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The effect of flaxseed supplementation on body weight and body composition: A systematic review and meta-analysis of 45 randomized placebo-controlled trials

Authors:
  • Institute of Social and Preventive Medicine, University of Bern

Abstract

Flaxseed consumption may be inversely associated with obesity; however, findings of available randomized controlled trials (RCTs) are conflicting. The present study aimed to systematically review and analyse RCTs assessing the effects of flaxseed consumption on body weight and body composition. PubMed, Medline via Ovid, SCOPUS, EMBASE and ISI Web of Sciences databases were searched up to November 2016. Mean changes in body composition indices including body weight, body mass index (BMI) and waist circumference were extracted. Effect sizes were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). Heterogeneity between studies was assessed with the I(2) test. Publication bias and subgroup analyses were also performed. The quality of articles was assessed via the Jadad scale. A total of 45 RCTs were included. Meta-analyses suggested a significant reduction in body weight (WMD: -0.99 kg, 95% CI: -1.67, -0.31, p = 0.004), BMI (WMD: -0.30 kg m(-2) , 95% CI: -0.53, -0.08, p = 0.008) and waist circumference (WMD: -0.80 cm, 95% CI: -1.40, -0.20, p = 0.008) following flaxseed supplementation. Subgroup analyses showed that using whole flaxseed in doses ≥30 g d(-1) , longer-term interventions (≥12 weeks) and studies including participants with higher BMI (≥ 27 kg m(-2) ) had positive effects on body composition. Whole flaxseed is a good choice for weight management particularly for weight reduction in overweight and obese participants.
Obesity Treatment/Prevention
The effect of flaxseed supplementation on body weight
and body composition: a systematic review and meta-
analysis of 45 randomized placebo-controlled trials
M. Mohammadi-Sartang,
1,2
Z. Mazloom,
1,2
H. Raeisi-Dehkordi,
1,2
R. Barati-Boldaji,
2,3
N. Bellissimo
4
and
J. O. Totosy de Zepetnek
4
1
Department of Clinical Nutrition, School of
Nutrition and Food Sciences, Shiraz University
of Medical Sciences, Shiraz, Iran,
2
Meta-
Research Innovation Office, School of Nutrition
and Food Sciences, Shiraz University of
Medical Sciences, Shiraz, Iran,
3
Department of
Community Nutrition, School of Nutrition and
Food Sciences, Shiraz University of Medical
Sciences, Shiraz, Iran, and
4
School of Nutrition,
Ryerson University, Toronto, Ontario, Canada
Received 3 January 2017; revised 2 March
2017; accepted 9 March 2017
Address for correspondence: Z. Mazloom,
Department of Clinical Nutrition, School of
Nutrition and Food Sciences, Shiraz University
of Medical Sciences, Shiraz, Iran.
Email: zohreh.mazloom@gmail.com
Summary
Flaxseed consumption may be inversely associated with obesity; however,
findings of available randomized controlled trials (RCTs) are conflicting. The
present study aimed to systematically review and analyse RCTs assessing the
effects of flaxseed consumption on body weight and body composition.
PubMed, Medline via Ovid, SCOPUS, EMBASE and ISI Web of Sciences
databases were searched up to November 2016. Mean changes in body
composition indices including body weight, body mass index (BMI) and waist
circumference were extracted. Effect sizes were expressed as weighted mean
difference (WMD) and 95% confidence intervals (CI). Heterogeneity between
studies was assessed with the I
2
test. Publication bias and subgroup analyses
were also performed. The quality of articles was assessed via the Jadad scale.
A total of 45 RCTs were included. Meta-analyses suggested a significant
reduction in body weight (WMD: 0.99 kg, 95% CI: 1.67, 0.31,
p= 0.004), BMI (WMD: 0.30 kg m
2
, 95% CI: 0.53, 0.08, p= 0.008)
and waist circumference (WMD: 0.80 cm, 95% CI: 1.40, 0.20,
p= 0.008) following flaxseed supplementation. Subgroup analyses showed that
using whole flaxseed in doses 30 g d
1
, longer-term interventions (12 weeks)
and studies including participants with higher BMI (27 kg m
2
) had positive
effects on body composition. Whole flaxseed is a good choice for weight
management particularly for weight reduction in overweight and obese
participants.
Keywords: Body mass index, body weight, flax, obesity.
Abbreviations: ALA α-linolenic acid; BMI body mass index; CI confidence
interval; PCOS polycystic ovary syndrome; RCTs randomized controlled trials;
SD standard deviation; SEs standard errors; SDG secoisolariciresinol diglucoside;
WC waist circumference; WMD weighted mean difference.
Introduction
Obesity is a major health concern and an important risk
factor for diabetes, cardiovascular disease and cancer.
According to the World Health Organization in 2014, more
than 1.9 billion adults were overweight (body mass index
[BMI] 25 kg m
2
), and 600 million were obese
(BMI 30 kg m
2
) (1,2). It is predicted that ~1.12 billion
individuals will be obese by 2030 (2). The increasing
prevalence of obesity and its related metabolic abnormalities
(e.g. dyslipidaemia, insulin resistance and hypertension) has
created an urgent need for finding an effective approach to
obesity reviews doi: 10.1111/obr.12550
© 2017 World Obesity Federation Obesity Reviews
reduce obesity (3). A large body of evidence suggests a
potential of utilizing functional foods or dietary
nutraceuticals for the management of obesity and associated
abnormalities (46).
Flaxseed (a.k.a. linseed) is a functional food that is a rich
source of α-linolenic acid (ALA), an omega-3 fatty acid
found in vegetables (7,8). Previous studies have shown
anti-inflammatory, antithrombotic and antiarrhythmic pro-
perties of ALA (9). Flaxseed oil contains 5062% ALA,
while whole flaxseed contains 22% ALA (10). Further,
flaxseed contains a high quantity of soluble dietary fibre
(1113) and is a rich food source of lignan, one of the
three major groups of phytoestrogens (14). Flaxseed and
its components have been shown to be beneficial in
reducing risk of cardiovascular diseases, diabetes, blood
pressure and hyperlipidaemia (1517); its consumption
may also positively influence body weight, and by
extension obesity (1820).
Despite increased research on flaxseed in the last decade,
there are inconsistencies between trials examining its effects
on body composition indices. Some trials suggest an inverse
association between flaxseed consumption and body
composition indices (21,22), while others show no little or
reduction in body composition compared with control
following flaxseed supplementation (2325). The present
study performed a comprehensive systematic review and
meta-analyses of available randomized controlled trials
(RCTs) to help quantify the overall effects of flaxseed
products on body composition indices in adults.
Materials and methods
Search strategy
Preferred Reporting Items for Systematic Reviews and
Meta-Analyses statement guidelines were followed as a
framework for reporting meta-analyses of RCTs (26). A
systematic literature search was conducted in medical
databases including PubMed, Medline via Ovid, SCOPUS,
EMBASE and ISI Web of Sciences up to November 2016
using the following subject headings (MeSH) and non-
MeSH keywords: flax* OR flaxseed* OR flax seed*OR
flax-seed*OR linseed* OR lignan* OR Linum
usitatissimum*(Supporting Information S1). The search
was confined to RCTs exploring the influence of flaxseed
or its products (whole or ground flaxseed, lignin
supplement and flaxseed oil) using the English language,
and only studies among human participants were included.
The reference list of related articles, reviews and meta-
analyses were hand-searched for additional relevant studies.
Two independent investigators (H. R. D. and R. B. B.)
screened titles and abstracts for relevant studies, and
discrepancies were resolved using a third investigator
(M. M. S.). The PubMedsMy NCBI(National Centre
for Biotechnology Information) email alert service was
created for identifying new articles that may be published
after our search.
Inclusion criteria
Publishes studies were included if they met the following
criteria: (i) full-text articles written in the English
language; (ii) RCTs with either parallel or crossover
design; (iii) conducted among adults (age 18 years);
(iv) intervention duration of at least 2 weeks; (v) no use
of hormone replacements, fish oil or ALA in the control
group; and (vi) assessed body weight, BMI and waist
circumference (WC) as outcome measures (sufficient
information including standard deviation [SD], standard
error [SE] or 95% confidence interval [CI] must have been
available at baseline and at end study in both flaxseed
and control group). Studies were not included if we were
unable to extract the net effect of the flaxseed intervention
(i.e. if flaxseed was supplemented as an adjunct to another
supplement, the control group containing that
supplement).
Quality assessment
The quality of eligible studies was evaluated
independently by two investigators (M. M. S. and
Z. M.) using the quantitative 5-point Jadad scale (27).
Articles were assigned 0 or 1 point for each of the
following five criteria: (i) randomization, (ii) suitable
method of randomization, (iii) double blinding, (iv)
suitable method of double blinding and (v) explanation
and reason of withdrawals and dropouts (27). Articles
with scores with 3 and 2 were considered of high and
low quality, respectively (28).
Data extraction
Eligible RCTs were reviewed independently by two
authors (H. R. D. and R. B. B.), and the following data
were extracted using a standardized electronic form: first
authors name, publication year, study location, sample
size (enrolment and number completed), type and dose
of intervention and placebo, study design, duration of
the intervention, patients status and other information
including age and sex. Mean and SD of outcome
measures at study baseline, post-intervention and/or
change between baseline and post-intervention were
recorded. For studies reporting data at multiple doses
or multiple time points, only the highest dose of
supplementation at end study were extracted. Three
studies included a fish oil arm that we did not assess in
accordance with our inclusion criteria (2931).
2Flaxseed and body composition M. Mohammadi-Sartang et al.obesity reviews
© 2017 World Obesity FederationObesity Reviews
Quantitative data synthesis and statistical analysis
We evaluated the influence of flaxseed supplementation on
change of the following outcomes: (i) mass (kg); (ii) BMI
(kg m
2
) and (iii) WC (cm). Effect sizes for the meta-
analysis were defined as weighted mean difference (WMD;
value at end trial minus the value at baseline) and 95%
CI. In the event of no reported SD of the mean difference,
it was calculated as follows: SD = ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
SD baselineðÞ2þ½
p
SD end studyðÞ22RSD baselineSD end studyðÞ:
A correlation coefficient of 0.5 was assumed as this R
value is a conservative estimate between 0 and 1 (32). When
SE was reported in place of SD, we converted it SD for
analyses: SD = SE × ffiffi
n
p, where nis the number of
participants in each group. If interested outcomes were
reported as median and range, all mean and SD values were
estimated using the method described by Hozo et al. (33).
Plot digitizer software was used to extract data when the
outcome variable was presented in graphic form only. Pre-
defined subgroup analyses were performed on different
types of flaxseed, supplementation duration, participant
BMI, participant sex, type of study and quality assessment
using the Jadad scale. Random-effects meta-regression
analysis was performed using an unrestricted maximum
likelihood method to explore the association between
changes in body composition indices and duration and dose
of flaxseed supplementation.
Statistical heterogeneity between studies was evaluated
using CochransQ-test (significance set at p<0.1) and I
2
(50% assumed to indicate substantial heterogeneity
among studies). In the presence of heterogeneity, pooled
effect size was calculated using a random-effects model;
otherwise, we applied a fixed-effects model. Sensitivity
analysis was used to explore the extent to which inferences
might depend on a particular study using the leave-one-
out method (i.e. removing a single trial at a time and
repeating the analyses) (34). Publication bias was assessed
by funnel plot, Beggs rank correlation and Eggers weighted
regression tests. In the event of publication bias, the Duval
and Tweedie trim and filland fail-safe Nmethods were
utilized (35). All statistical analyses were performed using
Comprehensive Meta-Analysis (CMA) V2 software
(Biostat, Englewood, NJ, USA) (36) with a level of
significance of p<0.05.
Results
A total of 2,592 reports were initially identified; after
removing duplicates (n= 1,259), 1,333 articles remained.
Of the 1,333 articles, 1,264 were excluded because they
were either not RCTs in humans or unrelated to our
present meta-analyses according to inclusion criteria. A
total of 69 potentially relevant articles were chosen for
full-text evaluation and detailed examination. Among
the full-text articles evaluated, 24 studies were excluded
for the following reasons: duplicate report (n= 2), not
randomized placebo-controlled studies (n= 2), no
anthropometric measurements performed (n= 17) and
use of flaxseed in combination with other components
without an appropriate control group (n= 3). Forty-five
eligible RCTs with 49 treatment arms were included in
the meta-analyses (2125,30,31,3774). Of these, 28
articles reported effects of flaxseed on weight (21
23,25,31,37,38,40,4345,4749,5154,57,59,62,63,66
68,71), 35 articles on BMI (21,22,24,25,30,31,3739,42
44,4651,53,5562,6466,6871,74) and 13 articles on
WC (21,22,31,39,41,44,48,55,60,61,66,72,73). The study
selection process is shown in Fig. S1.
Characteristics of the included studies
Study characteristics of the 45 eligible articles are presented
in Table S1. Data were pooled from the 45 studies
comprising 48 treatment arms; sample size ranged from 9
to 277. Overall, 2,789 participants were randomly assigned
in these trials, and 2,561 participants (91.82%) completed
the studies. Mean age of the participants ranged from 25.6
to 67 years. Nine of the 45 trials were performed exclusively
on women (31,38,41,43,45,48,51,57,75) and nine on men
(40,44,46,54,56,63,65,70,74), and the remaining trials
included both sexes; however, three studies did not mention
sex composition of participants (58,67,68). Eligible studies
were published between 1995 and 2016, and most of them
were conducted in the USA (31,37,38,46,52,57,60,61,66,70,75),
Canada (22,23,4143,48,50,67), Iran (21,59,69,71,73) and
Brazil (24,39,44,45,49). The remaining studies were conducted
in China (62,72), Australia (40,56,63,74), Greece (64,65),
Germany (47), Denmark (51), Romania (58) India (53) and
Japan (54).
Twenty-two treatment arms used whole
(21,22,24,38,42,44,46,48,49,53,57,67,68,7173), ground
(25,43,45,58,66) or deffated (52) flaxseed for the
intervention. Sunflower seed (38), raw rice (44), collagen
(45), wheat germ (48), manioc flour (49), cassava flour
(24), wheat bran (52,66) and wheat (67) were used for the
control groups. Eighteen treatment arms supplemented
flaxseed oil for the intervention (23,30,31,39,40,47,50,54
56,5961,6365,69,70,74), while the control group was
provided canola oil (50,56), corn oil (54,70), olive oil
(30,40,55,60), soybean oil (31,75), safflower oil (6365),
sunflower oil (23,47), MCT oil (59), n-6 oil (74) or placebo
(22,39). One study used both whole flaxseed and flaxseed
oil (22), and five studies used flaxseed lignan
(37,41,45,51,62); the controls in these studies were assigned
placebo. Three studies (21,72,73) incorporated lifestyle
advice only for the control group, while the intervention
group was assigned lifestyle advice and 30 g d
1
flaxseed.
Two other studies (46,58) provided a low-fat or regular diet
Flaxseed and body composition M. Mohammadi-Sartang et al.3obesity reviews
© 2017 World Obesity Federation Obesity Reviews
for the control group, and the intervention group was
provided the same diet in combination with additional
flaxseed.
A wide range of flaxseed supplementation doses were
utilized in the study designs: whole flaxseed 13 to
90 g d
1
, flaxseed oil 1 to 15.4 g of ALA per day and lignan
50 to 600 mg d
1
. Supplementation duration varied from 3
to 48 weeks. Participant characteristics also varied between
studies, many focusing on special and diseased populations:
metabolic syndrome (70,72,73), type 2 diabetes
(22,30,41,62), cardiovascular disease (42,44,67), obesity
(24,49,66), hyperlipidaemia (38,47,50,52,58,64,65,68,71),
postmenopausal women (45,57), polycystic ovary
syndrome (31), prostate cancer (46), haemodialysis
(25,59), diabetic nephropathy (69), non-alcoholic fatty liver
disease (21), fire-fighters (23), normolipidaemic men (63),
healthy adults (37,40,48,51,5456,60,61,74) and older
adults (39).
Data quality
Twenty-nine trials were classified as high quality
(Jadad score 3) (23,24,30,31,3739,4143,46
49,51,52,54,55,57,59,60,62,63,65), and 16 trials
were of low quality (Jadad score <3)
(21,22,25,40,44,45,50,53,56,58,61,64,66,68,71,73).
The last column of Table 1 provides the quality
assessment results of the studies.
Three of the 45 included articles did not report
randomization (53,58,68), but excluding these three
studies had no impact on the meta-analyses. Thirty-
two studies did not adequately explain the
randomization procedure (21,22,25,3741,43
45,47,4958,60,61,63,64,66,68,70,71,73,74). Twenty
studies reported double blinding (24,30,31,37
39,41,43,4749,51,54,57,59,60,62,67,69,70), but 28
studies did not clearly describe the blinding procedure
(2123,25,31,38,40,42,4447,50,53,54,56,58,60,61,64
66,68,69). Details of dropouts were provided in all the
studies.
Meta-analysis results
Twenty-eight studies with 30 treatment arms including a
total of 1,837 participants reported body weight as an
outcome measure. Pooled results from the random-effects
model showed that a reduction in body weight was
significant following flaxseed consumption (WMD:
0.99 kg, 95% CI: 1.67, 0.31, p= 0.004) with
significant heterogeneity (I
2
= 50.00%, p= 0.001) (Fig. 1A).
Thirty-five trails with 38 treatment arms including a total
of 2,209 participants reported BMI as an outcome measure.
Pooled results from the random-effects model showed that
BMI was reduced in the flaxseed group compared with the
control group (WMD: 0.30 kg m
2
, 95% CI: 0.53,
0.08, p= 0.008), with significant heterogeneity among
the studies (I
2
= 54.93%, p<0.001) (Fig. 1B).
Thirteen studies with 14 treatment arms including a total
of 912 subjects reported WC as an outcome measure.
Pooled results from the random-effects model showed that
WC was reduced following an intervention of flaxseed or
its derivatives (WMD: 0.80 cm, 95% CI: 1.40, 0.20,
p= 0.008), with no significant heterogeneity among the
studies (I
2
= 46.94%, p= 0.027) (Fig. 1C).
Sensitivity analysis
Effect sizes for the influence of flaxseed on body weight
were robust in the sensitivity analysis, suggesting that
omission of each trial did not have a significant effect on
the results (Fig. S2A). However, effects of flaxseed on BMI
and WC were sensitive to studies performed by Yari et al.
(73) and Taylor et al. (22), respectively. Removing these
two studies from the analyses rendered the effect of flaxseed
on BMI and WC non-significant (Fig. S2BC).
Subgroup analysis
Results of the subgroup analyses are summarized in Table 1.
When stratified on the basis of type of intervention (whole
flax, flaxseed oil and lignan), a significant reduction in body
weight was observed in trials using whole flaxseed (WMD:
1.75 kg, 95% CI: 2.87, 0.63, p= 0.002), but not
flaxseed oil (WMD: 0.37 kg, 95% CI: 1.48, 0.74,
p= 0.514) or lignan extract (WMD: 0.20 kg, 95%
CI:0.23, 0.63, p= 0.363). BMI was also decreased in the
interventions using whole flaxseed (WMD: 0.63 kg m
2
,
95% CI: 1.17 to 0.09, p= 0.021), but not flaxseed oil
(WMD: 0.004 kg m
2
, 95% CI: 0.08, 0.09, p= 0.930)
or lignan extract (WMD: 0.10 kg m
2
, 95% CI: 0.06,
0.26, p= 0.234). Finally, WC decreased in studies using
whole flaxseed (WMD: 1.21, 95% CI 1.96, 0.46,
p= 0.001), but not in flaxseed oil (WMD: 0.05, 95%
CI: 1.06, 0.96, p= 0.921).
The subgroup analyses performed to identify the
effective dose of whole flaxseed on body composition
showed that body weight (WMD: 0.21 kg, 95% CI:
0.34, 0.09, p= 0.001) and BMI (WMD: 0.60 kg m
2
,
95% CI: 0.81, 0.39, p<0.001) were reduced in whole
flaxseed doses 30 g d
1
, but not in lower doses. With
regard to duration of supplementation, there was a
reduction in body weight (WMD: 1.50 kg, 95% CI:
2.41, 0.60, p= 0.001), BMI (WMD: 0.44 kg m
2
,
95% CI: 0.73, 0.16, p= 0.002) and WC (WMD:
0.69 cm, 95% CI: 1.61, 0.32, p= 0.003) among
trials with 12 weeks of duration, compared with those
lasting <12 weeks.
4Flaxseed and body composition M. Mohammadi-Sartang et al.obesity reviews
© 2017 World Obesity FederationObesity Reviews
Table 1 Results of subgroup analysis of included randomized controlled trials in meta-analysis of flaxseed supplementation and body composition indices
Variables Type of intervention Duration Baseline BMI Gender RCT type Study quality
Body weight WF FXO LIG 12 <12 27 <27 F M Both RP RC Low (<3) High (3)
No. of comparison 18 7 4 18 12 13 17 7 4 19 22 8 14 16
WMD, 95% CI 1.75, 2.87,
0.63 0.37,
1.48, 0.74
0.20,
0.23, 0.63 1.50, 2.41,
0.0.60
0.138,
0.96, 1.23 1.80,
3.30,
2.35
0.17,
0.46,
0.11
0.46,-
3.04, 2.10
0.72,
6.32,
7.52
1.20,
2.01,
0.39
1.31
2.18,
0.45
0.19,
0.23,
0.62
2.19,
3.68,
0.71
0.15,
0.44,
0.13
pvalue 0.002 0.514 0.363 0.001 0.806 0.019 0.242 0.722 0.610 0.003 0.003 0.378 0.004 0.282
I
2
(%) 61.65 0.00 0.00 69.74 0.00 49.51 0.00 0.00 0.00 68.27 54.69 0.00 50.33 0.00
p-heterogeneity <0.001 0.994 0.944 <0.001 1.00 0.011 0.893 1.00 0.990 <0.001 0.001 1.00 0.016 0.914
BMI WF FXO LIG 12 <12 27 <27 F M Both RP RC Low (<3) High (3)
No. of comparison 19 15 3 19 18 24 13 6 7 25 18 9 14 23
WMD,95% CI 0.63, 1.17
to 0.09
0.004,
0.08, 0.09
0.10,
0.06, 0.26 0.44,:
0.73, 0.16
0.146,
0.35, 0.61 0.55,
1.04,
0.06
0.02,
0.08.
0.14
0.28,
0.54.
0.03
0.16,
0.87,
0.55
0.36,
0.65,
0.07
0.43,
0.73,
0.12
1.00,
0.06,
0.26
0.66,
1.23,
0.08
0.004,
0.07,
0.08
pvalue 0.021 0.925 0.234 0.002 0.565 0.028 0.633 0.028 0.660 0.015 0.005 0.232 0.025 0.918
I
2
(%) 50.24 0.00 0.00 76.46 0.00 66.04 0.00 0.00 18.54 66.34 64.04 0.00 47.26 0.00
p-heterogeneity 0.007 0.548 0.950 <0.001 1.00 <0.001 0.690 0.997 0.288 <0.001 <0.001 0.999 0.026 0.864
WC WF FXO LIG 12 <12 27 <27 F M Both RP RC Low (<3) High (3)
No. of comparison 7 6 1 9 5 9 5 2 1 11 12 2 7 7
WMD, 95% CI 1.21, 95%
CI 1.96, 0.46 0.05, 95%
CI: 1.06,
0.96
1.50,
12.72,
9.72
0.69, 95%
CI: 1.61,
0.32
0.22, 95%
CI: 1.40,
1.86
1.12,
1.97,
0.26
0.50,
1.34,
0.34
1.44,
3.04,
0.16
1.36,
1.68,
3.68
0.80,
1.47,
0.14
0.83,
1.44,
0.22
0.28,
3.75,
3.94
1.82,
2.92,
0.72
0.37,
1.09,
0.34
pvalue 0.001 0.921 0.793 0.003 0.784 0.010 0.245 0.079 0.465 0.017 0.007 0.878 0.001 0.305
I
2
(%) 70.53 0.00 0.00 63.04 0.00 62.17 0.00 0.00 0.00 54.37 54.24 0.00 64.52 0.00
p-heterogeneity 0.002 0.974 1.00 0.006 0.899 0.007 0.676 0.618 1.00 0.016 0.013 0.741 0.010 0.821
BMI, body mass index; F, female; FXO, flaxseed oil; LIG, lignans; M, male; RC, randomized crossover design; RCT, randomized controlled trial; RP, randomized parallel design; WC, waist circumference; WF,
whole flaxseed; WMD, weight mean difference.
Flaxseed and body composition M. Mohammadi-Sartang et al.5obesity reviews
© 2017 World Obesity Federation Obesity Reviews
Figure 1 Forest plot detailing weighted mean difference and 95% confidence intervals (CIs) for the impact of flaxseed supplementation on body
composition indices. BMI, body mass index. [Colour figure can be viewed at wileyonlinelibrary.com]
6Flaxseed and body composition M. Mohammadi-Sartang et al.obesity reviews
© 2017 World Obesity FederationObesity Reviews
When stratified on the basis of BMI status, flaxseed
consumption reduced body weight, BMI and WC among
participants with BMI 27, but not among participants
with BMI <27 (Table 1). We also observed a significant
reduction in BMI in women compared with men, with mean
changes of 0.28 kg m
2
(95% CI: 0.54, 0.03, p= 0.03)
and 0.16 kg m
2
(95% CI: 0.87, 0.55, p= 0.66),
respectively.
A significant reduction in body weight, BMI and WC was
found in studies using a parallel design but not crossover
Figure 2 Meta-regression plots of the association between mean changes in body composition indices and duration of flaxseed supplementation. The
size of each circle is inversely proportional to the variance of change. BMI, body mass index; CI, confidence interval; WC, waist circumference.
Flaxseed and body composition M. Mohammadi-Sartang et al.7obesity reviews
© 2017 World Obesity Federation Obesity Reviews
design when assessing based on the type of RCTs. Finally,
subgroup analyses suggested significant reducing effects of
flaxseed and its derivatives on body weight, BMI and WC
in low-quality studies, but not in high-quality studies.
Meta-regression
The effect of flaxseed intervention on body weight (slope:
0.049; 95% CI: 0.06 to 0.03; p= 0.02), BMI (slope:
0.007; 95% CI: 0.01 to 0.0001; p= 0.046) and WC
(slope: 0.015; 95% CI: 0.11 to 0.04; p= 0.028) were
associated with supplementation duration (Fig. 2AC).
When assessing the influence of flaxseed and flaxseed
derivatives dose (whole flaxseed or flaxseed oil, expressed
as ALA g d
1
and lignan extract), no association effects
were found with body weight, BMI or WC (Table S2).
Publication bias
Funnel plots revealed asymmetry in the meta-analyses of
flaxseed consumption on body weight and BMI, but there
was no sign of publication bias with respect to WC. Using
the trim and fillmethod for adjusting publication bias,
seven and six potentially missing studies were imputed for
the meta-analyses of body weight and BMI, respectively
(Fig. S3). Corrected effect sizes after imputation of
potentially missing studies, as well as results of Eggers
linear regression, Beggs rank correlation and fail-safe N
tests, are summarized in Table S3.
Discussion
The present systematic review and meta-analyses of
RCTs explored the effects of flaxseed product
consumption on body composition indices in adults.
Our major findings indicate that participants ingesting
flaxseed products had lower body weight, BMI and
WC after the intervention than controls. However,
subgroup analyses revealed that body composition
indices were reduced with whole flaxseed consumption
only, in trials lasting 12 weeks, and among participants
with BMI 27 kg m
2
.
Flaxseed is a rich source of plant lignans (primarily
secoisolariciresinol diglucoside [SDG]) (12,13); in fact,
flaxseed contains more than 100 times higher SDG than
most other foods (76). Purified lignans in the form of SDG
have been shown to reduce visceral (abdominal) fat in mice
compared with those not consuming SDG (77). The authors
suggested that the high content of SDG may contribute to
the overall effects of flaxseed via a reduction of mRNA
levels of sterol regulatory element-binding proteins that
are involved in TAG synthesis (77). SDG may also be useful
in regulating adiponectin levels and can prevent or reduce
obesity through increased fat oxidation in skeletal muscle
(77,78). In the present meta-analyses, five studies used
lignin supplements (37,41,45,51,62), but subgroup analysis
revealed that lignan did not have any benefit for body
composition in adults. The limited data on humans make
it difficult to draw conclusions regarding the effects of
lignan on obesity. Further, flaxseed oil did not significantly
reduce body weight, BMI and WC, supporting previous
studies reporting no effects of ALA on body composition
(40,47,54,59).
We did observe reductions in body composition indices
with whole flaxseed, however, possibly owing to the high
fibre content (25% soluble form) (13,79). Dietary fibre,
particularly soluble fibre, has anti-obesity effects that have
been shown to decrease body weight (80). Dietary fibre
may help prevent weight gain or promote weight loss via
delayed gastric emptying, inducing feelings of fullness by
absorbing large amounts of water (81), and/or increasing
the concentration of short chain fatty acids that act to
enhance satiety by a variety of mechanisms (82). Further,
dietary fibre can induce viscosity and reduce re-uptake of
bile acids, subsequently reducing micelle formation and
lipid uptake (83,84).
The present meta-analysis found that duration of
flaxseed supplementation had an effect on body
composition indices. Subgroup analysis showed a
significant reduction in body weight, BMI and WC
following intervention durations of 12 weeks. These
findings may be explained by the subsequent increase in
circulating ALA after flaxseed supplementation. ALA is
converted to eicosapentaenoic acid (20:5 n-3) and
docosahexaenoic acid (22:6 n-3) in the body (85); the
anti-obesity effects of eicosapentaenoic acid and
docosahexaenoic acid have been shown in previous studies
(8688). In the long-term supplementation, concentrations
of these long chain omega-3 fatty acids are increased (89),
potentiating the anti-obesity effects of flaxseed.
Furthermore, dietary fibre consumption leads to a gradual
increase in intestinal gut flora (90), which may enhance
lignan absorption (91) and result in the formation of the
main component of mammalian lignans, enterolactone
(92). An inverse relationship between enterolactone and
obesity has been observed (93,94).
Positive effects of flaxseed interventions were observed
among participants with BMI 27 kg m
2
.These
findings suggest that higher BMI has a potent moderating
impact on the effects of flaxseed consumption on changes
in body composition. In other words, it appears that
individuals with higher BMI were more likely to be
positively affected by the supplementation. Our meta-
analysis also showed that the influence of flaxseed on
BMI was more striking in women than in men; however, as
three articles did not report the sex composition of the
participants, the exact sex-specificity effect of flaxseed
remains unclear.
8Flaxseed and body composition M. Mohammadi-Sartang et al.obesity reviews
© 2017 World Obesity FederationObesity Reviews
Limitations
The present study has several limitations; the findings
should be interpreted with caution. First, our results
showed that body weight, BMI and WC were reduced in
low-quality studies but not in higher-quality studies.
Second, the protocol design differences between studies
may have affected our findings. Crossover trials utilized a
washout period of anywhere between 2 (52) and 12 weeks
(41,62), creating different carry-over effects between trials.
This may, in part, help explain the significant reduction
effect observed in parallel design versus crossover design.
In most of the included crossover studies (seven of 12),
the duration of supplementation was <12 weeks, perhaps
providing explanation as to why we observed a significant
effect of flaxseed on body weight, BMI and WC in studies
lasting 12 weeks but not in lower durations. Third,
significant heterogeneity between studies indicates that
the effects of flaxseed on body weight and BMI are not
uniform, likely owing to employing different
methodologies and assessing different populations. Finally,
more than half the eligible studies had a small sample size
(30 of 44 included studies had a sample size lower than 50
participants).
Further, it should be noted that sensitivity analyses
revealed that the results of BMI and WC were highly
determined by the studies of Yari et al. (73) and Taylor
et al. (22), respectively. It is likely that more studies will
help confirm whether flaxseed and its products affect
BMI and WC.
Conclusions
The current meta-analysis pooled results from 45 RCTs
regarding the effects of flaxseed consumption on body
composition indices; we believe that our findings are
valuable for researchers and clinicians. Our findings show
that supplementation of whole flaxseed for more than
12 weeks in individuals with a BMI higher than 27 kg m
2
may reduce body weight, BMI and WC. Flaxseed
consumption may be a valuable dietary approach for the
prevention and treatment of obesity, and many trials have
explored the effects of flaxseed interventions on body
composition. However, more research is needed with larger
sample sizes, adequate durations and well-designed trials
lasting over 12 weeks in order to confirm the beneficial
effects of flaxseed consumption on body composition.
Future research should determine the ideal quantity of
flaxseed for weight loss.
Acknowledgements
The authorsresponsibilities were as follows: M. M. S. and
Z. M. conceived the study. M. M. S. carried out the literature
search. H. R. D. and R. B. B. carried out data extraction and
independent reviewing. M. M. S. and Z. M. assessed the
quality of included studies. M. M. S. performed data
analysis and interpretation. M. M. S. wrote the manuscript.
Z. M., N. B. and J. T. revised the manuscript. The
manuscript has been read and approved by all authors.
Conflict of interest statement
The research did not receive any specific grant from funding
agencies in the public, commercial or not-for-profit sectors.
The authors declared that they have no potential conflicts of
interest.
Supporting information
Additional Supporting Information may be found online in
the supporting information tab for this article. http://dx.doi.
org/10.1111/obr.12550
Table S1 Demographic characteristics of the included
studies.
Table S2 Meta-regression between changes in body
composition indices and administered doses of various
flaxseed products.
Table S3 Assessment of publication bias in the impact of
flaxseed supplementation on body composition indices.
Figure S1 Flow diagram of the study selection procedure
showing the number of eligible randomized controlled trials
for the meta-analysis of the impact of flaxseed
supplementation on body composition indices.
Figure S2 Leave-one-out sensitivity analysis of the impact of
flaxseed supplementation on body composition indices.
Figure S3 Funnel plots detailing publication bias in the
studies selected for analysis of flaxseeds effects on body
composition indices. Trim and fill method was used to
impute for potentially missing studies. Open circles
represent observed published studies; closed circles
represent imputed unpublished studies. BMI, body mass
index; WC, waist circumference.
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12 Flaxseed and body composition M. Mohammadi-Sartang et al.obesity reviews
© 2017 World Obesity FederationObesity Reviews
... 5 Systematic analyses of RCTs showed that flaxseed is a good option for improving body composition and weight management especially in overweight and obese groups, however, it emphasizes that more research is needed to prove these results. 12 The systematic review and meta-analysis aimed to evaluate the effectiveness of herbal medicine in obesity and metabolic syndrome managements demonstrates that flaxseed can reduce appetite, but its anti-obesity effects is still controversial. 13 Although these researches have strongly supported the efficiency of flaxseed consumption in enhancing inflammation and body composition, there is nothing in the way of accurate findings regarding this influence in overweight prediabetes patients. ...
... However, the Shareghfarid et al 5 systematic review in relation to evaluating the effect of flaxseed supplement on body composition delineates that flaxseed has positive effects on body composition in individuals with BMI of ⩾ 30. 12 Besides, consuming flaxseed oil in obese individuals with non-alcoholic fatty liver disease led to reduction in body fat. 30 It assumed that higher BMI has a potent moderating impact on effectiveness of this supplement regarding body composition. ...
... So, whole flaxseed is a good choice for weight management especially in overweight and obese participants. 12 Indeed, further investigations are essential to evaluate the effect of various source of flaxseed on groups with different BMI ranges. ...
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Background: Flaxseed has rich content of alpha linolenic acid for preventing pro inflammatory process. The aim of present study is exploring the effect of flaxseed oil supplementation on inflammatory biomarkers and body composition in overweight adults with pre-diabetes. Material and methods: this double-blind randomized clinical trial conducted with 80 overweight pre-diabetic patients in 2 clusters (flaxseed oil group (2000-mg daily) and control group) across a 14-week period. Anthropometric indices, body composition and inflammatory indices were measured between 2 groups before and after the treatment. Result: this study found a significant decrease in visceral fat level in the intervention group (P = .009) and control group (P = .004) at the end of the survey. However, the mean change of it (P = .06) was not significant. Also, this study showed that percentage of body fat (P = .31) and its mean change (P = .6) did not have significantly different between the 2 groups at the 14th week. The skeletal muscle% had a significant rise in the intervention group (P = .005) and control group (P = .003) by the end of 14th week. However, the mean change of it (P = .19) was not significant between the 2 groups. In addition, there was no significant change in the fasting blood glucose (P = . 7), C reactive protein (P = .12) and TNF-α (P = .22) between the 2 groups at the end of study. Conclusion: It showed that flaxseed oil supplementation cannot improve body composition and inflammation.
... It was suggested that the degree of health benefits (e.g., cholesterol lowering, improved glycemic control, satiety, weight loss) is proportional to the viscosity of the gelling fiber [22]. Meta-analysis of 45 randomized placebo-controlled trials showed that consumption of whole flaxseed, possibly due to high fiber content had led to significant reduction in body weight, BMI and waist circumference [23]. It was suggested that individual component in flaxseed has greater health potential than the whole flaxseed [24]. ...
... It was suggested that individual component in flaxseed has greater health potential than the whole flaxseed [24]. Findings from previous research showed the potential of flaxseed mucilage in combating obesity [17,20,23,24], however clinical evidence of flaxseed mucilage, especially at a lower dose compared to the whole flaxseed, has not yet been established. The potential of flaxseed mucilage in weight management is promising and to the best of our knowledge, clinical evidence on weight loss effect of flaxseed mucilage was not available. ...
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Introduction: The aim of this study was to evaluate the benefit and tolerability of two dosages of a proprietary flaxseed mucilage (IQP-LU-104) in reducing body weight in overweight and moderately obese individuals. Methods: In a double-blind, randomized, placebo-controlled, bi-center trial, 108 participants (Body Mass Index (BMI) 25 to < 35 kg/m2) were randomly allocated to receive either IQP-LU-104 high dose (104HD), IQP-LU-104 low dose (104LD), or placebo. Participants were instructed to consume 1 sachet of the investigational product (containing IQP-LU-104 or matching placebo) before or with main meals twice daily and to follow a balanced but hypocaloric diet (20% reduction of individual's daily energy requirements) for 12 weeks. At week 0 (baseline), week 4, 8 and 12 of the intervention periods, the participants' body weight, BMI, body fat composition and waist and hip circumferences were measured. Blood samples were collected for safety assessment at screening visit (week -2) and at the end of the study. Adverse events were assessed by the investigators through interviewing the participants and were recorded at every visit post screening. Results: At the end of the 12-week study, body weight reduction was greater in the 104HD group (4.96 ± 1.89 kg, p < 0.001 vs. placebo) and 104LD group (3.70 ± 2.57 kg, p < 0.001 vs. placebo) compared to the placebo group (1.33 ± 2.05 kg). 68% and 46% of participants in the 104HD group (p < 0.001 vs. placebo) and 104LD group (p = 0.002 vs. placebo) respectively experienced at least 5% weight loss, compared to 9% of participants in the placebo group. Significant decreases in waist and hip circumferences were observed in both the 104HD and 104LD groups compared to the placebo group (each p < 0.001). 104HD group had significantly higher reduction in body fat mass (4.25 ± 5.86 kg) than the placebo group (1.06 ± 3.20 kg) (p = 0.002). Respiratory tract infections and gastrointestinal symptoms were the main adverse events reported and none of the adverse events were related to the intake of IQP-LU-104. Conclusion: Results demonstrated IQP-LU-104 is safe and efficacious in body weight reduction at both dosages in overweight and moderately obese individuals.
... Flaxseed oil has different effects, including anti-inflammatory (Oomah, 2001), anti-chemotactic (Monk et al., 2016), antioxidant (Barthet, Klensporf-Pawlik, & Przybylski, 2014), anti-atherosclerotic (Zanwar, Hegde, & Bodhankar, 2014), and anti-microbial (Mohammed & Hameed, 2018). In addition, flaxseed supplementation produces various potentially protective effects against chronic diseases, such as obesity (Mohammadi-Sartang et al., 2017), dyslipidemia , diabetes (Mohammadi-Sartang, Sohrabi, Barati-Boldaji, Raeisi-Dehkordi, & Mazloom, 2018), and metabolic syndrome (Tamtaji et al., 2020). Some trials claimed flaxseed could improve BP in adults (Dodin et al., 2005; Rodriguez-Leyva et al., 2013), whereas others did not (Billinsky et al., 2013;Dewell, Marvasti, Harris, Tsao, & Gardner, 2011). ...
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We systematically reviewed randomized clinical trials (RCTs) to elucidate the overall effects of flaxseed oil consumption on blood pressure (BP) in patients with metabolic syndrome and related disorders. PubMed, Scopus, Cochrane Library, and ISI Web of Science databases were systematically searched until March 31, 2020, to find RCTs that examined the effect of flaxseed oil consumption on BP. Weighed mean difference (WMD) was pooled using a random-effects model. Standard methods were used for the assessment of heterogeneity, sensitivity analysis, and publication bias. Meta-analysis of five trials (6 arms) showed significant reductions in systolic (WMD: À3.86 mmHg, 95% CI: À7.59 to À0.13, p = .04) BP (SBP) after flaxseed oil consumption. However, the overall effect illustrated no significant change in diastolic (WMD:
... In a meta-analysis reported that consumption of flax seeds, flaxseed oil, or flaxseed lignan significantly reduced weight, BMI, and waist circumference as compared with the placebo [22]. Some previous studies have also demonstrated anti-obesity effects of plant-based source of omega-3 in NAFLD [23][24][25]. ...
Article
Objective: Recently, omega-3 fatty acids and antioxidants co-supplementation was considered as alternative treatment in the management of nonalcoholic fatty liver disease (NAFLD). This trial evaluated effects of Camelina sativa oil (CSO) as a rich source of omega-3 fatty acids and antioxidants on anthropometric indices, lipid profile, liver enzymes, and adiponectin in NAFLD patients. Participants and methods: This triple-blind, placebo-controlled, randomized clinical trial was conducted on 46 NAFLD patients who were randomly assigned to either a CSO supplement or placebo for 12 weeks. Both groups received a loss weight diet. Levels of liver enzymes, adiponectin, lipid profile, atherogenic index, and anthropometric indices were assessed for all patients at baseline and post-intervention. Results: CSO caused significant differences in weight, BMI, waist circumference, waist-to-hip ratio, triglyceride, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), TC/HDL-c, LDL-c/HDL-c, atherogenic index, alanine aminotransferase, and adiponectin concentrations in the CSO group compared with the placebo group (P < 0.046 for all). No significant differences were found in hip circumference, neck circumference, HDL-c, and other liver enzymes in the CSO group compared with the placebo group (P = 0.790, P = 0.091, P = 0.149, P < 0.159 for liver enzymes, respectively). Discussion and conclusion: This study showed that CSO supplementation for 12 weeks causes significant changes in all of anthropometric indices (except hip circumference and neck circumference), ALT, lipid profile (except HDL-c), atherogenic index, and adiponectin in NAFLD patients.
... Flaxseed's mass reducing effects are just as effective in humans. A meta-analysis of 45 randomized controlled trials concluded that whole flaxseed (>30 g/d) significantly lowers body weight, body mass index (BMI), and waist circumference with the biggest benefits in obese human subjects [103]. We predict that consistently consumed whole flaxseed should reduce omental adiposity and thereby decrease the inflammatory crosstalk between the omentum and the ovarian tumor. ...
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We used an LC-MS/MS metabolomics approach to investigate one-carbon metabolism in the plasma of flaxseed-fed White Leghorn laying hens (aged 3.5 years). In our study, dietary flaxseed (via the activity of a vitamin B6 antagonist known as “1-amino d-proline”) induced at least 15-fold elevated plasma cystathionine. Surprisingly, plasma homocysteine (Hcy) was stable in flaxseed-fed hens despite such highly elevated cystathionine. To explain stable Hcy, our data suggest accelerated Hcy remethylation via BHMT and MS-B12. Also supporting accelerated Hcy remethylation, we observed elevated S-adenosylmethionine (SAM), an elevated SAM:SAH ratio, and elevated methylthioadenosine (MTA), in flaxseed-fed hens. These results suggest that flaxseed increases SAM biosynthesis and possibly increases polyamine biosynthesis. The following endpoint phenotypes were observed in hens consuming flaxseed: decreased physiological aging, increased empirical lifespan, 9–14% reduced body mass, and improved liver function. Overall, we suggest that flaxseed can protect women from ovarian tumor metastasis by decreasing omental adiposity. We also propose that flaxseed protects cancer patients from cancer-associated cachexia by enhancing liver function.
... It has been reported that adiponectin levels and its gene expression increased following weight loss [29]. On the other hand, axseed can cause weight loss due to their high ber content and active ingredients [30]. However, in our study, no signi cant change was observed in the weight of patients in the intervention group compared to the control group. ...
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Introduction: Inflammatory bowel disease (IBD) is one of the most common gastrointestinal diseases that can affect people of all ages. Adipokines secreted from adipose tissue have been shown to play an important role in the pathogenesis of ulcerative colitis (UC). The aim of this study was to evaluate the effect of supplementation with your seed on the concentrations of adiponectin, resistin and visfatin in patients with UC. Methods: This trial is an open-labeled randomized controlled trial which conducted among 70 patients with UC. Patients were randomly divided into two groups: flaxseed and control. Patients in the intervention were received 30 g/day flaxseed powder for 12 weeks. Anthropometric, nutritional and biochemical factors of patients were evaluated at the beginning and end of the intervention period. Results: Totally, 64 patients (36 men and 28 women) with mean age of 31.12 ± 9.67 included in the final analysis. There wasn’t any significant difference between two groups in term of baseline weight and height (P>0.05). After the 12 weeks' intervention, flaxseed supplementation led to a significant reduction in the resistin (-4.85 ± 1.89 vs. -1.10 ± 2.25, P<0.001) and visfatin concentration (-1.33± 1.14 vs. -0.53 ± 1.63, P=0.018). Moreover, we found a significant increase in the adiponectin levels after the flaxseed supplementation (3.49 ± 1.29 vs. -0.35 ± 0.96, P<0.001). Conclusion: It has been reported in this study that flaxseed supplementation could exert beneficial effects on adipokine levels in patients with UC. Trial registration: IRCT registration no. IRCT20180311039043N1
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Background Prediabetes and type 2 Diabetes Mellitus (T2DM) are characterized by increased blood sugar concentration and insulin resistance. Although there are only a few reports of potential benefits of flaxseed’s consumption on different metabolic parameters, there is no evidence of its effect among people with these conditions. Objectives The present systematic review and meta-analysis aimed to assess the effect of flaxseed supplementation on glycemic control variables and insulin resistance in prediabetes and T2DM. Methods A literature search was conducted through PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science, to identify Randomized Control Trials (RCTs) that evaluated the effect of milled or ground flaxseed supplementation on fasting blood glucose, HbA1c, insulin concentrations, or HOMA-IR. The data were analyzed using Comprehensive Meta-Analysis (CMA) software version 3.3 in a fixed-effect model. Results Seven studies were included in the systematic review and the meta-analysis, the results showed a significant reduction on fasting blood sugar (SMD: −0.392, 95% CI: −0.596, −0.187, p = <0.001, I² = 64.81%) insulin concentrations, (SMD: −0.287, 95% CI: −0.534, −0.041, p = 0.022, I² = 32.53%), HbA1c (SMD: −0.442, 95% CI: −0.770, −0.114, p = 0.008, I² = 11.058%), and HOMA-IR (SMD: −0.284, 95% CI: −0.530, −0.038, p = 0.024, I² = 0.00%) after flaxseed supplementation. Conclusions Flaxseed supplementation seems to improve glycemic control variables and insulin resistance in prediabetes and T2DM; however, more RCTs are needed to have more decisive evidence about doses, method of supplementation, and the possible effect of synergy with the dietetic treatment.
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Background and aims (Poly)phenols might contribute to prevent cardiovascular disease, but limited prospective studies exist among adolescents. This study aimed to evaluate within-subject longitudinal changes in (poly)phenols intakes and food group contributors while also exploring the association with metabolic syndrome risk (MetS) during 10 years of follow up in European adolescents becoming young adults. Methods and Results In 164 participants (58% girls, 13-18y at baseline) from Ghent, Zaragoza and Lille, longitudinal data (2006-2016) on (poly)phenol intake was retrieved via 2 or 3 24h recalls. Linear and logistic longitudinal regression tested the association of (poly)phenols intake (total and classes) with Mets risk or its components (waist-height-ratio, HDL cholesterol, LDL cholesterol, triglycerides, blood pressure and insulin resistance index), adjusted for age, sex, country and other nutrient intakes. The total (poly)phenols intake was 421±107 mg/day (192 mg/1000kcal/day) at baseline, while 610±101 mg/day (311 mg/1000kcal/day) at follow-up. The three major food sources for (poly)phenols were ‘chocolate’, ‘fruit and vegetable juices’, ‘cakes and biscuits’ during adolescence and ‘coffee’, ‘tea’ and ‘chocolate’ during adulthood. Phenolic acid intake was associated with less LDL increase over time, while stilbene intake with a steeper increase in triglycerides over time. Conclusions Differences in major (poly)phenols contributors over time were partially explained by age-specific dietary changes like increased coffee and tea during adulthood. Some significant (poly)phenols-MetS associations might argue for nutrition-based disease prevention during adolescence, especially since adolescents had low (poly)phenols intake.
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Given the evidence of the health benefits of plant-based diets and long-chain n-3 fatty acids, there is keen interest in better understanding the role of alpha-linolenic acid (ALA), a plant-derived n-3 fatty acid, on cardiometabolic diseases and cognition. There is increasing evidence for ALA largely based on its major food sources (i.e., walnuts and flaxseed); however, this lags behind our understanding of long-chain n-3 fatty acids. Meta-analyses of observational studies have shown that increasing dietary ALA is associated with a 10% lower risk of total cardiovascular disease and a 20% reduced risk of fatal coronary heart disease. Three randomized controlled trials (AlphaOmega trial, Prevención con Dieta Mediterránea [PREDIMED] trial, and Lyon Diet Heart Study) all showed benefits of diets high in ALA on cardiovascular-related outcomes, but the AlphaOmega trial, designed to specifically evaluate ALA effects, only showed a trend for benefit. Randomized controlled trials have shown that dietary ALA reduced total cholesterol, low-density-lipoprotein cholesterol, triglycerides, and blood pressure, and epidemiological studies and some trials also have shown an anti-inflammatory effect of ALA; which collectively account for, in part, the cardiovascular benefits of ALA. A meta-analysis reported a trend toward diabetes risk reduction with both dietary and biomarker ALA. For metabolic syndrome and obesity, the evidence for ALA benefits is inconclusive. The role of ALA in cognition is in the early stages but shows promising evidence of counteracting cognitive impairment. Much has been learned about the health benefits of ALA and with additional research we will be better positioned to make strong evidence-based dietary recommendations for the reduction of many chronic diseases.
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The aim of this study was to evaluate the efficacy of flaxseed supplementation plus lifestyle modification in comparison with lifestyle modification alone in the management of metabolic syndrome (MetS). A randomized controlled clinical trial was conducted on 44 patients with MetS. Participants were assigned to receive either the lifestyle advice and 30-g brown milled flaxseed daily or only the lifestyle advice as the control group. The percentage of individuals with MetS decreased from baseline by 50% and 82% in the control and intervention group, respectively. The reversion rate of central obesity was higher in the flaxseed group (36%) than control group (13%). Moreover, greater reduction in insulin resistance was observed in flaxseed group in comparison with control group (p < 0.001). Body weight, waist circumference, and body mass index decreased significantly in both groups with a significantly greater reduction in flaxseed group in comparison with controls (p < 0.05). There were no significant changes in blood pressure in any groups. Our results indicate that co-administration of flaxseed with lifestyle modification is more effective than lifestyle modification alone in management of MetS; whether these effects will be sustained with longer treatment durations remains to be determined. Copyright © 2016 John Wiley & Sons, Ltd.
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Scope: To investigate the effects of n-3 fatty acid supplements, both marine and plant-based, on glycemic traits in Chinese type 2 diabetes (T2D) patients. Method and results: In a double-blind randomized controlled trial, 185 recruited Chinese T2D patients were randomized to either fish oil (FO, n = 63), flaxseed oil (FSO, n = 61) or corn oil group (CO, served as control group, n = 61) for 180 days. The patients were asked to take corresponding oil capsules (4 capsules/day), which totally provided 2 g/day of eicosapentaenoic acid + docosahexaenoic acid in FO group and 2.5 g/day of alpha-linolenic acid in FSO group. No group×time interaction was observed for HOMA-insulin resistance, fasting insulin or glucose. Significant group×time interaction (P = 0.035) was observed for glycated haemoglobin (HbA1c), with HbA1c decreased in FO group compared with CO group (P = 0.037). We also found significant group×time interactions for lipid traits, including low-density lipoprotein cholesterol (P = 0.043), total cholesterol (TC) (P = 0.021), total cholesterol/ high-density lipoprotein cholesterol (TC/HDL-C) (P = 0.009) and triacylglycerol (TG) (P = 0.003), with the lipid profiles improved in FO group. No significant effects of FSO on glycemic traits or blood lipids were observed. Conclusions: Marine n-3 PUFA supplements may improve glycemic control and lipid profiles among Chinese type 2 diabetic patients. This article is protected by copyright. All rights reserved.
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Systematic reviews should build on a protocol that describes the rationale, hypothesis, and planned methods of the review; few reviews report whether a protocol exists. Detailed, well-described protocols can facilitate the understanding and appraisal of the review methods, as well as the detection of modifications to methods and selective reporting in completed reviews. We describe the development of a reporting guideline, the Preferred Reporting Items for Systematic reviews and Meta-Analyses for Protocols 2015 (PRISMA-P 2015). PRISMA-P consists of a 17-item checklist intended to facilitate the preparation and reporting of a robust protocol for the systematic review. Funders and those commissioning reviews might consider mandating the use of the checklist to facilitate the submission of relevant protocol information in funding applications. Similarly, peer reviewers and editors can use the guidance to gauge the completeness and transparency of a systematic review protocol submitted for publication in a journal or other medium.
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Purpose: The aim of this study was to investigate the effects of flaxseed oil consumption on serum systemic and vascular inflammation markers, and oxidative stress in hemodialysis (HD) patients. Methods: In this randomized, double-blind, clinical trial, 34 HD patients were randomly assigned to either the flaxseed oil or the control group. The patients in the flaxseed oil group received 6 g/day flaxseed oil for 8 week, whereas the control group received 6 g/day medium-chain triglycerides (MCT) oil. At baseline and the end of week 8, serum concentrations of high-sensitive C-reactive protein (hs-CRP), soluble intercellular adhesion molecule type 1 (sICAM-1), soluble vascular cell adhesion molecule type 1 (sVCAM-1), sE-selectin, and malondialdehyde (MDA) were measured after a 12- to 14-h fast. Results: Serum hs-CRP, a systemic inflammation marker, and sVCAM-1, a vascular inflammation marker, reduced significantly in the flaxseed oil group at the end of week 8 compared to baseline (P < 0.05), and the reductions were significant in comparison with the MCT oil group (P < 0.05). There were no significant differences between the two groups in mean changes in serum sICAM-1, sE-selectin, and MDA. Conclusion: This study indicates that daily consumption of 6 g flaxseed oil reduces serum hs-CRP and sVCAM-1, which are two risk factors for CVD. Therefore, the inclusion of flaxseed oil in the usual diet of HD patients can be considered as a strategy for reducing CVD risk factors.
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Background: Both fish (FO) and flaxseed oils (FLX) are n-3 polyunsaturated fatty acids (PUFA). Fish oil contains long chain while FLX contains essential n-3 PUFA. We demonstrated that FO altered insulin secretion and resistance in polycystic ovary syndrome (PCOS) women but FLX did not. Surprisingly, the effects of FO were similar to those of the n-6 PUFA-rich soybean oil (SBO). Since increased branched chain (BCAA) and aromatic amino acids (AA) affect insulin secretion and resistance, we investigated whether FO, FLX and /or SBO affect plasma metabolites, especially AA. Methods and findings: In this six-week, randomized, 3-parallel arm, double-blinded study, 54 women received 3.5 g/day FO, FLX or SBO. In 51 completers (17 from each arm), fasting plasma metabolites were measured at the beginning and at the end. As compared to FLX, FO and SBO increased insulin response and resistance as well as several BCAA and aromatic AA. Pathway analysis indicated that FO exerted the largest biochemical impact, affecting AA degradation and biosynthesis, amine, polyamine degradation and alanine, glycine, l-carnitine biosynthesis and TCA cycle, while FLX had minimal impact affecting only alanine biosynthesis and l-cysteine degradation. Conclusion: Effects of FO and SBO on plasma AA were similar and differed significantly from those of the FLX. The primary target of dietary PUFA is not known. Dietary PUFA may influence insulin secretion and resistance directly and alter plasma AA indirectly. Alternatively, as a novel concept, dietary PUFA may directly affect AA metabolism and the changes in insulin secretion and resistance may be secondary.
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Background Data on the effects of flaxseed oil omega-3 fatty acids supplementation on wound healing and metabolic status in subjects with diabetic foot ulcer (DFU) are scarce. Objective This study was conducted to evaluate the effects of flaxseed oil omega-3 fatty acids supplementation on wound healing and metabolic status in subjects with DFU. Methods The current randomized, double-blind, placebo-controlled trial was conducted among 60 subjects (aged 40-85 years old) with grade 3 DFU. Subjects were randomly allocated into two groups (30 subjects each group) to receive either 1000 mg omega-3 fatty acids from flaxseed oil supplements or placebo twice a day for 12 weeks. Results After the 12-week intervention, compared with the placebo, omega-3 fatty acids supplementation resulted in significant decreases in ulcer length (-2.0±2.3 vs. -1.0±1.1 cm, P=0.03), width (-1.8±1.7 vs. -1.0±1.0 cm, P=0.02) and depth (-0.8±0.6 vs. -0.5±0.5 cm, P=0.01). Additionally, significant reductions in serum insulin concentrations (-4.4±5.5 vs. +1.4±8.3 μIU/mL, P=0.002), homeostasis model of assessment-estimated insulin resistance (-2.1±3.0 vs. +1.0±5.0, P=0.005) and HbA1c (-0.9±1.5 vs. -0.1±0.4%, P=0.01), and a significant rise in the quantitative insulin sensitivity check index (+0.01±0.01 vs. -0.005±0.02, P=0.002) were seen following supplementation with omega-3 fatty acids compared with the placebo. In addition, omega-3 fatty acids supplementation significantly decreased serum high sensitivity C-reactive protein (hs-CRP) (-25.5±31.5 vs. -8.2±18.9 μg/mL, P=0.01), and significantly increased plasma total antioxidant capacity (TAC) (+83.5±111.7 vs. -73.4±195.5 mmol/L, P<0.001) and glutathione (GSH) concentrations (+60.7±140.2 vs. -15.5±129.7 μmol/L, P=0.03) compared with the placebo. Conclusions Overall, omega-3 fatty acids supplementation for 12 weeks among subjects with DFU had beneficial effects on parameters of ulcer size, markers of insulin metabolism, serum hs-CRP, plasma TAC and GSH levels. In addition, flaxseed oil omega-3 fatty acids may have played an indirect role in wound healing due to its effects on improved metabolic profiles.
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Background: Potential effects of resveratrol consumption on cardiovascular disease risk factors and body weight in overweight/obese adults have not been fully elucidated. Our present analysis was to evaluate the effects of resveratrol consumption on risk markers related to cardiovascular health in overweight/obese Individuals. Methods: Multiple literature databases were systematically searched, and 21 studies were included. Effect sizes were expressed as weighted mean difference (WMD) and 95% confidence interval (CI), and heterogeneity was assessed with the I2 test. Publication bias and subgroup analyses were also performed. Results: There were variations in reporting quality of included studies. Resveratrol intervention significantly lowered total cholesterol (WMD, -0.19 mmol/L; 95% CI, -0.32 to -0.06; P = 0.004), systolic blood pressure (WMD, -2.26 mmHg; 95% CI, -4.82 to -0.49; P = 0.02), and fasting glucose (WMD, -0.22 mmol/L; 95% CI, -0.42 to -0.03; P = 0.03). Heterogeneity was noted for these outcomes (35.6%, 38.7% and 71.4%, respectively). Our subgroup analysis showed significant reductions in total cholesterol, systolic blood pressure, diastolic blood pressure, glucose, and insulin in subjects ingesting higher dose of resveratrol (≥300 mg/day). Conclusion: Our finding provides evidence that daily resveratrol consumption might be a candidate as an adjunct to pharmacological management to better prevent and control cardiovascular disease in overweight/obese individuals.
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A two-arm randomized open labeled controlled clinical trial was conducted on 50 patients with non-alcoholic fatty liver disease (NAFLD). Participants were assigned to take either a lifestyle modification (LM), or LM +30 g/day brown milled flaxseed for 12 weeks. At the end of the study, body weight, liver enzymes, insulin resistance and hepatic fibrosis and steatosis decreased significantly in both groups (p< 0.05); however, this reduction was significantly greater in those who took flaxseed supplementation (p < 0.05). The significant mean differences were reached in hepatic markers between flaxseed and control group, respectively: ALT [-11.12 compared with -3.7 U/L; P< 0.001], AST [-8.29 compared with -4 U/L; p < 0.001], GGT [-15.7 compared with -2.62 U/L; p < 0.001], fibrosis score [-1.26 compared with -0.77 kPa; p = 0.013] and steatosis score [-47 compared with -15.45 dB/m; p = 0.022]. In conclusion, flaxseed supplementation plus lifestyle modification is more effective than lifestyle modification alone for NAFLD management.