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From a health perspective it may be good that green tea does not contain all-too much caffeine. From a fat loss perspective, it clearly lacks caffeine.

When it comes to dietary supplements, people like to pay tons of money for unproven ingredients with funky names and dubious or non-existent safety profiles; agents that have been scientifically proven to work, are save and cheap, on the other hand, are non-sellers or at least considered to be non-effective.

Obviously, I cannot really explain why that is the case (I suspect it is because people effect drug-like effects without drug-like side-effects from supps and are thus always on the lookout for the "next big"... hoax), I can tell you, though, that a recent study that is going to be published in one of the upcoming issues of the Journal of Strength and Conditioning Research (Jo. 2015) shows that caffeine and green tea, two supplements that belong to the previously described category, are everything but useless.
In said study, Edward Jo and colleagues investigated the effects of a caffeine + green tea polyphenol mix (250mg caffeine + 400mg of a green tea extract with 50% EGCG and 5mg of caffeine per serving) on (a) metabolic rate and fat oxidation at rest, as well as following a bout of sprint interval exercise (SIE) and (b) the performance during a standardized sprint-interval test.

The study was a double-blind, randomized, placebo-controlled, crossover study that involvd 12 subjects (male: n=11; female:1 n=1) whose antroprometric data, i.e "body mass=76.1±2.2 kg; height= 169.8±1.6 cm; BMI= 22.7±3.0 kg/m2; body fat %= 21.6±2.0% [DXA data]" (Jo. 2015), already tell you that they were healthy recreationally active, but not necessarily athletic (it may be worth mentioning that they were relatively stim-naive with an intake of < 201mg of caffeine per day).

Figure 1: Energy expenditure (kcal/h) and fat oxidation (g/day) measure before (at rest) and during (during SIE) the sprint interval exercise 10 and 55 minutes after the ingestion of caffeine + GTE or placebo (Jo. 2015).

During the two testing sessions at the Human Performance Research Laboratory of the California State Polytechnic University, the subjects' resting energy expenditure (REE) was measured for 45 minutes starting 10 minutes after the ingestion of the aforementioned caffeine + polyphenol mix - a mix that was consumed on an empty stomach after an 8-h overnight fast (don't be fooled by the way the scientists report their data in "g/day" and kcal/day - I changed the latter, already but the values for fat in g would have become to small - we are talking about 45 + 30 min and a 24h measurement here).
After the initial 45-minutes, during which the subjects' resting energy expenditure had been measured, the subjects were placed on a computer-integrated cycle ergometer on which they performed a standardized 30 minute sprint interval exercise (SIE) protocol., the scientists describe as follows:

"Sprint-Interval Exercise Protocol. The SIE protocol was performed on the Velotron DynaFit Pro cycle ergometer and comprised of four 30-second maximal effort intervals each separated by 5 minutes of low-intensity, constant workload cycling (Figure 2). First, the ergometer was properly adjusted for the subject. Adjustment specifications for each subject was recorded during their familiarization visit and repeated for all experimental trials. Subjects initiated the SIE protocol with a 5-minute interval of low-intensity cycling at a constant workload of 75W. Immediately after, subjects cycled with maximal effort for 30 seconds against an added resistance that is 7.5% of BW for males and 7.2% for females. These two intervals were repeated three additional times. After the last 30-second sprint interval, the subjects performed an additional low-intensity 75W interval plus an extra 3 minutes of cool-down at a constant workload of 30W. The total duration of the SIE protocol was 30 minutes" (Jo. 2015).

A workout that had little effect on the effect of the caffeine + green tea combo which did, as you can see, when you compare the "at rest" and "during SIE" values in Figure 1, increase the energy at rest and during sprint interval training to a similar extent. More specifically, the increase in energy expenditure and fat oxidation was - within the margin of inter-individual variability - in the range of +10% during both conditions.

Figure 2: Illustration of the sprint interval exercise test performed 55 min after ingesting the supplement (Jo. 2015).

In view of the fact that we may safely assume that this effect should last for at least 2-3h this can be a practically relevant effect if it is complemented by a reduced energy intake and a caloric deficit. If the latter is not present, even the extremest increases in fat oxidation and energy expenditure will fizzle out and be as irrelevant as the effect of the caffeine + green tea combination on exercise average and peak power (W) during the sprint training, Jo et al. observed in their study... and "Yes!", that is disappointing, but in view of the low dose of caffeine and the non-existent effects of green tea on performance during a test like this not really surprising.
References:

• Jo et al. "Dietary Caffeine And Polyphenol Supplementation Enhances Overall Metabolic Rate And Lipid Oxidation At Rest And After A Bout Of Sprint Interval Exercise." Journal of Strength & Conditioning Research: Post Acceptance: November 23, 2015. doi: 10.1519/JSC.0000000000001277

"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'.

You will remember that I am not exactly a fan of green tea extracts. In spite of the fact that there are studies that suggest reductions of both thyroid hormone and testosterone production, when you consume high(er) amounts, their anti-inflammatory effects appear to help (obese) people lose weight. In view of the fact that a recent study suggests that this does not interfere with the adaptational response to exercise, like vitamin C + E, for example (learn more), they are thus still among the most promising over-the-counter anti-obesity agents.

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 waredownloadsoft 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).

But that's not all. The scientists also took a look at the potential mediators of increased energy expenditure and fatty acid use like catecholamines and they did so in normal-weight young women (age: 21.5 +/- 0.5 years; body mass: 65.7 +/- 1.8 kg; BMI: 24.3 +/- 0.4 kg/m²; maximal oxygen consumption; VO2max): 32.1 +/- 1.7 mL/kg/min) and not the usual subjects: Overweight or obese post-menopausal women or male and female patients with type II diabetes.
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).

It is thus all the more important to put the effects the consumption of three GTE (250 mg of camellia sinesis extract w/ 187.5 mg polyphenols, 125 mg EGCG) or placebo (cellulose) capsules the day before and one capsule 90 min before a 20-min intermittent sprinting exercise (ISE) cycling protocol consisting of

• 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 

had on the metabolism of the fourteen untrained non-habitual coffee or green tea drinkers (< 2 cups per day) during the exercise, as well as before and after the ISE protocol:

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.

Overall, the results of the study do thus support the ubiquitous claim that the ingestion of green tea extracts can significantly increase the fat oxidation at rest, during and after exercise when compared to placebo. In spite of the fact that the conclusion of the abstract to the study at hand makes it appear as if that was a practically highly relevant finding, there's one question neither the abstract nor the full-text of the paper actually address: Do the increase in fatty oxidation and the (albeit non-significant) increases in total and resting energy expenditure mean that consuming green tea extracts is going to help young, healthy, non-overweight women like the subjects in the study at hand lose body fat?
References:

• 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.

Green tea smoothies - If you don't want to waste more than 60% of green tea's precious EGCG content, you better don't blend it with too much other stuff

While the previously discussed effect of milk on the bioavailability of the polyphenols from green tea (the beverage) is probably negligible, a recent study from the University of Cranberra suggests that the inhibitory effect of food on the absorption of the major catechins in green tea may be significant enough to say that it's important to take them away from food.

To assess the effects of different food matrices on the bioavailability of capsulated green tea supplements, Naumovski et al. came up with a systemic absorption test healthy fasted humans.
On three separate days, their four healthy, normal-weight participants (3 males and 1 female aged 18-64 years) had to come to the clinic fasted (10h of fasting minimum). At the laboratory, the participants ingested 500 mg of EGCG given either as

• two capsules (2 × 250 mg) with 100 mL of water only (without any breakfast), 
• two capsules (2 × 250 mg) provided with 50 g of Special K breakfast cereal (Kellogg’s, Pagewood, NSW, Australia), or
• in form of 200 mL of full cream milk or EGCG (500 mg) that had been incorporated in 200 g of strawberry sorbet 

All treatments were ingested within 5 min and no additional food was taken for a further 4 h. All participants were provided with a lunch and a drink three hours after ingesting the EGCG, which consisted of a sandwich (bread, ham, cheese, tomato, lettuce) and 200 mL of orange juice.
To determine the effect of the different food items on the absorption of EGCG, the scientists used blood samples that were taken before the ingestion of the capsules / sorbet, 30min, 1h, 2h, 3h, 5h, and 8h afterwards by the means of a previously installed intravenous catheter (BD, North Ryde, NSW, Australia).

Figure 1: The mean plasma EGCG concentration-time curves for the three different methods of oral delivery: capsules without breakfast (green), capsules with breakfast (purple) and strawberry sorbet (red). The values are means ± the standard error of the means for the four participants (n = 4 | Naumovski. 2015).

As the data in Figure 1 shows the amount of EGCG that actually made it into the blood of the study participants was significantly (and practically relevantly) reduced when the capsulse were ingested with food or the EGCG was incorporated into the sorbet.
References:

• Naumovski, Nenad, Barbara L. Blades, and Paul D. Roach. "Food Inhibits the Oral Bioavailability of the Major Green Tea Antioxidant Epigallocatechin Gallate in Humans." Antioxidants 4.2 (2015): 373-393.

Hot or not? That could be a matter of health or ah... well almost death ;-)

Usually a "tea" is a hot beverage, right? No? Well, ok there's ice-tea, but even the coolest of all teas is initially brewed with hot, sometimes almost boiling water. A practice of which a recent study from the  Universidade Tecnológica Federal do Paraná in Brazil suggests that it may actually impair some of the beneficial effects of Baldo, White, Black and Mate tea.

How come? Well, in the study Vanessa de Carvalho Rodrigue, et al. conducted, it made a huge difference in terms of the total phenol and flavenoid content of the extracts (=the aformentioned teas) when the scientists used cold water instead of water that was 80°C "hot".
During the hot extraction procedure, a total of 2.0 g of the sample was extracted with 100 mL of water distilled at 80 °C. In contrast to how you would do it at home, though, the extraction process was propelled by stirring the glass for 450s (7:30 min). A similar procedure was used for the cold extract. The only differences were that (a) the extraction was done with 20 ml cold water and only 0.5 g of tea and (b) took 120 minutes during which the infusion was kept still, at room temperature (20–25 °C), and was stirred manually every 30 min (Damiani et al., 2014).

All extracts were filtered, transferred to Falcon tubes and immediately frozen at −20 °C (dark) for later analysis in order to prevent oxidation by light and oxygen.

Figure 1: Total phenol & flavenoid content tea after extraction with hot or cold water (de Carvalho Rodrigues. 2015).

The analysis yielded interesting results, because in contrast to what you may have expected not all hot water or extracts were inferior to their cold water counterparts. In the teas with generally lower phenol and flavenol intake, using the hot water to extract the active ingredients lead to significant (lemon grass and carqueja) increases of the total phenol and flavenoid content of the extracts.
What matters more than phenol and flavenol numbers, though, are (a - primarily) the antioxidant activity of the their sum (see Figure 2) and (b - secondarily) the presence of specific bioactive compounds like theobromine, chlorogenic acid or even caffeine (see Table 1).
Interestingly, significant differences were seen for the the often-tested DPPH+ (diphenylpicrylhydrazyl) radical scavenging activity only for Carqueja, Lemongrass and Mate (see Figure 2, left), and no significant effects were observed for the content of any of the bioactive agents. With the latter, the content varied, albeit not systematically and not with statistical significance.

Figure 2: Total antioxidant activity of the hot and cold extracts from various teas according to DPPH+ and TROLOX assays; sign. effects were observed only in the TROLOX assay (de Carvalho Rodrigues. 2015).

That's in contrast to the antioxidant activity in the ABTS˙+ or TROLOX test (Figure 2, right) where significant differences were observed for all teas. What is surprising, though is that these were not necessary in line with the total anti-oxidant activity which was increased in the cold extract of the Bodo tea, for example (it's anti-oxidant activity still was more than 50% lower).
References:

• de Carvalho Rodrigues, V., da Silva, M. V., dos Santos, A. R., Zielinski, A. A. F. and Haminiuk, C. W. I. (2015), Evaluation of hot and cold extraction of bioactive compounds in teas. International Journal of Food Science & Technology. doi: 10.1111/ijfs.12858

If you drink green tea 24/7 you don't have to wonder if your thyroid is sluggish and your belly growing.

I've alluded to the anti-thyroid effects of green tea extracts in previous articles. That simply drinking green tea (albeit excessively) would trigger the exact same effects, though, is news. News I got from a very recent study from the Zagazig University Faculty of Medicine in Egypt.

The authors, Abulfadle K. A., Bakhaat G. A., Shaik R. and Tantry B. A., studied the effect of excessive green tea intake on body weight and serum thyroid hormones in male mice and compared their results to what happens if the rodents are fed only fluoride and caffeine.
To confirm the ill effects of excessive green tea intake on thyroid gland, the scientists measured both, the level of thyroid hormone and the weight of the thyroid of their 30 male albino mice who were divided into five groups.

• Control (C) group (6 mice) receiving distilled water. 
• Green tea (GT) treated group; 6 mice were given a 5 gm% tea hot water extract as their sole water supply (that's similar to you drinking 1-2 L or more). 
• Fluoride (FL) treated group, 6 mice were given fluorine excess solution as their only water supply. 
• Caffeine (Caf) treated group, 6 mice were treated with caffeine (6.25 mg/kg ip | that's only 0.51 mg/kg body weight for a human and thus not exactly much). 
• Propylthiouracil (PTU) treated group, a substance of which we know that it interferes with the synthesis of thyroid hormone, 6 mice were treated with PTU (10 mg/kg ip). 

Each of the five groups wass treated with the corresponding substance for 30 days, then sacrificed under ether anesthesia, blood was collected to study serum levels of T3 and T4.
As you can see in Figure 1, there was the expected significant decrease in serum T3 and T4 in the PTU treated group (T3 = 0.72±0.03). Similar, albeit less pronounced decreases were seen in the green tea (T3 = 0.96±0.04) and the fluoride (T3 = 0.93±0.04), but not in the caffeine group where only the T3 levels were significantly suppressed (T3 = 1.46±0.08) in comparison to the control group (T3 = 1.71±0.05).

Figure 1: Effect of green tea, fluoride & caffeine on final body weight, T3 and T4 | data is expressed in % of control; *P < 0.05 compared to control. ***P < 0.001 compared to control. #P > 0.05 compared to control (Abulfadle. 2015).

In conjunction with these significant decreases in T3 and T4, the scientists observed an increase of the rodents' final total body weight, but no change of the relative thyroid weight (that's in contrast to studies using purified green tea catechins, only, where the thyroid was sign. enlarged | Chandra. 2010) in comparison to the control group.
References:

• Abulfadle, Khaled Abdelfattah, et al. "Effect of Excessive Green Tea Versus Fluoride and Caffeine on Body Weight and Serum Thyroid Hormones in Male Mice." Journal of Physiology and Pharmacology Advances 5.2 (2015): 565-573.
• Chandra, Amar K., and Neela De. "Goitrogenic/antithyroidal potential of green tea extract in relation to catechin in rats." Food and Chemical Toxicology 48.8 (2010): 2304-2311.
• Chandra, Amar K., Neela De, and Shyamosree Roy Choudhury. "Effect of different doses of un-fractionated green and black tea extracts on thyroid physiology." Human & experimental toxicology 30.8 (2011): 884-896.
• Hase, Tadashi, et al. "Anti-obesity Effects of Tea Catechins in Humans [和文]." Journal of oleo science 50.7 (2001): 599-605.
• Kato, Kenji, et al. "(-)-Epigallocatechin gallate inhibits thyroid hormone‑stimulated osteocalcin synthesis in osteoblasts." Molecular medicine reports 4.2 (2011): 297-300.
• Sakamoto, Y., et al. "Goitrogenic effects of green tea extract catechins by dietary administration in rats." Archives of toxicology 75.10 (2001): 591-596.
• Wolfram, Swen, Ying Wang, and Frank Thielecke. "Anti‐obesity effects of green tea: From bedside to bench." Molecular nutrition & food research 50.2 (2006): 176-187.