Journal Title (Medline/Pubmed accepted abbreviation): Scand. J. Med. Sci. Sports
Page numbers: 598-605
Background: Endurance training has been shown to improve the body’s ability to burn fat. Also, in mice, long-term consumption of green tea extract (GTE) has also shown to increase the body’s ability to burn fat.
Hypothesis: Does GTE supplementation enhance the improvement of fat utilization that is gained from endurance training?
Subjects: Twelve healthy men, age 23 ± 2 yrs old
Experimental design: randomized, double-blind, placebo-controlled
Treatments: Green tea extract (GTE): 340 mL of beverage containing 572.8 total catechins, or a placebo (contents not disclosed). Both beverages contained about 77 mg of caffeine.
Protocol: Initially, participants were evaluated for VO2peak (also known as VO2max), ventilation threshold (thought of as “endurance”), maximum heart rate, respiratory exchange ratio (RER) and VO2drift using a stationary bicycle. The participants were then instructed to consume one serving of either the GTE or a placebo every day during the training period. As part of the endurance training program, the participants cycled at 60% of their VO2peak for 60 min/day, 3 days/wk, for 10 wks. Workload was adjusted as VO2peak changed with training. After training, they were then evaluated for the same exercise parameters. Both before and after the training period, blood samples were acquired at rest, 30 min after the commencement of cycling, and 30 min after cycling was completed. Blood was analyzed for glucose, glycerol (a breakdown product of triglycerides, i.e. fat), and free fatty acids.
GTE supplementation in conjunction with exercise training slightly increased fat oxidation compared with training without GTE supplementation.
The authors suggest that an increase in exercise with GTE supplementation increases the rate of fat burning, which in turn can promote weight loss. The increase in aerobic capacity of the subjects during the supplementation period implies that the subjects were not involved in regular endurance training before this study, so it would be expected that the additional exercise (without compensatory increase in energy consumption; the authors showed no increase in food intake) would promote weight loss. On average, the subjects did not lose weight or alter their BMI. This observation is puzzling and not discussed in the article.