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Open access Protocol
Effects of diet on obesity- related BMJ Open: first published as 10.1136/bmjopen-2021-050579 on 13 January 2022. Downloaded from
anthropometric characteristics in adults:
a protocol for an umbrella review of
meta- analyses of randomised
controlled trials
1 1 1 1 2
Shunlian Fu , Qian Zhou , Lijun Yuan, Zinan Li, Qiu Chen
To cite: Fu S, Zhou Q, Yuan L, ABSTRACT Strengths and limitations of this study
et al. Effects of diet on Introduction There have been many meta- analyses of
obesity- related anthropometric randomised controlled trials on the influence of different
characteristics in adults: a diets on obesity- related anthropometric characteristics in ► The included outcomes contain as comprehensive a
protocol for an umbrella review adults. However, whether diet interventions can effectively range of obesity-rela ted anthropometric character-
of meta- analyses of randomised decrease obesity- related anthropometric characteristics istics as possible.
controlled trials. BMJ Open remains unclear. The objective of this study is to ► A substantial number of original research papers
2022;12:e050579. doi:10.1136/ and participants are included.
bmjopen-2021-050579 summarise and synthesise the evidence on the effects ► This paper covers types of food as comprehensively
► Prepublication history and of diet on obesity- related anthropometric characteristics as possible.
additional supplemental material in adults by an umbrella review of meta- analyses of ► We will try to address the heterogeneity of included
for this paper are available randomised controlled trials. systematic reviews.
online. To view these files, Methods and analysis We will first retrieve English ► This umbrella review will be limited by including only
please visit the journal online articles only published before 15 December 2021 by full texts in English language.
(http://dx.doi.org/10.1136/ searching PubMed, Embase and Web of Science. Only
bmjopen-2021-050579). articles that are meta- analyses of randomised controlled
trials will be included. Three researchers will independently
Received 24 February 2021 screen the titles and abstracts of retrieved articles and 1–5
Accepted 21 December 2021 economics. What is more concerning is
check the data extracted from each eligible meta-analysis.
In each meta-analysis, we will consider calculating the that the number of individuals with obesity http://bmjopen.bmj.com/
and overweight continues to rise.2–7 Many
effect size of the mean difference of the effect of each studies have documented an association
diet on obesity- related anthropometric characteristics between obesity and various chronic diseases
in adults using a random- effect model or a fixed- effect
model according to heterogeneity. Study heterogeneity such as cancer, type 2 diabetes, cardiovas-
2 statistics) and small- study effects cular disease, hypertension, stroke, dyslip-
(Cochrane’s Q and I
2–6 8–10
(Egger’s test or Begg’s test) will be considered. Evidence of idaemia and reproductive disorder.
each effect size will be graded according to the NutriGrade People usually use a multifactorial stepwise
scoring system. We will use AMSTAR- 2 (A Measurement approach consisting of behavioural therapy, on January 4, 2023 by guest. Protected by copyright.
Tool to Assess Systematic Reviews V.2) to assess the lifestyle and dietary interventions, and
methodological quality of each meta- analysis. medical pharmacotherapy to manage obesity.
© Author(s) (or their Ethics and dissemination This umbrella review will However, interventions that are mostly based
employer(s)) 2022. Re- use provide information on the effects of different diets on on educational, behavioural or pharmaco-
permitted under CC BY- NC. No obesity- related anthropometric characteristics in adults.
commercial re- use. See rights Ethical approval is not necessary for this study. We will logical measures are not very effective in
11 12
and permissions. Published by publish the completed umbrella review and related data preventing and treating obesity. Over-
BMJ. online. weight/obesity is often caused by a long- term
1Hospital of Chengdu University PROSPERO registration number CRD42021232826. energy imbalance between intake and expen-
of Traditional Chinese Medicine, 13
Chengdu, Sichuan, China diture, leading to weight gain. Diet charac-
2Department of Endocrinology, terised by a low intake of high- energy- dense
Hospital of Chengdu University INTRODUCTION foods and a high intake of low- energy- dense
13
of Traditional Chinese Medicine, The problem of obesity and overweight has foods can counteract such an imbalance.
Chengdu, Sichuan, China become extremely serious either in adults Diet is a major modifiable determinant of
Correspondence to or in children, and in 2016 more than half obesity, and diet quality has been defined as
Dr Qiu Chen; of adults in the world were overweight or the degree to which a diet reduces the risk of
chenqiu1005@ cdutcm. edu. cn obese, putting a huge burden on global non- communicable diseases.14 15 Therefore,
Fu S, et al. BMJ Open 2022;12:e050579. doi:10.1136/bmjopen-2021-050579 1
Open access
dietary intervention is the cornerstone of addressing the inclusion criteria and exclusion criteria. A detailed flow BMJ Open: first published as 10.1136/bmjopen-2021-050579 on 13 January 2022. Downloaded from
obesity epidemic. chart of article selection is shown in online supplemental
Diet can produce changes in anthropometric param- figure 1. The second step is to make a forest plot showing
eters and body composition of overweight and obese the effect of different diets on different parameters. We
16 will score the included literature. If there are several
patients. Some studies found that whole grains, fruits,
nuts, beans and fish are associated with a reduced risk of included articles describing the effects of the same food
obesity, while refined grains, red meat and sugary bever- on the same obesity-related parameters, we will select the
13 17 18 one with the highest score and present them in a forest
ages are associated with an increased risk. After
extensive research, intervention studies have shown short- plot.
term effects between optimal intake of food and treat- Eligibility criteria
ment of obesity. However, there is little information on
the role of specific food groups and their optimal intake Types of participants
in preventing obesity. Also, there has been no study that The general human population will be considered,
focused on any existing evidence on the effect of dietary regardless of sex, race and region.
factors (single food and beverages, alcohol, macronutri- Types of exposure (intervention)
ents and micronutrients) on obesity-related anthropo - The intervention is the different types of diet. Based on
metric characteristics, including body mass index (BMI), 13 23 24
waist circumference (WC), body fat, hip circumference previously published literature, we will divide diets
(HC) and waist to hip ratio (WHR). Thus, it is critical into the following: dietary patterns, including ketogenic
to develop and evaluate the validity of dietary differences diet, Mediterranean diet, etc; food groups, foods and
and assess diet quality in a population, as well as test their beverages, including whole grain, fruit, nut, legume, dairy
ability to predict weight and adiposity. A clear public products, eggs, meat, fish, fats (eg, butter), oil, tea, garlic,
health plan that assesses the strength, precision and influ- gum, refined grains, sugar-sweetened beverages, etc; and
19–21 macronutrients, micronutrients (vitamins, minerals) and
ence of potential bias needs to be established. fibre.
Therefore, we plan to establish a clear public health plan
that provides potential new insights that can be used in Types of comparator
future research on developing preventive nutrition strat- Foods that were different from the intervention group
egies and a convenient tool to screen for those at risk of will be considered as the control group.
undernutrition or overnutrition. In this umbrella review
of meta- analyses, we aimed to conduct an umbrella review Types of outcome
of meta-analyses of randomised controlled trials (RCT) to The main outcome is the pooled mean difference in WC
comprehensively summarise and synthesise the evidence (in centimetres), pooled mean difference in BMI (in
on the effects of diet on obesity-related anthropometric kilograms per square metre), pooled mean difference in
characteristics in adults. Furthermore, we aimed to assess fat mass (body fat; in kilograms) or pooled mean differ- http://bmjopen.bmj.com/
methodological quality using validated tools to identify ence in HC (in centimetres). The secondary outcome is
the optimal intake of these food groups to reduce the risk pooled mean difference in weight change (in kilograms),
of each outcome separately. pooled mean difference in lean mass (in kilograms),
pooled mean difference in free fat mass (in kilograms) or
METHODS AND ANALYSIS pooled mean difference in WHR.
Protocol registration and reporting of findings
We have registered the article with the International Inclusion criteria
Prospective Register of Systematic Reviews (https:// We considered including meta-analyses of RCT because on January 4, 2023 by guest. Protected by copyright.
www.crd.york.ac.uk/prospero/) on 23 January 2021. We the results of RCT are more convincing than the results of
25
referred to the Preferred Reporting Items for Systematic other types of studies. We aimed to study the influence
22 of diet on obesity-related parameters in adults. Because
Analysis Protocols 2015 checklist (see
Review and Meta-
online supplemental table 1). We will provide any amend- body weight, WC and other anthropometric parameters
ments to the protocol as supplementary materials in the in adults are not as susceptible to growth and develop-
publication of the final results. ment, the results on the influence of diet on these anthro-
Patient and public involvement pometric parameters could be more reliable. To better
The study is an umbrella review focusing on the effects and more accurately evaluate the impact of these foods
of diet on obesity-related anthropometric characteris - on obesity-related parameters, we will only consider
tics. We did not set any restrictions to region or sex of including articles where the outcomes contain at least
the included population. There is no patient or public two of the following items: WC, BMI, fat mass (body fat)
involvement in this study. and HC. Meanwhile, to better compare the influence
of different foods on obesity-related parameters, we will
Study design unify the units of these weight parameters as follows: WC
We divide the process into two steps. The first step is in centimetres, BMI in kilograms per square metre, fat
to screen out the included literature according to the mass in kilograms and HC in centimetres. At the same
2 Fu S, et al. BMJ Open 2022;12:e050579. doi:10.1136/bmjopen-2021-050579
Open access
time, to quantitatively study the effects of these foods on number of included studies, intervention diet, control BMJ Open: first published as 10.1136/bmjopen-2021-050579 on 13 January 2022. Downloaded from
obesity- related parameters, we will consider including diet, number of included studies, number of subjects
articles that reported pooled mean difference in obesity- included in the intervention group, number of subjects
related parameters between the intervention and the included in the control group, duration of interven-
control group. tion, study population, outcomes of interest, baseline of
outcomes of interest and the final results after the inter-
Exclusion criteria vention. All data will be recorded in Excel according to
We will not include articles on the effects of diet on obesity- previously designed content.
related parameters among pregnant and lactating women
given that pregnant and lactating women are highly Assessment of methodological quality and of certainty in the
influenced by other factors. We will not include confer- findings
ences, abstracts, correspondence, etc. If an article has We will assess the quality of included systematic reviews
incomplete data, we will exclude the article if complete using AMSTAR- 2 (A Measurement Tool to Assess System-
27
data cannot be obtained after contacting the author. We atic Reviews V.2), which includes 16 items (7 critical
will not include articles that examine the effects of diet domains and 9 non- critical domains). According to the
on obesity- related parameters among people with infec- tool, two reviewers will classify the results of the included
tious diseases, severe acute and chronic diseases, etc. We systematic reviews as high, moderate, low and critically
will also exclude articles where we could not identify the low. If the study has no or one non- critical weakness, we
effect of the intervention food on obesity-related parame - will appraise it as high; if more than one non-critical weak -
ters. To quantitatively study the effects of diet on obesity- ness, we will appraise it as moderate; if one critical flaw
related parameters, we will not include systematic reviews with or without non-critical weakness, we will appraise it
without meta- analysis. as low; and if more than one critical flaw with or without
non- critical weakness, we will appraise it as critically low.
Information source and search strategy 28
In addition, we will carry out NutriGrade grading
We will only retrieve English articles published before 15 for obesity- related parameters for each diet to assess
December 2021 by searching PubMed and Embase. We 28
certainty in the findings. The NutriGrade scoring system
did not set any restrictions when searching. We will only comprises seven items with a total score of 10 for system-
include articles that are meta- analyses of RCT. There have atic reviews and meta- analyses of RCT. The following are
been several umbrella reviews that summarised the role the seven items: (1) risk of bias, study quality and study
23 24 26
of diet in type 2 diabetes incidence, and by refer- limitations (3 points); (2) precision (1 point); (3) hetero-
ring to their search terms we determined the following geneity (1 point); (4) directness of evidence (1 point);
keywords: diet or beverages or soy or sugar or egg or (5) publication bias (1 point); (6) funding bias (1 point);
macronutrient or micronutrient. More details are shown and (7) study design (2 points). Studies with a total score
in online supplemental tables 2 and 3. We will import the of ≥8, 6–7.99, 4–5.99 and 0–3.99 points are graded as http://bmjopen.bmj.com/
search results into the EndNote V.X9 software and use having high, moderate, low and very low confidence in
it to remove duplicate articles. We will also include grey the effect estimate, respectively.
literature. If necessary, we will contact the corresponding
authors of the included systematic reviews to collect Data analysis
missing data on the main endpoints or to ask regarding First, we will recalculate the summary effect and 95% CI
unclear information. using a random- effect model by DerSimonian and Laird
after adjusting for most confounders in the published
Data extraction meta- analyses. If the same outcome is presented by on January 4, 2023 by guest. Protected by copyright.
Two researchers will separately check the data extracted sex or race in the published meta-analysis, we will first
from each eligible meta-analysis. If there is a disagree - combine the effect size using fixed-effect methods before
ment, a third researcher will join the analysis. We will conducting the overall meta-analysis. Second, we will use
extract the following data from the included meta- 2
I statistics or Cochran’s Q test to determine the magni-
analyses: first author and year of publication, number of 29
tude of heterogeneity. For Cochrane’s Q test, we will
included studies, intervention diet, control diet, number consider the result as significant heterogeneity when
of included studies, number of subjects included in the 2
p<0.1; for I statistics, we will classify the result as signif-
intervention group, number of subjects included in the 2
icant heterogeneity when the I value is ≤50%. Third, we
control group, duration of intervention, study popula- will estimate publication bias and small- study effect by
tion, outcomes of interest and pooled effect size of the Egger’s test (as confirmed by a p value of <0.1) or Begg’s
mean difference of outcomes of interest, along with 95% 30
test (as confirmed by a p value of <0.1). If the published
CI, p values, heterogeneity (I index), publication bias meta- analysis has missing information, we will not recal-
(Egger’s test and Begg’s test values) and the quality of culate the meta- analysis and will only extract the effect
the studies included in each meta-analysis. For primar y size. In addition, a series of subgroup analyses, such as
studies included in the meta-analyses, we will extract classification by disease, sex and race, will be performed.
the following data: first author and year of publication, We will also show our results according to food groups,
Fu S, et al. BMJ Open 2022;12:e050579. doi:10.1136/bmjopen-2021-050579 3
Open access
such as whole grains, refined grains, fruit, nut, legume, ETHICS AND DISSEMINATION BMJ Open: first published as 10.1136/bmjopen-2021-050579 on 13 January 2022. Downloaded from
dairy products, eggs, meat, fish, fats, oil, tea, garlic, This is an umbrella review. We will not conduct any exper-
gum and sugar- sweetened beverages. Finally, we will use iments on humans or animals so we will not consider an
AMSTAR- 2 to assess the methodological quality in tabular ethical review. We will publish the results of this umbrella
form for each review. NutriGrade will be used to evaluate review in a peer- reviewed journal.
the quality of evidence, which will be presented in tabular
form. All statistical analyses will be conducted using Contributors All authors contributed to the design of this protocol. SF, QZ, LY,
Review Manager (RevMan, V.5.3 for Macintosh; The ZL and QC initiated the project. The protocol was drafted by SF and was refined
Cochrane Collaboration) and the PASW V.20.0 statistical by QZ. Statistical advice was provided by QC. SF was responsible for drafting the
manuscript. All authors contributed to the manuscript and read and approved the
package for Macintosh (SPSS). final manuscript.
Funding The article is funded by the ‘Pilot project of collaboration between
traditional Chinese medicine and western medicine for major and difficult diseases’
(CYW2019079) and the funder was not involved in the writing.
DISCUSSION Competing interests None declared.
By an umbrella review of meta-analyses of RCT , Dinu et Patient consent for publication Not required.
31
al published an article on the effects of popular diets Provenance and peer review Not commissioned; externally peer reviewed.
on anthropometric and cardiometabolic parameters. Supplemental material This content has been supplied by the author(s). It has
However, they only sorted out the effects of dietary not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been
patterns on BMI and weight, as well as other cardiometa- peer- reviewed. Any opinions or recommendations discussed are solely those
32 of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and
bolic parameters. Akhlaghi and colleagues thought soy
showed no overall statistically significant effect on weight, responsibility arising from any reliance placed on the content. Where the content
33 includes any translated material, BMJ does not warrant the accuracy and reliability
WC or fat mass. However, Mu and colleagues held that of the translations (including but not limited to local regulations, clinical guidelines,
soy products significantly reduced body weight, BMI, terminology, drug names and drug dosages), and is not responsible for any error
body fat per cent and WC in overweight or obese Asian and/or omissions arising from translation and adaptation or otherwise.
populations, and more significant effects were observed Open access This is an open access article distributed in accordance with the
34 Creative Commons Attribution Non Commercial (CC BY- NC 4.0) license, which
in non- menopausal women. Asbaghi and colleagues permits others to distribute, remix, adapt, build upon this work non-commercially ,
found that magnesium supplementation did not affect and license their derivative works on different terms, provided the original work is
35
body weight, BMI and WC, while Askari et al found properly cited, appropriate credit is given, any changes made indicated, and the use
a significant reduction in BMI following magnesium is non- commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
36
supplementation and Rafiee et al found that magne- ORCID iDs
sium supplementation was associated with lower WC only Shunlian Fu http://orcid.org/0000-0003-2002-6606
in obese subjects. Qian Zhou http://orcid.org/0000-0001-6957-9821
Generally, interventional studies that investigate the
relationship between food intake and obesity-related http://bmjopen.bmj.com/
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