meta-analysis was performed to assess the impact of dietary crude protein ("protein") and dietary crude fat ("fat") on the fecal microbiota composition in healthy dogs. Sixteen publications met the eligibility criteria for the meta-analysis, yielding a final data set of 314 dogs. Diets were classed as low, moderate, high, or supra in terms of protein or fat content. Sequence data from each publication were retrieved from public databases and reanalyzed using consistent bioinformatic pipelines. Analysis of community diversity indices and unsupervised clustering of the data with principal coordinate analysis revealed a small effect size and complete overlap between protein and fat levels at the overall community level. Supervised clustering through random forest analysis and partial least squares-discriminant analysis indicated alterations in the fecal microbiota composition at a more individual taxonomic level, corresponding to the levels of protein or fat. The Prevotellaceae Ga6A1 group and Enterococcus were associated with increasing levels of protein, while Allobaculum and Clostridium sensu stricto 13 were associated with increasing levels of fat. Interestingly, the random forest analyses revealed that Sharpea, despite its low relative abundance in the dog's fecal microbiome, was primarily responsible for the separation of the microbiome for both protein and fat. Future research should focus on validating and understanding the functional roles of these relatively low-abundant genera.

Improving sarcopenia in older adults: a systematic review and meta-analysis of randomized controlled trials of whey protein supplementation with or without resistance training

OBJECTIVES

The aim of the study was to comprehensively analyze the effects of whey protein (WP)-enriched supplement intake with or without resistance training (RT) in older patients, either from the community or hospital, who were diagnosed with sarcopenia according to the EWGSOP or AWGS criteria.

METHODS

This meta-analysis study was registered in PROSPERO (CRD42023407885). We searched the PubMed, Embase, Web of Science, and Cochrane Library databases for RCTs up to June 1, 2023. Standardized mean differences (SMD) with 95% confidence intervals (CI) were used to estimate the pooled results.

RESULTS

Ten RCT studies, including 1154 participants, were included and analyzed. The primary outcomes were the changes in muscle mass, strength, and physical performance. In WP group versus (vs.) Isocaloric placebo (PLA)/Routine consultation (RC) group, WP significantly increased the appendicular skeletal muscle mass index (SMD: 0.47, 95%CI: 0.23, 0.71), appendicular skeletal muscle mass (SMD: 0.28, 95%CI: 0.11, 0.45) and gait speed (SMD: 1.13, 95%CI: 0.82, 1.44) in older patients with sarcopenia. In WP with RT group vs. PLA/ RC group, there was significant increase in handgrip strength (SMD: 0.67, 95%CI: 0.29, 1.04). In addition, in the secondary outcomes, WP significantly reduced interleukin-6, significantly increased insulin-like growth factor-1 and albumin, promoted participants' intake of total energy and protein, enhanced activities of daily living scores in patients, and had no significant effect on BMI, weight, or fat mass.

CONCLUSION

This review confirms that WP can improve various aspects of older adult with sarcopenia, thereby enhancing their overall physical condition. More studies should be conducted to validate this result and further explore the effects of WP and RT in patients with sarcopenia.

A systematic review and meta-analysis of randomized controlled trials to evaluate plant-based omega-3 polyunsaturated fatty acids in nonalcoholic fatty liver disease patient biomarkers and parameters

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is prevalent in 25-30% of British and European populations, representing a potential global public health crisis. Marine omega-3 (n-3) polyunsaturated fatty acids offer well-evidenced benefits to NAFLD biomarkers; however, the effect of plant-based n-3 has not been evaluated with a systematic review and meta-analysis.

OBJECTIVE

The review aimed to systematically evaluate the effect of plant-based n-3 supplementation on NAFLD surrogate biomarkers and parameters.

DATA SOURCES

Medline (EBSCO), PubMed, CINAHL (EBSCO), Cochrane Central Register of Controlled Trials, the International Clinical Trials Registry Platform, and Google Scholar databases were searched to identify randomized controlled trials published between January 1970 and March 2022 evaluating the impact of plant-based n-3 interventions on diagnosed NAFLD. The review followed the PRISMA checklist and is PROSPERO registered (CRD42021251980).

DATA EXTRACTION

A random-effects model and generic inverse variance methods synthesized quantitative data, followed by a leave-one-out method for sensitivity analysis. We identified 986 articles; after the application of selection criteria, six studies remained with 362 patients with NAFLD.

RESULTS

The meta-analysis showed that plant-based n-3 fatty acid supplementation significantly reduced alanine aminotransferase (ALT) (mean difference: 8.04 IU/L; 95% confidence interval: 14.70, 1.38; I2 = 48.61%) and plasma/serum triglycerides (44.51 mg/dL; 95% confidence interval: -76.93, -12.08; I2 = 69.93%), alongside body-composition markers in patients with NAFLD (P < 0.05).

CONCLUSION

Plant-based n-3 fatty acid supplementation improves ALT enzyme biomarkers, triglycerides, body mass index, waist circumference, and weight loss when combined with lifestyle interventions to increase physical activity and a calorie-controlled diet. Further research is needed to identify the most effective plant-based n-3 sources in larger numbers of patients with NAFLD over longer study durations.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42021251980.

Gathering the Evidence on Diet and Depression: A Protocol for an Umbrella Review and Updated Meta-Analyses

Our objectives are to perform (1) an umbrella review on diet and depression, (2) a systematic review update on dietary patterns and depression, and (3) updated meta-analyses using studies from the previous two objectives. Systematic reviews examining the relationships between diet and depression and primary studies on the relationship between dietary patterns and depression will be systematically retrieved via several databases. All articles identified through the database searches will be imported into Covidence. Following duplicates removal, two authors will independently perform title and abstract screening and full-text assessment against eligibility criteria. Data will be extracted using tables developed for both systematic reviews and primary studies. The methodological quality of systematic reviews will be assessed using the AMSTAR-2 tool. The risk of bias in randomized trials, cohort and cross-sectional studies, as well as case-control studies, will be assessed with the Cochrane risk-of-bias (RoB-2) tool, the NHLBI Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, and the NHLBI Quality Assessment Tool for Case-Control studies, respectively. For each dietary variable, data extracted will be used to produce: (1) a summary of systematic reviews' characteristics and results table, (2) a summary of the primary studies characteristics table, (3) a qualitative summary of results from the primary studies table, and (4) a quantitative summary of results in the form of forest plots. The certainty of evidence will be assessed using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. Upon completion, this systematic review will be the most comprehensive and up-to-date synthesis of currently available evidence on the relationships between diet and depression. It will serve as a key reference to guide future research and as a resource for health professionals in the fields of nutrition and psychiatry. PROSPERO CRD42022343253.

The Influence of n-3PUFA Supplementation on Muscle Strength, Mass, and Function: A Systematic Review and Meta-Analysis

The effects of omega 3 polyunsaturated fatty acids (n-3PUFA) supplementation on skeletal muscle are currently unclear. The purpose of this systematic review was to synthesize all available evidence regarding the influence of n-3PUFA supplementation on muscle mass, strength, and function in healthy young and older adults. Four databases were searched (Medline, Embase, Cochrane CENTRAL, and SportDiscus). Predefined eligibility criteria were determined according to Population, Intervention, Comparator, Outcomes, and Study Design. Only peer-reviewed studies were included. The Cochrane RoB2 Tool and the NutriGrade approach were used to access risk of bias and certainty in evidence. Effect sizes were calculated using pre-post scores and analyzed using a three-level, random-effects meta-analysis. When sufficient studies were available, subanalyses were performed in the muscle mass, strength, and function outcomes according to participant's age (<60 or ≥60 years), supplementation dosage (<2 or ≥2 g/day), and training intervention ("resistance training" vs. "none or other"). Overall, 14 individual studies were included, total 1443 participants (913 females; 520 males) and 52 outcomes measures. Studies had high overall risk of bias and consideration of all NutriGrade elements resulted in a certainty assessment of moderate meta-evidence for all outcomes. n-3PUFA supplementation had no significant effect on muscle mass (standard mean difference [SMD] = 0.07 [95% CI: -0.02, 0.17], P = 0.11) and muscle function (SMD = 0.03 [95% CI: -0.09, 0.15], P = 0.58), but it showed a very small albeit significant positive effect on muscle strength (SMD = 0.12 [95% CI: 0.006, 0.24], P = 0.04) in participants when compared with placebo. Subgroup analyses showed that age, supplementation dose, or cosupplementation alongside resistance training did not influence these responses. In conclusion, our analyses indicated that n-3PUFA supplementation may lead to very small increases in muscle strength but did not impact muscle mass and function in healthy young and older adults. To our knowledge, this is the first review and meta-analysis investigating whether n-3PUFA supplementation can lead to increases in muscle strength, mass, and function in healthy adults. Registered protocol: doi.org/10.17605/OSF.IO/2FWQT.

The effects of consuming a Mediterranean style diet on associated COVID-19 severity biomarkers in obese/overweight adults: A systematic review

Background

COVID-19 severity is strongly associated with high Body Mass Index (BMI) (≥25kg/m²) amongst adults and elevated inflammatory markers have enabled prediction of disease progression. The composition of a Mediterranean diet provides favourable outcomes on weight reduction and inflammatory markers.

Aim

This systematic review aimed to investigate the effects of consuming a Mediterranean diet on BMI and inflammatory markers of obese/overweight adults (≥18 years) at risk of developing severe COVID-19 outcomes.

Methods

PubMed Central, Cochrane Library and MEDLINE databases were searched to identify randomised controlled trials published between January 2010 to August 2021 evaluating the impact of Mediterranean diet on BMI and inflammatory markers in overweight/obese adults. The review followed the PRISMA checklist, used Cochrane Collaboration search strategies, and is PROSPERO registered (CRD42021277070). Two authors independently screened and evaluated studies for methodological quality. Papers were extracted and included based eligibility, despite risk of bias scores.

Results

Of 65 extracted records, six studies met the eligibility criteria and were included. Reductions in BMI, TNF-α, IL-6 and hs-CRP were reported amongst most findings, the majority of which were significant.

Conclusion

The main findings indicate a hypocaloric, fibre dense Mediterranean diet is a short-term (<4 months) mitigation strategy to significantly reduce BMI and inflammatory markers amongst overweight/obese adults at risk of developing severe COVID-19 outcomes. Further research is now needed to examine the role of Mediterranean diet in COVID-19 prevalence, severity, morbidity and mortality.

The Effect of Vitamin D Supplementation on the Severity of Symptoms and the Quality of Life in Irritable Bowel Syndrome Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Irritable bowel syndrome (IBS), a gastrointestinal disorder affecting 7–12% of the population, is characterized by abdominal pain, bloating, and alternating bowel patterns. Data on risk and protective influences have yielded conflicting evidence on the effects of alternative interventions, such as vitamin D. This review focuses on the effects of vitamin D on IBS. A systematic review and meta-analysis considered all articles published until 4 April 2022. The search for randomized controlled trials assessing vitamin D efficacy in IBS with outcomes, primary (Irritable Bowel Severity Scoring System (IBS-SSS)) and secondary (IBS quality of life (IBS-QoL) and serum level of calcifediol (25(OH)D)), was performed on six databases, Google Scholar, Web of Science, SCOPUS, EMBASE, PubMed (MEDLINE), and Cochrane Central Register of Controlled Trials. We included six trials with 616 patients. The pooled analysis found no difference between vitamin D and placebo in improving IBS-SSS (MD: −45.82 with 95% CI [−93.62, 1.98], p = 0.06). However, the pooled analysis favored vitamin D over placebo in improving the IBS-Qol (MD: 6.19 with 95% CI [0.35, 12.03], p = 0.04) and serum 25(OH)D (MD: 25.2 with 95% CI [18.41, 31.98], p = 0.00001). Therefore, further clinical trials are required to reach clinically applicable and generalizable findings.

Commentary on 'Guidelines for the provision of nutrition support therapy in the adult critically ill patient: The American Society for Parenteral and Enteral Nutrition'

As authors of recent meta-analyses evaluating lipids for parenteral nutrition^1,2 and/or the ESPEN Expert Group: lipids in the intensive care unit³ we welcome the updating of the ASPEN guidelines for clinical nutrition in adult critically ill patients,⁴ but would like to remark on certain aspects that cause us concern This article is protected by copyright. All rights reserved.

Methods used to select results to include in meta-analyses of nutrition research: a meta-research study

OBJECTIVES

To investigate how often review authors encounter multiple results from included studies that are eligible for inclusion in a particular meta-analysis, and how often methods to select results are specified.

METHODS

MEDLINE and Epistemonikos were searched (January 2018 - June 2019) to identify systematic reviews with meta-analysis of the association between food/diet and health-related outcomes. A random sample of these reviews was selected, and for the first presented ('index') meta-analysis, rules used to select effect estimates to include in this meta-analysis were extracted from the reviews and their protocols. All effect estimates from the primary studies that were eligible for inclusion in the index meta-analyses were extracted (e.g. when a study report presented effect estimates for blood pressure at 3 weeks and 6 weeks, both unadjusted and adjusted for covariates, and all were eligible for inclusion in a meta-analysis of the effect of red meat consumption on blood pressure, we extracted all estimates and classified the study as having "multiplicity of results").

RESULTS

Forty-two systematic reviews with 325 studies (104 randomized, 221 non-randomized) were included; 14 reviews had a protocol. In 29% of review protocols and 69% of reviews, authors specified at least one decision rule to select effect estimates when multiple were available. In 68% of studies included in the index meta-analyses, there was at least one type of multiplicity of results.

CONCLUSIONS

Authors of systematic reviews of nutrition studies should anticipate encountering multiplicity of results in the included primary studies. Specification of methods to handle multiplicity when designing reviews is therefore recommended.

Individual Participant Data Meta-Analysis Provides No Evidence of Intervention Response Variation in Individuals Supplementing With Beta-Alanine

Currently, little is known about the extent of interindividual variability in response to beta-alanine (BA) supplementation, nor what proportion of said variability can be attributed to external factors or to the intervention itself (intervention response). To investigate this, individual participant data on the effect of BA supplementation on a high-intensity cycling capacity test (CCT110%) were meta-analyzed. Changes in time to exhaustion (TTE) and muscle carnosine were the primary and secondary outcomes. Multilevel distributional Bayesian models were used to estimate the mean and SD of BA and placebo group change scores. The relative sizes of group SDs were used to infer whether observed variation in change scores were due to intervention or non-intervention-related effects. Six eligible studies were identified, and individual data were obtained from four of these. Analyses showed a group effect of BA supplementation on TTE (7.7, 95% credible interval [CrI] [1.3, 14.3] s) and muscle carnosine (18.1, 95% CrI [14.5, 21.9] mmol/kg DM). A large intervention response variation was identified for muscle carnosine (σIR = 5.8, 95% CrI [4.2, 7.4] mmol/kg DM) while equivalent change score SDs were shown for TTE in both the placebo (16.1, 95% CrI [13.0, 21.3] s) and BA (15.9, 95% CrI [13.0, 20.0] s) conditions, with the probability that SD was greater in placebo being 0.64. In conclusion, the similarity in observed change score SDs between groups for TTE indicates the source of variation is common to both groups, and therefore unrelated to the supplement itself, likely originating instead from external factors such as nutritional intake, sleep patterns, or training status.

Lysine requirements of finishing boars and gilts: A meta-analysis

The expected increase in boar (pig entire male) production while societal concerns for castration increase requires good estimations of their nutrient requirements. In this work, a meta-analytical approach was used to overcome the inconsistent results between studies that compared lysine requirements of boars and gilts. For this meta-analysis, data from 14 different studies analysing the effect of increasing dietary lysine on growth performance of finishing pigs, 70-100 kg average body weight, were extracted from 11 publications. Those studies represented 128 different treatments (53 for boars and 75 for gilts). Diets were reformulated based on NRC (2012) ingredient values to calculate standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and daily SID Lys intake using average daily feed intake (ADFI). As expected, no evidence for differences in ADFI (P = 0.303) was observed between boars and gilts. However, boars grew faster (P < 0.001) and had higher gain to feed (G:F; P < 0.001). The divergent effect of SID Lys:NE on average daily gain (ADG) and G:F was analysed in a quadratic polynomial model showing different parameters for each sex (P < 0.001). Although performance between sexes was similar at low SID Lys:NE, differences were greater at higher SID Lys:NE. Furthermore, broken-line linear, broken-line quadratic (BLQ) and quadratic polynomial (QP) models were fitted to each sex to determine SID Lys:NE and SID Lys daily intake requirements to maximize ADG and G:F. Overall, QP models showed the best fit, and reported that to reach maximum ADG 0.88 (95% CI:[0.82-0.94]) or 1.01 (95% CI:[0.91-1.11]) g SID Lys/MJ, NE was required for gilts and boars, respectively. However, boar ADG was best fitted by BLQ using SID Lys daily intake as independent variable, with the requirement for maximum ADG at 24.2 (95% CI:[21.3-27.2]) g SID Lys/day. The three models reported wide confidence intervals for the requirements at maximum performance, and consequently those were overlapped when comparing boars and gilts. Maximum boars' productive performance when dietary lysine was not limiting was 116% of gilts, and at those levels the amount of SID Lys intake required per kg gain was similar between both sexes. Thus, because ADFI and Lys efficiency of gain was similar, the requirement differences were driven by the increased growth rate and gain to feed ratio between boars and gilts. In conclusion, the present study confirmed a greater productive response of boars compared to gilts when increasing dietary lysine.

Interventions to improve physical activity in colorectal cancer survivors: protocol for a systematic review and meta-analysis of randomized controlled trials

AIM

To examine the effectiveness of physical activity (PA) interventions on changes in PA among colorectal cancer survivors, including an examination of theoretical versus atheoretical-driven approaches, with a special focus on their effectiveness across ethnic and racial minorities.

DESIGN

Systematic review with aggregated data meta-analyses.

DATA SOURCES

Using six databases (Cochrane Central Register of Controlled Trials, PubMed, PsycINFO, CINAHL with full text, Scopus and Web of Science), we will screen for randomized controlled trials written in English from May 1, 1993 up to December 31, 2020.

REVIEW METHODS

Dual study-selection and data abstraction will be performed. The Behavior Change Technique Taxonomy (v1) will be used to examine behavior change techniques among selected studies, while the Theory Coding Scheme will be used to assess the extent of theory use. Risk of bias will be assessed using the revised Cochrane risk-of-bias tool for randomized trials, while the strength of the evidence will be assessed using the Grading of Recommendations Assessment, Development, and Evaluation instrument. In addition, intervention delivery will be appraised using the Template for Intervention Description and Replication. Changes in PA from each study will be calculated using the standardized mean difference effect size (Hedge's g). Results will be pooled using the inverse-variance heterogeneity model. Heterogeneity (Cochran's Q) and inconsistency (I² ) will be examined, while small-study effects (publication bias) will be evaluated using the Doi plot and LFK Index. Meta-regression will also be conducted to examine for potential associations between changes in physical activity and selected covariates (theoretical versus atheoretical-driven approaches, race/ethnicity).

DISCUSSION

This systematic review will identify specific racial/ethnic minorities for whom interventions are most effective and summarize the evidence of the effectiveness of theoretical vs. theoretical based intervention.

IMPACT

This systematic review can direct policymakers and practitioners towards actions that are likely to bring about positive physical activity behaviour change.

The influence of acute exercise on bone biomarkers: protocol for a systematic review with meta-analysis

BACKGROUND

Bone is a plastic tissue that is responsive to its physical environment. As a result, exercise interventions represent a potential means to influence the bone. However, little is currently known about how various exercise and participant characteristics interact to influence bone metabolism. Acute, controlled, interventions provide an in vivo model through which the acute bone response to exercise can be investigated, typically by monitoring circulating bone biomarkers. Currently, substantial heterogeneity in factors such as study design, quality, exercise, and participant characteristics render it difficult to synthesize and evaluate the available evidence. Using a systematic review and meta-analytic approach, the aim of this investigation is to quantify the effect of an acute exercise bout on circulating bone biomarkers as well as examine the potential factors that may moderate this response, e.g., variation in participant, exercise, and sampling characteristics.

METHODS

This protocol was designed in accordance with the PRISMA-P guidelines. Seven databases (MEDLINE, Embase, Sport Discus, Cochrane CENTRAL, PEDro, LILACS, and Ibec) will be systematically searched and supplemented by a secondary screening of the reference lists of all included articles. The PICOS (Population, Intervention, Comparator, Outcomes and Study Design) approach was used to guide the determination of the eligibility criteria. Participants of any age, sex, training, or health status will be considered for inclusion. We will select studies that have measured the bone biomarker response before and after an acute exercise session. All biomarkers considered to represent the bone metabolism will be considered for inclusion, and sensitivity analyses will be conducted using reference biomarkers for the measurement of bone resorption and formation (namely β-CTX-1 and P1NP). Multi-level, meta-regression models within a Bayesian framework will be used to explore the main effect of acute exercise on bone biomarkers as well as potential moderating factors. The risk of bias for each individual study will be evaluated using a modified version of the Downs and Black checklist while certainty in resultant outcomes will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

DISCUSSION

A better understanding of the bone metabolic response to an acute bout of exercise has the potential to advance our understanding of the mechanisms through which this stimulus impacts bone metabolism, including factors that may moderate this response. Additionally, we will identify current gaps in the evidence base and provide recommendations to inform future research.

SYSTEMATIC REVIEW REGISTRATION

This protocol was prospectively registered in the Open Science Framework Registry ( https://osf.io/6f8dz ).

Relative validity of FFQ to assess food items, energy, macronutrient and micronutrient intake in children and adolescents: a systematic review with meta-analysis

FFQ are one of the most widely used tools of research into nutritional epidemiology, and many studies have been conducted in several countries using this dietary assessment method. The present study aimed to evaluate the relative validity of FFQ, in comparison with other methods, in assessing dietary intake of children and adolescents, through a systematic review. Four electronic databases (Embase, PubMed, Scopus and Web of Science) found sixty-seven articles, which met the inclusion criteria (healthy children and adolescents from 3 to 18 years of age; journal articles written in English, Spanish and Portuguese between 1988 and March 2019; results showing the comparison between the FFQ with other methods of assessment of dietary intake). The articles were analysed by two independent reviewers. A meta-analysis was conducted using correlation coefficients as estimate effects between the FFQ and the reference standard method. Subgroup analysis and meta-regression were performed to identify the probable source of heterogeneity. In fifty-five of the sixty-seven studies, a single dietary assessment method was used to evaluate the FFQ; nine combined the two methods and three used three reference methods. The most widely used reference method was the 24-h recall, followed by the food record. The overall relative validity of the FFQ to estimate energy, macronutrient, certain micronutrient and certain food item intakes in children and adolescents may be considered weak. The study protocol was registered in PROSPERO under number CRD42016038706.