Green Tea, Energy Expenditure, and Fat Oxidation

ABSTRACT
Background: Current interest in the role of functional foods in
weight control has focused on plant ingredients capable of interfering
with the sympathoadrenal system.
Objective: We investigated whether a green tea extract, by
virtue of its high content of caffeine and catechin polyphenols,
could increase 24-h energy expenditure (EE) and fat oxidation
in humans.
Design: Twenty-four–hour EE, the respiratory quotient (RQ), and
the urinary excretion of nitrogen and catecholamines were measured
in a respiratory chamber in 10 healthy men. On 3 separate
occasions, subjects were randomly assigned among 3 treatments:
green tea extract (50 mg caffeine and 90 mg epigallocatechin gallate),
caffeine (50 mg), and placebo, which they ingested at
breakfast, lunch, and dinner.
Results: Relative to placebo, treatment with the green tea extract
resulted in a significant increase in 24-h EE (4%; P < 0.01) and
a significant decrease in 24-h RQ (from 0.88 to 0.85; P < 0.001)
without any change in urinary nitrogen. Twenty-four–hour urinary
norepinephrine excretion was higher during treatment with
the green tea extract than with the placebo (40%, P < 0.05).
Treatment with caffeine in amounts equivalent to those found in
the green tea extract had no effect on EE and RQ nor on urinary
nitrogen or catecholamines.
Conclusions: Green tea has thermogenic properties and promotes
fat oxidation beyond that explained by its caffeine content
per se. The green tea extract may play a role in the control of
body composition via sympathetic activation of thermogenesis,
fat oxidation, or both. Am J Clin Nutr 1999;70:1040–5.

Reference
Dulloo, A. G., Duret, C., Rohrer, D., Girardier, L., Mensi, N., Fathi, M., & Chantre, P. (1999). Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation. American Journal of Clinical Nutrition, 70, 1040–1045.

My Take
This one of four studies listed on the Hydroxcut website to support their product. This study was done six years prior to the study I reported on previously (Berube-Patent et al., 2005), and was very similar. It was suggested that interfering with the sympathetic nervous system (SNS) and its neurotransmitter norepinephrine would help in weight loss because thermogenesis and fat oxidation are under the control of the SNS. Certain plants are thought to have a thermogenic effect by interfering with catecholamine release and activity.

Here is a little background paraphrased from the paper…

Green tea is made from unfermented Camellia sinensis leaves and contains polyphenol, which is a chemical that occurs naturally in some plants. A type of polyphenol is flavonoids, which is thought to have a health benefit due to containing catechins. Green tea contains the highest amount of catechins of all the teas because of how it is processed. Four polyphenol catechins in green tea are: gallocatechin (GC), epigallocatechin (EGC), epicatechin (EC), and epigallocatechin gallate (EGCG). In a given cup of tea, there can be between 80 to 100 mg of polyphenols. In addition, Green tea also contains about 50 mg of caffeine per cup.

Caffeine inhibits the phosphodiesterase-induced breakdown of cyclic AMP (cAMP), meaning that there is more cAMP. cAMP is an intracellular mediator for the actions of catecholamines on thermogenesis. Caffeine also helps to decreases adenosine leading to reduced central nervous system fatigue, this in turn causes an increased norepiephrine release. An enzyme called COMT breaks down norepinephrine at the synaptic junctions, this along with phosphodiesterases, adenosine, and certain prostaglandins help to regulate the amount of norepinephrine and its interactions with adrenoceptors. However, COMT can be inhibited by tea polyphenols which would prolonged the effect of norepiephrine on thermogenesis and fat metabolism. This was seen in the study by increased norepiephrine in the urine in the Green Tea group due to less breakdown of norepiphrine and an increased amount in the circulation. The researcher’s proposed mechanism for the results was that the catechins inhibited COMT, which increased the life of norepinephrine. Also, caffeine inhibited phosphodiesterases and increased the life of cAMP which overall increased norepiephrine’s effect on thermogenesis.

Overall this paper proves that Green Tea Extract increases fat metabolism, thermogenesis, and can aid in body composition changes, as well as provides mechanisms to explain these finding; however, I think it is important to see if it actually is applicable to the brand Hydroxcut. In the study subjects received one of three treatments, 1) green tea extract containing 50 mg of caffeine and 90 mg of ECGC, 2) 50 mg of caffeine, or 3) a placebo. All three treatments were taken three times per day for totals of: 1) 150 mg caffeine and 270 mg of ECGC, 2) 150 mg caffeine, no ECGC and 3) no caffeine or ECGC. Hydroxycut is also meant to be taken three times per day, and contains the following: at least 600 mg of caffeine/day and at least 351 mg of ECGC per day. More of both are included, but it is hard to quantify the exact amount due to how the ingredients are listed on the label, see http://www.hydroxycut.com/products/hydroxycut/hydroxycut_faqs.shtml. Comparing the researched amount, and the amount included in the product, it is seen that the product includes more than what was need to increase energy expenditure 4% in the study, therefore I would think there is a possibility the product can increase energy expenditure even more. On the other hand, in the study it was shown that the increased energy expenditure was not accompanied by an increase in heart rate, but that was at a dose lower than what is seen in the product, so this can possibly be a concern. It is interesting that after 10 years on the market, Hydroxcut has no listed scientific reviewed studies on the website or indexed in PubMed looking at the combination of ingredients in their product, instead they sight research (that is 10 years old) on key ingredients as their proof that it works. Perhaps, the company does not want consumers to know how the ingredients actually interact and work together. In conclusion, I think that Green Tea Extract has beneficial effects on weight loss, and while Hydroxcut may too; more research needs to be done.