Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans by Venables MC, Hulston CJ, Cox HR, Jeukendrup AE.
BACKGROUND: Green tea consumption is reportedly associated with
various health-promoting properties. For example, it has been shown
to promote fat oxidation in humans at rest and to prevent obesity
and improve insulin sensitivity in mice.
OBJECTIVE: We investigated the effects of acute ingestion of
green tea extract (GTE) on glucose tolerance and fat oxidation
during moderate-intensity exercise in humans. DESIGN: Two studies
were performed, both with a counter-balanced crossover design. In
study A, 12 healthy men performed a 30-min cycling exercise at 60%
of maximal oxygen consumption (VO2max) before and after
supplementation. In study B, 11 healthy men took an
oral-glucose-tolerance test before and after supplementation. In
the 24-h period before the experimental trials, participants
ingested 3 capsules containing either GTE (total: 890 +/- 13 mg
polyphenols and 366 +/- 5 mg EGCG) or a corn-flour placebo (total:
1729 +/- 22 mg).
RESULTS: Average fat oxidation rates were 17% higher after
ingestion of GTE than after ingestion of placebo (0.41 +/- 0.03 and
0.35 +/- 0.03 g/min, respectively; P < 0.05). Moreover, the
contribution of fat oxidation to total energy expenditure was also
significantly higher, by a similar percentage, after GTE
supplementation. The insulin area under the curve decreased in both
the GTE and placebo trials (3612 +/- 301 and 4280 +/- 309
microIU/dL . 120 min, respectively; P < 0.01), and there was a
concomitant increase of 13% in insulin sensitivity.
CONCLUSIONS: Acute GTE ingestion can increase fat
oxidation during moderate-intensity exercise and can improve
insulin sensitivity and glucose tolerance in healthy young men.
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