Now that even baseball
players may need to seek new, more natural performance
aids, will Japanese green tea sets become standard in
dugouts and athletic training tables around the world?
A new study tested the effect of regularly
taking green tea extract (GTE) and found that over 10
weeks, endurance exercise performance was boosted up
to 24% with 0.5% GTE supplementation, and 8% with 0.2%
by-weight addition to food.
Reporting in the online edition of the American Journal
of Physiology-Regulatory, Integrative and Comparative
Physiology researchers at the Biological Sciences Laboratories
of Kao Corp., Tochigi, Japan, said the 8-24% increase
in swimming time-to-exhaustion was "accompanied by lower
respiratory quotients and higher rates of fat oxidation."
The results "indicate that GTE is beneficial for improving
endurance capacity and support the hypothesis that the
stimulation of fatty acid utilization is a promising
strategy for improving endurance capacity," according
to the study entitled, "Green tea extract improves endurance
capacity and increases muscle lipid oxidation in mice."
Research was conducted by Takatoshi Murase, Satoshi
Haramizu, Akira Shimotoyodome, Azumi Nagasawa and Ichiro
Tokimitsu, working at Kao Corp., a Japanese maker of
healthcare products, including green tea beverages.
Results came from the equivalent of about 4 cups
of tea a day
Although it's difficult to extrapolate from mice eating
GTE as a food supplement to a major leaguer or Olympic
swimmer sipping green tea, the study's lead author,
Takatoshi Murase said: "We estimate that an athlete
weighing 75 kilograms (165 pounds) would have to drink
about four cups (0.8 liter) of green tea daily to match
the effect in our experiments."
"One of our important findings," Murase pointed out,
"was that a single high-dose of GTE or its active ingredients
didn't affect performance. So it's the long-term ingestion
of GTE that is beneficial." (Murase based his calculations
of mouse-to-human tea/GTE consumption equivalents on
work his lab is doing on the anti-obesity effects of
GTE on mice and humans.)
In an era when professional and amateur athletes are
always looking for ways to improve performance, and
most people want to improve their health and exercise
capabilities, "the efficacy of dietary interventions
is still controversial," the authors acknowledge. They
note that green tea and cacao contain a class of polyphenols
called catechins, which consist mainly of epigallocatechin
gallate (EGCG), epicatechin gallate and gallocatechin
gallate. Catechins have been reported to have various
physiological and pharmacological properties over the
The Kao lab "recently demonstrated that the long-term
consumption of tea catechins was beneficial in counteracting
the obesity-inducing effects of a high-fat diet, and
that their effects may be attributed, at least in part,
to the activation of hepatic lipid catabolism" in mice.
"Overall," the authors said, "observations so far suggest
that thermogenesis and fat oxidation are stimulated
by the intake of catechins."
Working hypothesis and study methods
"To confirm our hypothesis that catechins affect endurance
exercise capacity (i.e. time to exhaustion) by increasing
lipid utilization, in this study we examined the effect
of catechin-rich GTE intake on the endurance capacity
of Balb/c mice swimming in an adjustable-current water
pool. We also analyzed changes in energy metabolism,
especially lipid metabolism. We demonstrated that GTE
intake improved endurance capacity and this was accompanied
by an increase in lipid catabolism. Our results support
the hypothesis that stimulation of lipid metabolism
is a promising strategy for improving the capacity for
The ideas for the experiment come from the fact that
"skeletal muscles utilize carbohydrates, lipids and
amino acids as energy sources, but the ratio in which
they are used varies with the intensity of exercise
and the level of fitness" as well as the type of exercise
involved. For instance "during endurance exercise, excess
glucose is undesirable because it induces insulin secretion,
which in turn simultaneously inhibits lipid metabolism
and stimulates lactate production. Conversely, enhanced
availability and utilization of free fatty acids are
considered to reduce carbohydrate utilization, which
in turn spare glycogen and suppresses lactate production
and results in an increase in endurance."
To test what effects GTE and its components would have
on endurance exercise, the researchers ran two experiments.
In the first, swimming endurance capacity was measured
at eight weeks of age and the mice were divided into
four groups of 10 each. All subjects had unlimited access
to water for exercise. For 10 weeks, controls ate a
standardized diet only, while experimental animals had
this diet supplemented with 0.2% and 0.5% GTE by weight.
During this period experimental mice were exercised
in a pool twice a week, but non-exercise mice weren't.
The second experiment was similar to the first but
the experimental groups received a diet containing 0.1%
to 0.5% EGCG for 10 weeks.
At the beginning of the experiment, the mice swam about
26 minutes until they were exhausted. After 10 weeks
on the training regimen, the time-to-exhaustion for
the exercise-control mice (no GTE or EGCG supplement)
rose to about 33 minutes, showing the effects of unaided
practice on endurance capacity. From the first week
of the experiment, the mice on GTE showed greater improvement
compared with the exercise-controls. By week eight,
the improved performance of mice on 0.5% GTE was significantly
better (39 minutes) than the exercise-controls (33 minutes)
at a 0.05 level, while improvement in weeks 9 and 10
(40 minutes vs. 33 minutes) were significant at the
GTE effects not matched by EGCG alone suggesting
other additional influences
In the global search for enhanced athletic performance
(and health and fitness), the Kao team said they "have
shown that GTE improved endurance capacity and that
the improvement was dose-dependent. A similar effect
was observed in mice fed EGCG, a major constituent of
GTE, suggesting that the effects of GTE were mediated
at least in part by EGCG.
"However, because the effects of EGCG appear weak compared
with those of GTE, we cannot rule out a possible contribution
from other components of GTE. Although long-term intake
of GTE enhanced endurance capacity, no marked effects
were observed after a single dose of GTE, suggesting
that some biochemical changes induced by habitual GTE
intake, such as up-regulation of muscular beta-oxidation,
contributed to the improvement in endurance capacity."
The study found that plasma NEFA (non-esterified fatty
acid) measured immediately after exercise slightly,
but significantly, increased in mice fed tea catechins.
Though they concede that the effect of plasma fatty
acid level on endurance capacity is controversial, they
say that increased supply of circulating fatty acids
would "induce the uptake of fatty acids, and thereby
stimulate lipid metabolism in muscle."
Indeed, lab results showed that muscular beta-oxidation
was higher in GTE-fed mice (compared with non-exercise
and exercise-control mice), "suggesting that GTE enhanced
the capacity of muscle to catabolize lipids and utilize
fatty acids as an energy source." Conversely, GTE lowered
plasma lactate concentrations, which would be raised
by glycogen breakdown and glycolytic flux, they note.
Taken together the experimental results "suggest that
habitual exercise and the intake of GTE enhance fatty
acid availability, catabolism and utilization in muscle,
and this is accompanied by a reduction in carbohydrate
use, which together result in prolonged swimming times
Controlling for caffeine
Kao researchers controlled for possible influences
of caffeine and possible weight-fat changes that might
Aware that previous studies were criticized by the
possible role of caffeine on fatty acids and exercise,
the Kao researchers reduced the amount of caffeine in
supplements. "In addition, we observed no changes in
plasma NEFA level under resting conditions, suggesting
that caffeine-stimulated lipolysis did not occur under
these conditions. Thus our results overall suggest that
the effects observed in this study are not attributable
to caffeine. In particular, our findings that purified
EGCG improved endurance capacity supports this conclusion."
- The "precise molecular mechanism by which GTE stimulates
fatty acid metabolism is unclear at present (and)
remains to be elucidated."
- For instance, the researchers wrote, "it is possible
that the anti-oxidant properties of tea catechins
mediate their effects on endurance capacity."
- And finally they noted: "Although the clinical
efficacy of GTE has not yet been confirmed in human
studies, our results suggest that GTE may be a useful
tool for improving endurance capacity."