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

Abstract

Background: The cardio-metabolic and antioxidant health benefits of caffeinated green tea (GT) relate to its catechin polyphenol content. Less is known about decaffeinated extracts, particularly in combination with exercise. The aim of this study was therefore to determine whether a decaffeinated green tea extract (dGTE) positively influenced fat oxidation, body composition and exercise performance in recreationally active participants.

Methods: Fourteen, recreationally active males participated in a double-blind, placebo-controlled, parallel design intervention (mean ± SE; age = 21.4 ± 0.3 yrs; weight = 76.37 ± 1.73 kg; body fat = 16.84 ± 0.97%, peak oxygen consumption [[Formula: see text]] = 3.00 ± 0.10 L·min(-1)). Participants were randomly assigned capsulated dGTE (571 mg·d(-1); n = 7) or placebo (PL; n = 7) for 4 weeks. Following body composition and resting cardiovascular measures, participants cycled for 1 hour at 50% [Formula: see text], 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.

Results: Total fat oxidation rates increased by 24.9% from 0.241 ± 0.025 to 0.301 ± 0.009 g·min(-1) with dGTE (P = 0.05; ηp(2) = 0.45) by week 4, whereas substrate utilisation was unaltered with PL. Body fat significantly decreased with dGTE by 1.63 ± 0.16% in contrast to PL over the intervention period (P < 0.001; ηp(2) = 0.84). No significant changes for FFA or blood pressure between groups were observed. dGTE resulted in a 10.9% improvement in performance distance covered from 20.23 ± 0.54 km to 22.43 ± 0.40 km by week 4 (P < 0.001; ηp(2) = 0.85).

Conclusions: A 4 week dGTE intervention favourably enhanced substrate utilisation and subsequent performance indices, but did not alter TFA concentrations in comparison to PL. The results support the use of catechin polyphenols from dGTE in combination with exercise training in recreationally active volunteers.

Keywords: Body composition; Exercise performance; Fat oxidation; Green tea.

Figure 1

Weekly contribution of substrate to total energy expenditure (EE) for the PL group. Figure 1 shows the contribution of both fat and carbohydrate (based on oxidation rates) to energy expenditure during submaximal exercise for the placebo condition. Data are presented as mean ± SE. PL, Placebo; FAT, average fat oxidation rates; CHO, average carbohydrate oxidation rates. No significant differences were found with ANOVA (P > 0.05).

Figure 2

Weekly contribution of substrate to total energy expenditure (EE) for the dGTE group. Figure 2 shows the contribution of both fat and carbohydrate (based on oxidation rates) to energy expenditure during submaximal exercise for the dGTE condition. Data are presented as mean ± SE. dGTE, decaffeinated green tea extract; FAT, average fat oxidation rates; CHO, average carbohydrate oxidation rates. ^Adenotes significant overall group × time interaction effect compared with PL (Figure 1; P = 0.05). ^Bdenotes significant overall time interaction effect in conjunction with PL (Figure 1; P ≤ 0.03). ¹ denotes significant interaction over time within GTE only (P ≤ 0.05).

Figure 3

Total fatty acid concentrations pre and post exercise. Figure 3 shows the absolute total fatty acid concentrations at rest and post exercise for both treatment conditions at week 0 and week 4. Data are presented as mean ± SE. PL, Placebo; dGTE, decaffeinated green tea extract. No significant differences were found with ANOVA (P > 0.05).

Figure 4

Distance covered and average power output during the performance trial. Figure 4 shows the distance covered and average power output elicited during the 40 minute performance trial for both treatment conditions at week 0, 2 and 4 of the intervention. Data are presented as mean ± SE. PL, Placebo; dGTE, decaffeinated green tea extract. ^Adenotes significant overall group × time interaction effect (P ≤ 0.001). ^Bdenotes significant overall time interaction effect (P < 0.001). ¹denotes significant within group time interaction effect only (P = 0.039). ^*denotes significant difference (P ≤ 0.02) to baseline only within group. ^#denotes significant difference to week 2 within group only (P = 0.03).