All teas contain high quantities of several polyphenolic components such as epicatechin, epicatechin gallate, epigallocatechin and, the most abundant and probably the most pharmacologically active, epigallocatechin gallate.
EGCG (Epigallocatechin-3-Gallate), the most abundant catechin in green tea, representing approximately 35% of total catechins, has received the most attention as a potential anti-obesigenic agent. Long term treatment (12 wks) with green tea extract containing 115 mg EGCG daily significantly reduced body fat (7%), body weight (2%), and BMI (2%) in men and women.
Possible mechanisms include:
1) decreasing digestive activity,
2) increasing lipolytic activity,
3) decreasing lipogenic activity,
4) increasing fat oxidation and thermogenesis,
5) modulation of the activity and expression of lipoprotein lipase,
6) decreasing the cell number and size of adipocytes, and
7) decreasing hormone-stimulated proliferation of preadipocytes and their differentiation to adipocytes.
From caffeine, that is also present in green tea, it has been reported that it has thermogenic effects and can stimulate fat oxidation in vitro, in part through sympathetic activation of the central nervous system.
Daily increases in thermogenesis of approximately 300–400 kJ can eventually lead to substantial weight loss. The sympathetic nervous system is involved in the regulation of lipolysis, and the sympathetic innervation of white adipose tissue may have an important role in the regulation of total body fat in general.
Fat oxidation is mainly under the control of the sympathetic nervous system (SNS). Therefore, there are a number of approaches to increase SNS activity either directly (by -adrenergic agonists) or indirectly (by norepinephrine releasers and reuptake inhibitors). Interestingly, a number of compounds extracted from plants such as caffeine from coffee and tea, ephedrine from ephedra, and capsaicin from pungent spices can modulate catecholamine release and activity. The main catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline), and dopamine.
Caffeine also affects the thermogenesis by inhibiting the enzyme phosphodiesterase. This enzyme degrades intracellular cyclic amino mono phosphate.51 Phosphodiesterase usually hydrolyses cyclic adenosine monophosphate (cAMP) to AMP, but after consumption of caffeine, cAMP concentration rises and SNS activity will be increased and inactive hormone-sensitive lipase will be activated, which promotes lipolysis.
Tea and thermogenesis
