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To determine whether the glycemic index (GI) and insulinemic index (II) of dates could be altered by Arabic coffee consumption. This randomized cross-over study was conducted at the Department of Nutritional Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom from November 2009 to February 2010. Healthy subjects (5 males, 5 females) were recruited to the study. They were fed Khulas dates either with water, or with Arabic coffee. Plasma glucose and insulin responses were measured using standardized methods. Responses were compared with a pure glucose solution matched for available carbohydrate. The GI and II were calculated using standardized methods, and results were presented as means and standard error of mean. Glucose and insulin responses were compared using repeated measures analysis of variance. The GI of dates was 55 +/- 6, which increased to 63 +/- 5 for dates consumed with Arabic coffee (p=0.08). No significant difference was observed between the II for dates, and the II of dates consumed with Arabic coffee (p=1.00). Arabic coffee consumption modestly increased the plasma glucose response of dates compared to that of dates consumed with water. Insulin levels were not significantly affected. The modestly higher glycemic response to dates in the presence of Arabic coffee indicates that this custom may be considered detrimental to health.
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Arabic coee increases the glycemic index but not
insulinemic index of dates
Muneera Q. Al-Mssallem, MSc, PhD, Jonathan E. Brown, MSc, PhD.
923
ABSTRACT


55

     
      


 ±
      

6 ± 55 
5 ± 63
p= 0.08

p = 1.00

         



Objectives: To determine whether the glycemic index
(GI) and insulinemic index (II) of dates could be
altered by Arabic coee consumption.
Methods: is randomized cross-over study was
conducted at the Department of Nutritional Sciences,
Faculty of Health and Medical Sciences, University of
Surrey, Guildford, United Kingdom from November
2009 to February 2010. Healthy subjects (5 males,
5 females) were recruited to the study. ey were
fed Khulas dates either with water, or with Arabic
coee. Plasma glucose and insulin responses were
measured using standardized methods. Responses
were compared with a pure glucose solution matched
for available carbohydrate. e GI and II were
calculated using standardized methods, and results
were presented as means and standard error of mean.
Glucose and insulin responses were compared using
repeated measures analysis of variance.
Results: e GI of dates was 55 ± 6, which increased
to 63 ± 5 for dates consumed with Arabic coee
(p=0.08). No signicant dierence was observed
between the II for dates, and the II of dates consumed
with Arabic coee (p=1.00).
Conclusion: Arabic coee consumption modestly
increased the plasma glucose response of dates
compared to that of dates consumed with water.
Insulin levels were not signicantly aected. e
modestly higher glycemic response to dates in the
presence of Arabic coee indicates that this custom
may be considered detrimental to health.
Saudi Med J 2013; Vol. 34 (9): 923-928
From the Department of Food and Nutritional Sciences (Al-Mssallem),
Faculty of Agricultural and Food Sciences, King Faisal University,
Al-Hassa, Kingdom of Saudi Arabia, and the Department of
Nutritional Sciences (Brown), Faculty of Health and Medical Sciences,
University of Surrey, Guildford, United Kingdom.
Received 2nd April 2013. Accepted 14th August 2013.
Address correspondence and reprint request to: Dr. Muneera Q.
Al-Mssallem, Department of Food and Nutritional Sciences, College of
Agricultural and Food Sciences, King Faisal University, PO Box 420,
Al-Hassa 31982, Kingdom of Saudi Arabia. Tel. +966 505959598.
Fax. +966 (3) 5801251. E-mail: mmssallem@kfu.edu.sa
www.smj.org.sa Saudi Med J 2013; Vol. 34 (9)
Disclosure. is study was supported by a grant from
King Faisal University, Al-Hassa, Kingdom of Saudi
Arabia.
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Glucose and insulin responses of dates with coee ... Al-Mssallem & Brown
Saudi Med J 2013; Vol. 34 (9) www.smj.org.sa
The relationship between coee consumption and
the risk of developing type 2 diabetes mellitus
(T2DM) has been studied in short-term randomized
controlled trials and epidemiologic studies.1-3 ese
studies have shown that high consumption of coee
beverage is associated with better glucose tolerance, and
a substantially lower risk of T2DM.1,3 is may in part,
be related to coee phenolic constituents where coee is
considered the major source of chlorogenic acids (CGA)
in the human diet.4,5 e CGA and other phenolic
compounds in coee may inhibit glucose absorption
via interference with glucose transporters.3,6,7 Also,
CGAs have been shown to aect glucose metabolism by
increasing insulin sensitivity.4,5 Nevertheless, ingestion
of coee has also been shown to increase the area under
the glucose and insulin curves, and to reduce insulin
sensitivity,8-10 in response to high and low glycemic index
(GI) meals. is eect was associated with the presence
of caeine in the coee beverage, which has also been
shown to have important physiological eects.8,9 ere is
evidence that dietary habits and lifestyle play important
roles in developing, or preventing chronic diseases,
such as diabetes.3,11 Saudi populations habitually enjoy
consuming Arabic coee, which is mainly made from
Arabica coee beans which are lightly roasted, and then
mixed with cardamom.12 Arabic coee is traditionally
served along with varieties of dates on a daily basis. e
GI for dierent varieties of dates ranges from 46-57.13-16
Interestingly, the rst documentation of the GI for
dates came from a Saudi Arabian variety known as
Khulas, which had a GI of 57.13 A later study showed
that the GI of dates can be reduced to 36 when they
are consumed with sour milk.17 A typical adult Saudi
may consume between 20 and 120 g of dates with
60-300 mL of Arabic coee at one sitting. However,
although the eects of consuming dates with sour milk
are known, the metabolic impact of consuming dates
with Arabic coee has not been investigated previously.
It is apparent from our knowledge of the constituents
of coee that both benecial and detrimental outcome
could occur in terms of glucose and insulin levels by
consuming coee. e eect of consuming dates and
Arabic coee has not been investigated before, and as
this is a traditional dietary habit in the Arabian Gulf
countries, we were interested on its eect on blood
glucose. erefore, this study aimed to investigate the
glucose and insulin responses to the ingestion of an
equivalent amount of 50 g of available carbohydrate
from dates with water, and dates with Arabic coee.
Methods. Total phenol content determination. e
standardized Folin-Ciocalteu method18 was applied to
determine the level of total phenols in Arabic coee
colorimetrically using the Folin-Ciocalteus reagent
(Sigma Chemical Company Ltd., Poole, UK). Coee
beverage was prepared by dissolving coee particles (4
g) in 100 mL boiled Milli-Q water. Ten mL of coee
beverage was added to a screw-capped tube containing
8 mL of 1.2 M hydrochloric acid in 50% methanol/
water. e samples were then placed in a water bath
at 80ºC for 3 hours. A reagent blank was made using
Folin-Ciocalteus reagent diluted 1 in 9. e calibration
standards were made using epicatechin at a concentration
range of 0.025 - 0.3 mg/mL, in which 100 μL of each of
these solutions were also reacted with Folin-Ciocalteu’s
reagent. For analysis of the coee samples, 100 μL was
used and reacted with the diluted Folin-Ciocalteu’s
reagent. e colorimetric measurement was carried out
at 720 nm.
Liquid chromatography-mass spectrometry (LC-MS)
analysis. Arabic coee (Coea Arabica) was analyzed
for CGA, other components with a similar structure
to CGA, and also other phenolic compounds. Coee
particles (375 g) were dissolved into 20 mL Milli-Q
boiling water and left to stand for 2 minutes. en, 10
mL of this coee solution was transferred to a test tube
containing 0.5 mL of Carrez A and then vortex mixed.
Carrez B reagent (0.5 mL) was added and the sample
was vortex mixed, and then centrifuged at 4000xg for
20 minutes at 4ºC. Peaks were obtained corresponding
to the retention times of a number of phenols and
chlorogenic acids. eir identity was conrmed from
their fragmentation patterns of standard compounds
found within the Arabic coee.
e GI and II determination. Subjects. A randomized
cross-over design carried out in accordance with the
FAO/WHO guidelines for GI testing was used.19 is
study was conducted at the Department of Nutritional
Sciences, Faculty of Health and Medical Sciences,
University of Surrey, Guildford, United Kingdom from
November 2009 to February 2010. e study design
received ethical approval from the University of Surrey
Ethics Committee (EC/2009/95/FHMS) and approved
in accordance with the Helsinki II declaration. Ten
healthy volunteers (5 men and 5 women, aged 30.8±
2.8 years) were recruited from the post-graduate
student and sta population at the University of
Surrey by distribution of both e-mails and posters. All
volunteers gave informed written consent. Weight,
height, fasting blood glucose, and blood pressure
were measured at baseline. e inclusion criteria were
healthy men and women aged between 18-60 years old
and free from medication with the exception of minor
analgesics. Participants were excluded from the study
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www.smj.org.sa Saudi Med J 2013; Vol. 34 (9)
Glucose and insulin responses of dates with coee ... Al-Mssallem & Brown
when they have had familial or personal history of
psychiatric disorders, epilepsy, sleep disorders, diabetes,
cardiovascular disease, or food allergies, taken any
medication, or were pregnant women.
Food test. Khulas dates (Phoenix dactylifera L.)
and Arabic coee (Coea Arabica) were prepared in a
kitchen at the Clinical Investigation Unit (University
of Surrey). A portion of dates (which contained 50 g
of available carbohydrate) was served to subjects with
water, or Arabic coee (no sugar added) on 4 separate
sessions. On a further 3 separate occasions, a solution
containing 50 g pure glucose (Fisher Scientic, UK)
was given. Volunteers were asked to eat the dates and
consume the drink within 10 minutes.
Blood sample collection. Participants arrived at the
Clinical Investigation Unit at the University of Surrey at
0830 hour each study day of testing after an overnight
fast (10-12 hours). Blood samples were obtained by
nger pricks using preset lancets (Accu-chek Softclix
Pro., Brighton, East Sussex, UK) at fasting, and at 15,
30, 45, 60, 90, and 120 minutes after consuming the
dates, dates with Arabic coee (no added sugar), or
standard glucose solution. Blood samples were collected
into 300 μL plastic microvette tubes (SARSTED Ltd.,
Leicester, UK) coated with uoride oxalate, and were
immediately centrifuged at 3000×g for 10 minutes at
4°C. e resultant plasma was transferred into separate
300 μL plastic plain microvette tubes (SARSTED Ltd.,
Leicester, UK). e tubes were then frozen and kept in
the freezer at -20°C until analysis (within 4 weeks).
Glucose measurement. e plasma glucose
concentration was determined using an automatic
analyser (YSI 2300 STAT plus, Yellow Springs,
Analytical Technologies, YSI, UK). It was an enzymatic
method applied to the enzyme glucose oxidase in
aqueous solution to oxidize the glucose and produce
hydrogen peroxide. e hydrogen peroxide was then
oxidized, and the current product was proportional to
the concentration of the glucose. Twenty-four samples
were analyzed in each run along with 3 quality control
(QC) samples. Within each run the coecient of
variation of the QC1 was 2.5%, QC2 - 3.6%, and QC
3 - 1.8 %. e incremental area under the glucose curve
(iAUC) for the reference glucose drink, dates, and dates
with Arabic coee was calculated using the trapezoid
rule. e GI values of dates and dates with Arabic coee
for each subject were calculated as follows:
GI of dates or dates with Arabic coee = iAUC
for dates or dates with Arabic coee / iAUC for
reference × 100
e GI value of dates with water and dates with Arabic
coee was calculated as the average value obtained for
10 subjects.
Insulin determination. Enzyme linked
immunosorbent assay (ELISA) was employed for
measuring plasma insulin concentrations. Samples were
thawed at room temperature and then centrifuged at
3000xg for 5 minutes to remove insoluble debris. e
QCs, standards (Invitron Ltd, Monmouth, UK), and
samples (25 μL per each) were incubated with the
labelled antibody solution (Invitron Ltd, Monmouth,
UK) at 37°C for 2 hours, and unbound labelled
antibodies were removed using the wash buer (Invitron
Ltd, Monmouth, UK) according to the manufacturer’s
instructions. e insulin was then measured using the
microtiter plate luminometer (Luminescent plate reader
Centro LB 960, Berthold, Germany). All readings
obtained from the luminometer were multiplied by 6 to
convert the units (mU/L) into pmol/L. Two QCs (low
and high) were used, and their CVs were 6.6% (low)
and 4.9% (high).
Statistical analysis. Results were checked for
normality using the Kolmogorov-Smirnov test (K-S
test) and expressed as a means ± one standard error of
the mean (SEM). Two factors repeated measures analysis
of variance (ANOVA) was used to analyze dierences in
the mean of glucose and insulin. In addition, a single
factor repeated measures ANOVA was used, as well,
to analyze dierences in the iAUC for glucose and
insulin (Statistical Package for Social Sciences version
16 for Windows [SPSS Inc, Chicago, IL, USA]). If a
signicant interaction was obtained following ANOVA,
a Bonferroni step-wise post hoc test was performed to
determine the location of the variance. All data were
examined using a 2-tailed approach with a level of
p<0.05 considered as signicant.
Results. Phenol analysis. e amount of total
phenols in Arabic coee was calculated to be 1.2 mmol
epicatechin equivalents/L using the standard curve
presented in Figure 1. Figure 2 shows the compounds
that were identied within the Arabic coee sample.
e LC-MS analysis showed that the Arabic coee
contained CGAs and caeine. e most abundant
derivative was a caeoyl quinic acid. e highest
peak was shown for 5-Caeoyl quinic acid followed
by 3-Caeoyl quinic acid, Caeoyl quinic acid, and
Caeine. However, p-coumaroyl quinic acid, feruloyl
quinic acid, and dicaeoyl quinic acid were also
observed in relatively small amounts. Identication was
based on their retention time compared to that of the
standard, absorbance spectrum, and MS fragmentation
pattern.
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Saudi Med J 2013; Vol. 34 (9) www.smj.org.sa
Figure 1 - Standard calibration curve for epicatechin.
Figure 2 - Liquid chromatography-mass spectrometry analysis for Arabic
coee.
Figure 3 - Plasma glucose responses over 2 hours following consumption
of reference glucose, dates, and dates with Arabic coee.
Results are presented as mean ± standard error of mean.
Glycemic index was measured using standard procedures.19
A 2-factor (treatment and time) repeated measures ANOVA
was used to analyze dierences in the means of glucose levels
within the dates, dates with Arabic coee, and standard
glucose consumed. No signicant dierences were observed
(p=0.08).
Figure 4 - Plasma insulin responses over 2 hours following consumption
of reference glucose, dates, and dates with Arabic coee.
Results are presented as mean ± standard error of mean.
Insulinemic index was measured using standard procedures.19
A 2-factor (treatment and time) repeated measures ANOVA
was used to analyze dierences in the means of the insulin
levels within the dates, dates with Arabic coee, and standard
glucose consumed. No signicant dierences were observed
(p=1.00).
Table 1 - Characteristics of subjects included in a study at the University
of Surrey, Guildford, United Kingdom (N=10).
Characteristics Mean ± SEM Range
Age (year) 30.8 ± 2.8 18-48
Weight (kg) 75.0 ± 5.4 60-108
Height (m) 1.73 ± 0.02 1.60-1.87
Body mass index (kg/m2) 24.0 ± 1.2 20.7-31.7
Diastolic blood pressure (mm Hg) 72.5 ± 3.2 54.0-86.5
Systolic blood pressure (mm Hg) 122.1 ± 2.8 105.6-135.0
Fasting blood glucose (mmol/L) 5.2 ± 0.1 4.5-5.8
Determination of GI and II. Subjects’ characteristics
are shown in Table 1. ey had an average age of 30
years, with normal weight, blood pressure, and fasting
blood glucose levels. As shown in Figure 3, peak
glucose levels occurred at 30 minutes for standard
glucose, dates, and dates with Arabic coee. At this
time, the response to the standard glucose solution was
signicantly higher than the response to both dates, and
dates with Arabic coee (p=0.05, t=2.25). Similarly, the
glucose response at 45 and 60 minute time points for
subjects consuming dates with water was signicantly
lower (p=0.017, t=-2.93) than that for subjects
consuming dates with Arabic coee (p=0.041, t=-2.37).
It appeared that Arabic coee ingestion increased the
glucose peak rise by approximately 0.4 mmol/L. e
iAUC for plasma glucose concentrations over 2 hours
postprandial period following consumption of standard
glucose solution was 180 ± 13, for dates - 96 ± 11, and
dates with Arabic coee - 112 ± 11. From this, the
GI for dates with water was found to be 55 ± 6, and
dates with Arabic coee was found to be 63 ± 5. e
mean GI value for dates with water was lower than that
for dates with Arabic coee, however, the dierence
927
www.smj.org.sa Saudi Med J 2013; Vol. 34 (9)
Glucose and insulin responses of dates with coee ... Al-Mssallem & Brown
did not quite reach statistical signicance (p=0.08,
t=-1.9, n=10). Plasma insulin for the standard glucose
solution dates with water and dates with Arabic coee
peaked at 30 minutes after the ingestion of the foods,
and then declined towards the baseline level by 120
minutes (Figure 4). Similar patterns were evident for
all. e iAUC for plasma insulin concentrations was
also calculated, and the II for dates with water was 64
± 7, and for dates with Arabic coee was 62 ± 8. e
iAUC of insulin for dates with water and dates with
Arabic coee was much lower than that observed for
standard glucose solution. is lower iAUC, however,
was not suciently low enough to be signicantly lower
than the iAUC for glucose. ere was no signicant
dierence in the plasma insulin response between dates
and dates with Arabic coee (p=1.00, t=0.16).
Discussion. is study examined the impact of
Saudi Arabian Khulas dates on glucose and insulin,
with and without simultaneous consumption of Arabic
coee. e Khulas dates variety was chosen as it is the
most famous variety consumed in Saudi Arabia.20 Also,
the GI of this variety has been reported previously,
which can be used for comparison with our data.13,15
In this study, the GI value of 55 was obtained for
Khulas dates and this compared well with previous
studies.13,15 It is well known that coee contains many
phenolic compounds such as CGA, which may have
a potential eect on glucose and insulin levels.3,6,7 e
possible role of CGA in glucose metabolism could be
due to the inhibition of glucose transporters (Na+-
dependent glucose transporter) or digestive enzymes
(α-amylase and α-glucosidase), which could potentially
inuence the amount of glucose absorbed and reduce
glucose release.3 Also, consumption of coee (400 mL
containing 350 mg CGA) may aect the secretion
of gastrointestinal peptides (glucose-dependent
insulinotropic polypeptide (GIP) and glucagon-like
peptide-1 (GLP-1) by decreasing GIP and increasing
GLP-1, leading to slow intestinal glucose absorption.7,21
In addition, the CGA may reduce plasma glucose output
from the liver by inhibiting glucose-6-phosphatase
activity.3,6,21 e benecial eects of CGA may appear at
high concentrations of the coee beverage, or for long
periods of frequent coee consumption. is might be
the reason why we have not seen an eect in our study
because it was a study examining the acute eects of
coee, or because the concentration of the Arabic coee
beverage was too low. is ndings is similar to that of
Louie et al.22 ey observed that there was no dierence
between the postprandial glucose and insulin levels of
decaeinated coee versus water owing to a lower CGA
content that was in the decaeinated coee beverage
consumed. Nevertheless, it must be emphasized that
the aim of this study was to study the eect of Arabic
coee as it is normally consumed rather than as a more
concentrated beverage.
It is evident from other studies that the phenols, which
are poorly absorbed from the human small intestine
and are likely metabolized to their metabolites.23 For
example, approximately 33% of CGA is only absorbed
and approximately two-thirds of it reach the colon, and
may be metabolized to caeic acid and quinic acid.6 It
has reported that the level of CGA that seems to have
health benets would range from 0.5-2.5 g/day.1-5 Our
LC-MS results for Arabic coee have shown that the
coee used in this study certainly contained an array
of CGA (Figure 2), but its total phenols’ concentration
was just 1.2 mmol/L. is concentration may have been
too low to elicit a signicant eect on plasma glucose
and insulin levels. Our study has indicated that the
consumption of coee with dates exacerbates the plasma
glucose response in healthy volunteers compared to the
consumption of dates with water. In a similar way, an
increase in the area under glucose and insulin curves and
reduction in the insulin sensitivity has been observed
with the ingestion of coee with meals.7-9 All these
eects were proposed to be associated with the presence
of caeine in the coee, which increases AUC of glucose
and insulin.8,9 Caeine is a phosphodiesterase inhibitor
which can increase the concentration of cyclic adenosine
monophosphate (cAMP). Increased concentrations of
cAMP have been associated with an impaired glucose
tolerance after the consumption caeinated coee
beverage.7 Caeine can also inhibit muscle glucose
uptake as it acts as adenosine receptor antagonist.6,24 It
is clear that the consumption of Arabic coee with dates
had a modest eect bordering on a signicant eect.
In contrast to these short-term controlled trials, which
have shown the eects of caeine, this eect might be
modied during long periods of coee consumption
among heavy and chronic coee consumers.3 Indeed,
better glucose tolerance and a substantially lower risk
of T2DM was associated with the high consumption
of coee.2,3
ere are some limitations to this study. Clearly,
this was an assessment of only one variety of dates and
as such, it is quite a small study. However, the results
provide useful information on a famous variety of dates
consumed with Arabic coee, which has not been
reported previously. It is unfortunate that there are
no insulinemic data on dates, or dates consumed with
coee in order to create comparison with our ndings.
928
Glucose and insulin responses of dates with coee ... Al-Mssallem & Brown
Saudi Med J 2013; Vol. 34 (9) www.smj.org.sa
In conclusion, consumption of dates with Arabic
coee is a traditional practice in Saudi Arabia. We
found that this habit of ingestion dates, at the same time
with drinking Arabic coee, increased slightly glucose
response (p=0.08) in healthy people. is eect may
due to the presence of caeine, which has been found to
impair glucose tolerance and decreases insulin sensitivity
in previous clinical trials. As such, these ndings could
be applied on people with diabetes, and we would
assume that consumption of dates would have an eect
on plasma glucose levels in diabetic individuals similar
to that eect seen in healthy people. e inuence of
the coee beverage indicates that some detrimental
eects can occur, and consumption of a decaeinated
coee may be wise. Further research, particularly long
term studies, may be required to ascertain the clear
detrimental eect of dates with Arabic coee on blood
glucose, insulin, and triglycerides levels. In addition,
as our coee was caeinated coee, it is useful to
investigate the eect of decaeinated Arabic coee on
blood glucose and insulin levels.
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... It has reported that a typical adult Saudi may consume between 20 and 120 g of dates at one sitting (Al-Mssallem and Brown, 2013). Recently, there is a fluctuation in date's consumption among Saudi populations due to major changes in dietary habit and availability of other fresh fruits and sweets (Al-Mssallem, 2014;Al-Eid et al., 2015). ...
... In this study, the weighted average of dates consumption for the 3 age groups was 80 g/day. It was reported that a typical adult Saudi may consume between 20 and 120 g of dates at one sitting (Al-Mssallem and Brown, 2013). However, it was mentioned that the average per capita consumption of Saudi dates reached about 95 g/day (Al-Eid et al., 2015). ...
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... It has reported that a typical adult Saudi may consume between 20 and 120 g of dates at one sitting (Al-Mssallem and Brown, 2013). Recently, there is a fluctuation in date's consumption among Saudi populations due to major changes in dietary habit and availability of other fresh fruits and sweets (Al-Mssallem, 2014;Al-Eid et al., 2015). ...
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