International Journal of Obesity (2012) 36, 1485 -- 1493
& 2012 Macmillan Publishers Limited All rights reserved 0307-0565/12
www.nature.com/ijo
REVIEW
Effect of dairy consumption on weight and body composition
in adults: a systematic review and meta-analysis of randomized
controlled clinical trials
This paper has been amended from an Original Article to a Review since Advance Online Publication
AS Abargouei1,2, M Janghorbani3, M Salehi-Marzijarani3 and A Esmaillzadeh1,2
BACKGROUND: Although several observational and experimental studies have investigated the effect of dairy consumption
on weight and body composition, results are inconsistent.
OBJECTIVE: This systematic review and meta-analysis was conducted to summarize the published evidence from randomized
controlled clinical trials (RCTs) regarding the effect of dairy consumption on weight, body fat mass, lean mass and waist
circumference (WC) in adults.
DESIGN: PubMed, ISI Web of Science, SCOPUS, Science Direct and EMBASE were searched from January 1960 to October 2011
for relevant English and non-English publications. Sixteen studies were selected for the systematic review and fourteen studies
were included in meta-analysis.
RESULTS: Our search led to 14, 12, 6 and 8 eligible RCTs that had data on weight, body fat mass, lean mass and WC, respectively.
Overall, mean difference for the effect of dairy on body weight was 0.61 kg (95% confidence interval (CI): 1.29, 0.07,
P ¼ 0.08). Increased dairy intake resulted in 0.72 kg (95% CI: 1.29, 0.14, P ¼ 0.01) greater reduction in fat mass, 0.58 kg
(95% CI: 0.18, 0.99, Po0.01) gain in lean mass and 2.19 cm (95% CI: 3.42, 0.96, P-value o0.001) further reduction in WC
than that in controls. Subgroup analysis revealed that increasing dairy intake without energy restriction in both intervention
and control groups does not significantly affect weight, body fat mass, lean mass and WC; consumption of high-dairy weight
loss diets led to 1.29 kg (95% CI: 1.98, 0.6, Po0.001) greater weight loss, 1.11 kg (95% CI: 1.75, 0.47, P ¼ 0.001) greater
reduction in body fat mass, 0.72 kg (95% CI: 0.12, 1.32, P ¼ 0.02) gain in body lean mass and 2.43 cm (95% CI: 3.42, 1.44,
Po0.001) additional reduction in WC compared with controls.
CONCLUSION: Increased dairy consumption without energy restriction might not lead to a significant change in weight
or body composition; whereas inclusion of dairy products in energy-restricted weight loss diets significantly affects weight,
body fat mass, lean mass and WC compared with that in the usual weight loss diets.
International Journal of Obesity (2012) 36, 1485--1493; doi:10.1038/ijo.2011.269; published online 17 January 2012
Keywords: dairy; weight; body fat mass; body lean mass; waist circumference; clinical trials
INTRODUCTION
Obesity is an important public health problem worldwide, and its
prevalence is increasing in both developed and developing
countries.1 At least 2.8 million adults die each year as a result of
being overweight or obese. Furthermore, a World Health Organization fact sheet states that diabetes (44%), ischemic heart disease
(23%) and cancer burdens (7% and 41% based on type) are
attributable to overweight and obesity.1 Obesity is now an epidemic
worldwide,1 and the recent increase in its prevalence suggests a
strong determinant role of environmental factors in its etiology.1,2
Dairy consumption has been extensively studied for its possible
roles in body weight regulation.3 According to a report by the
International Dairy Federation, per capita consumption of dairy
products is higher in western countries than that in non-western
countries.4 On the other hand, prevalence of overweight and
obesity is higher in western populations as well.5 Although several
observational and experimental studies have investigated the
association between dairy consumption and weight change, the
role of dairy consumption in weight loss is still to be fully
explored.3,6 Available data conflict on the effect of dairy product
consumption on weight loss.3,6,7 The primary support for the
negative association between dairy intake and obesity originated
from cross-sectional studies,3 and a meta-analysis provided
information on the inverse association of calcium intake (from
dairy and other sources) with weight status in cross-sectional
studies.3 These findings were not confirmed by cohort studies
about the effect of dairy consumption;7 such that in a recent
systematic review of cohort studies, eight investigations---three in
children8 - 10 and five in adults11 - 15---showed a protective association of dairy intake against weight gain and another reported
a significant protective association only in adult males who
were initially overweight,16 whereas seven studies reported no
1
Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran; 2Department of Community Nutrition, School of Nutrition and Food Science, Isfahan
University of Medical Sciences, Isfahan, Iran and 3Department of Epidemiology and Biostatistics, School of Public Health, Isfahan University of Medical Sciences, Isfahan, Iran.
Correspondence: Dr A Esmaillzadeh, Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, PO Box 81745,
Isfahan, Iran.
E-mail: [email protected]
Received 23 August 2011; revised 15 November 2011; accepted 5 December 2011; published online 17 January 2012
Dairy intake, weight and body composition
AS Abargouei et al
1486
effect16 - 22 and one reported an increased risk (among children).23
Others have reported both a decreased and increased risk
of incident obesity depending on the type of dairy intake.15,24
Owing to the heterogeneity of cohort studies, as well as
inconsistent exposure and outcome measures, no meta-analysis
has been done on their findings.
Well-designed clinical trials are the best way to assess the effect of
dairy intake on weight and body composition. It has been
postulated that dairy consumption affects weight control, but
findings from randomized controlled clinical trials (RCTs) have been
conflicting. Several studies have suggested the beneficial effects of
dairy consumption on weight loss.25 - 29 For instance, consumption
of a dairy-rich (three servings per day) weight loss diet has resulted
in a 5 kg additional weight loss compared with the conventional
weight loss diet.27 However, several RCTs have failed to reach
significant conclusions,27,30 - 32 and some others have even documented their significant effects of weight gain.33 - 35
Although the effect of dairy consumption on body weight and
composition has been reviewed extensively,3,6,36 - 38 we are aware
of no meta-analysis of RCTs in this regard. Inconsistent results
from RCTs might be explained by different study designs, dose
and duration of intervention, variety of age groups and gender. An
advantage of meta-analysis to narrative reviews is the potential to
yield less biased summaries of the published findings. Therefore,
the goals of this report were to conduct a systematic review and, if
possible, a meta-analysis of published RCTs to summarize the
evidence on the effect of dairy consumption on body weight and
composition and to identify possible sources of heterogeneity
between studies.
MATERIALS AND METHODS
Search strategy
We searched for relevant English and non-English publications by
using the online databases of PubMed, ISI Web of Science,
SCOPUS, Science Direct and EMBASE for the period from January
1960 to October 2011. We also contacted experts in the field and
searched reference lists of the published papers. The keywords
used in our search strategy were selected from the Medical
Subject Headings (MeSH) database and were included as: ‘dairy’ or
‘calcium’ or ‘milk’ or ‘yogurt’ and ‘obese’ or ‘obesity’ or ‘overweight’ or ‘fat mass’ or ‘adiposity’ or ‘adipose’ or ‘weight’ or ‘body
mass index’ or ‘waist circumference (WC)’.
Eligibility criteria
To be included in the meta-analysis, a published study had to meet
the following criteria: (1) original article; (2) randomized controlled
trial; (3) adult human population; and (4) dairy or one of the natural
dairy products as the main independent variable. When there were
multiple publications from the same population or cohort, only
data from the most recent report were included. Information on
study design, participant characteristics, measurement of weight
change and randomization was extracted independently by two
reviewers (ASA and AE). Discrepancies were resolved by discussion.
A total of 18 randomized controlled trials were considered for
inclusion in this systematic review and meta-analysis.25 - 35,39 - 45
Excluded studies
Eligible studies were read more carefully by ASA and AE for any
methodological difference. We found that two papers,33,41 which
administered energy restriction, had confined the energy intake
into a defined certain value in both intervention and control groups,
whereas other studies restricted the energy intake of participants to
the amount of 500 kcal less than their computed daily energy
requirement. Because restriction of energy to fixed values can
directly affect weight change,33,41 we preferred not to include
the results of these two studies in the systematic review and
International Journal of Obesity (2012) 1485 - 1493
meta-analysis; however, findings from the maintenance phase of
study done by Zemel et al.41 were included in our systematic
review. Besides restriction of energy intake to a fixed value, these
two studies had some other distinct features. The study by Bowen
et al.33 compared a high-dairy diet with a high-protein diet, whereas
those we included in the meta-analysis used a high-dairy diet versus
diets with the same amount of protein. Another RCT done by Zemel
et al.41 was a two-phase RCT that had 3 months of energy restriction
to 1200-- 1500 kcal per day and a 6-month maintenance phase.
Zemel et al.41 in their study had an intervention on physical activity,
and they could not practically raise total intake of dairy and calcium
(dairy consumption in intervention group: 1.2 servings per day
versus 1.1 servings per day for controls). Therefore, we excluded
these two papers from the meta-analysis. Further readings also
revealed that a study by Eagan et al.42 was an analysis of 1-year
follow-up of another intervention done by Gunther et al.32; therefore, this study was removed too. One study35 had not presented
data needed for meta-analysis. We included the findings of
this study in our systematic review but not in the meta-analysis.
After these exclusions, 14 studies were left: 4 papers that assessed
the effects of high-dairy diets (without energy restriction),30 - 32,34
9 papers that assessed the effects of high-dairy weight loss
diets (with energy restriction)25,26,28,29,39,40,43 - 45 and 1 study with
two phases (with and without restriction)27 for meta-analysis. All
mentioned papers had data on weight, 12 papers had data on fat
mass,25 - 32,39,43 - 45 6 studies reported data for lean mass26 - 28,30,32,45
and 8 papers contained data for WC.25 - 28,31,40,43,45
Data extraction
We extracted data on publication (the first author’s last name, year
of publication and country of population studied), number of
individuals in intervention and control groups, duration of
intervention, age, gender, mean and s.d. of change in weight,
fat mass, lean mass and WC. Two studies had not reported mean
and s.d. of weight change,34,35,40 but presented means at baseline
and after intervention. We calculated mean difference for these
studies by the use of post-intervention data and included these
papers in our meta-analysis. Another study by Baran et al.35 that
had not reported mean and s.d. of weight change was included in
the systematic review but not in the meta-analysis. One of the
above-mentioned studies that was done by Barr et al.34 had
reported their results in men and women separately. Therefore,
we included the findings of this study as two separate studies in
the meta-analysis.34 Two studies had not reported s.d. of mean
changes in anthropometric measures but reported P-value for
comparison of means between intervention and control
groups.27,30 Therefore, we computed the s.d. for these studies
and used them in the meta-analysis. For five studies26 - 29,45 that
had reported s.e.m., we calculated s.d.s. One recently published
study had not reported mean change for weight, fat mass and WC.
These data were taken by contacting authors.45
Statistical analysis
The mean difference and s.d. of changes in anthropometric
measures (including weight, fat mass, lean mass and WC) was
used for the meta-analysis. Summary mean estimates with their
corresponding s.d.s were derived by the method of DerSimonian
and Laird46 by using random effects model, which incorporates
between-study variability. Meta-regression and subgroup analyses
were performed to check for the specific source of heterogeneity.
Between subgroups heterogeneity was evaluated using a fixed
effect model. Statistical heterogeneity between studies was
evaluated with Cochran’s Q test.47 Sensitivity analysis was used
to explore the extent to which inferences might depend on a
particular study or group of studies. Publication bias was assessed
by visual inspection of funnel plots.48 In these funnel plots, the
difference in mean change of weight and other indices were
& 2012 Macmillan Publishers Limited
Dairy intake, weight and body composition
AS Abargouei et al
displayed against the inverse of the square of the standard error
(a measure of the precision of the studies). Formal statistical
assessment of funnel plot asymmetry was done with Egger’s
regression asymmetry test and adjusted rank correlation test.49
Reported P-values are from the intercept of the regression
analysis, which provides a measure of asymmetry. In addition,
Begg’s adjusted rank correlation test was used.49 Statistical
analyses were carried out by the use of Stata, version 11.2 (Stata
Corp., College Station, TX, USA). P-values that were less than 0.05
were considered statistically significant.
RESULTS
In total, for the 14 studies included in the meta-analysis, 883 adults
aged 18 -- 85 years were enrolled. Our preliminary analysis
indicated slightly greater weight loss among those with high
dairy intake compared with those with low dairy intake (0.61 kg
(95% confidence interval (CI): 1.29, 0.07, P ¼ 0.08)). However,
there was a significant heterogeneity between studies (P ¼ 0.04;
Figure 1). To find the source of variation, we categorized the
studies into two major groups: those that administered energy
restriction (almost 500 kcal per day less than the estimated
energy requirement) for both intervention and control
groups,25,26,28,29,39,40,43 - 45 and those that did not use an energy
restriction.30 - 32,34 One study27 that had two phases of energy
restriction and weight maintenance (without energy restriction)
was considered in both categories.
Characteristics of RCTs (without energy restriction) included in
the systematic review are presented in Table 1. Two out of seven
papers in this category had no reported data on weight change
and its s.d.; therefore, we did not include them in metaanalysis.35,41 For five studies27,30--32,34 included in meta-analysis,
participants’ age ranged between 18 and 85 years. Duration of
intervention varied between 21 and 48 weeks. In these studies,
increasing calcium intake by 400 -- 850 mg per day via dairy
products in intervention group was compared with control
subjects who had maintained their habitual diet. None of these
individual studies found a statistically significant effect of dairy
consumption on weight. Among a total of 453 subjects, the
pooled standard difference in mean weight change was 0.33 kg
(95% CI: 0.35, 1.00, P ¼ 0.34; Figure 1). No heterogeneity was
found between studies included in this subgroup (P ¼ 0.67).
Characteristics of nine RCTs that administered high-dairy weight
loss diets (with energy restriction) and included in this systematic
review are presented in Table 2. Participants’ age in these studies
ranged between 18 and 70 years. Duration of intervention varied
between 8 and 48 weeks. In these RCTs, additional calcium intake
of 550 -- 1000 mg per day via dairy products in intervention group
was compared with control subjects who consumed 290 -- 800 mg
calcium daily. Total energy intake had been restricted to 500 kcal
less than the requirement for both groups. Among a total of 430
subjects, the pooled mean difference in mean weight change was
1.29 kg (95% CI: 1.98, 0.6, Po0.001; Figure 1). Heterogeneity
was not significant between studies (P ¼ 0.33).
Meta-analysis on 12 eligible studies25 - 32,39,43 - 45 that presented
data on fat mass showed that among a total of 638 adults aged
18 -- 70 years, the pooled estimated standard difference was
0.72 kg (95% CI: 1.29, 0.14, P ¼ 0.01), with a significant
between-study heterogeneity (P ¼ 0.007) (Figure 2). Subgroup
analysis based on energy restriction demonstrated that for nine
RCTs with energy restriction,25 - 29,39,43 - 45 the pooled standard
difference in means among a total of 331 subjects was 1.11 kg
(95% CI: 1.75, 0.47, P ¼ 0.001). No significant heterogeneity was
found (P ¼ 0.33). When we considered data from four RCTs27,30 - 32
that did not administer energy restriction, we observed that
among a total of 253 subjects, the pooled standard difference in
means was 0.16 kg (95% CI: 0.97, 0.66, P ¼ 0.71), with a
significant between-study heterogeneity (P ¼ 0.02). We could not
find the source of this heterogeneity even after further subgroup
analyses based on sex, age group and meta-regression.
Figure 1. Forest plot of randomized controlled trials illustrating weighted mean difference in weight change between the dairy-supplemented
and control groups for all eligible studies as well as for subgroup analysis based on energy restriction. For all the studies combined,
slightly greater weight loss was seen among those with high dairy intake compared with those with low dairy intake (P-value for
heterogeneity ¼ 0.04, Q test, I2 ¼ 41.2% and t2 ¼ 0.64). Meta-analysis of studies that administered high dairy intake without energy
restriction showed no significant effect of dairy intake on weight change (P-value for heterogeneity ¼ 0.67, Q test, I2 ¼ 0% and t2 ¼ 0.0).
For studies that administered energy restriction, we found the significant effect of dairy intake on weight loss (P-value for heterogeneity ¼ 0.32,
Q test, I2 ¼ 12.5% and t2 ¼ 0.15).
& 2012 Macmillan Publishers Limited
International Journal of Obesity (2012) 1485 - 1493
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Dairy intake, weight and body composition
AS Abargouei et al
1488
Table 1.
Randomized controlled trials (without energy restriction) that were eligible to be included in the systematic review
Author
Subjects
and
gender
Country
Age
range
(years)
Duration
(weeks)
Intervention
Calcium intake (mg per day)
Interventiona
Controla
Palacios
et al.30
13 F/3
M
Puerto
Rico
22 - 50
21
4 Daily
servings of
dairy
products
1337±380
463±325
Wennersberg
et al.31
76 F/37
M
30 - 65
24
625±259
244
adults
19 - 65
24
3 - 5 Portions
of dairy
products
daily
3 Servings
per day of
dairy
products
1145±425
Zemel
et al.41
Finland,
Norway
and
Sweden
USA
1325±254
579±166
Zemel
et al.27
23 F/11
M
USA
26 - 55
24
3 Servings of
dairy
products
daily
1124±53
458±96
Gunther
et al.32
90 F
USA
18 - 30
48
Barr
et al.34
129 F/
71 M
Canada
55 - 85
12
1300 1400 mg Ca
per day via
dairy
products
3 Servings of
fluid milk
Baran
et al.35
37 F
USA
30 - 42
144
Increase
dietary
intake of
calcium by
an average of
610 mg per
day via fluid
milk
Variables
presented
Result
Mean (s.d.)
weight, fat
and lean mass
at baseline
and after
intervention
Mean (s.d.)
change in
weight, fat
mass and WC
Not reported
High-dairy diet alone
did not affect body
composition
Mean (s.d.)
change in
weight, mean
change and Pvalue for fat
mass, lean
mass and WC
1131.29±337.2 742.4±321.5 Mean (s.d.)
change in
weight, fat
and lean mass
1404±296 F;
1556±400 M
654±218 F;
745±222 M
2163±583
1850±334
Mean (s.d.)
weight at
baseline and
after
intervention
Mean change
in weight, s.d.
or P-value was
not provided
Body composition
was not different
between the groups
No difference when
unadjusted. The lowdairy group gained
more weight, BMI
and trunk fat in the
University of
Tennessee
No significant
change in weight but
significant change in
fat mass, lean mass
and WC
Increased dairy
intake did not affect
weigh, fat and lean
mass
The milk group
gained more weight
than controls
Milk group gained
more weight than
the controls
Abbreviations: BMI, body mass index; F, female; M, male; WC, waist circumference. aMean±s.d.
We found a significant effect of dairy intake on increasing lean
body mass in the whole data set26 - 28,30,32,45 (the pooled estimated
standard difference: 0.58 kg; 95% CI: 0.18, 0.99, Po0.01; P-value for
heterogeneity ¼ 0.07); subgroup analysis based on energy restriction showed that the effect is significant for four RCTs26 - 28,45 that
administered energy restriction (0.72 kg; 95% CI: 0.12, 1.32,
P ¼ 0.02, P-value for heterogeneity ¼ 0.06) and nonsignificant for
three RCTs27,30,32 without energy restriction (0.35 kg; 95% CI:
0.15, 0.86, P ¼ 0.17, P-value for heterogeneity ¼ 0.29; Figure 3).
Eight studies25 - 28,31,40,43,45 had reported data on WC. For all
studies combined, we found the pooled estimated standard
difference of 2.19 cm (95% CI: 3.42, 0.96, Po0.001, P-value for
heterogeneity ¼ 0.03; Figure 4). When the subgroup analysis was
performed based on energy restriction, we observed that for seven
RCTs25 - 28,40,43,45 that administered energy restriction in a total of 289
subjects, high dairy intake had resulted in a greater reduction in WC
compared with that in control group (the pooled standard difference in means: 2.43 cm; 95% CI: 3.42, 1.44, Po0.001, P-value
for heterogeneity ¼ 0.60). Such a finding was not obtained for two
International Journal of Obesity (2012) 1485 - 1493
RCTs27,31 that had not administered energy restriction (2.68 cm;
95% CI: 8.02, 2.66, P ¼ 0.32, P-value for heterogeneity ¼ 0.01).
In a sensitivity analysis, we found that the effect of dairy foods
on body weight and fat mass was not substantially modified by
the result of a certain study. However, owing to the small number
of studies (without energy restriction) that presented data for WC
and lean mass, excluding each study could change the overall
effect size. We did not find any evidence of publication bias for
studies assessing dairy’s effect on weight (P ¼ 0.68, Egger’s test)
and lean body mass (P ¼ 0.32), despite a slight asymmetry in Begg’s
funnel plot (Figure 5). With regard to body fat and WC, we reached a
significant publication bias by funnel plot and Egger’s test (P ¼ 0.03
and P ¼ 0.01, respectively); however, this was not verified by Begg
and Mazumdar test (P ¼ 0.47 and P ¼ 0.28, respectively).
DISCUSSION
We found that increasing dairy consumption to about
recommended daily intakes in adults, who do not follow any
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AS Abargouei et al
1489
Table 2.
Randomized controlled trials (with energy restriction) that were eligible to be included in the systematic review
Author
Subjects
and
gender
Country
Age
range
(years)
Duration
(weeks)
Intervention
Variables presented
Result
Calcium intake (mg per day)
Intervention
p4
Servings of
dairy
products
per day
3 - 4 Daily
servings of
dairy
products
Van Loan
et al.39
71
adults
USA
20 - 50
12
Smilowitz
et al.40
36 F/9
M
USA
18 - 35
12
Josse
et al.45
54 F
Canada
19 - 45
16
3 - 4 Daily
servings of
dairy
products
Fagih
et al.25
42 F
Iran
20 - 50
8
3 Servings
of low-fat
milk
Zemel
et al.26
49
adults
USA
18 - 35
12
3 Daily
servings of
dairy
products
Zemel
et al.27
25 F/4
M
USA
26 - 55
24
3 Daily
servings of
dairy
products
Zemel
et al.28
27 F/7
M
USA
18 - 50
12
6 oz
Servings of
fat-free
yogurt
Thompson
et al.43
36
adults
USA
25 - 70
48
4 Servings
of dairy
products
HarveyBerino
et al.44
48
adults
USA
18 - 60
48
3- 4
Servings of
dairy
products
Zemel
et al.29
22
adults
USA
18 - 60
12
3 Daily
servings of
dairy
products
a
Controla
1288.4±94.6
434.6±56.6
1244.8±108
449.0±69.7
Mean (s.d.) change in
weight and body fat
Increased dairy
intake led to
greater weight
and fat loss
Mean (s.d.) for weight Percent change
and WC at baseline
of
and after intervention anthropometric
measurements
was not different
between the
groups
1200±19
299±22
Mean (s.d.) change in Percent change
weight, fat mass, lean of
mass and WC
anthropometric
measurements
was not different
between the
groups
1302±107.56 495.46±163.87 Mean (s.d.) change in Subjects in the
weight, fat mass and milk group lost
WC
more weight, fat
mass and WC
than the controls
1400
500
Mean (s.e.) change in Dairy-rich diet
weight, fat mass, lean augmented
mass and WC
weight loss by
targeting fat
compartment
1037±27
468±23
Mean and P-value for Subjects in the
change in weight, fat dairy group lost
mass, lean mass and more weight, fat
WC
mass and WC and
less lean mass
than the controls
1077±22
495±28
Mean (s.e.) change in Subjects in the
weight, fat mass, lean dairy group lost
mass and WC
more weight, fat
mass and WC and
less lean mass
than the controls
1387.4±152.9
799.6±166.5
Mean (s.d.) change in Mean changes in
weight, fat mass and weight, fat mass
WC
and WC were not
different between
the groups
1239±355
574±157
Mean (s.d.) change in Change in weight
weight and body fat and body fat was
not different
between the
groups
1137±164
430±94
Mean (s.e.) change in Mean loss of
weight and body fat, weight, fat mass
mean change in WC
and WC was
were presented only significantly
in figure and data
higher in the
were not shown
dairy group
Abbreviations: F, female; M, male; WC, waist circumference. aMean±s.d.
calorie-restricted diet, would not affect weight, fat mass, lean body
mass and WC. However, consumption of high-dairy calorierestricted diets might result in a greater weight loss and higher
reduction of WC and fat mass compared with conventional
calorie-restricted diets. Our findings indicated that increased dairy
& 2012 Macmillan Publishers Limited
intake might lead to gain in lean body mass. To the best of our
knowledge, this is the first meta-analysis of RCTs assessing the
effect of dairy intake on weight and body composition.
It must be kept in mind that we could not include two
papers35,41 that met our inclusion criteria but lacked required
International Journal of Obesity (2012) 1485 - 1493
Dairy intake, weight and body composition
AS Abargouei et al
1490
Figure 2. Forest plot of randomized controlled trials illustrating weighted mean difference in fat mass between the dairy-supplemented and
control groups for all eligible studies as well as for subgroup analysis based on energy restriction. For all the eligible studies combined, the
significant effect of dairy intake on reducing fat mass was observed (P-value for heterogeneity o0.01, Q test, I2 ¼ 56.1% and t2 ¼ 0.51).
For nine RCTs with energy restriction, the effect was also significant (P-value for heterogeneity ¼ 0.33, Q test, I2 ¼ 12.0% and t2 ¼ 0.11).
However, data from four RCTs that did not administer energy restriction indicated no significant effect of dairy intake on body fat mass
(P-value for heterogeneity ¼ 0.02, Q test, I2 ¼ 70.7% and t2 ¼ 0.46).
Figure 3. Forest plot of randomized controlled trials illustrating weighted mean difference in lean body mass between the dairysupplemented and control groups for all eligible studies as well as for subgroup analysis based on energy restriction. For all the studies
combined, the significant effect of dairy consumption on lean body mass was seen (P-value for heterogeneity ¼ 0.07, Q test, I2 ¼ 48.9%
and t2 ¼ 0.13). For four RCTs that administered energy restriction, high dairy intake had resulted in a greater gain in lean body mass
compared with that in the control group (P-value for heterogeneity ¼ 0.06, Q test, I2 ¼ 59.7% and t2 ¼ 0.21). Such a finding was not obtained
for three RCTs that had not administered energy restriction (P-value for heterogeneity ¼ 0.29, Q test, I2 ¼ 19.5% and t2 ¼ 0.05).
data about weight change. Baran et al.35 found that increased
dairy intake would result in weight gain compared with the
controls; however, as the main end point of the study was not
weight change, they did not perform further analysis on weight
change difference. Zemel et al.41 showed no difference in weight
between high-dairy group and controls. In both above-mentioned
International Journal of Obesity (2012) 1485 - 1493
studies35,41 as well as in another study done by Barr et al.,34 total
energy intake was significantly increased due to the inclusion of
dairy products in the diet. This was not the case for four other
studies27,30 - 32 that administered dairy products without energy
restriction. Therefore, one might conclude that dairy consumption
(without calorie restriction) would result in a significant weight
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Dairy intake, weight and body composition
AS Abargouei et al
1491
Figure 4. Forest plot of randomized controlled trials illustrating weighted mean difference in WC between the dairy-supplemented and
control groups for all eligible studies as well as for subgroup analysis based on energy restriction. For all the studies combined, the significant
effect of dairy consumption on WC was seen (P-value for heterogeneity ¼ 0.03, Q test, I2 ¼ 53.4% and t2 ¼ 1.63). For seven RCTs that
administered energy restriction, high dairy intake had resulted in a greater reduction in WC compared with that in the control group (P-value
for heterogeneity ¼ 0.60, Q test, I2 ¼ 0.0% and t2 ¼ 0.0). Such a finding was not obtained for two RCTs that had not administered energy
restriction (P-value for heterogeneity ¼ 0.01, Q test, I2 ¼ 84.7% and t2 ¼ 12.8).
Figure 5. Begg’s funnel plots (with pseudo 95% CIs) of the difference in means (DMs) versus the s.e.s of the MDs (mean differences)
for studies that assessed the effect of dairy intake on weight (a), fat mass (b), lean body mass (c) and WC (d). The horizontal line shows
the pooled DMs calculated with the DerSimonian and Laird random effects model. We did not find any evidence of publication bias
for studies assessing dairy’s effect on weight and lean body mass. With regard to body fat and WC, we reached a significant publication
bias by funnel plot; however, this was not verified by Begg and Mazumdar test.
gain and increased body fat mass and WC due to increased energy
intake. However, with the findings of all such studies combined,
we did not find any evidence supporting this hypothesis. In
contrast, our findings confirm the suggestions made by recent
narrative reviews on the effect of dairy consumption on weight
change.3,6 Dougkas et al.3 expressed that the majority of studies
found no significant weight gain by dairy consumption when
energy intake was not restricted. The same conclusion was also
& 2012 Macmillan Publishers Limited
reached by Lanou and Barnard6 when they reviewed studies that
used dairy or calcium supplements as an intervention.
We found that inclusion of dairy products in weight loss diets
might accelerate weight reduction. The amount of dairy products
used in published papers was equivalent to the provision of
550 -- 1000 mg additional calcium for overweight or obese subjects
as compared with the consumption of 200 -- 800 mg calcium in the
control group. Our findings also demonstrated that consumption
International Journal of Obesity (2012) 1485 - 1493
Dairy intake, weight and body composition
AS Abargouei et al
1492
of high-dairy weight loss diets would result in a greater reduction
in fat mass and WC and a further increase in lean body mass.
These results indicate that dairy consumption would help people
to lose weight from fat compartments of the body, particularly
from abdominal adipose tissue, which has been reported as a
main determinant of cardiovascular risk factors.50
Narrative reviews that considered the effect of increasing dairy
intake along with energy restriction have reached conflicting
findings. For instance, Dougkas et al.3 found five RCTs with energy
restriction in their review, and reported that three studies showed
no evidence,33,43,44 whereas two studies27,28 found significant
effect of increasing dairy consumption along with weight loss
diets on weight reduction. However, the search methodology
used by Dougkas et al.3 seems to be incomplete because we
found 11 studies that assessed the effect of dairy-rich weight loss
diets on weight change.25 - 29,33,39 - 41,43,44 These studies had some
inconsistencies in their method of intervention that can affect the
interpretation of their results. Two of the mentioned studies
restricted total energy intake of their subjects to a fixed calorie33,41
(that is, 1200 -- 1400 kcal per day); others administered an energy
intake of 500 kcal less than subjects’ requirements.
Several underlying mechanisms for the effect of dairy products
on body weight and composition are proposed. It has been
suggested that calcium supplementation can affect adipocyte
lipid metabolism, fat oxidation, fatty acid absorption and
postprandial fat metabolism. Furthermore, there are some findings
that suggest dairy constituents other than calcium, such as
conjugated linoleic acid, medium-chain fatty acids and proteins,
may play a role. Evidence about the effect of dairy on appetite
regulation has been accumulating recently and some of its
constituents, such as dairy protein, calcium and fat, have been
proposed for this kind of effect. All these possible underlying
mechanisms have been extensively reviewed and discussed by
Dougkas et al.3 Despite these mechanisms, we found the
beneficial effects of dairy only in energy-restricted studies.
Therefore, it might be hypothesized that appetite-lowering effects
of dairy work more efficiently along with energy-restricted diets.
This hypothesis remains to be examined in future studies.
The majority of cross-sectional studies about the relationship
between dairy consumption and body weight, composition or
abdominal fat accumulation in adults found a significant inverse
association.51 - 59 Some studies failed to find any relationship,53,60,61 and one study showed inconsistent results based on
the kind of dairy product.62 Cross-sectional studies cannot reach a
casual relationship; therefore, to detect a causal relationship one
would need to look at cohort studies. Findings from cohort studies
on the association of dairy intake and weight change are
inconclusive.7 So far, many RCTs have been published worldwide
about the effect of increasing dairy consumption on weight
change and body composition. This makes meta-analysis of their
results possible. RCTs are the most appropriate study designs to
show casual effects, and meta-analysis of their results can lead to a
more reliable conclusion.
It must be kept in mind that some RCTs included in the current
meta-analysis had small sample sizes. Furthermore, the duration of
follow-up for studies that administered dairy intake with energy
restriction was short, such that only a few investigations had
followed the participants for more than 12 weeks. In addition,
most published papers were from the United States and limited
data are available from other countries, particularly from nonwestern populations. As our findings, particularly those for body
composition indicators (fat mass, lean body mass and WC), are
based on a limited number of RCTs, further investigations are
required to come to a better understanding.
In conclusion, our systematic review and meta-analysis on RCTs
indicated that increasing dairy consumption without energy
restriction might not lead to a significant change in weight and
body composition, whereas inclusion of dairy products in weight
International Journal of Obesity (2012) 1485 - 1493
loss energy-restricted diets would result in a greater reduction of
weight, fat mass and WC and gain in lean body mass compared
with the conventional weight loss diets.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
AUTHOR CONTRIBUTIONS
ASA and AE contributed to the conception, design, statistical analyses, data
interpretation and manuscript drafting. MJ and MSM contributed to the data
analysis. All authors contributed to the approval of the final manuscript for
submission.
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