after withering, crushing, rolling, fermenting and drying of fresh
tea leaves [30]. Because during this process, the tea leaves have
been shredded, so there are more edges and more surface area as
well as a breakdown of leaf proteins, which increases the availability
of freed caffeine and therefore more caffeine can be
extracted in water [31]. As results, the increase of plasma caffeine
was concomitant with the reduction of adipose tissue gain and
related blood and liver triglycerides whereas fecal caffeine was not.
Consistent with other studies [22,32,33], we believe that the high
absorption of caffeine from GTD and more from BTD may be efficient
in the decrease of adipose tissue mass in rats fed HFD.
Therefore, caffeine from tea decoction, especially from BTD could
be considered as an additional potential factor for stimulating
thermogenesis and promotes fat oxidation. However, the caffeine
content of GTD and BTD cannot completely explain the reduction of
adipose tissue mass because it was demonstrated that thermogenic
effect of tea extract containing both caffeine and catechin polyphenols
is greater than that of an equivalent amount of caffeine
[34]. Thus, the caffeine may act independently or synergistically
with catechins and theaflavins of GTD and BTD [23]. The antiobesity
effect of caffeine from tea, especially in animals, has been
observed in different experimental conditions [35]. Hence, the
intake of caffeine doses (0.025e0.1%) for 21 days reduced body fat
mass gain in rats fed a high-fat diet in a dose dependant manner
[35]. This reduction was concomitant with an increase of serum
epinephrine, norepinephrine, dopamine and free fatty acid levels,
suggesting an active catecholamine synthesis and lipolysis [35]. In
addition, the caffeine consumption showed to inhibit the enzyme
phosphodiesterase and leading to increase intracellular cAMP as
well as sympathetic nervous system and lipase activities, which
promotes lipolysis [36]. Accordingly, and being richer in TFs and
caffeine than the GTD, BTD was found more efficient in term of
reduction of abdominal adipose tissue gain and lowering blood and
liver lipids.
Some other phenolic compounds, including vanillic acid ester,
kaempferol 3-glycoside and gentissic acids were found in GTD and
BTD although as little amounts. It has been reported that D-glucosyl-
kaempferol isolated from Sauropus at a dose of 60 mg/kg
significantly reduced food intake in rats by 15%, resulting in decreases
in body weight and free triglyceride without obvious histopathological
changes [37]. Unlike to synthetic or isolated glucosylkaempferol
compounds, it is difficult to highlight the distinctive
effect of kaempferol from GTD and BTD on the decrease of adiposity
or body weight gains because of the interference of several polyphenolic
compounds present in tea decoctions. However, we can
consider that the anti-adiposity effect of these simple phenolics
present in tea is far lower than that of gallic acid, known for its
powerful action on the modulation of dietary lipids digestion and
adiposity.
In summary, chronic administration of short-time tea decoctions
(15-min GTD or 15-min BTD) during 10-weeks, dramatically
reduced lipid digestion, lowering liver and blood lipids,
adipose tissue mass and body weight gains in rats fed HFD. The data
showed a higher efficiency of BTD compared to GTD, which confer
to these traditional cooking beverages, rich in TPC mostly EGCG and
TFs as well as caffeine, a natural alternative in the prevention of
obesity.