|"Yes", GTE will increase your total energy expenditure (TEE) and decrease the ratio of glucose to fat you're burning at rest and during your workouts, but "NO", it won't make your abs appear w/out dietin'.|
With that being said, the increase in fatty oxidation is often mentioned when people try to explain why green tea helps (obese) people lose fat.
As a SuppVersity reader, however, you know that a mere increase in the use of fats over carbohydrates will not translate into practical weight loss. Against that background it is important to investigate the effects of green tea extracts on both, the respiratory exchange ratio (RER), which is the quotient of glucose / fat that's used to fuel your basal and exercise-induced metabolic demands, as well as their effects on your total energy expenditure.
Luckily, a recent study from the Charles Darwin University and the University of New South Wales in Australia includes both measures of changes in RER, resting energy expenditure (REE) and the total energy expenditure (REE + activity induced energy expenditure).
|Figure 1: Diagrammatic representation of the study design. * indicates blood collection. Lactate assessed at *1, *2, *4, *6, *9; catecholamines at *1, *4, *5, and glycerol at *1–*9 (Gahreman. 2015).|
Yes, it's official: Unlike vitamin C + E, GTE will not impair your gains! Ewa Jówko et al. (2015) were able to show that the consumption green tea extract (GTE) supplements in in dosages of only 245 mg polyphenols (including 200 mg catechins, among them 137 mg epigallocatechin-3-galate) does prevent the oxidative stress induced by repeated cycle sprint tests (RST) in sprinters without hindering the training adaptation in antioxidant enzyme system. What it does not do, either, is to decrease the exercise-induced muscle damage, or improve the sprint performance during the sprinters preparatory phase of their training cycle, though. Needless to say that studies involving different subject groups, dosages and training modalities would be required to eventually confirm that there are no anti-hormetic effects w/ GTE.I have plotted the most relevant results of experiment the design of which is represented graphically in in Figure 1 for you in Figure 2. Please note that only the changes in VO2 which are indicative of an increased oxidation of fatty acids and the corresponding RER, the quotient of carbohdydrate oxidation and fat oxidation changed significantly.
|Figure 2: Response at rest and during and after intermittent sprinting exercise in the green tea and placebo conditions; data expressed as relative differences between GTE and PLA (Gahreman. 2015).|
- a 5-min warm-up at 30 W, and 20 min of ISE on a Monark Ergomedic 839E ergometer at 110 RPM during the sprint phase and 40 RPM during the recovery phase (pedal resistance for the sprint phase was calculated as 60% of each participant’s maximal power output)
- during which the subjects performed a total of sixty 8-s/12-s bouts totaling 8 min of sprinting and 12 min of easy pedaling recovery
|Table 1: Mean power output, rating of perceived exertion, and lactate response to the sprinting and recovery components of the intermittent sprinting exercise for the placebo and green tea conditions (mean and SEM | Gahrmen. 2015).|
- There was a significant increase in fat oxidation post-exercise compared to at rest in the placebo condition (p < 0.01).
- After GTE ingestion, however, at rest and post-exercise, fat oxidation was significantly greater (p < 0.05) than that after placebo.
- Plasma glycerol levels at rest and 15 min during post-exercise were significantly higher (p < 0.05) after GTE consumption compared to placebo.
- There was no significant increase in total energy expenditure during or after exercise, though - that's in line with results Gregersen et al. (2009) generated in a study in normal-weight men, but different from some studies in normal-weight-to-moderately overweight men like Dullo et al. (1999) that report increases in TEE of ~2,8% over both, placebo and caffeine.
- Compared to placebo, plasma catecholamines increased significantly after GTE consumption and 20 min after ISE (p < 0.05 | not shown in Figure 2).
- The effects are almost certainly not triggered by caffeine, because the capsules contained only 20mg of caffeine and previous studies have shown that only oral dose of more than 100 mg caffeine will elicit a significant increase in thermogenic response (Bracco. 1995; Dulloo. 1998 - suggest that 600-1,000mg/day is necessary for sign. increases in thermogenesis).
- It's also worth noting that there were no significant differences in mean power output, RPE, lactate levels, RPM (Table 1), and HR levels between the GTE and placebo trials. This leaves little doubt that the effects were not mediated by direct ergogenic effects (= higher exercise performance / effort) in response to the GTE supplementation.
- Lastly, it should be said that even though this was not tested in the study at hand, previous clinical trials like Bérubé-Parent et al. (2005) report identical thermogenic effects for low and high dosages of GTE. Thus, simply taking more GTE probably wouldn't have changed the results considerably.
- Bérubé-Parent, Sonia, et al. "Effects of encapsulated green tea and Guarana extracts containing a mixture of epigallocatechin-3-gallate and caffeine on 24 h energy expenditure and fat oxidation in men." British Journal of Nutrition 94.03 (2005): 432-436.
- Bracco, David, et al. "Effects of caffeine on energy metabolism, heart rate, and methylxanthine metabolism in lean and obese women." American Journal of Physiology-Endocrinology and Metabolism 269.4 (1995): E671-E678.
- Dulloo, A. G., et al. "Normal caffeine consumption: influence on thermogenesis and daily energy expenditure in lean and postobese human volunteers." The American journal of clinical nutrition 49.1 (1989): 44-50.
- Dulloo, Abdul G., 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." The American journal of clinical nutrition 70.6 (1999): 1040-1045.
- Gahreman, Daniel, et al. "Green Tea, Intermittent Sprinting Exercise, and Fat Oxidation." Nutrients 7.7 (2015): 5646-5663.
- Gregersen, Nikolaj T., et al. "Effect of moderate intakes of different tea catechins and caffeine on acute measures of energy metabolism under sedentary conditions." British journal of nutrition 102.08 (2009): 1187-1194.
- Hill, Alison M., et al. "Can EGCG reduce abdominal fat in obese subjects?." Journal of the American College of Nutrition 26.4 (2007): 396S-402S.
- Jówko, Ewa, et al. "The effect of green tea extract supplementation on exercise-induced oxidative stress parameters in male sprinters." European journal of nutrition (2014): 1-9.
- Phung, Olivia J., et al. "Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis." The American journal of clinical nutrition 91.1 (2010): 73-81.
- Rains, Tia M., Sanjiv Agarwal, and Kevin C. Maki. "Antiobesity effects of green tea catechins: a mechanistic review." The Journal of nutritional biochemistry 22.1 (2011): 1-7.