Applied nutritional investigationEffects of olive oil and tomato lycopene combination on serum lycopene, lipid profile, and lipid oxidation
Introduction
Mediterranean diets are thought to protect against cardiovascular disease and this effect has been credited to a variety of foods such as fruits and vegetables, olive oil, and red wine [1]. The beneficial dietary components of some of these foods include carotenoids in fruits and vegetables, monounsaturated fat and polyphenolic compounds in olive oil, and flavanoids in red wine [2], [3]. Among the carotenoids, lycopene, present in tomatoes and tomato products, probably has the highest antioxidant capacity [4].
Epidemiologic and case-control studies have suggested a possible beneficial effect of high dietary intake and/or high serum or tissue levels of lycopene because of a decreased risk of cardiovascular diseases [5], [6], [7], [8], [9]. Population studies have shown a positive association between reported intake of lycopene-rich foods and plasma levels [10], [11]. Intervention studies have observed increased serum lycopene levels with increased intake of tomatoes and tomato products, the richest source of lycopene [12], [13], [14].
Lycopene availability from food may depend on several factors. Season, heating, and processing of tomato products may change the amount of bioavailable lycopene. Prolonged heat treatment (>2 h at 100°C) of tomatoes decreases the total carotenoid content and more so in peeled than in unpeeled tomatoes [15]. Single-meal studies have shown higher serum levels of lycopene when tomatoes have been consumed cooked rather than raw [16], [17], [18] and when the tomatoes have been cooked with fat than without [18], [19], possibly because cooking or heating weakens the bond between lycopene and the tissue matrix and facilitates the passage of lycopene into a lipophilic phase, making it more bioavailable [17]. Cooking or processing has been reported to transform all-trans-lycopene to cis-lycopene [20], [21], which is better absorbed, probably because cis-isomers are more soluble in bile acid micelles, although studies have suggested that lycopene is resistant to heat-induced all-trans to cis conversion under conditions regularly employed in the food industry or during food preparation [22].
Similarly, 3- and 5-d meal studies have suggested that dietary fat influences plasma levels of lycopene when tomatoes are consumed with olive oil rather than without oil [23], [24]. However, our previous 14-d study of a lycopene-rich diet showed that a high monounsaturated fat-enriched sunflower oil diet (36% of energy as total fat and 23.6% of energy as monounsaturated fat) induced similar effects on serum lycopene levels as a high-carbohydrate, low-fat diet (15% of energy as total fat and 4.1% of energy as monounsaturated fat) [25].
Studies have also compared the effect of carotenoid-controlled fruit and vegetable intakes with high monounsaturated fat versus those with high-carbohydrate, low-fat intake on oxidation of isolated low-density lipoprotein (LDL) cholesterol [26], [27], a risk factor for coronary heart disease (CHD) [28], [29]. In one study the dietary carotenoid intake was controlled and serum carotenoid levels were measured to confirm similarity [27]; however, in another study [26], intakes of fruit and vegetables were controlled but serum levels of carotenoids were not measured to ascertain whether the lower susceptibility of LDL to oxidation on the monounsaturated fat diet was due to differences in fat intake or a combination of differences in fat intake and serum carotenoid levels. Another study compared the effect of 7-d consumption of tomato products with extra virgin olive oil versus sunflower oil on antioxidant activity as measured by ferric-reducing ability of plasma and found an increased activity with olive oil [30].
Although extra virgin olive oil is the type most studied with respect to CHD, this oil may not be the cooking oil preferred by Australians because of its strong flavor and cost. Extra virgin and virgin oils are ideal for Mediterranean cooking and for salads; for other cooking styles and for people without a Mediterranean background, refined or light olive oil may be more palatable because of its milder flavor, light texture, and lower cost. Refined olive oil constituted 73% of olive oil imports in 2000 to 2001 [31]. However, it will have fewer antioxidants because some of these compounds are removed in refining.
To our knowledge, no study has examined the effect of short-term intake (10 d) of a carotenoid-controlled lycopene-enriched diet with high or low amounts of refined olive oil on serum lycopene levels.
Section snippets
Materials and methods
Healthy non-smoking men and women who were 22 to 70 y old and had no history of heart disease were invited to take part in the study by newspaper advertisements and a university newsletter. Exclusion criteria included the use of any medication that affects blood lipids or blood pressure, use of vitamin and/or mineral supplements, pregnancy, or lactation.
The scientific ethics committee of the Launceston General Hospital (Tasmania, Australia) approved the study protocol, and informed written
Results
Twenty-four subjects participated in the study. Three subjects withdrew within the first 4 d of the first dietary period for personal reasons. Twenty-one subjects (15 women and 6 men; 44.4 ± 12.3 y old, mean ± standard deviation) completed the study (Table 1). Nine participants commenced the OO diet first and 12 the LO diet.
Nutrient intake data, calculated from the 4-d diet records on the two dietary periods, are presented in Table 2. Intakes of carbohydrates and fat were in the target range.
Discussion
The study compared the effects of a lycopene-rich diet high in olive oil and a lycopene-rich diet low in olive oil on serum lycopene levels, serum lipids, and some measurements of antioxidant status. Unlike many previous studies, the olive oil used was refined olive oil, which has fewer polyphenolic compounds, which have a beneficial effect in decreasing CHD. This present investigation confirmed the results of other studies by showing an increase in serum lycopene with an increase in dietary
Acknowledgments
H. J. Heinz (Melbourne, Australia) provided the tomato products and I. G. A. Moonah (Tasmania, Australia) provided the olive oil for the study. Elaine Whitham (Toxicology/Special Biochemistry, Department of Chemical Pathology, Women’s and Children’s Hospital, Adelaide, Australia) performed the carotenoid analysis. Dr. Iain Robertson, MMedSci., M.M., M.P.H. (School of Human Life Sciences) provided biostatistical support. Mr. Dale Kunde (School of Human Life Sciences) and James Sharman
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This study was funded by the Clifford Craig Medical Research Trust, Launceston, Tasmania, Australia.