The effect of a decaffeinated green tea extract formula on fat oxidation, body composition and exercise performance

All testing took place in the Human Physiology Laboratory, University of Hertfordshire. Participants were instructed to refrain from consuming caffeinated products for 48 hours prior to initial testing, and not be consuming other supplementation.

Peak oxygen consumption (\( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \)) was assessed at least one week prior to experimental trials using a standard incremental step protocol increasing by 30 W each 3 minutes until volitional exhaustion as previously reported [27]. Tests were performed on a Monark Ergomedic 874E stationary bike (Monark Exercise AB, Varberg, Sweden) using a Metalyser 3B automated gas-analyser (Cortex Biophysik, Leipzig, Germany). On a separate occasion, subjects undertook a familiarisation trial to confirm exercise intensity at 50% \( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \). This intensity was selected based on pilot work in which average fat oxidation rates during sustained submaximal exercise were statistically greater at 50% \( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \) compared to both 40 and 60% \( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \).

Participants were randomly assigned to an experimental or placebo group, and provided with either capsulated dGTE (571 mg·d⁻¹ dGTE, delivering 70% or 400 mg·d⁻¹ EGCG (equivalent to 6–7 cups of green tea per day), Changsha Active Ingredients Group Inc., Changsha, China*), or placebo (700 mg·d⁻¹ corn flour). All participants received capsules on a weekly basis to monitor compliance, with instructions to consume one capsule daily before breakfast with 250 ml water. *Analysis of the main active ingredient (EGCG) was undertaken prior to and independently of the main study by Changsha Active Ingredients Group Inc., using high performance liquid chromatography. The certificate of analysis provided by the supplying company demonstrated that the product contained 91.21% total catechins, from which 70.74% was EGCG. The product did not appear to be assessed for other catechins, so it is likely that the remaining percentage comprised other catechins (GCG, EGC, GC, EC, ECG, etc.).

A randomised, double blind, placebo controlled parallel design was employed over a 4 week intervention. Participants completed three laboratory trials at week 0, 2 and 4 under controlled conditions following an overnight fast. Upon arrival, nude body mass (Seca 780, Hamburg, Germany), height (Seca 200 stadiometer, Hamburg, Germany) and body composition [28] (Tanita Body Segmental Analyser 418-BC, Tokyo, Japan) were assessed.

Participants were then fitted with a Polar FS2c telemetric monitor (Polar Electro Ltd., Kempele, Finland) and seated for 5 minutes prior to resting heart rate and blood pressure readings (Omron MX3 plus, Kyoto, Japan). A venous wholeblood sample was then collected into duplicate 4 ml K₃EDTA Vacutainers (Greiner Bio-One GmbH, Kremsmunster, Austria) by a qualified phlebotomist. Samples were centrifuged for 10 minutes at 2000 rpm, with aliquotted plasma immediately frozen at −80°C for later assessment of TFA.

Exercise trials comprised a submaximal assessment and performance stage. During the submaximal assessment, participants exercised for one hour at 50% \( \dot{\mathrm{V}} \)O_2peak on a Monark Ergomedic 874E cycle ergometer. Gas exchange data was recorded continuously throughout exercise using a Metalyser 3B gas analyser, with average data taken over the final 45 minutes of submaximal exercise. Rating of perceived exertion (RPE) [29] and heart rate were recorded every 20 minutes.

Rates of total carbohydrate oxidation (CHO_TOT), total fat oxidation (FAT_TOT) (g·min⁻¹) and energy expenditure (EE) (kJ·min⁻¹) were calculated from \( \dot{\mathrm{V}}{\mathrm{O}}_2 \) and \( \dot{\mathrm{V}}{\mathrm{CO}}_2 \) (L·min⁻¹) using stoichiometric equations [30], with protein oxidation assumed negligible, as follows:

Upon completion, seated blood pressure and post exercise venous sampling was repeated as previously described. Following this, participants were instructed to undertake a 40 minute self-paced performance trial using a Computrainer erogometer system (RaceMate Inc., Seattle, USA). Distance covered (km) and power output (W) were recorded each 10 minutes, with only time elapsed visible to the subjects. Verbal encouragement was provided each 10 minutes. At the end of the exercise trial, subjects recovered for 5 minutes at 50 W.

All participants recorded a 3 day dietary recall preceding each exercise trial to assess for habitual dietary compliance. Dietary analyses were undertaken using Dietplan 6.50 (Forestfield Software Ltd, West Sussex, United Kingdom), with no differences reported between groups for macronutrients and/or energy intake. Additionally, participants were requested to consume similar meals the day before the exercise trials at regular time intervals to provide increased control of oxidation variables. This was based on pilot work assessment of fat oxidation stability at 50% \( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \) (assessed by calculating the amount of time (minutes) throughout the exercise that was spent within ±0.02 g·min⁻¹ of the average fat oxidation rate, expressed as a percentage for each individual), which was greater when the 24 hour pre exercise period was controlled for dietary intake (68.22 ± 5.70%) compared to when only the evening meal preceding the testing session was controlled (60.78 ± 8.42%).

The standardised menu was based on typical foods consumed by participants at breakfast, lunch and dinner, and provided similar caloric intake to habitual dietary records (values as calorie totals and per kilogram mean bodyweight: energy intake: 2484.70 kcal·d⁻¹ (32.68 kcal·kg⁻¹·d⁻¹); carbohydrate: 1127.7 kcal·d⁻¹ (14.83 kcal·kg⁻¹·d⁻¹); fat: 565.4 kcal·d⁻¹ (7.43 kcal·kg⁻¹·d⁻¹) and protein: 791.96 kcal·d⁻¹ (10.42 kcal·kg⁻¹·d⁻¹). Throughout the intervention period, participants were instructed to minimise consumption of polyphenol rich foods. Participants were additionally required to cycle for one hour at 50% \( \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} \) three times per week as part of a regulated exercise programme. All participants provided training diaries to monitor compliance.

All blood analyses for TFA were independently undertaken by ABS Laboratories (Biopark, Welwyn Garden City, Hertfordshire) employing previously validated methods [31]. TFA concentrations were based on assessment of palmitic, palmitoleic, stearic, oleic and linoleic acids. Briefly, 100 μl plasma aliquots were spiked with internal standard (heptadecanoic acid), with free fatty acids being extracted using the ‘Dole Extraction Solvent’ (isopropanol/heptane/sulphuric acid (1 M) (40:10:1)). After drying under nitrogen, the extracts were re-suspended using 200 μL of dichoromethane and the FFAs derivatised using diethylamine and Deoxo-Fluor. The diethylamide derivatives were then extracted into heptane. The heptane was then removed using nitrogen in a dry-block at 70°C. The dried extracts were reconstituted into 100 μL of heptane and quantified by gas chromatography using a mass spectrometer as the detector in the selected ion monitoring (SIM) mode.