The Role of Tea Catechins and Caffeine in Relation to Energy Metabolism
Condition: Obesity
Study type: Interventional

Summary: 
      The aim of this study is to elucidate the role of specific catechins, a mixture of catechins
      and caffeine in relation to weight control with particular emphasis on energy metabolism and
      fat oxidation.
    

Detailed description: 
      Obesity is the result of an imbalance between energy intake (EI) and energy expenditure (EE).
      Thus, two ways to treat obesity are to reduce EI or increase EE. Bioactive food ingredients
      affecting energy metabolism, e.g. EE, fat oxidation, satiety and EI may help people to
      successfully control or manage their weight. Green tea, one of the most widely consumed
      beverages in the world, may possess beneficial effects on the treatment of obesity.

      Green tea is made from the leaves of Camellia sinensis species of the Theaceae family. Green
      tea is the non- fermented/oxidised products, in contrast to black tea that is fully
      fermented/oxidised. Green teas contain high quantities of catechins and caffeine which are
      believed to be the active components affecting energy metabolism. EGCG is the most abundant
      catechin and has received the most attention (Yang et al., 2000). Caffeine represents
      approximately 3 to 5 % of the dry weight of green tea (Dufresne et al., 2001, Yang et al.,
      2000). It is general accepted that caffeine consumption is related to an increase in EE
      (Astrup et al., 1990), whereas the relation between catechins and energy metabolism is
      recently discovered.

      In a study by Dulloo et al (1999), ten healthy men were assigned to 3 treatments: 1) green
      tea extract containing 150 mg/day caffeine and 270 mg/day of EGCG, 2) caffeine (150 mg/day)
      or 3) placebo. Ingestion of green tea extract (taken with each meal) increased 24-h EE by 4 %
      (328 kJ), reflecting its stimulatory effect on thermogenesis. This study also found a
      reduction in the respiratory quotient (RQ) during the green tea extract treatment, suggesting
      an increase in fat oxidation. However, Kovacs et al. (2004) did not report any changes in
      24-h EE or RQ after same supplementation with green tea capsules, which may be explained by
      different background caffeine consumption.

      Recently, two medium term studies have reported of increased fat oxidation after 8 and 12
      weeks, respectively, supplementation with tea catechin containing beverage (Ota et al., 2005,
      Harada et al., 2005). In addition, Nagao et al. (2005) have shown that a daily consumption of
      tea beverage containing 690 mg/day catechins for 12 weeks reduced body fat area by 8%
      compared to the control group. Thus, catechins may not only promote EE, but also mildly
      reduce body fat.

      Several potential mechanisms responsible for the altered energy and fat metabolism have been
      proposed. Dulloo et al. (1999) have suggested a synergistic interaction between catechins and
      caffeine due to sympathetically released noradrenaline (NA). Since catechins are known to be
      capable of inhibiting catechol O-methyltransferase (COMT) (the enzyme that degrades NA)
      (Borchardt & Huber, 1975), and caffeine to inhibit trancellular phosphodiesterases (enzymes
      that break down NA-induced cAMP), it is proposed that the green tea extract, via its
      catechins polyphenols and caffeine, is effective in stimulating thermogenesis by relieving
      inhibition at different control points along the NA-cAMP axis. Taken together, both caffeine
      and tea catechins would be expected to increase and/or prolong the stimulatory effects of
      norepinephrine on energy and lipid metabolism.

      Several animal studies have been conducted to elucidate the anti-obese mechanisms of green
      tea extracts.

        -  Increased hepatic β-oxidation of fatty acids in mice after 4 weeks high fat diet with
           supplementation with tea catechins (74% EGCg, 18% ECg, 6% GCg, 2% others) (Murase et
           al., 2002 and 4 weeks high fat diet with supplementation with EGCg (Klaus et al., 2005).
           On the other hand, fatty acid synthase (FAS) was not altered by tea catechins, which may
           indicate that the simulation of fatty acid oxidation, rather than suppression of
           lipogenesis, is the predominant contribution (Murase et al., 2002).

        -  Modulated appetite and reduces food intake through the leptin receptor-independent
           pathway (Kao et al., 2000)

        -  Intraperitoneal administration of EGCg may reduce the diet digestibility resulting in
           increased faecal excretion of lipids (Klaus et al., 2005)

        -  Green tea extract (8% caffeine and 25% catechins (~70% EGCg)) stimulates brown adipose
           tissue thermogenesis and energy expenditure, which may be due to the prolonged effect of
           noradrenalin (Dulloo et al., 2000).

      Large variations in catechin content and chemical structures occur during preparation and
      manufacturing of green tea products and therefore also among the studies. EGCg is the most
      intensely studied catechin. However, the plasma bioavailability of EGCg is lower than of EGC
      and EG (Henning et al., 2004), suggesting that non-galloylated catechins are better absorbed
      than the galloylated (Manach et al., 2005).

      In addition, it is not known whether epimerization of catechins alters the effect on energy
      and fat metabolism (Harada et al., 2005, Ota et al., 2005, Xu et al., 2004). Therefore, it is
      not clear whether the reported effects are due to the total quantity of catechins, the
      chemical structure of specific catechins (e.g. epimerization and galloylation), and/or the
      caffeine content or other components of in the mix.

      Methods

      The study is a 5-way crossover double blind placebo controlled design. At each test day,
      energy expenditure and fat oxidation are measured via indirect calorimetry for 13 hours in
      one of two whole body respiratory chambers.
    

Intervention name(s): green tea; Mix of catechins and caffeine; EGCG; EGC; Caffeine; Placebo
Intervention type(s): Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement
Intervention description(s): different catechin combinations; 3 tablet a day; 3 tablets a day; 3 tablets a day; 3 tablets a day; 3 tablets a day
Other intervention name(s): epigallocatechin gallate; Epigallocatechin
Intervention MeSH terms: Epigallocatechin gallate; Caffeine
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: catechins; caffeine; energy expenditure; fat oxidation; appetite