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CONSUMPTION OF TOMATO PRODUCTS WITH OLIVE OIL BUT NOT
SUNFLOWER OIL INCREASES THE ANTIOXIDANT ACTIVITY OF PLASMA
ALISON LEE,DAVID I. THURNHAM,and MRIDULA CHOPRA
Northern Ireland Centre for Diet and Health, School of Biomedical Sciences, University of Ulster, Coleraine,
Northern Ireland, UK
(Received 5June 2000; Revised 15 August 2000; Accepted 7September 2000)
Abstract—Health benefits of lycopene from tomato products have been suggested to be related to its antioxidant
activity. Dietary fat may influence the absorption and hence the plasma levels and antioxidant activity of lycopene. In
the present study, we have compared the effect of consumption of tomato products with extra-virgin olive oil vs. tomato
products plus sunflower oil on plasma lycopene and antioxidant levels. Results show that the oil composition does not
affect the absorption of lycopene from tomato products because similar levels of plasma lycopene (mean ⫾SD) were
obtained on feeding tomatoes (providing approximately 46 mg lycopene/d) for 7 d with either olive oil (0.66 ⫾0.26 vs
1.20 ⫾0.20
mol/l, p⬍.002) or sunflower oil (0.67 ⫾0.27 vs. 1.14
mol/l, p⬍.001). However, consumption of
tomato products with olive oil significantly raised the plasma antioxidant activity (FRAP) from 930 ⫾150 to 1118 ⫾
184
mol/l, p⬍.01) but no effect was observed when the sunflower oil was used. The change (supplementation minus
start values) in FRAP following the consumption of tomato products with oil was significantly higher for olive oil
(190 ⫾101) than for sunflower oil (⫺9.6 ⫾99, p⬍.005). In conclusion, the results of the study show that consumption
of tomato products with olive oil but not with sunflower oil improves the antioxidant activity of the plasma. © 2000
Elsevier Science Inc.
Keywords—Tomato, Lycopene, Antioxidant, FRAP, Olive oil, Sunflower oil, Free radicals
INTRODUCTION
The protective effect of the Mediterranean diet against
the risk of cancer and cardiovascular disease has been
attributed to various dietary components, e.g., carote-
noids from fruits and vegetables, flavonoids from the red
wine and monounsaturated and polyphenolic compo-
nents of the olive oil [1,2]. In vivo supplementation
studies on human subjects with “Mediterranean foods”
have shown protective effects on several risk factors
linked to cardiovascular disease [3–6]. In case of caro-
tenoids, it has been suggested that the dietary fat can
influence the absorption and also the antioxidant effects
of these compounds [7,8]. Lycopene, a major carotenoid
present in tomatoes, has been reported to show antioxi-
dant activity both in vitro and in vivo [9,10]. Heating
tomatoes with fat is suggested to increase the bioavail-
ability of lycopene [8] but it is not known whether the
composition of fat can affect the bioavailability and
plasma antioxidant activity when consumed with tomato
products. Both mono- and polyunsaturated fats are con-
sidered “healthier” than saturated fat since the latter is
associated with higher blood cholesterol concentrations
[11]. In addition, in human supplementation studies,
monounsaturated fatty acids have been shown to reduce
[6] and polyunsaturated fatty acids to increase the oxi-
dation of low-density lipoprotein (LDL) [12,13].
The present study was conducted to determine
whether cooking of tomatoes with different oils (olive oil
vs. sunflower oil) affects the plasma lycopene concen-
tration and total plasma antioxidant activity.
METHODS
Subjects and study design
Eight healthy subjects (5 female, 3 male), average age
22 years (range 20–24) were recruited for the study.
Address correspondence to: Dr. Mridula Chopra, NICHE, School of
Biomedical Sciences, University of Ulster, Coleraine BT52 1SA,
Northern Ireland, UK; Tel: ⫹44 (0) 2870 324057/324870; Fax: ⫹44
(0) 2870 324965; E-Mail: m.chopra@ulst.ac.uk; mridulachopra@
hotmail.com.
Free Radical Biology & Medicine, Vol. 29, No. 10, pp. 1051–1055, 2000
Copyright © 2000 Elsevier Science Inc.
Printed in the USA. All rights reserved
0891-5849/00/$–see front matter
PII S0891-5849(00)00440-8
1051
Subjects’ lipid profile, blood count, and liver function
were within the normal range. Average weight and body
mass index of the subjects were 60 ⫾2.1 Kg and 22 ⫾
2.6 Kg/m
2
, respectively. Ethical approval for the study
was obtained from the University of Ulster Ethical Com-
mittee and all subjects gave signed informed consent
prior to participation in the study. Two subjects withdrew
at the beginning of the study: one did not turn up for the
baseline blood sample and a second subject withdrew for
personal reasons. Six subjects (5 female and 1 male)
completed the study. Subject number was considered
sufficient for the study as several studies have shown a
significant effect of treatment with a smaller number
(5–7) of subjects [5,14,15]. Subjects were allowed to
continue their normal dietary habits but asked to incor-
porate an additional intake of tomato products with either
olive or sunflower oil.
The study period was 5 weeks. Blood samples were
obtained from subjects following an overnight fast of at
least 10 h. At the baseline, 15 ml blood sample (10 ml in
heparinized, 5 ml in plain tubes) was obtained with
Vacutainers (Becton Dickinson Vacutainer Systems, Ce-
dex, France) and subjects were asked to consume 200 g
of tomato soup (Heinz Co. Ltd., Uxbridge, UK) provid-
ing approximately 33 mg lycopene, and 230 g canned
tomatoes (Safeway, Middlesex, UK) providing approxi-
mately 13 mg lycopene, with 20 ml of olive oil (Greek
extra-virgin olive oil, Safeway, Middlesex, UK) every
day for 7 d. Tomato soup was heated with oil prior to
consumption and most subjects either consumed it on its
own or with bread. Canned tomatoes were also con-
sumed after heating with oil and mixed with other food
(i.e., meat, pasta, lasagne, vegetables, etc.). At the end of
the first supplementation period, a second blood sample
was obtained. Subjects were asked to return after a 3
week washout period and were supplemented for a fur-
ther 7 d with the similar amounts of tomato products plus
20 ml sunflower oil (Flora sunflower oil, Crawley, UK)
and blood samples were obtained before and after the
supplementation. Fatty acid composition and vitamin E
content of the oils is shown in Table 1.
Subjects were asked to complete food diaries 2 d prior
to the supplementation and during the supplementation
weeks. These food diaries were used to check compli-
ance and to calculate the exact intake of lycopene using
the database on lycopene content of tomato-based prod-
ucts [16,17]. All subjects consumed the specified
amounts of tomato products and oils, and other dietary
habits of subjects remained consistent during the course
of the study.
Blood collection and analysis
The following analyses were done on the blood: Se-
rum samples were analyzed for triglycerides (TG) and
cholesterol (total, LDL, and HDL) at the local health
authority laboratory. Li-heparin blood was used to mea-
sure plasma lycopene levels using high performance
liquid chromatography (HPLC) [18], and the antioxidant
activity of the plasma was measured on COBAS FARA
centrifugal analyzer using the test to assay ferric-reduc-
ing ability of the plasma (FRAP, total antioxidant activ-
ity) [19].
Lipid analysis and antioxidant activity measurements
were done on the fresh samples. For the plasma lycopene
analysis, all samples were stored at ⫺80°C and the
analysis of the whole batch of samples was done on the
same day and completed within 6 weeks of completion
of the study.
A pooled plasma sample stored at ⫺80°C was used to
measure the precision of the HPLC and FRAP assay.
Within-assay precision calculated from five measure-
ments of the same sample was 0.18% for the FRAP assay
and 6% for the plasma lycopene levels. Between-assay
precision calculated from the analysis of the stored
plasma at each blood sampling time was found to be 4%
for the FRAP assay.
Statistical analysis
The data was found to be skewed. The statistical
analysis was therefore done on the log
10
transformed
data with the level of significance set at p⬍.05. Fol-
lowing a significant effect of time with ANOVA re-
peated measures analysis, within-subject comparisons
were done using paired t-test to detect which time peri-
ods were different. The results are shown as the geomet-
ric mean (antilog of logarithm data) and standard devi-
ation (antilog [log mean plus standard deviation] ⫺
geometric mean).
RESULTS AND DISCUSSION
In our previous study [17,20] we have shown that an
increase in the dietary intake of carotenoid to 30 mg/d for
one week increases the resistance of LDL to oxidation. A
Table 1. Fatty Acid Composition of the Oil
Concentration/100 ml
Flora
sunflower oil Greek-extra-virgin
olive oil
Saturated fatty acid 12.0 g 2.0 g
Monounsaturated fatty acid — 10.0 g
Poly-unsaturated fatty acid 63.0 g 1.1 g
Vitamin E 65.0 mg 4.7 mg
1052 A. LEE et al.
supplementation period of 7 d was selected in the present
study because in our previous study we did not find a
significant difference in plasma carotenoids between d 7
and 14 of supplementation. In the present study, the
mean dietary intake of lycopene was increased from ⬍5
mg/d to 46 mg/d during the supplementation period. The
consumption of similar amounts of tomato products with
olive oil and sunflower oil produced respectively approx-
imately 80% and 70% increase in the plasma lycopene
levels, but the percent increase was not significantly
different between the two oils used during the supple-
mentation period. Although both olive oil and sunflower
oil contained vitamin E (Table 1), no change in the
plasma
␣
-tocopherol was observed during the supple-
mentation period. Polyunsaturated fatty acid rich oil is
reported to have a larger impact on reducing triglyceride
concentration than monounsaturated fatty acid rich oil
[21]. However, in the present study a reduction in trig-
lycerides was observed only following olive oil supple-
mentation (p⫽0.01). Supplementation with both oils
failed to show an effect on the plasma cholesterol levels.
Most studies that show a lipid lowering effect of sun-
flower or olive oil have included a supplementation pe-
riod of ⱖ2 weeks [21,22]. It is therefore possible that the
size of the group and/or duration of the experiment were
not sufficient to show a major change in blood lipid
levels. Nevertheless, the change in lipids when compared
for olive oil and sunflower oil treatment periods was
found to be significantly different for LDL cholesterol
between the two treatment periods (Table 3).
Day to day variability in antioxidant status is reported
to be low in unsupplemented subjects [23,24]. In the
present study, following supplementation of tomato
products with extra-virgin olive oil a significant increase
in the plasma antioxidant activity (FRAP) was observed
(p⫽.004, paired t-test on log-transformed data), but the
FRAP activity tended to decrease when tomato products
were fed with sunflower oil (Table 2). It is known that a
diet rich in monounsaturated fatty acids inhibits [6] and
polyunsaturated fatty acids increases [13] the oxidation
of LDL. The results of the present study suggest that the
composition of oil used for cooking tomato products may
affect the antioxidant activity of plasma. Other antioxi-
dant carotenoids, i.e.,

-carotene, lutein, and

-cryptox-
anthin were not changed during the study period (results
not shown). Also, since the plasma tocopherol levels
were not changed during the supplementation period, it is
unlikely that the changes in antioxidant activity seen
were related to the tocopherol present in the oils. How-
ever, extra-virgin olive oil also contains high amounts of
phenolic derivatives [25]. Since plasma phenolic com-
pounds were not measured, it is difficult to assess
whether changes in plasma antioxidant activity could be
related to the phenolic acid constituents of the olive oil.
The feeding of tomato products with olive oil for 1
week was followed by a 3 week washout period and a
further supplementation with sunflower oil and tomato
products. The plasma lycopene returned to the baseline
after the washout period but the plasma antioxidant ac-
tivity remained significantly higher than the baseline
(p⫽.01, Table 1). It has been reported that oil supple-
mentation can have prolonged effects [26] and effects of
induced fatty acid modifications remain for a long time
in the biological systems [27,28]. Unfortunately it was
Table 2. Plasma Lycopene, FRAP, and Lipid Levels Before and After Supplementation with Tomato Products Plus Different Oils
Tomato products with olive oil
Mean ⫾SD Tomato products with sunflower oil
Mean ⫾SD
Baseline Week 1 Week 4 Week 5
Dietary lycopene
mg/d ⬍546⫾10 ⬍346⫾12
Plasma lycopene
mol/l 0.66 ⫾0.26
a
1.20 ⫾0.20
b
0.67 ⫾0.27
a
1.14 ⫾0.35
b
Plasma a-tocopherol
mol/l 19.0 ⫾3.6
ab
19.4 ⫾3.8
a
19.5 ⫾5.0
ab
21.0 ⫾4
b
Triglycerides
mmol/l 0.88 ⫾0.13
a
0.68 ⫾0.27
b
0.97 ⫾0.33
ab
0.92 ⫾0.18
a
Total cholesterol
mmol/l 3.78 ⫾0.53 3.91 ⫾0.35 3.90 ⫾0.66 3.78 ⫾0.50
LDL cholesterol
mmol/l 1.85 ⫾0.54 2.10 ⫾0.37 1.85 ⫾0.62 1.68 ⫾0.65
HDL cholesterol
mmol/l 1.49 ⫾0.20 1.47 ⫾0.18 1.55 ⫾0.23 1.62 ⫾0.21
Total: HDL ratio 2.53 ⫾0.47 2.66 ⫾0.47 2.52 ⫾0.59 2.33 ⫾0.57
FRAP
mol/l 930 ⫾150
a
1118 ⫾184
b
1049 ⫾186
bc
1009 ⫾181
ac
Effect of supplementation was measured using paired-t-test on log
10
transformed data. Results shown are geometric means and standard deviation.
Those not sharing a common superscript
abc
were significantly different at p⬍.05.
1053Tomato and oil intervention in humans
not possible to do fatty acid and polyphenol analysis to
confirm whether the effects seen following the washout
period were related to the oil consumption. The con-
sumption of tomato products with sunflower oil pro-
duced no further increase in the FRAP and if anything,
plasma antioxidant activity tended to decrease and was
significantly lower than that measured following the ol-
ive oil supplementation (p⫽.007, paired t-test). The
change in plasma FRAP (supplementation minus start
values) was also significantly different when tomato
products were consumed with olive oil or sunflower oil
(p⫽.002, Table 3).
In conclusion, the preliminary results indicate that the
oil composition (olive oil vs. sunflower oil) does not
affect the bioavailabilty of lycopene from tomato prod-
ucts. The oil composition however, may affect the anti-
oxidant activity of the plasma. Further studies are needed
to provide clarification on whether the antioxidant effects
seen in the present study were related to the olive oil or
the combination of olive oil and tomato products.
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Change following consumption of
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p⫽Olive oil Sunflower oil
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mol/l) 0.533 ⫾0.15 0.471 ⫾0.20 ns
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shown where they were less than .1.
1054 A. LEE et al.
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