Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men

¹ From Health Care Products Research Laboratories No.1, Kao Corporation, Tokyo (TN, YK, SS, SM, TH, YT, and IT)

² Supported by Kao Corporation.

³ Address reprint requests to I Tokimitsu, Health Care Products Research Laboratories No.1, Kao Corporation, 2-1-3, Bunka, Sumida-ku, Tokyo, 131-8501, Japan. E-mail: tokimitsu.ichirou{at}kao.co.jp.

ABSTRACT  
Background: Catechins, the major component of green tea extract, have various physiologic effects. There are few studies, however, on the effects of catechins on body fat reduction in humans. It has been reported that the body mass index (BMI) correlates with the amount of malondialdehyde and thiobarbituric acid–reactive substances in the blood.

Objective: We investigated the effect of catechins on body fat reduction and the relation between oxidized LDL and body fat variables.

Design: After a 2-wk diet run-in period, healthy Japanese men were divided into 2 groups with similar BMI and waist circumference distributions. A 12-wk double-blind study was performed in which the subjects ingested 1 bottle oolong tea/d containing 690 mg catechins (green tea extract group; n = 17) or 1 bottle oolong tea/d containing 22 mg catechins (control group; n = 18).

Results: Body weight, BMI, waist circumference, body fat mass, and subcutaneous fat area were significantly lower in the green tea extract group than in the control group. Changes in the concentrations of malondialdehyde-modified LDL were positively associated with changes in body fat mass and total fat area in the green tea extract group.

Conclusion: Daily consumption of tea containing 690 mg catechins for 12 wk reduced body fat, which suggests that the ingestion of catechins might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity.

Key Words: Green tea extract • catechins • humans • body fat • malondialdehyde-modified LDL • double-blind controlled study

INTRODUCTION  
High body fat increases the risk of diabetes, hyperlipidemia, and hypertension, which leads to arteriosclerotic disease. There is an increased risk of death associated with these diseases as well as with increased body fat (1-3). Body fat increases with an increase in dietary lipid intake (4, 5). Therefore, recommendations of lifestyle changes, and of changes in dietary content in particular, are often made for primary prevention and improvement of these diseases.

Polyphenols have recently attracted attention because of their physiologic activity. Green tea, long consumed in Asian countries (mainly Japan and China), contains low-molecular-weight polyphenols consisting mainly of flavanol (flavan-3-ol) monomers, which are referred to as catechins. There are several isomers of this compound: catechin, catechin gallate (Cg), gallocatechin, gallocatechin gallate (GCg), epicatechin, epicatechin gallate (ECg), epigallocatechin, and epigallocatechin gallate (EGCg). Normally, 10–20% of the catechins in green tea leaves are epigallocatechin and EGCg (6). A portion of ingested EGCg is absorbed and widely distributed throughout the body (7). The ingestion of tea extract or catechins induces antioxidant (8), antiviral (9), antiplaque-forming (10), and anticancer (11) activities, as well as decreases in blood pressure (12) and blood sugar (13). Lipid metabolism studies in animals, tissues, and cells have found that tea extract and catechins reduce triacylglycerol and total cholesterol concentrations (14, 15), inhibit hepatic and body fat accumulation (16, 17), and stimulate thermogenesis (18). In humans, there have been few studies on the effects of catechins on body fat, but the effects on energy expenditure (EE) and oxidative consumption have been examined (19, 20). One study of the effects of catechins on body weight found a tendency toward decreased body weight and waist circumference, but no comparative controls were included in the study (21).

Studies reported that body mass index (BMI; in kg/m²) correlates with the amount of thiobarbituric acid-reactive substances (TBARS) and malondialdehyde in the blood (22, 23). These studies suggested that obesity might be related to an increase in lipid oxidizability. To examine the hypothesis that continuous ingestion of catechins reduces body fat in humans, we performed a double-blind controlled study in healthy men (n = 38) who were normal-weight to overweight and in whom the intake of catechins and caffeine from other foods was minimized. The effects of catechins on the blood variables and oxidized LDL and the association between body fat variables and oxidized LDL were investigated.

SUBJECTS, MATERIALS, AND METHODS  
Subjects
The subjects were 38 male employees of Kao Corporation (Tokyo), aged 24–46 y, whose body weight was normal to overweight, according to the criteria of the National Institutes of Health for BMI (24).

The study was performed under the supervision of an occupational health physician, in accordance with the regulations of the Kao Corporation Ethics Committee for Internal Clinical Studies and in conformity with the Helsinki Declaration. The conditions and procedures of the investigation were reviewed with all subjects before they gave written informed consent.

Materials
Green tea extract (GTE) was prepared by using 2 extraction methods. To prepare one version (GTE-A), green tea leaves underwent extraction with hot water, and the extract was reduced to a powder by using the spray-dry method. The powder was dissolved in methanol-water, discolored with the use of an octadecyl silica column, and freeze-dried (10). To prepare another version (GTE-B), which is decaffeinated, the GTE obtained with hot water was reduced to a powder by using the spray-dry method, and then the extract was dissolved in hot water and mixed with an equal volume of chloroform. The aqueous phase was recovered with 3 volumes of ethanol, and the extract was freeze-dried after removal of the solvent (10). The total catechin content was 33.0 g/100 g in the GTE-A powder and 85.6 g/100 g in the GTE-B powder. For preparation of the test beverage, 9 g oolong tea leaves underwent extraction with 100 mL distilled water at 80 °C for 5 min, and the extract was used as the base beverage. Two types of beverage were prepared: one beverage containing a high amount of catechins and a control beverage. The beverage with a high catechin content was prepared by adding both GTEs to the base beverage and adjusting the total catechin content to 700 mg/340 mL base beverage. For the control beverage, both GTEs were added to the base beverage, and the total catechin content was adjusted to 20 mg/340 mL base beverage; this is the same ratio of catechin components to the caffeine content as in the beverage with a high catechin content. To avoid oxidation and to maintain quality throughout the study period, 50 mg ascorbic acid/100 mL beverage was added to the beverages, and the beverages were sterilized by high-temperature heat sterilization at 138 °C for 30 min. Aliquots of 340 mL were distributed in 340-mL polyethylene terephthalate bottles.

The amounts of catechin, Cg, gallate catechin, GCg, epicatechin, ECg, epigallocatechin, and EGCg in the test beverage were measured by using HPLC carried out on an L-column ODS (4.6 mm diameter x 250 mm length; Chemicals Evaluation and Research Institute, Tokyo). The HPLC conditions were as follows: column temperature, 35 °C; sample size, 10 µL (0.1 mol acetic acid solution/L); mobile phase, 0.1 mol acetic acid/L (solution A), 0.1 mol acetic acid-acetonitrile/L (solution B); gradient conditions, 0–5 min ratio of solution A to solution B = 97:3, 5–37 min A:B = 80:20, 37–43 min A:B = 80:20, 43–43.5 min A:B = 0:100, and 43.5–48.5 min A:B = 0:100; flow rate, 1.0 mL/min; and measurement wavelength, 280 nm. Catechin, Cg, gallocatechin, GCg, epicatechin, ECg, epigallocatechin, and EGCg in proportions of 40, 100, and 200 µg/mL with a purity of 98% (Kurita Water Industries Ltd, Tokyo) in 0.1 mol acetic acid-methanol/L were used as standards. The calibration curves were prepared from the peak area of 10 µL of each standard solution.

The water content of the test beverage was ascertained by measuring the weight before and after drying at atmospheric pressure and at 105 °C by using a forced-circulation warm-air dryer. The protein content of the test beverage was calculated by using nitrogen x 6.25, and the amount of nitrogen was measured by using the Kjeldahl method. For protein quantification, the amount of nitrogen in caffeine (amount of caffeine x 56/194, with 56 and 194 being the MW of 4 nitrogens and caffeine, respectively) was subtracted from the total amount of nitrogen.

For lipid quantification, the test beverage was deproteinized by using a 7% copper sulfate solution, and the pH was adjusted to 6–7; the sample then underwent extraction with diethylether for 16 h with the use of a Soxhlet extractor. The lipid content of the test beverage was ascertained by measuring the weight before and after removal of the solvent. The ash content was ascertained by measuring the weight of the sample with the use of the direct ash method by heating at 550 °C.

Dietary fiber was quantified by using the enzyme-weight method. Dried powder of the test beverage (10 g) was combined with 40 mL phosphate buffer (0.08 mol/L; pH 6.0) and 0.1 mL of a thermostable -amylase (Termamyl 120 L; Novo-Nordisk A/S, Bagsværd, Denmark), which was then incubated in a boiling water bath for 30 min. After cooling, the solution was adjusted to pH 7.5 ± 0.1 with the use of sodium hydroxide and combined with 0.1 mL of 50 mg protease/mL (product no. P-5380; Sigma-Aldrich Co, St Louis) in phosphate buffer (pH 6.0), and the mixture was incubated at 60 °C for 30 min. After cooling, the solution was adjusted to pH 4.3 ± 0.3 with the use of hydrochloric acid and combined with 0.1 mL amyloglucosidase solution (product no. A-9913, Sigma-Aldrich Co), and the mixture was incubated at 60 °C for 30 min. Next, the solution was combined with 4 volumes of 95% ethanol at 60 °C, kept at room temperature for 1 h, and filtered. The residue was washed 3 times with 78% ethanol, 2 times with 95% ethanol, and 2 times with acetone, and then it was dried at 105 °C overnight, and the weight was measured. This procedure was repeated twice—first for measurement of the ash content after incineration treatment and again for protein quantification by using the Kjeldahl method. The dietary fiber content was calculated by subtracting the protein content from the ash content.

Sodium was measured by atomic absorption spectrometry at a wavelength of 589.6 nm with the use of an acetylene-air flame. To quantify the sodium content, the dried powder of the test beverage was combined with 1% HCl and allowed to stand overnight.

For ascorbic acid measurement, a 10% solution was filtered, and 1 mL of the filtrate was combined with 1 mL of 5% metaphosphoric acid. This solution was oxidized by combining the sample with a few drops of 0.2% dichlorophenolindophenol and 2 mL of 2% thiourea–5% metaphosphoric acid, which was followed by the addition of 0.5 mL of 2% 2,4-dinitrophenylhydrazone in 4.5 mol sulfuric acid/L. This solution was then heated at 40 °C for 16 h to produce osazone and combined with 3 mL ethyl acetate; the sample was shaken for 1 h and quantified by using HPLC. The HPLC conditions were as follows: column, Silica-1100-N (4.6 mm diameter x 100 mm length; Senshu Scientific Co, Ltd, Tokyo), column temperature, 35 °C; mobile phase, ethyl acetate:hexane:acetic acid:water = 60:40:5:0.05; flow rate, 1.5 mL/min; and measurement wavelength, 495 nm.

Caffeine was quantified by using HPLC after the dried powder was dissolved in methanol and adjusted to the specified volume. The HPLC conditions were as follows: column, Mightysil RP-18 Aqua (5 µm particle size; 4.5 mm x 150 mm diameter; Kanto Kagaku, Tokyo); column temperature, 50 °C; mobile phase, the ratio of 0.03 mol acetate buffer/L (pH 4) to acetonitrile = 850:30; flow rate, 2.0 mL/min; and measurement wavelength, 270 nm. Tannin was measured as tannic acid by using the Folin-Denis method.

Carbohydrates were calculated as the residue of these substances. Energy was calculated by using the energy conversion coefficients (ie, protein, 16.7 kJ/g; lipid, 37.7 kJ/g; and carbohydrate, 16.7 kJ/g).

Protocol
Before the study, all subjects were taught to calculate their energy and lipid intakes by using 2 guidebooks, the Standard Tables of Food Consumption in Japan, 4th edition (25), and the New Calorie Guide Book for Daily Diet (26). The energy intake (EI) required for living activity strength 1 (a Japanese term, equivalent to a physical activity level of 1.3), based on the subject's advance activity report, was calculated by using the equation below from the standard table (25):

RESULTS  
Analysis of the test beverages
The contents and analyzed ingredient values of catechin, Cg, gallocatechin, GCg, epicatechin, ECg, epigallocatechin, and EGCg in the test beverages are shown in Table 1. The total catechin content was 689.9 mg/340 mL beverage in the high-catechin beverage and 21.8 mg/340 mL in the control beverage.

View this table:
TABLE 1. Composition of test beverages¹

 
Dietary condition of the subjects
Three subjects were excluded from the analysis because of a marked change in their living environment during the study (control group, n = 18; GTE group, n = 17). The daily EI was 8.7 ± 0.1 MJ at week 0 and 8.8 ± 0.1 MJ at week 12 in the control group and 8.6 ± 0.1 MJ at week 0 and 8.6 ± 0.1 MJ at week 12 in the GTE group. Those daily energy values were very close to the Japanese standard, which is 9.0–9.4 MJ in men 20–40 y old at living activity strength 1 (35), and 90% of the values were 8.3–8.5 MJ. The mean (± SE) daily lipid intake was 59.2 ± 0.8 g at week 0 and 61.4 ± 0.9 g at week 12 in the control group and 61.5 ± 1.4 g at week 0 and 59.6 ± 0.8 g at week 12 in the GTE group. There were no significant differences between the 2 groups. The mean values of each variable were calculated every 4 wk and analyzed by using a two-factor repeated-measures ANOVA, and there was no significant difference between groups.

Effects on the anthropometric values and body composition
Because one subject in the control group did not consent to CT imaging at weeks 4 and 8, analyses of the control group for weeks 4 and 8 were performed in 17 subjects. There was no significant difference in the initial value of any variable between the 2 groups (Table 2). There was a significant time-by-group interaction for body weight, BMI, waist circumference, body fat mass, and SFA (Table 2). The decrease in waist circumference between the initial measurement and that at week 12 in the GTE group was significantly greater than that in the control group (–3.4 ± 0.5 cm and –1.6 ± 0.4 cm, respectively; Table 2). The decrease in skinfold thickness between the initial measurement and that at week 12 in the GTE group was significantly greater than that in the control group (–3.3 ± 0.7 mm and –1.3 ± 0.7 mm, respectively; Table 2). The decrease in TFA between the initial measurement and that at week 12 in the GTE group was significantly greater than that in the control group (–26.7 ± 6.0 cm² and –6.7 ± 5.8 cm², respectively; Table 2). The decrease in SFA between the initial measurement and that at week 12 in the GTE group was significantly greater than that in the control group (–16.7 ± 3.0 cm² and –4.4 ± 4.1 cm², respectively; Table 2).

View this table:
TABLE 2. Changes in anthropometric variables and body composition after consumption of either control or high-catechin beverages for 12 wk¹

 
Effects on blood variables and side effects
There was no significant difference between the groups in the initial value of any variable (Table 3). There was a significant time-by-group interaction for vitamin E and MDA-LDL concentrations (Table 3). Among the variables for which standard values for Japanese have been established (36), the mean values did not deviate from the standard values throughout the study period.

View this table:
TABLE 3. Changes in blood variables after consumption of either control or high-catechin beverages for 12 wk¹

 
The occupational health physician assessed the subjects every 4 wk. The physician reported no side effects related to the study.

Effects on blood MDA-LDL and the association between MDA-LDL and body fat variables
Because the initial MDA-LDL values tended to differ between groups, the variable was compared on the basis of the change by week 12, and we took 100% as the initial value. The decrease in MDA-LDL between the initial measurement and that at week 12 in the GTE group was significantly greater than that in the control group (67.5 ± 6.1% and 89.5 ± 6.0%, respectively; P < 0.05). To investigate the association between MDA-LDL and body fat variables, linear regression analysis was performed within each group. The percentage value of MDA-LDL in week 12 was used as an independent value, and the percentage values of each anthropometric variable and abdominal fat area in week 12 were used as dependent values. In the GTE group, the percentage value of MDA-LDL at week 12 was significantly associated with the percentage values of body fat mass (R² = 0.646, P = 0.0001) and TFA (R² = 0.273, P = 0.0313) (Figure 1). In the control group, however, those associations were not observed (P > 0.05).

View larger version (21K):
FIGURE 1.. Associations between the percentage of malondialdehyde-modified LDL (MDA-LDL) concentration at week 12 and the percentage of body fat mass (A) and total fat area (B) at week 12 in the green tea extract (GTE) group (• and —; n = 17) and the control group ( and - - -; n = 18).A: GTE group, y = 78.62 + 0.21x (R² = 0.646, P of slope = 0.0001); control group, y = 97.07 –0.07x (R² = 0.001, P of slope = 0.9080). B: GTE group, y = 77.36 + 0.18x (R² = 0.273, P of slope = 0.0313); control group, y = 104.41 –0.08x (R² = 0.034, P of slope = 0.4664).

 

DISCUSSION  
In the current study, the samples were prepared in beverage form so that the subjects could easily consume them every day for 12 wk. The base beverage was oolong tea, which is the most widely sold tea in Japan (37). The average consumption of green tea and of catechins in Japan is calculated to be 2 g tea leaves/d and 200–400 mg catechin/d (6). Before conducting this study, for clarification of the effect of catechins, the caffeine content in the test beverages was adjusted to a minimal amount, and the consumption of beverages and foods containing large amounts of catechins or caffeine was prohibited so as to minimize the effect of other food-derived catechins and caffeine. Dietary control, aimed at weight loss for both groups, was included as a benefit for subjects in the control group: the standard daily EI was set to 90% of the value calculated from the body surface area and daily living activities. Under these conditions, body weight, BMI, waist circumference, body fat mass, and SFA were significantly lower in the GTE group than in the control group. At week 12, the decrease in waist circumference, skinfold thickness, TFA, and SFA from the initial measurements was significantly greater in the GTE group than in the control group. The percentage difference in the changes in weight, BMI, waist circumference, body fat mass, skinfold thickness, TFA, and SFA between the GTE and control groups was 1.5%, 1.5%, 2.0%, 3.7%, 6.9%, 7.9%, and 7.5%, respectively. These results indicate that catechins not only promoted EE (18, 19) but also mildly reduced body fat in humans, as suggested by Chantre et al (21). Substances related to lipid metabolism and metal ions in the blood were also investigated, but there was no significant difference between the groups in any variable except vitamin E and MDA-LDL; nor were there any side effects.

Dulloo et al (18) observed that the addition of 200 nmol EGCg/mL increased thermogenesis in brown fat tissue of rat and that there was a synergistic effect between caffeine and EGCg. They also found that consumption of GTE (270 mg EGCg/d) increased EE and the oxidation of lipids in another human study (19). In those reports, they suggested that those effects were due to an inhibitory effect of catechins on the activity of catechol-O-methyltransferase (COMT), which is a catecholamine-degrading enzyme, and to an inhibitory effect of caffeine on phosphodiesterase that results in an increase in noradrenalin-induced thermogenesis and the maintenance of that increase (20). Other studies, however, reported that plasma EGCg concentrations were only 4.5 nmol/mL after the intake of 525 mg EGCg/d in humans (38), and that the maximum in vitro inhibitory effect on the activity of COMT by 100 µmol flavonoids/L was 64% (39). These results indicate that the increase in thermogenesis and the reduction in body fat in humans cannot be completely explained by an inhibitory effect on COMT, and therefore another mechanism must be involved in the decrease in body fat induced by catechins.

Chemically modified, degenerated lipoproteins such as oxidative stress–induced MDA-LDL and 4-hydroxynonenal lysine–LDL are observed in atheroma in humans and rabbits (40). Holvoet et al (41) measured plasma MDA-LDL in humans and suggested both that an increase in plasma MDA-LDL can be used as a marker of unstable atherosclerotic cardiovascular disease and that blood MDA-LDL is an independent factor not correlated with LDL cholesterol. Previously, MDA-LDL was measured indirectly by using TBARS, and there are many reports that catechins prevent an increase in serum TBARS. In 2 reports, increases in BMI were significantly correlated with concentrations of TBARS (22) and malondialdehyde (23) in blood. The current studies suggest that obesity might be related to an increase in lipid oxidizability. In addition, there is an interaction between nuclear factor- B and peroxisome proliferator–activated receptors (PPARs). PPARs are important transcription factors for lipid metabolism; for example, mRNA of ß-oxidation enzymes is up-regulated by PPAR- (42-45). Because nuclear factor- B is regulated by a redox regulatory system, it is possible that such a system also regulates body fat metabolism. This hypothesis led us to measure MDA-LDL by using an enxyme-linked immunosorbent assay and an anti–MDA-LDL antibody (ML25) to investigate the antioxidizing activity of ingested catechins and also to compare body fat variables. In the GTE group, the changes in the concentrations of MDA-LDL were positively associated with the changes in body fat mass and TFA. These results suggest that the accumulation of body fat might be associated with an increase in lipid oxidizability and that a redox regulatory system might be involved individually in the body fat–and MDA-LDL–reducing effects of catechins. Further investigation is needed to clarify the relation between a redox regulatory system and the body fat–reducing mechanism.

Catechins reduce serum lipids by inhibiting small-intestine micelle formation in animals (46), and they limit the absorption of sugars by inhibiting -glucosidase activity (47). There was no significant difference in serum lipids or blood sugar between the groups; however, the initial values might have been too low for any effects to be detected. Thus, the amount of catechins ingested in this study might not have been sufficient to inhibit micelle formation or -glucosidase activity.

In conclusion, long-term consumption of beverages containing catechins inhibits the formation of oxidized lipids such as MDA-LDL, and this is a risk factor for developing arteriosclerosis. Moreover, catechin intake decreases body fat. These results suggest that catechins contribute to the prevention of and improvement in various lifestyle-related diseases, particularly obesity. These findings also suggest that regulation of a redox regulatory system might influence the accumulation of body fat.

ACKNOWLEDGMENTS  
We sincerely thank Toshio Fujiwara at Dokkyo University School of Medicine for guidance and advice.

TN, YK, SS, and SM conducted the study. YK and SS contributed to data collection and database management. SM and TH assisted in the statistical analyses and contributed to data analyses. YH provided the samples, and TN designed and contributed to the writing of the manuscript. IT served as laboratory director, oversaw the writing of the manuscript, and was responsible for the diagnosis and recruitment of participants. None of the authors of this manuscript had any conflicts of interest.

REFERENCES  

1. Pi-Sunyer FX. Health implications of obesity. Am J Clin Nutr 1991;53:1595–603.
2. Seidell JC, Verschuren WM, van Leer EM, Kromhout D. Overweight, underweight, and mortality: a prospective study of 48,287 men and women. Arch Intern Med 1996;156:958–63.
3. Kannel WB, Cupples LA, Ramaswami R, Stokes J, Kreger BE, Higgins M. Regional obesity and risk of cardiovascular disease: the Framingham Study. J Clin Epidemiol 1991;44:183–90.
4. Fricker J, Fumeron F, Clair D, Apfelbaum M. A positive correlation between energy intake and BMI in a population of 1312 overweight subjects. Int J Obes 1989;13:663–81.
5. Nelson LH, Tucker LA. Diet composition related to body fat in a multivariate study of 203 men. J Am Diet Assoc 1996;96:771–7.
6. Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334–50.
7. Nakagawa K, Miyazawa T. Absorption and distribution of tea catechin, (-)-epigallocatechin-3-gallate, in the rat. J Nutr Sci Vitaminol (Tokyo) 1997;43:679–84.
8. Yoshino K, Hara Y, Sano M, Tomita I. Antioxidative effects of black tea theaflavins and thearubigin on lipid peroxidation of rat liver homogenates induced by tert-butyl hydroperoxide. Biol Pharm Bull 1994;17:146–9.
9. Nakayama M, Suzuki K, Toda M, Okubo S, Hara Y, Shimamura T. Inhibition of the infectivity of influenza virus by tea polyphenols. Antiviral Res 1993;21:289–99.
10. Hattori M, Kusumoto IT, Namba T, Ishigami T, Hara Y. Effect of tea polyphenols on glucan synthesis by glucosyltransferase from Streptococcus mutans. Chem Pharm Bull 1990;38:717–20.
11. Katiyar SK, Mukhtar H. Tea in chemoprevention of cancer: epidemiologic and experimental studies. Int J Oncol 1996;8:221–38.
12. Henry JP, Stephens-Larson P. Reduction of chronic psychosocial hypertension in mice by decaffeinated tea. Hypertension 1984;6:437–44.
13. Matsumoto N, Ishigaki F, Ishigaki A, Iwashin H, Hara Y. Reduction of blood glucose levels by tea catechin. Biosci Biotech Biochem 1993;57:525–7.
14. Nanjo F, Hara Y, Kikuchi Y. Effects of tea polyphenols on blood rheology in rats fed a high-fat diet. In: Ho CT, ed. Food phytochemicals for cancer prevention: teas, spices and herbs. Washington, DC: American Chemical Society, 1994:76–82.
15. Chan PT, Fong WP, Cheung YL, Huang Y, Ho WKK, Chen ZY. Jasmine green tea epicatechins are hypolipidemic in hamsters (Mesocricetus auratus) fed a high fat diet. J Nutr 1999;129:1094–101.
16. Chaudhari PN, Hatwalne VG. Effect of epicatechin on liver lipids of rats fed with choline deficient diet. Ind J Nutr Diet 1977;14:136–9.
17. Ishigaki A, Tonooka F, Matsumoto N, Hara Y. Suppression of the accumulation of body and liver fat by tea catechin. Shizuoka, Japan: Organizing Committee of International Symposium on Tea Science, 1991:309–13.
18. Dulloo AG, Seydoux J, Girardier L, Chantre P, Vandermander J. Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity. Int J Obes Relat Metab Disord 2000;24:252–8.
19. Dulloo AG, Duret C, Rohrer D, et al. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr 1999;70:1040–5.
20. Rumpler W, Seale J, Clevidence B, et al. Oolong tea increases metabolic rate and fat oxidation in men. J Nutr 2001;131:2848–52.
21. Chantre P, Lairon D. Recent findings of green tea extract AR25 (Exolise) and its activity for the treatment of obesity. Phytomedicine 2002;9:3–8.
22. Van Gaal LF, Vertommen J, De Leeuw IH. The in vitro oxidizability of lipoprotein particles in obese and non-obese subjects. Atherosclerosis 1998;137:S39–44.
23. Prazny M, Skrha J, Hilgertova J. Plasma malondialdehyde and obesity: is there a relationship? Clin Chem Lab Med 1999;37:1129–30.
24. Sawa H. Outline of research activitites of the National Institute of Health and Nutrition. Outline of research activities in 1999. Internet: http://www.nih.go.jp/eiken/english/research/pdf/nenpo99_e.pdf (accessed 18 July 2002).
25. Standard tables of food composition in Japan 2000. 4th ed. Tokyo: Kagawa Nutrition University Publishing Division, 2000:417–9 (in Japanese).
26. The new calorie guide book for daily diet. Tokyo: Kagawa Nutrition University Publishing Division, 2002 (in Japanese).
27. The National Nutrition Survey, Japan in 1998. Tokyo: Dai-ichi Shuppan Publishing Co Ltd, 2000:65 (in Japanese).
28. Tokunaga K, Matsuzawa Y, Ishikawa K, Tarui S. A novel technique for the determination of body fat by computed tomography. Int J Obes 1983;7:437–45.
29. Vitamins. In: Henry R, Cannon D, Winkelman J. eds. Clinical chemistry: principles and technics. 2nd ed. New York: Harper & Row, 1974:1374–81.
30. Abe K, Katsui G. Fluorometric determination of tocopherol in serum. J Jpn Soc Nutr Food 1975;28:277–80 (in Japanese).
31. Kotani K, Maekawa M, Kanno T, Kondo A, Toda N, Manabe M. Distribution of immunoreactive malondialdehyde-modified low-density lipoprotein in human serum. Biochim Biophys Acta 1994;1215:121–5.
32. Connerty HV, Briggs AR. Determination of serum calcium by means of orthocresolphthalein complexone. Am J Clin Pathol 1966;45:290–6.
33. Drewes PA. Direct colorimetric determination of phosphorus in serum and urine. Clin Chim Acta 1972;39:81–8.
34. Kuwa K. Ion selective electrode. J Med Technol 1990;34:1353–8 (in Japanese).
35. Standard tables of food composition in Japan 2000. 4th ed. Tokyo: Kagawa Nutrition University Publishing Division, 2000:410 (in Japanese).
36. SRL.info. Tokyo: SRL, Inc. Internet: http://www.srl.info/srlinfo/kensa_ref_CD/index.htm (accessed 30 October 2001).
37. Fancy drink. In: 2001 Food marketing handbook. Tokyo: Fuji Keizai Co, Ltd, 2001:89–97 (in Japanese).
38. Nakagawa K, Okuda S, Miyazawa T. Dose-dependent incorporation of tea catechins, (-)-epigallocatechin-3-gallate and (-)-epigallocatechin, into human plasma. Biosci Biotechnol Biochem 1997;61:1981–5.
39. Borchardt RT, Huber JA. Catechol O-methyltransferase. 5. Structure-activity relationships for inhibition by flavonoids. J Med Chem 1975;18:120–2.
40. Yla-Herttuala S, Palinski W, Rosenfeld ME, et al. Evidence for the presence of oxidatively modified low density lipoprotein in atherosclerotic lesions of rabbit and man. J Clin Invest 1989;84:1086–95.
41. Holvoet P, Perez G, Zhao Z, et al. Malondialdehyde-modified low density lipoproteins in patients with atherosclerotic disease. J Clin Invest 1995;95:2611–9.
42. Beier K, Volkl A, Fahimi D. TNF-alpha downregulates the peroxisome proliferator activated receptor-alpha and the mRNAs encoding peroxisomal proteins in rat liver. FEBS Lett 1997;412:385–7.
43. Parmentier JH, Schohn H, Bronner M, et al. Regulation of CYP4A1 and peroxisome proliferator-activated receptor alpha expression by interleukin-1 beta, interleukin-6, and dexamethasone in cultured fetal rat hepatocytes. Biochem Pharmacol 1997;54:889–98.
44. Neve BP, Fruchart JC, Staels B. Role of the peroxisome proliferator-activated receptors (PPAR) in atherosclerosis. Biochem Pharmacol 2000;60:1245–50.
45. Poynter ME, Daynes RA. Peroxisome proliferator-activated receptor alpha activation modulates cellular redox status, represses nuclear factor-kappa B signaling, and reduces inflammatory cytokine production in aging. J Biol Chem 1998;273:32833–41.
46. Muramatsu K, Fukuyo M, Hara Y. Effect of green tea catechins on plasma cholesterol level in cholesterol-fed rats. J Nutr Sci Vitaminol (Tokyo) 1986;32:613–22.
47. Ikeda I, Imasato Y, Sasaki E, et al. Tea catechins decrease micellar solubility and intestinal absorption of cholesterol in rats. Biochim Biophys Acta 1992;1127:141–6.