Daily consumption of a synbiotic yogurt
decreases energy intake but does not improve
gastrointestinal transit time: a double-blind,
randomized, crossover study in healthy adults
Hilary M F Tulk†, Diane C Blonski†, Lauren A Murch, Alison M Duncan and Amanda J Wright*
Objective: Probiotic and synbiotic products are widely marketed to healthy individuals, although potential benefits
for these individuals are rarely studied. This study investigated the effect of daily consumption of a synbiotic yogurt
on gastrointestinal (GI) function in a sample of healthy adults.
Subjects/Methods: In a randomized crossover double-blind study, 65 healthy adults consumed 200 g/day of
yogurt with (synbiotic) or without (control) added probiotics (Bifidobacterium lactis Bb12, Lactobacillus acidophilus
La5, Lactobacillus casei CRL431) and 4 g inulin for two 15-day treatment periods, each preceded by a 6-week
washout period. GI transit time (GTT), duration of colour (DOC), GI symptoms and dietary intake were assessed and
analyzed using repeated measures ANOVA, including PRE-treatment GTT as a covariate. Participants were grouped
as short GTT (STT, n = 50, ≤32.7 h) or long GTT (LTT, n = 15, >32.7 h) based on their PRE-treatment GTT assessment.
Results: POST-treatment GTT and DOC were not different between synbiotic and control, and did not change from
PRE-treatment, within the STT or LTT groups. There were no changes in GI symptom ratings, indicating that both
yogurts were well tolerated. In STT, energy, fat and protein intakes were decreased from baseline with synbiotic
(p= 0.055, p = 0.059 and p= 0.005, respectively) and dietary fibre intake was higher POST-treatment with synbiotic
versus control (p= 0.0002). In LTT, decreases in energy and fat intakes with synbiotic were not significant (p= 0.14
and p =0.18, respectively) and there were no differences in dietary fibre intake.
Conclusion: Consuming 200 g/day of synbiotic yogurt did not significantly alter GTT in healthy adults, but was well
tolerated and helped to reduce overall energy intake.
Keywords: Synbiotics, Yogurt, Gastrointestinal transit, Energy intake
It is well established that the gastrointestinal (GI) micro-
biota impacts overall health and that the quantities and
types of bacteria composing the microbiota can be opti-
mized by dietary factors, particularly prebiotics and
probiotics . Consequently, consumers are turning to
probiotic-containing foods for relief of specific condi-
tions or to improve overall health . However, evidence
to support health claims for probiotics and synbiotics
(containing prebiotics and probiotics) in the general popu-
lation, the main group to whom these products are
marketed, is limited [2,3]. The efficacy of synbiotics can
vary depending on the probiotic strain and the food matrix
can affect probiotic survival and potential health benefits
[4,5]. Strain- and product-specific research to substantiate
the efficacy of probiotics in improving or maintaining GI
health in healthy consumers is required [2-4,6].
Probiotics have traditionally been used to treat GI dis-
eases and disturbances, including lactose intolerance, rota-
virus and antibiotic associated diarrhea, inflammatory
bowel disease and constipation [3,7,8]. Consumption of
fermented dairy products containing Bifidobacterium lactis
* Correspondence: email@example.com
Department of Human Health and Nutritional Sciences, University of Guelph,
Guelph, Ontario N1G 2W1, Canada
© 2013 Tulk et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Tulk et al. Nutrition Journal 2013, 12:87
DN-173010 (≥108CFU/g) has been shown to improve
bowel movement frequency and consistency in women
with constipation , to decrease initially long GI transit
times (GTT) in healthy women , men  and older
adults [12,13], and to improve overall GI well-being and di-
gestive symptoms in healthy women . Intestinal transit
time tended to decrease (p = 0.055) in healthy Japanese
women with slow transit times (> 40 hours) whom con-
sumed 170 g/day yogurt containing 108CFU/g of the same
probiotic strain .
A growing body of work exists with respect to poten-
tial GI health benefits of dairy products containing vari-
ous probiotic strains [16-18] including Bifidobacterium
lactis Bb12 and Lactobacillus acidophilus La5 [19-21].
Savard et al.  showed that these probiotics con-
sumed for 4 weeks from a commercial yogurt survived
GI transit and led to increases and decreases, respect-
ively, in the presence of beneficial and potentially patho-
genic gut bacteria. Consumption of yogurts containing
Bb12, in combination with Lactobacillus acidophilus
La5, has also been shown to suppress H. pylori infections
, to improve antioxidant status in participants with type
2 diabetes , and to maintain serum insulin levels in
pregnant women .
Prebiotics are non-digestible carbohydrates that select-
ively stimulate the growth of beneficial bacteria in the
GI tract . Fructooligosaccharides, in particular inulin,
are commonly added to foods in concentrations from
0.6-2.1 g/100 g . Inulin is a soluble prebiotic fibre that
has been shown to increase fecal Bifidobacteria spp.
levels , to increase stool bulk and frequency when
initially low , and to exert a mild laxative effect in
elderly people with constipation . As well, 16 g/day
of inulin and oligosaccharides decreased subjective hun-
ger scores and increased concentrations of plasma gut
peptides that regulate food intake, suggesting a satiety
effect in healthy adults . However, research to estab-
lish the relevance of satiety-promoting foods, in terms of
their long-term ability to modulate food intake and to
beneficially impact body weight, is required. Also, while
there is rationale for enriching foods with prebiotics,
some studies have associated prebiotic consumption, in-
cluding inulin, with mild GI side effects [29-31]. Since
functional foods that modulate energy and increase fibre
intake may be an important strategy in addressing over-
weight, obesity and their associated conditions [29,31,32],
research addressing the tolerance of prebiotics in the gen-
eral population is warranted.
Consumption of dairy products, including yogurt, by
North American and European consumers is consider-
able and dairy products currently lead the probiotic mar-
ket . This is, in part, due to the healthy perceptions
and familiarity consumers have with fermented dairy
products containing live bacteria  and to the fact that
live strains of probiotics can be added to these products
relatively easily . Yogurt, in particular, is considered
to be a suitable synbiotic food matrix  since it is
intrinsically thickened and its texture should remain ac-
ceptable if prebiotic fibre-addition induces further thick-
ening . Addition of a prebiotic to dairy products
containing probiotics has also been shown to improve the
survival of probiotic bacteria during their shelf-life [36,37].
Therefore, synbiotics are an exciting area of growth for the
dairy sector . More broadly, a growing body of evidence
supports a role for various synbiotic supplements and
foods in improving GI disturbances [14,38-42].
There is also evidence that fibre-enriched yogurts can
suppress short-term appetite and may be effective in
controlling food intake [43,44]. For example, yogurt was
found to have greater satiating effects than isocaloric
fruit-based or dairy fruit beverages  and the effect
was enhanced when yogurt was enriched with 6 g of inu-
lin . Therefore, optimizing the microbial population
of the GI tract through the consumption of synbiotics
could be a strategy in preventing obesity, in addition to
other chronic diseases such as inflammatory bowel dis-
orders, and some cancers [3,29,32,47]. This study inves-
tigated whether daily consumption of a synbiotic yogurt
improves GI function in a sample of healthy Canadian
adults. GTT, GI symptoms and food intake were com-
pared between participants with short or long baseline
GTT following consumption of a synbiotic yogurt or a
control product without added probiotics and inulin.
This study was conducted at the Human Nutraceutical Re-
search Unit (HNRU) in the Department of Human Health
and Nutritional Sciences at the University of Guelph and
was approved by the University’s Human Research Ethics
Board. A randomized crossover double-blind design was
utilized and consisted of two 15-day treatment periods,
each preceded by a 6-week washout period.
Healthy males and females (18 to 65 y, BMI 18–35 kg/m2)
were recruited from the local community and pre-screened
using a phone/email questionnaire. Individuals were ex-
cluded if they had food allergies or intolerances, GI disor-
ders or disease or if they regularly used medications
(except hormonal contraceptives), natural health products
or dietary supplements, or had used antibiotic medica-
tion <3 months prior to the study. Individuals who smoked
or were elite or varsity athletes and/or training for a major
athletic event, and females who were pregnant, lactating or
not practicing birth control, were also excluded. All partici-
pants provided written informed consent and attended an
orientation session prior to the study.
Tulk et al. Nutrition Journal 2013, 12:87
Page 2 of 9
Determination of gastrointestinal transit time
GTT was measured using capsules containing 0.25 g of
carmine red (Sensient Colours Canada Ltd., Kingston, ON)
and 0.15 g of carbon black (Castleguard Health Services,
Paris, ON). Carmine red is a non-digestible food colourant
that produces a distinct red colour in the feces [48,49]
which is enhanced by the presence of carbon black .
Participants consumed 2.0 g carmine red and 0.5 g
carbon black with breakfast on two mornings, sepa-
rated by 72 h, for duplicate determination of GTT.
They recorded the date and time of capsule consump-
tion and the date, time and colour of all subsequent
bowel movements until both doses of colour had
passed. GTT was defined as the length of time (h) be-
tween capsule consumption and appearance of red
colour in the feces and is reported as the average time
for both doses to appear in the feces. The duration of
red colour (DOC) in the feces was also calculated, as
a secondary indicator of GI transit. DOC was defined
as the length of time (h) between capsule consump-
tion and the last appearance of red colour in the feces
and is reported as the average time for both doses to
disappear from the feces. DOC relates to the amount
of time the bowel mucosa is exposed to digesta, in-
cluding possible carcinogens .
At the start of the 6-week washout period, a baseline
GTT assessment was completed to familiarize partici-
pants with the GTT assessment protocol and to screen
for participants with difficulty detecting the red colour in
their feces. Baseline GTT data was used for preliminary
examination of the distribution of GTT within partici-
pants. GTT assessments were completed PRE-treatment
(commencing 3 days prior to Day 1) and POST-treatment
(commencing on Day 13) during each 15-day treatment
Participants were instructed to maintain their usual life-
style and dietary habits with specific instructions to
avoid yogurt products and foods with added prebiotics
or probiotics, with the exception of the study treatments.
The study treatments were industrially manufactured
vanilla flavoured yogurts with (symbiotic) and without
(control) the addition of Bifidobacterium lactis Bb12
(≥107CFU/g), Lactobacillus acidophilus La5 (≥107CFU/g),
Lactobacillus casei CRL431 (≥107CFU/g) and 2 g inulin
(average degree of polymerization ≥ 10, Beneo Raftiline)
per 100 g serving. Probiotic counts ≥ 109CFU per 100 g
serving were verified by pour plate count methods
throughout the treatment period. Both yogurts were pro-
duced using identical starter cultures and milk ingredients
and were manufactured for each treatment period separ-
ately so that the products were consumed at the same
point in their shelf life. Treatments were packaged as 100 g
servings in opaque white cups, stored under refrigeration
and provided to participants immediately prior to the
start of each treatment period. Per 100 g serving, the yo-
gurts contained 100 kcal, 3.0 g protein, 18.0 g carbohydrate
and 3.0 g fat. Participants were instructed to consume two
100 g servings of yogurt per day during each treatment
period and to keep the yogurt refrigerated. Participants
recorded the date, time, and other details about their
yogurt consumption in a daily study diary.
Baseline anthropometric data
Five days prior to the first treatment period, participants
reported to the HNRU after a 12–14 h overnight fast.
Height was measured to the nearest 0.1 cm using a
stadiometer (SECA Portable Stadiometer 214, Hanover,
MD, USA) and body weight was measured to the nearest
0.1 kg using a calibrated digital scale (Acculab SV-100,
Edgewood, NY, USA). Body fat (%) was determined by
bioelectric impedance analysis (BodyStat 1500™, BodyStat
Ltd., Douglas, IOM).
A modified version of the GI symptom rating scale (GSRS)
 was used to evaluate changes in perceived GI symp-
toms at Days 1, 7 and 15 of each treatment period. The
modified GSRS included 5 questions pertaining to abdom-
inal discomfort, stomach grumbling, bloating, belching,
and flatulence, each scored as 0 for ‘no symptoms’ to 3 for
‘extreme symptoms’ , and one question each related to
consistency and frequency of bowel movements scored as
0 to 4, where 0 and 4 indicated opposite extremes and 2 in-
dicated normal consistency or frequency.
Three-day food records were collected at the start of
the first 6-week washout period (baseline) and on Days
13–15 of each treatment period (POST-treatment).
Participants were provided with detailed instructions
for food record completion. Food records were reviewed
with a study coordinator upon submission, analyzed
using The Food Processor® SQL version 10.3.0.0 (ESHA
Research Salem, OR, USA) and 3-day means for en-
ergy, fat, protein, carbohydrate and dietary fibre were
Data and statistical analysis
The intra-individual variation in PRE-treatment GTT as-
sessment data was examined for each participant. Par-
ticipant data was excluded from statistical analysis if the
PRE-treatment GTT was significantly different between
synbiotic and control or if the coefficient of variation for
PRE-treatment GTT was ≥40%. Participants were grouped
as short GTT (STT) or long GTT (LTT) based on
 and . The distribution of PRE-treatment GTT was
Tulk et al. Nutrition Journal 2013, 12:87
Page 3 of 9
examined using a histogram to determine a cut-off point
for grouping of participants as STT or LTT (Figure 1).
GTT was analyzed for effect of treatment within
STT and LTT groups, both between treatments (using
repeated measures ANOVA on POST-treatment values
and controlling for participant, treatment and treat-
ment order and including PRE-treatment values as a
covariate), and within treatments (using a paired t-test
on PRE- and POST-treatment values within a treatment).
Baseline anthropometric data were compared between
STTand LTTgroups using an unpaired t-test. GSRS scores
were analyzed within STT and LTT groups for effect of
time (i.e. Days 1 vs. 7 vs. 15) within treatments and for
the effect of treatment within study days, using Chi
squared analysis. Dietary intake data was analyzed within
STT and LTT groups for effect of time (i.e. baseline vs.
POST-treatment) within treatments and for effect of treat-
ment (on POST-treatment values), both using unpaired
t-tests. All statistical analyses were performed using SAS
version 9.1 (SAS Institute, Inc., Cary, NC) and a signifi-
cance level of p <0.05.
Participant flow and GTT grouping
Of the 300 potential participants screened by phone or
email, 158 attended a screening appointment and 127 were
eligible for the study, assigned participant numbers and in-
vited to complete a baseline GTT assessment. 111 partici-
pants completed the baseline GTT assessment. Of these,
28 subsequently dropped out or were excluded from the
study due to scheduling conflicts (n=9), use of antibiotics
or other medications (n=3), difficulty swallowing the
capsules (n=2), GI upset or diarrhea (n=6), or not wish-
ing to continue (n=8). Therefore, 83 participants entered
the first treatment period, during which 4 participants
discontinued their participation due to illness (n = 2),
scheduling conflicts (n=1), and antibiotic use (n=1). After
completion of the first treatment period, 10 participants
were excluded from the study due to GI upset (i.e. diarrhea)
during the GTT assessments (n=5), non-compliance to
study protocol (n=1), commencement of antibiotics or
prescription drugs (n=2) or scheduling conflicts (n=2).
After analysis of the PRE-treatment GTT for intra-
individual variation ≥40%, 4 more participants were ex-
cluded. The distribution of PRE-treatment GTT for each
treatment period was examined for the 65 participants
whose data was included in the statistical analysis. GTT
data was divided at the 75th percentile with participants
grouped as either short GTT (STT; n=50, ≤32.7 h) or long
GTT (LTT; n=15, >32.7 h). Sample size was estimated at
41 participants for the STT group and 17 participants for
the LTT group using effect sizes (i.e. time reductions) of
4 hours for STT and 10 hours for LTT, standard deviation
estimates of 5 for STT and 8 for LTT, a power of 95%, an
alpha of 0.05 and 2-sided testing.
At baseline, participants had a mean age of 28.6 y, body
weight of 72.1 kg, height of 171.2 cm, BMI of 24.4 kg/m2
and body fat of 23.0%. There were no significant differ-
ences in participant characteristics between the STT and
LTTgroups (Table 1). The STTgroup consisted of 23 men
and 27 women, whereas the LTTgroup consisted predom-
inantly of women (n=15) versus men (n=3).
Figure 1 Histogram depicting the distribution of PRE-treatment GTT1. Abbreviations: GTT, gastrointestinal transit time.1Distribution of
PRE-treatment GTT values, measured in duplicate in two separate GTT assessments, for each participant (n =65).
Tulk et al. Nutrition Journal 2013, 12:87
Page 4 of 9
Gastrointestinal transit time assessments
There were no significant differences in POST-treatment
GTT or DOC between the synbiotic and control yogurts
within either the STT or the LTT groups. Similarly, within
the STT and LTT groups there were no significant differ-
ences between PRE-treatment and POST-treatment GTT
or DOC, within either the synbiotic or control yogurts
Both the synbiotic and control yogurts were well tolerated,
based on participant ratings of abdominal discomfort, ab-
dominal rumbling, abdominal bloating, belching, flatu-
lence, bowel movement consistency and bowel movement
frequency assessed by GSRS scores, within or between
treatments, within both the STT or LTTgroups (Figure 2).
Dietary intake data is presented in Table 3. In the STT
group, energy, fat and protein intakes decreased from
baseline following consumption of the synbiotic yogurt
(p = 0.055, p = 0.059 and p = 0.005, respectively) and
carbohydrate intake decreased from baseline following
consumption of the control yogurt (p=0.008). In the LTT
group, energy and fat decreased from baseline following
consumption of the synbiotic yogurt, but these changes did
not reach statistical significance (p=0.14 and p=0.18,
respectively). In the STTgroup, dietary fibre intake did not
significantly change with consumption of the synbiotic, but
decreased from baseline with consumption of the control
(p=0.0002) and was significantly higher POST-treatment
with the synbiotic versus control treatment (p=0.0002). In
the LTT group, there was no significant change in dietary
fibre intake from baseline with the synbiotic (p=0.25) or
control (p=0.24) or POST-treatment differences between
the synbiotic and control (p=0.58).
Although claims of improved GI function are widely im-
plied in the marketing of probiotic and synbiotic dairy
products, the roles of these products in improving GI
function in healthy individuals requires further investiga-
tion. Furthermore, there are few reports of typical GTT
in healthy Canadians. To our knowledge, this study is
the first to examine the effects of a synbiotic yogurt on
measures of GI function and dietary intake in healthy
The average PRE-treatment GTT in this study was in
the range of 30 h, based on all participants. This is
slightly lower than the 41.0 ±18.9 h reported for a sam-
ple of healthy Canadian adults consuming their habitual
diet and determined using fecal x-ray monitoring for
passage of radiopaque pellets . Consuming a synbiotic
yogurt did not change GTT or DOC from baseline and
was not different from the control yogurt, for either the
STT or LTTgroups. Past research demonstrates that DOC
can vary even among individuals with the same frequency
of bowel movements, particularly in those with longer
transit times . In this study, high variability in DOC
was observed in both STT and LTT PRE- and POST-
Our STT and LTT groups had baseline GTT 25.2 ±
0.4 h and 49.5± 4.3 h, respectively. In a recent study,
GTT, measured using the dye marker technique, was
lowered in women, especially those with functional
constipation (transit time ≥48 h), whom consumed
two 125 g servings of synbiotic yogurt containing 0.625 g
inulin and oligofructose with Bifidobacterium lactis
Bb12 (109-1010CFU/g) and Lactobacillus casei CRL
Table 1 Baseline characteristics for all participants and
for STT and LTT groups1
All participantsSTT LTT
(n= 65)(n=50) (n=15)
Malesn= 26 n= 23n=3
Females n= 39 n= 27n=12
Age (y)28.6± 11.3 28.0± 10.630.7±13.2
Height (cm) 171.2±8.9171.0±8.5 171.9± 8.9
Body weight (kg)
Body mass index (kg/m2)
72.1± 15.3 72.4± 14.171.0±18.5
24.4± 4.0 24.6±3.523.8±4.6
Body fat (%)23.0± 8.922.4±8.525.9±9.3
1Mean ± SD.
Table 2 Average GTT (h) and DOC (h) for participants with STT and LTT PRE- and POST-treatment1
All participantsSTT (n=50) LTT (n= 15)
Synbiotic ControlSynbioticControl SynbioticControl
GTT PRE31.0±16.6 29.8±12.726.1± 4.124.4±4.451.7± 28.7 47.8±14.8
GTT POST30.6±18.3 31.1±15.426.3± 8.2 26.7± 10.4 48.8± 33.945.7±20.3
DOC PRE50.4±20.1 52.1±22.944.6±15.1 45.4± 13.4 71.4± 22.1 73.6±32.9
DOC POST52.8±28.351.5±22.0 44.7±14.9 46.3± 15.982.0± 43.568.2±30.1
Abbreviations: GTT gastrointestinal transit time, DOC duration of colour, STT short gastrointestinal transit time, LTT long gastrointestinal transit time, PRE pre-treatment,
1Mean ± SD.
Tulk et al. Nutrition Journal 2013, 12:87
Page 5 of 9
Figure 2 STT (a) and LTT (b) GSRS scores for PRE, POST 7 and POST 15 days of treatment1,2,3,. Abbreviations: GSRS, gastrointestinal
symptom rating scale; STT, short gastrointestinal transit time; LTT, long gastrointestinal transit time; PRE, pre-treatment; POST, post-treatment.
1Average GSRS scores.2Mean ± SD.3Questions 1–5 scored as 0 for ‘no symptoms’ to 3 for ‘extreme symptoms’ and questions 6 & 7 scored as 0
to 4, where 0 and 4 indicated opposite extremes and 2 indicated normal bowel movement consistency or frequency.
Tulk et al. Nutrition Journal 2013, 12:87
Page 6 of 9
(1 × 109- 6 × 109CFU/g) daily for 15 days . Simi-
larly, consumption of 2 daily servings for 14 days of
a commercial yogurt containing B. animalis DN-173
010 (108CFU/g) and fructoligosaccharide by women
with and without functional constipation improved
measures of bowel evacuation . Sairanen (2007)
used radio-opaque marker detection in feces and, simi-
lar to the present study, found no improvements in
transit time in healthy men and women whom, for
3 weeks, consumed 600 mL fermented milk with 12 g
inulin and probiotics (Bifidobacterium longum BB536,
Bifidobacterium spp. 420 and Lactobacillus acidophilus
145) versus fermented milk with the probiotics or a
fermented milk control. In that study, average base-
line transit times for the treatment groups ranged from
48.6±25.6 to 53.5±22.4 h.
There is consistent evidence to support the benefits of
probiotic-enriched dairy products in improving GTT,
even with relatively short nutrition interventions, if GTT
is initially slow [9,10,12,13]. However, in healthy individ-
uals, there is minimal room for improvement in GTT,
the measurements of which can vary from 20 to 30%,
even with strict dietary controls [47,51,52]. Therefore,
the relatively short initial GTT of the healthy and relatively
young (28.6±11.3 years) participants in the present study
may help to explain the finding of no improvements in
GTT. Of note, the physiological significance of small
changes in GTT potentially induced in healthy individuals
has not been confirmed. Conceivably, it would be undesir-
able for a product to excessively shorten a GTT such that
it had laxative effects .
Differences between the results of the current study and
those previously reported may be related to differences in
probiotic strain and dosage, prebiotic type and concentra-
tion, and food matrix. The use of different techniques to
determine GI transit may also explain apparent inconsist-
encies between studies. In the present study, use of the dye
marker technique, while relatively non-invasive, inexpen-
sive and conducive to studies with a relatively large num-
ber of participants, relies on participant self-reports of
timing for dye ingestion and fecal appearance. It also can-
not reveal transit times within specific segments of the GI-
tract, where differences may exist .
Probiotic-containing foods are generally well tolerated,
with minimal adverse side effects or undesirable GI
symptoms . However, the tolerability of products
containing both probiotics and prebiotics is understudied
and expected to be product-specific. In the current study,
supplementing the daily diet with probiotic- and inulin-
enriched yogurt was well tolerated by healthy adults.
Consumption of the same probiotic strains in yogurt also
did not result in incidence of adverse GI symptoms be-
yond that observed with the placebo yogurt . Simi-
larly consumption of 108to 1011CFU of Bifidobacterium
animalis and Lactobacillus paracasei per day did not in-
duce adverse effects and was generally well tolerated in
healthy adults . In comparison to a milk control, milk
fermented with Bifidobacterium lactis DN173010 was
found to improve overall GI symptoms in women who
reported minor digestive symptoms at baseline, mainly
due to improvements in gas-related symptoms . In
contrast, intestinal discomfort from gas production has
been implicated as a side effect of prebiotic consumption
. One study found that healthy adults experienced a
significant increase in GI symptoms when consuming
probiotic fermented milk with 12 g of inulin per day (4 g
per 200 ml serving) compared to the probiotic and con-
trol fermented milks . However, inulin consumed in
doses of 5 and 10 g is generally well tolerated .
Healthy adults whom consumed a supplement containing
probiotics which included Bb12 and La5, as in the
present study, reported beneficial effects on bowel habits
. A prebiotic dose of 5 g/day is reportedly sufficient
to elicit a positive effect on the GI microbial population
Table 3 Average energy and macronutrient intakes at baseline and POST treatment1,2,3,4
2526±7302253± 418 2470±478
93.8± 21.785.1±18.690.7± 20.2
Fat (g) 90.2±42.2
89.5± 35.675.2±20.6 95.8± 31.1
Total Carbohydrate (g)
341.4± 125.9319.4± 65.3316.8±63.6
Dietary Fibre (g)
29.3± 12.8 27.6± 7.625.3±7.9
Abbreviations: STT short gastrointestinal transit time, LTT long gastrointestinal transit time.
1Data are mean ± SD.
2Means in a row with different superscript letters a & b indicate a difference between treatments or from baseline within STT or LTT (p <0.05).
3Based on 3-day food records completed at commencement of first washout period.
4Data includes contributions from the investigational yogurts.
5Based on 3-day food records completed on Days 13, 14 and 15 of each treatment period.
6p= 0.055 between Baseline and Synbiotic.
7p= 0.059 between Baseline and Synbiotic.
Tulk et al. Nutrition Journal 2013, 12:87
Page 7 of 9
. The current study delivered 4 g of inulin per day (2 g
per 100 g serving) and was well tolerated by healthy
adults. Collectively, these results suggest that consump-
tion of fermented dairy products, including or in con-
junction with, a moderate amount of inulin (≤10 g per
day) does not induce undesirable GI symptoms in healthy
Analysis of dietary intake data revealed that energy in-
take was decreased in the STT and trended towards a de-
crease in the LTT during consumption of the synbiotic
yogurt. The consumption of prebiotic fibres, including
inulin-type fructans, can impact appetite-related endpoints
and may play a role in appetite regulation and energy in-
take [55,56]. Reductions in daily energy intake by 100 kcal,
similar to the 120 kcal observed in this study can impact
energy balance sufficiently to prevent weight gain .
This indicates that regular consumption of the synbiotic
could translate into measurable and beneficial changes in
dietary intake in free-living, healthy adults. In the LTT
group, no differences in dietary fiber intake were observed
between baseline and POST-treatment. However, in the
STT group dietary fibre intake significantly decreased in
the control group, but was maintained with consumption
of the synbiotic yogurt. This indicates that consuming two
daily servings of a synbiotic dairy product with 2 g inulin
may reduce energy intake, while contributing dietary fibre.
Since the average dietary fibre intake of adults in Canada
and the United States fails to meet Adequate Intakes of
38 g/day for males and 25 g/day for females , food-
based strategies that support this aim are warranted. The
current study is unique in that dietary intake was measured
in healthy Canadian adults after 15 days of supplementing
their diets with a synbiotic yogurt, whereas other studies
have measured short-term hunger and satiety in laboratory
settings [43-45]. Limitations of the study include the reli-
ance on self-reported nutrient intake by participants and
the fact that the significant reduction in energy intake was
observed in the STT, but not the LTTgroup.
Consumption of a synbiotic yogurt containing Bifido-
bacterium lactis Bb12, Lactobacillus acidophilus La5,
Lactobacillus casei CRL431 and inulin for 15 days did
not significantly alter measures of GTT in a sample of
65 healthy Canadian adults. However, it was well toler-
ated according to GI symptom scores and its consump-
tion was associated with reductions in energy intake.
The study adds to the limited literature investigating the
potential of synbiotic products to modulate GI function
in healthy adults.
GI: Gastrointestinal; GTT: Gastrointestinal transit time; DOC: Duration of
colour; STT: Short transit time; LTT: Long transit time; HNRU: Human
Nutraceutical Research Unit.
The authors were solely responsible for study design, data collection, analysis,
interpretation, manuscript preparation, and decision to publish the results.
HMFT & DCB jointly contributed to preparation of the manuscript, data
collection and analysis. LAM contributed to data collection and entry. AJW
and AMD jointly led the study as co-principal investigators and supervised all
personnel. All authors read and approved the final manuscript.
We gratefully acknowledge the study participants for their commitment to
the study and thank Parmalat Dairy & Bakery Inc. for their continued support.
We thank Barbara Bowes, Edita Dolabchian, Dawn Robinson, and the HNRU
undergraduate student volunteers for their help with data collection and Dr.
William Bettger for his advice throughout the research process.
Received: 7 November 2012 Accepted: 22 May 2013
Published: 20 June 2013
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Cite this article as: Tulk et al.: Daily consumption of a synbiotic yogurt
decreases energy intake but does not improve gastrointestinal transit
time: a double-blind, randomized, crossover study in healthy adults.
Nutrition Journal 2013 12:87.
Tulk et al. Nutrition Journal 2013, 12:87
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