Caffeine not Required for Performance Enhancing Effects of Green Tea in Recreational Athletes - 25% Increase in Fatty Acid Oxidation, 11% Increase in Maximal Endurance

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It may come as a surprise, but for the chronic, endurance enhancing effects of green tea supplements caffeine obviously isn't necessary. It appears, though, as if the effects were mediated solely by increases in fat oxidation.

Green tea supplements are all over the place... as fat burners, not performance enhancers, though. Against that background it's all the more surprising that researchers from the Anglia Ruskin University in the UK were now able to show that green tea supplements, even if they are decaffeinated will increase the rate of fatty oxidation and maximal distance covered during a 40 minute self-paced performance increased by 25% and 11% respectively.

Now that you know the main outcomes of the study and hand, it's about time to take a look at how the scientists arrived at the conclusion that "a 4 week dGTE intervention favourably enhanced substrate utilisation and subsequent performance indices, but did not alter TFA concentrations in comparison to PL" (Roberts. 2015).
The scientists recruited fourteen, recreationally active men (mean ± SE; age = 21.4 ± 0.3 yrs; weight = 76.37 ± 1.73 kg; body fat = 16.84 ± 0.97%, peak oxygen consumption [VO_ 2peak] = 3.00 ± 0.10 L·min−1) who participated in a study with a standardized double-blind, placebo-controlled, parallel design intervention. More specifically, the participants were randomly assigned to consume either

• 517mg/day of capsulated decaffeinated green tea extract (delivering 70% or 400 mg EGCG which is equivalent to 6–7 cups of green tea per day | dGTE group) or
• 517mg/day of an identically looking placebo supplement (PLA group)

over the complete 4 week study duration. This makes the study a chronic supplementation study which may partly explain that it did not require caffeine, an acute phase ergogenic, to see significant increases in exercise performance.

"Following body composition and resting cardiovascular measures, participants cycled for 1 hour at 50% VO_ 2peak, followed by a 40 minute performance trial at week 0, 2 and 4. Fat and carbohydrate oxidation was assessed via indirect calorimetry. Pre-post exercise blood samples were collected for determination of total fatty acids (TFA). Distance covered (km) and average power output (W) were assessed as exercise performance criteria" (Roberts. 2015).

In addition to the three testing sessions, all subects participated in three regular 60min steady-state cardio sessions at only 50% of their maximal VO2 (that's walking for almost everyone, expect the obese). Now, obviously, the previously highlighted total distance the subjects covered during the 40 minute performance trial increased in both groups (Figure 1, left). In the dGTE group, however, these changes were significantly more pronounced than in the placebo group.

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Figure 1: Total distance covered during the 40 minute performance trial (left) and substrate utilization (right) before and after the intervention in the placebo and dGTE groups (Roberts. 2015).

A different image emerges for the substrate utilization (Figure 1, right), where only the researchers recorded significant changes in the ratio of carbohydrate (grey part of the bar) to fat utilization (white part of the bar) only in the dGTE, yet not in the placebo group. Due to the "enormous" amount of energy we store in our fat tissue, this change in substrate utilization and concurrent conservation of muscle glycogen increased the amount of available energy and thus lead to a 10.9% increase in maximal endurance performance and a significantly greater reduction in rate of perceived exertion during exercise.

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Figure 2: Changes in body composition and heart rate over the 4-week study period (Roberts. 2015).

The changes in body fat %, body weight and heart rate, on the other hand, do not show a significant effect of dGTE supplementation. An observation (or non-existent observation) that should remind you that an increase in fatty acid oxidation does not equal an increase in body fate reduction.
References:

• Roberts, Justin D., et al. "The effect of a decaffeinated green tea extract formula on fat oxidation, body composition and exercise performance." Journal of the International Society of Sports Nutrition 12.1 (2015): 1.