Green Tea Supplementation, Fat Oxidation and Body Composition in Overweight Individuals

Overview

The purpose of this study is to investigate the effects of green tea extract (GTE) on fat oxidation, body composition and exercise performance in overweight individuals. The study will be conducted under laboratory conditions following an 8 week supplemental period. Participants will be required to attend the laboratory for a pre-screening/familiarisation trial followed by assessments at week 0 (baseline), week 2, 4 and 8. Across the intervention, participants will maintain habitual dietary intake and follow a prescribed exercise programme. Additionally participants will be randomised to either a placebo, green tea extract or GTE with antioxidant supplementation. It is hypothesised that the addition of antioxidants with GTE will enhance fat oxidation in overweight individuals more than GTE or placebo. It is further hypothesised that such improvements in fat oxidation due to GTE will lead to improvements in both body composition variables and submaximal exercise performance (metabolic efficiency) in overweight, but otherwise healthy persons.

The health benefits of polyphenols found in green tea (GT), the unfermented leaves of the tea plant, Camellia sinensis, are of current scientific interest. These health benefits, in part, relate to the bioactive catechin polyphenol content of GT, of which (-)-epigallocatechin-3-gallate (EGCG) can account for between 50-80% of the total catechin content. GT catechins have been proposed to influence metabolic and thermogenic activities in the short term, leading to enhanced fat oxidation capacity, although this has been disputed. Research investigating GT extracts (GTE) and exercise have produced conflicting results. Modest EGCG dosage in the short term (270 mg·d-1 EGCG for 6 days, and 68 mg·d-1 EGCG for 3 weeks) did not alter metabolic or performance variables in healthy or endurance trained volunteers. However, the inclusion of 100.5 mg·d-1 EGCG over a 10 week training period enhanced whole-body metabolic efficiency elsewhere. One confounding factor though is the use of caffeinated GTE in these studies. When decaffeinated GTE (dGTE) has been employed, 366 mg EGCG was found to acutely increase fat oxidation by 17%. Indeed a recent publication from our research group investigating the short term use of dGTE demonstrated positive changes in fat oxidation in healthy volunteers. However, less is known as to whether dGTE (or indeed combinations of dGTE with antioxidant nutrients which may improve GTE bioavailability) could provide similar results in overweight or sedentary individuals embarking on an exercise programme. The aim of this research proposal is therefore to assess the impact of two GTE strategies on fat oxidation, cardiometabolic health, visceral fat reduction, and exercise performance in a healthy, but overweight cohort undertaking a standardised exercise training programme. Research Questions: Q1: Does regular consumption of dGTE favourably enhance fat oxidation and/or improve variables associated with cardiometabolic health and body composition in comparison to a placebo supplement in healthy, but overweight individuals? Q2: Does a dGTE complex (including key antioxidant nutrients) enhance fat oxidation and/or improve variables associated with cardiometabolic health and body composition more so than dGTE or placebo supplementation in healthy, but overweight individuals? This study will involve participants attending sessions at Compass House, ARU, undertaking the following: * Baseline trial: all participants will attend a subject briefing, provide written, informed consent prior to participation. Following this, all participants will undertake a baseline test for maximal fat oxidation rates (FATmax) and oxygen uptake using a standardised incremental cycling exercise protocol and expired air analysis * Intervention period: participants will be randomly assigned to either dGTE (400mg EGCG daily), dGTE with antioxidants (150mg quercetin, 150mg alpha-lipoic acid) or placebo for 8 weeks. During this period, participants will undertake regular aerobic exercise (3x/ week; 45mins; at \~ FATmax intensity) * Experimental evaluation of progress will be assessed at weeks 0,2,4, and 8. During laboratory visits, participants will be required to have a single venepuncture blood sample, assessment of blood pressure/ body composition (skinfold, bioelectrical impedance, waist circumference), assessment of FATmax, and assessment of fat oxidation during steady state exercise at FATmax.