Original Article

European Journal of Clinical Nutrition (2010) 64, 704–713; doi:10.1038/ejcn.2010.47; published online 7 April 2010

Epigallocatechin-3-gallate and postprandial fat oxidation in overweight/obese male volunteers: a pilot study

Contributors: FT, MB, AB and JJ designed the research; GF, JB, AB, FA and MB performed the research; FT and MB analyzed the data; and FT and MB wrote the paper.

F Thielecke1,3, G Rahn2, J Böhnke2, F Adams2, A L Birkenfeld2, J Jordan2 and M Boschmann2,3

  1. 1DSM Nutritional Products, Basel, Switzerland
  2. 2Universitary Medicine Berlin, Charité Campus Buch, Franz Volhard Clinical Research Center and HELIOS Clinic Berlin Buch, Berlin, Germany

Correspondence: Dr M Boschmann, University Medicine Berlin, Charité Campus Buch, Franz Volhard Clinical Research Center at the Experimental & Clinical Research Center (ECRC), Lindenberger Weg 80, 13125 Berlin, Germany. E-mail: michael.boschmann@charite.de

3These authors contributed equally to this work.

Received 16 June 2009; Revised 15 February 2010; Accepted 18 February 2010; Published online 7 April 2010.

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Abstract

Objectives:

 

Drinking green tea is associated with many health benefits, including increased fat oxidation. We tested the hypothesis that epigallocatechin-3-gallate (EGCG), the main green tea catechin, increases fat oxidation in obese men.

Methods:

 

Ten healthy overweight/obese males (body mass index 31.3±0.8kg/m2) were studied in a randomized, placebo-controlled, double-blind crossover trial. Study supplements were low EGCG (300mg), high EGCG (600mg), caffeine (200mg), EGCG/caffeine (300mg/200mg) or placebo and were taken orally for 3 days. At the third day of supplementation, O2 consumption and CO2 production was measured by indirect calorimetry to assess energy expenditure and fat oxidation over 4h each after overnight fasting and after a standardized test meal.

Results:

 

Energy expenditure was not affected by any supplementation, neither after overnight fasting nor after the test meal. During the first 2h after overnight fasting, fat oxidation increased by 7.7 (not significant, NS), 15.2 (NS), 26.3 (P<0.05 vs placebo) and 35.4% (P<0.01 vs placebo and low EGCG), for low EGCG, high EGCG, caffeine and EGCG/caffeine, respectively. During the first 2h after the meal, the mean increase in fat oxidation was 33.3 (P<0.05 vs placebo), 20.2 (NS), 34.5 (P<0.05 vs placebo) and 49.4% (P<0.05 vs placebo) for low EGCG, high EGCG, caffeine and EGCG/caffeine, respectively.

Conclusions:

 

Low EGCG increases postprandial fat oxidation in obese men and this to the same extent as 200mg caffeine, whereas high EGCG does not exert this effect. Fasting fat oxidation is increased only by caffeine (with or without EGCG). There is no synergism of low EGCG and 200mg caffeine. Energy expenditure is not affected by EGCG.

Keywords:

EGCG; caffeine; energy expenditure; fat oxidation; calorimetry

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Introduction

Obesity is recognized as an increasing health burden. In 1999–2000 the age-adjusted prevalences of overweight and obese individuals in the United States was 64.5 and 30.5%, respectively (Flegal et al., 2002). There is a growing interest in alternate strategies for weight management. Green tea catechins (flavan-3-oles) have received particular attention, specifically epigallocatechin-3-gallate (EGCG), which represents about 43% of green tea catechin content (Scholz et al., 1995; Yang and Landau, 2000). Several studies have shown that green tea and green tea extracts (GTEs) high in EGCG reduce body weight and body fat tissue in humans when administered over 12 weeks (Hase et al., 2001; Chantre and Lairon, 2002; Tsuchida et al., 2002; Nagao et al., 2005, 2007; Chan et al., 2006; Kajimoto et al., 2006). However, the major mode of action is still unknown. Several mechanisms have been suggested including (a) inhibition of adipocyte differentiation and proliferation (Hung et al., 2005; Wolfram et al., 2005), (b) reduction of fat absorption (Juhel et al., 2000; Yang et al., 2001; Raederstorff et al., 2003) and (c) inhibition of catechol-O-methyltransferase, an enzyme that catalyzes noradrenalin degradation in the central nervous system, thereby prolonging the effects of noradrenalin (Borchardt and Huber, 1975; Rhodes, 1996). Recent human studies suggest that the antiobesity properties of GTE or oolong tea (high in EGCG) may partly be attributable to increased fat oxidation (Dulloo et al., 1999; Rumpler et al., 2001). In a randomized, double-blind, placebo-controlled trial, fat oxidation increased by 35% after supplementation with encapsulated GTE (Dulloo et al., 1999). In this trial, male volunteers consumed either placebo, 150mg caffeine or a GTE containing 270mg EGCG and 150mg caffeine within 24h. Caffeine at the utilized dose did not increase 24-h energy expenditure (EE) or fat oxidation. However, the increase in fat oxidation with GTE exceeded the one observed with caffeine alone, suggesting components other than caffeine contributing to the increase in fat oxidation. In another randomized crossover trial, 12 healthy volunteers consumed oolong tea, resulting in daily consumptions of 244mg EGCG and 270mg caffeine, or a comparable volume of water (control) within 24h (Rumpler et al., 2001). As a result, 24-h fat oxidation increased by 12% with oolong tea compared with control. However, these two trials used mixtures of catechins and caffeine; it is therefore not possible to deduce the individual contribution of the main active ingredients in green tea, that is, EGCG or caffeine, to increased fat utilization. However, a long-term investigation observed increases in fat oxidation of 37 and 32% for both sedentary and exercising healthy subjects when consuming daily a beverage containing 570mg green tea catechins (218mg EGCG) for 8 weeks (Ota et al., 2005). It is interesting that the beverage contained <40mg caffeine, suggesting that EGCG and/or other catechins are mainly responsible for this observation.

Yet, the effect of pure EGCG on energy metabolism and fat oxidation in humans has not been studied in detail. Therefore, in this study, we wanted to test the hypothesis that EGCG per se contributes to increased fasting and postprandial fat oxidation in overweight/obese volunteers.

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Methods

Subjects

In all, 12 male volunteers (body mass index 27–35kg/m2) were included in the study. All volunteers were healthy, nonsmoking and drug-free as determined by medical history, physical examination, and routine blood and urine tests. Specific exclusion criteria were intake of dietary supplements within the week before the study or during the study itself and habitual consumption of caffeine greater than or equal to300mg per day (greater than or equal to3–6 cups of coffee per day) and/or of green tea greater than or equal to5 cups per day. During the study, no caffeine and catechin-containing drinks and food were allowed. Volunteers were studied at the Franz Volhard Clinical Research Centre, Charité Universitary Medicine Berlin, Germany. The study protocol was approved by the Institutional Review Board of the Charité and all participants gave written informed consent before study entry.

Study design

In this double-blind crossover study, volunteers received encapsulated supplements over 3 days in a randomized manner. Daily supplement doses were 300mg (low) EGCG, 600mg (high) EGCG, 200mg caffeine, 300mg EGCG/200mg caffeine or placebo (lactose). To reach these dose levels, volunteers took two capsules per day with 50ml water, that is, one capsule at 1h before breakfast and dinner, respectively. Teavigo, a highly purified extract from green tea leaves (Camilla sinensis) containing minimum 94% EGCG and maximum 0.1% caffeine (DSM Nutritional Products, Basel, Switzerland), and caffeine (Sigma-Aldrich, Taufkirchen, Germany) were used for preparing the supplements. On the second day of supplementation, volunteers were hospitalized in our clinical research centre under controlled food intake and physical activity. In the morning of the third day at 0800h, metabolic measurements were started (Figure 1). There was a wash-out period of at least 7 days between the different treatments.

Figure 1.
Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Study design. Volunteers took the supplements (300mg EGCG, 600mg EGCG, 200mg caffeine, 300mg EGCG/200mg caffeine or placebo given in two doses/capsules per day) over 3 days in total. On the second day they arrived at the clinic where a standardized dinner was provided. On the following day, after a 12-h fast the daily dose was administrated. At 1h after capsule intake, fasting metabolic rate was measured for a total of 4h. At the end of this period, half of the daily dose was provided to keep the plasma levels from fasting to postprandial comparable. Then, monitoring was interrupted for 60min. A standardized test meal was provided and postprandial metabolic rate was measured for 4h.

Full figure and legend (64K)

Study protocol

Subjects stayed in the supine position throughout the whole test period of 8h with the exceptions described below. During the test, subjects were allowed to watch television. Before starting the test, baseline heart rate, beat-by-beat blood pressure (Finapres, Ohmeda, Louisville, CO, USA) and brachial arterial blood pressure (Dinamap, Critikon, Newport, UK) were measured. Then, one catheter was placed into a large antecubital vein for blood sampling at baseline and every 30min during the test. Metabolic measurements by indirect calorimetry were carried out over 4h each in the fasting and the postprandial state. There was a 1-h break in between the two blocks in which subjects consumed the standardized test meal, as well as 30min in the middle of each block during which the subjects were allowed to visit the bathroom. Thus, samples were obtained and analyzed in two 2-h intervals for each block (Figure 1).

The half-life of EGCG at the doses applied in this study varies from 1.9 to 4.3h (Ullmann et al., 2003). Therefore, half of the daily doses of EGCG and caffeine were provided 1h before the postprandial measurement to keep the plasma levels of EGCG and caffeine comparable with the fasting conditions.

The standardized test meal (bread, butter, cheese, ham, tomato and cucumber) was prepared by a dietician considering the individual energy requirement of each volunteer. The meal provided 5kcal/kg body weight with 50, 35 and 15% of energy from carbohydrates, lipids and proteins, respectively.

Measurements and calculations

Anthropometry
 

Body weight was measured with an electronic calibrated scale (Soehnle, Murrhardt, Germany) and height with a GPM anthropometer (Siber & Hegner, Zurich, Switzerland). Body mass index was calculated as body weight (kg)/(height (m))2.

Calorimetry
 

Oxygen consumption (VO2, ml/min) and carbon dioxide production (VCO2, ml/min) were measured by a ventilated hood system (Deltatrac II, GE Healthcare, Freiburg, Germany). Sampling rate was 1 per minute. Means of 15min sampling intervals were used to calculate fasting and postprandial EE, respiratory quotient (RQ), and fat (FOX) and carbohydrate (COX) oxidation rates according to the equations proposed by Ferrannini (1988). The RQ, the quotient of VCO2 and VO2, can vary between 1, which indicates 100% carbohydrate oxidation, and 0.7, which indicates 100% fat oxidation, and can be used for assessing changes in substrate oxidation rates.

Blood samples
 

Plasma insulin and glucose were measured according to international standards and nonesterified fatty acids (NEFA) by an automated colorimetric test (ABX Pentra 400 Chemistry Analyser, Horiba ABX, Bedfordshire, UK).

Statistics

For each subject, global fitting was used to compare the response curves for EE and RQ after the different supplements with the response curve for placebo. This is a nonlinear regression method in which one curve (placebo) for each subject is used as baseline, allowing evaluations of discrepancy of the other curve (test supplement). This method works in analogy to the paired samples t-test, using a pair of curves instead of a pair of values. Mean 2-h values of EE, RQ, FOX and COX within the 4h before meal and 4h after meal between the different treatments were compared by a paired t-test. P-values <0.05 were considered statistically significant. All data are given as means±s.e. if not stated otherwise. All statistical tests were performed with InStat, Version 3.0, Graphpad Software Inc, San Diego, CA, USA.

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Results

Twelve subjects were enrolled in the study, 10 subjects completed all five supplementation periods. One subject dropped out of the study after the second supplementation for reasons not related to the study. Another subject withdrew because of reluctance to use catheter. There were no adverse effects attributable to EGCG, neither with 300mg nor with 600mg for 3 days, or caffeine.

Screening characteristics of the enrolled study population are given in Table 1.


Time courses of EE

On placebo, resting EE was 5.79±0.26kJ/min and it remained at that level over the following 240min. Shortly after the test meal, EE rose to 6.59±0.36kJ/min followed by a slow but steady decline back to baseline levels at the end of testing (Figure 2).

Figure 2.
Figure 2 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Time course of energy expenditure (EE) before and after intake of a test meal under low EGCG (upper panel, left), high EGCG (upper panel, right), caffeine (lower panel, left) and caffeine/EGCG (lower panel, right), respectively (filled circles), vs placebo (open circles). For details of supplementation and meal composition refer Methods section. Data are given as mean±s.e., n=10.

Full figure and legend (176K)

Within the other treatment groups, resting EE was 5.68±0.26, 5.76±0.27, 6.01±0.22 and 5.98±0.21kJ/min on low EGCG, high EGCG, caffeine and EGCG/caffeine, respectively. In all the four groups, EE did not change significantly over the following 240min before the intake of the test meal and showed an almost identical postprandial time course vs placebo (Figure 2).

Time courses of RQ

Fasting RQ were 0.85±0.02, 0.87±0.02, 0.84±0.02, 0.84±0.02 and 0.82±0.01 for placebo, low EGCG, high EGCG, caffeine and EGCG/caffeine, respectively.

On placebo, RQ oscillated around 0.86 within the first pre-meal block, decreased then to 0.79±0.01 at t=280min, but returned to fasting values at the end of the second pre-meal block (Figure 3). After the test meal, RQ increased to 0.89±0.02 within the first post-meal block, but returned to the fasting value within the second post-meal block.

Figure 3.
Figure 3 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Time course of respiratory quotient (RQ) before and after intake of a test meal under low EGCG (upper panel, left), high EGCG (upper panel, right), caffeine (lower panel, left) and caffeine/EGCG (lower panel, right), respectively (filled circles), vs placebo (open circles). For details of supplementation and meal composition refer Methods section. Data are given as mean±s.e., n=10. *P<0.05, **P<0.01, ***P<0.001, test drug vs placebo. Differences between the curves in the indicated sections were tested by global fitting.

Full figure and legend (166K)

On low EGCG, time course of fasting RQ did not differ significantly from placebo. After the meal, RQ increased only slightly and remained at lower values during the first post-meal block (P<0.05, low EGCG vs placebo), but followed the time course under placebo in the second post-meal phase.

On high EGCG, time courses of fasting and postprandial RQ did not differ significantly from placebo values.

On caffeine, fasting RQ was significantly lower during the first (P<0.01 vs placebo) but did not differ significantly from placebo during the second pre-meal period. After the meal, RQ increased comparable to placebo during the first, but decreased to 0.81±0.01 and hence below the values on placebo during the second post-meal period (P<0.01 vs placebo).

On EGCG/caffeine, RQ was significantly lower during the two pre-meal periods (P<0.001 vs placebo). After meal intake, RQ increased but remained below the time course on placebo (P<0.001, EGCG/caffeine vs placebo).

Mean FOX

During the first pre-meal block, 300 and 600mg EGCG tended to increase FOX slightly by 0.29 and 0.57g/h compared with placebo; however, the changes did not reach statistical significance (Table 2). Caffeine and caffeine/EGCG increased FOX by 0.99g/h (P<0.05) and 1.33g/h (P<0.01), respectively, during that block. Although blunted for all supplementations, the findings for the second pre-meal block showed similar trends with significant increases of FOX only after caffeine and caffeine/EGCG. During the first post-meal block, only low EGCG increased FOX significantly (P<0.05 vs placebo), not high EGCG. Caffeine and caffeine/EGCG resulted in an increase in 1.18 and 1.69g/h, respectively (both P<0.05 vs placebo). During the second post-meal block, the delta in FOX was only slightly, but not significantly higher with 300 (0.44g/h) and 600mg EGCG (0.26g/h) vs placebo. However, the change in FOX after caffeine and caffeine/EGCG was with 1.16g/h (both P<0.05) still significantly higher vs placebo.


Mean COX

During the first pre-meal block, 300 and 600mg EGCG tended to reduce COX slightly by 1.21 and 1.42g/h, respectively, vs placebo; however, the changes were not statistically significant (Table 2). Caffeine and caffeine/EGCG reduced COX by 1.78 and 2.70g/h (both P<0.05), respectively. Similar findings were recorded for the second pre-meal block, with significantly lower COX only after caffeine/EGCG. During the first post-meal block, only low EGCG reduced COX significantly (P<0.05 vs placebo), not high EGCG. Although caffeine alone did not affect COX significantly, caffeine/EGCG reduced it (P<0.05 vs placebo). During the second post-meal block, the delta in COX was only slightly, but not significantly lower with 300 (−0.86g/h) and 600mg EGCG (−0.32g/h) vs placebo. However, the delta in COX after caffeine and caffeine/EGCG was 2.54 and 2.50g/h (both P<0.05), respectively, vs placebo. With caffeine, COX was also significantly lower vs low and high EGCG (P<0.05).

Blood glucose, insulin and NEFA

Fasting blood glucose and insulin did not differ significantly between the different supplementations. Within 90min after meal intake, glucose and insulin increased about 1.25- and fourfold, respectively, and returned to baseline until the end of the test, regardless of supplementation.

Fasting NEFA under placebo were 0.29±0.06mmol/l and did not change significantly over the entire pre-meal period (Figure 4). During the first post-meal block, NEFA decreased to 0.07±0.01mmol/l, but returned to baseline levels within the second post-meal block. NEFA profiles did not differ significantly under low and high EGCG supplementation when compared with placebo. In contrast, under caffeine or caffeine/EGCG, pre-meal NEFA levels were higher when compared with placebo, but the difference was not statistically significant. However, under the low EGCG dose, pre-meal NEFA were significantly lower vs caffeine (P<0.0001) and EGCG/caffeine (P<0.0001).

Figure 4.
Figure 4 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Plasma nonesterified fatty acids (NEFA) before and after intake of a test meal under low EGCG (upper panel, left), high EGCG (upper panel, right), caffeine (lower panel, left) and caffeine/EGCG (lower panel, right), respectively (filled circles), vs placebo (open circles). For details of supplementation and meal composition refer Methods section. Arrow indicates intake of the test meal. Data are given as mean±s.e., n=10. Fasting plasma NEFA concentrations were significantly lower for low EGCG vs caffeine and the combination EGCG/caffeine (P<0.001).

Full figure and legend (143K)

Resting blood pressure and heart rate

Heart rate (HR) and systolic (SBP) and diastolic blood pressure (DBP) was measured only in the morning of the third study day before supplementation. SBP was slightly higher after caffeine (129mmHg) vs placebo (125mmHg), whereas DBP was slightly higher after EGCG/caffeine (76mmHg) vs placebo (72mmHg). EGCG alone did not affect either SBP or DBP. HR was not affected by any of the supplements (Table 3).


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Discussion

Although a mixture of green tea catechins and caffeine increases fat oxidation in humans, the individual contributions of the major catechin EGCG and caffeine to this effect have not been studied yet. This study shows that EGCG can increase fat oxidation in overweight/obese males, particularly during postprandial conditions. As expected, caffeine had a pronounced effect on fat oxidation. However, combining the two ingredients did not result in a synergistic effect.

Impairments in the sympathetic nervous system-mediated lipid mobilization and oxidation may be important in the age-related increase in adiposity and insulin resistance (Blaak, 2000). The sympathetic nervous system activity can be increased either directly by β-adrenergic agonists or indirectly by norepinephrine releasers and reuptake inhibitors (Dulloo, 1993b; Landsberg and Young, 1993; Arch and Wilson, 1996). Interestingly, a number of plant-derived compounds, such as caffeine from coffee and tea, ephedrine from ephedra and capsaicin from pungent spices or GTE low in caffeine (<40mg/day), can modulate diet-induced thermogenesis and/or fat oxidation (Henry and Emery, 1986; Dulloo, 1993a, 1998; Yoshioka et al., 1998; Ota et al., 2005).

EGCG inhibits catechol-O-methyltransferase, an enzyme involved in the degradation of norepinephrine (Borchardt and Huber, 1975). As a consequence, norepinephrine can stimulate adrenoreceptors for a longer time. Caffeine inhibits the phosphodiesterase-induced degradation of intracellular cAMP (Dulloo et al., 1992). A prolonged stimulation of β-adrenoreceptors and increased intracellular cAMP levels lead to an increase in EE and fat oxidation. An overview of these sympathomimetic mechanisms is given in Figure 5.

Figure 5.
Figure 5 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Targets of different drugs within the sympathetic neuronal transmission to increase the availability of norepinephrine (NE) within the synaptic cleft (EGCG, ephedrine, amphetamine, sibutramine) or to prolong NE-induced increases in lipid mobilization and oxidation (caffeine). COMT, catechol-O-methyltransferase; VMA, vanillyl-mandelic acid; β-AR, β-adrenoreceptor; Gs, stimulatory G-protein; PDE, phosphodiesterase.

Full figure and legend (105K)

The maximum increase in both fasting (+35.4%) and postprandial (+49.4%) fat oxidation was achieved with 300mg EGCG/200mg caffeine, which is similar to the results reported by Dulloo et al. (1999) who used an encapsulated GTE with 270mg EGCG/150mg caffeine per day, which resulted in an increase in 24-h fat oxidation of 35.2%. Owing to the experimental setup in the study by Dulloo et al., it is not possible to distinguish between fasting and postprandial conditions. The same authors report that the increase in fat oxidation was greater with the GTE vs caffeine alone, suggesting a strong contribution of EGCG, as no significant changes in EE and lipid oxidation were observed with 150mg caffeine alone. The slightly higher increase in fat oxidation in our study might be attributable to the higher EGCG/caffeine content of our capsule preparation. In a similar trial, normal and overweight men received three times daily for 3 days either water, water+270mg caffeine, half-strength oolong tea (122mg EGCG/135mg caffeine) or full-strength oolong tea (244mg EGCG/270mg caffeine) (Rumpler et al., 2001). Relative to water, 24-h EE increased significantly by 2.9% (+281kJ/day) with the full-strength tea and by 3.4% (+331kJ/day) with caffeinated water. Fat oxidation increased significantly by 12 and 8% for the full-strength tea and the caffeinated water, respectively, whereas there was no significant difference in fat oxidation between the full-strength tea and caffeinated water.

The effects of acute ingestion of caffeine-free GTE was also tested during moderate-intensity exercise (Venables et al., 2008), in which 890mg polyphenols and 366mg EGCG increased fat oxidation by 17% compared with exercise alone.

In contrast to Dulloo et al. (1999), we did not observe an increase in EE at the utilized doses. In mice, EGCG increased fat oxidation without significantly affecting total EE (Klaus et al., 2005), suggesting that an increase in EE might be dependent on the caffeine content present in tea beverages. It is well documented that caffeine increases EE (Acheson et al., 1980; Dulloo et al., 1989; Astrup et al., 1990; Bracco et al., 1995; Horton and Geissler, 1996; Arciero et al., 2000; Belza et al., 2009). Energy expenditure also increased after ingestion of capsules containing 600mg caffeine and varying amounts of EGCG (Berube-Parent et al., 2005). According to a more recent study, 24-h EE increased significantly by 4.6% and fat oxidation nonsignificantly by 3.2g per 24h after consumption of a thermogenic beverage, based on a green tea extract containing inter alia 282mg EGCG, 300mg caffeine and 633mg calcium (Rudelle et al., 2007). On the basis of the literature analysis, the authors hypothesized that the principle active component in the tested beverage is caffeine, accounting for 75% of the observed response.

Another potential explanation for observed differences in EE and fat oxidation might be the form of application—capsules vs beverages. An increase in EE was found following daily consumption of 1500ml oolong tea preparations (Rumpler et al., 2001) or 750ml of a thermogenic beverage based on a green tea extraxt (see above) (Rudelle et al., 2007). These findings are in contrast to our observations in which capsules were taken with a rather small volume of water. Possibly, water intake in a sufficient high volume can affect the magnitude of the thermogenic effect of caffeine. The large volumes of the beverage in the studies by Rumpler et al. (2001) and Rudelle et al. (2007) would support this hypothesis. Water can also potentiate the pressor effect of ephedra alkaloids (Jordan et al., 2004). Recently, we found a prompt increase in EE by about 30% in men and women after drinking 500ml water and this effect was mediated by an increased sympathetic nervous system activity, obviously secondary to stimulation of osmosensitive afferent neurons (Boschmann et al., 2003, 2007). However, these results could not be confirmed by another group (Brown et al., 2006).

In our study, 300mg EGCG seemed to be optimal to increase fat oxidation, as doubling the daily EGCG dose to 600mg did not result in a further increased fat oxidation. Our finding is supported by others (Berube-Parent et al., 2005), who showed that 270mg EGCG, when given along with 600mg caffeine, is the optimal dose for affecting EE, as increasing EGCG to 600, 900 or even 1200mg with a constant intake of 600mg caffeine did not exert a greater response. The increase in 24-h EE was about 750kJ after 270mg EGCG/600mg caffeine, whereas fat oxidation was not altered and increasing EGCG did not exert additional effects on fat oxidation. Interestingly, GTE has beneficial effects on body weight regain in low, but not in high caffeine users (Westerterp-Plantenga et al., 2005). The cutoff level was 300mg caffeine per day. Therefore, it might be speculated that the rather high caffeine doses of 600mg (Berube-Parent et al., 2005) and 300mg (Rudelle et al., 2007) masked the effects of EGCG. The similar phenomena have been reported for ephedrine (Liles et al., 2007). A supra-additive synergistic effect of EGCG and caffeine (Dulloo et al., 1999) could not be confirmed by our data. However, within the early post-meal period, low EGCG was equipotent with caffeine, whereas within the late post-meal period, caffeine was equipotent with EGCG/caffeine with regard to the increase in fat oxidation. EGCG alone did not affect fat oxidation within the late post-meal period. This outcome could originate from the different half-life of EGCG (about 2h) and caffeine (about 4h). Therefore, EGCG affects obviously the early, whereas caffeine affects both early and late postprandial fat oxidation.

Although within the physiological range, fasting plasma NEFA were significantly higher with 200mg caffeine and the combination of 300mg EGCG/200mg caffeine when compared with 300mg EGCG alone, suggesting that lipid mobilization slightly exceeded the capacity of lipid oxidation when caffeine is consumed either alone or with EGCG.

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Conclusion

This pilot study provides for the first time evidence that a single green tea catechin, EGCG, can increase fat oxidation in obese men, at least within 2h after meal intake. Within this postprandial phase, EGCG is equipotent with caffeine with regard to fat oxidation.

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Conflict of interest

FT is employed by DSM Nutritional Products. The results of this study have no effect on his employment status.

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Acknowledgements

The authors thank Richard Gössl (DSM Nutritional Products, Kaiseraugst, Switzerland) for expert technical assistance. Gritt Stoffels and Stefan Engeli (University Hospital Charité Campus Buch, Berlin, Germany) were involved in the recruitment and assessment of volunteers in all human studies. The authors thank Dr Frida Dangardt (Sahlgrenska Academy at the University of Gothenburg, Sweden) for assisting in statistical analysis and Dr Marcella Trembley (DSM Nutritional Products, Kaiseraugst, Switzerland) for critical reading of the paper. Funding for this study was provided by DSM Nutritional Products.

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