Abstract
This study investigated the effect of decaffeinated green tea extract (dGTE), with or without antioxidant nutrients, on fat oxidation, body composition and cardio-metabolic health measures in overweight individuals engaged in regular exercise. Twenty-seven participants (20 females, 7 males; body mass: 77.5 ± 10.5 kg; body mass index: 27.4 ± 3.0 kg·m2; peak oxygen uptake (O2peak): 30.2 ± 5.8 mL·kg−1·min−1) were randomly assigned, in a double-blinded manner, either: dGTE (400 mg·d−1 (−)-epigallocatechin−3-gallate (EGCG), n = 9); a novel dGTE+ (400 mg·d−1 EGCG, quercetin (50 mg·d−1) and α-lipoic acid (LA, 150 mg·d−1), n = 9); or placebo (PL, n = 9) for 8 weeks, whilst maintaining standardised, aerobic exercise. Fat oxidation (‘FATMAX’ and steady state exercise protocols), body composition, cardio-metabolic and blood measures (serum glucose, insulin, leptin, adiponectin, glycerol, free fatty acids, total cholesterol, high [HDL-c] and low-density lipoprotein cholesterol [LDL-c], triglycerides, liver enzymes and bilirubin) were assessed at baseline, week 4 and 8. Following 8 weeks of dGTE+, maximal fat oxidation (MFO) significantly improved from 154.4 ± 20.6 to 224.6 ± 23.2 mg·min−1 (p = 0.009), along with a 22.5% increase in the exercise intensity at which fat oxidation was deemed negligible (FATMIN; 67.6 ± 3.6% O2peak, p = 0.003). Steady state exercise substrate utilisation also improved for dGTE+ only, with respiratory exchange ratio reducing from 0.94 ± 0.01 at week 4, to 0.89 ± 0.01 at week 8 (p = 0.004). This corresponded with a significant increase in the contribution of fat to energy expenditure for dGTE+ from 21.0 ± 4.1% at week 4, to 34.6 ± 4.7% at week 8 (p = 0.006). LDL-c was also lower (normalised fold change of −0.09 ± 0.06) for dGTE+ by week 8 (p = 0.038). No other significant effects were found in any group. Eight weeks of dGTE+ improved MFO and substrate utilisation during exercise, and lowered LDL-c. However, body composition and cardio-metabolic markers in healthy, overweight individuals who maintained regular physical activity were largely unaffected by dGTE.
Highlights
Green tea (GT) polyphenols have been widely investigated for their potential therapeutic health benefits from an antioxidant [1], anti-inflammatory [2,3], chemoprotective [4] and cardio-metabolic perspective [5,6,7]
The findings from the current study demonstrated that a moderate dose of decaffeinated GTE (dGTE) consumed over 8 weeks did not result in a statistically significant change on fat oxidation rates, but did produce a non-significant increase in both maximal fat oxidation (MFO) (+12.7%) and relative MFO (+13.9%)
Metabolic changes were observed by week 8 for dGTE+, with a large effect size reported for improvements in steady state substrate utilisation, evidenced by lower mean respiratory exchange ratio (RER) (−5.3%), improved relative Fat oxidation rates (FATOX) (+55.2%) and increased the contribution of fat to total EE (+64.8%)
Summary
Green tea (GT) polyphenols have been widely investigated for their potential therapeutic health benefits from an antioxidant [1], anti-inflammatory [2,3], chemoprotective [4] and cardio-metabolic perspective [5,6,7]. Subsequent catecholamine, cyclic adenosine monophosphate (cAMP) and lipolytic activity [9] These effects may enhance whole-body fat oxidation [10,11], and GT catechins may have important metabolic effects pertinent to reduced adipose tissue [12], improved body mass index (BMI) and/or body composition [10], and lowered circulating metabolites (e.g., low-density lipoprotein cholesterol (LDL-c) [13]). Such mechanisms have been challenged based on limited evidence from studies [14]. Regular consumption of GT catechins has been proposed to exert ‘calorierestriction-mimetic’ effects [15] over time, through modulated cell signalling (e.g., peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α), sirtuin 1
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