Obesity has become one of the major illnesses in America seeming more on the rise than in regression. Interestingly enough, green tea (Camellia sinensis Xihu Longjing) seems to show a string of successes in reducing obesity (e.g. Lin, 2006). (Incidentally too, green tea may reduce blood lipid levels but this association remains unclear). One such study was conducted by Paradee et al. (2008) on obese Thai. The researchers reasoned that both catechin polyphenols and caffeine "may be effective promoters of thermogenesis and fat oxidation, resulting in the reduction of body weight in Caucasians, Chinese, and Japanese" (25). They wanted to see whether the same effects would hold upon other races and ethnicities and so they therefore studied the effects of obesity-reduction of green tea on Thais.
The researchers, therefore, conducted a randomized, controlled trial on a large segment of 60 obese individuals. All the participants partook of a Thai diet that contained the same 3 meals (for 12 weeks, prepared by the Nutritional Unit at Srinagarind Hospital. The diet contained 65% carbohydrates, 15% protein, and 20% fat. Body weight, BMI, body composition, resting energy expenditure, and substrate oxidation were measured at baseline, and during weeks 4, 8, and 12 of the study. Serum levels of leptin and urine were also measured at baseline and during the 12th week. One group was fed green ta, another (the control) was given a placebo. Differences were calculated using two-group ANOVA with repeated measures.
In comparing the two groups, differences in weight loss were 2.70, 5.10, and 3.3kg during the 4th, 8th, and 12th weeks of the study, respectively. At the 8th and 12th weeks of the study, however, there was a significant difference in body weight loss whilst there were no significant differences in satiety score, food intake, or physical activity.
The researchers concluded that green tea can reduce body weight in obese Thai subjects by increasing energy expenditure and fat oxidation.
On the other hand, another study conducted that same year on obese women in Taiwan (Chung-Hua et al., 2008) found no significant differed whatsoever between green-tea group and placebo group. A randomized, double-blind, placebo-controlled clinical trial was conducted from July 2006 to June 2007 in Taipei Hospital, Taiwan. Seventy-eight of 100 obese women aged between
16 and 60 years participated. These participants had not received any weight-control factors within the last 3 months prior to study. The subjects were randomly divided into two groups: Group A and B. Group A (n= 41) received GTE (green teas) while Group B (n= 37) took cellulose as a placebo. They were fed one capsule three times each day for 12 weeks. body weight (BW), body mass index (BMI) and waist circumflex (WC) were measured at the beginning of the study and after 12 weeks of treatment with GTE. Researchers discovered only a 0.3% reduction in BW (0.15 kg) after 12 weeks of treatment with GTE. There was also no statistical difference in reduction in BW, BMI and WC between the two groups.
Although studies have shown the reverse, such as an epidemiological human study that showed that consumption of tea for more than 10 years led to a lower percentage of total body fat and smaller waist circumfluence (Wu et al., 2003), Hua et al. (2008) found no results in their 12-week study. This is something to be considered particularly since their sample was rather large and the study meticulously conducted. They also had a control group and made sure that their subjects did not receive other weight-control enablers. Some of these factors (including small samples and studies that were of short duration) were missing from other studies.
Given that green tea may have an effect in reducing weight, what is it of their properties that has this outcome?
FAS are an important enzyme that is inherent in the energy metabolism. The animal FAS component also has a molecular mass of 270 kDa which consists of synthesis of long-chain fatty acids from acetyl-CoA, malonyl-CoA and NADPH through its seven different domains . It has variously been thought that FAS may be a treatment for obesity. Apparently some FAS inhibitors (such as cerulenin, the ?-methylene-? - butyrolactone C75 (a synthetic inhibitor of FAS) and EGCG (epigallocatechin gallate)) reduce animal weight and inhibit animal appetite (ibid). EGCG and ECG (epicatechin gallate) are two main components of great tea and both of these are derivatives of FAS, which may lead us to conclude that green tea itself, may have obesity-inhibiting features. Various studies have been conducted on this; none have been conclusive.
One of the most recent studies was that conducted by Zhang et al. (2006) where they treated and analyzed an extraction of green tea leaves. Their analysis was mainly focused on discovering the mechanisms by which green tea may -- if correct -- inhibitory of obesity. They proposed that inhibitor was achieved by two isomers called CG and ECG, and that contrary to previous speculation some new potent FAS inhibitor(s) may be formed during the isolation processes of the green tea.
Apparently too the GTE (green tea extract) is more potent in inhibiting the FAS than the other two known inhibitors in green tea leaves, EGCG (epigallocatechin gallate) and ECG (epicatechin gallate). The researchers found too that (?)-CG (catechin gallate) was a potent inhibitor of FAS possibly explaining the contribution of GTE.
In a previous study, Ngao et al. (2005) had attributed the effects to Catechins, the major component of green tea extract. These catechins are epigallocatechin gallate (ECGS) which have been associated with obesity-reducing factors. The researchers reported that:
A portion of ingested EGCg is absorbed and widely distributed throughout the body. The ingestion of tea extract or catechins induces antioxidant, antiviral, antiplaque-forming, and anticancer activities, as well as decreases in blood pressure and blood sugar. Lipid metabolism studies in animals, tissues, and cells have found that tea extract and catechins reduce triacylglycerol and total cholesterol concentrations, inhibit hepatic and body fat accumulation, and stimulate thermogenesis (18).
In order to test their hypothesis that this catechin was a factor in obesity-reduction, the researchers conducted a double controlled study of a 2-week diet run-in period, where 38 healthy Japanese men were divided into 2 groups with similar BMI and waist circumference distributions. A 12-week double-blind study was performed where the participants of experimental group drank 1 bottle oolong tea containing 690 mg catechins whist the control group drank 1 bottle oolong tea containing 22 mg catechin.
The researchers discovered that the body weight, BMI, waist circumference, body fat mass, and subcutaneous fat area were all significantly lower in the green tea extract group than in the control group and that changes in the concentrations of malondialdehyde-modified LDL were positively associated with changes in body fat mass and total fat area in the green tea extract group.
The researchers thereupon concluded that catechin may be a key mechanism, for inhibiting obesity and it was this factor that produced the efficacy evident in green tea. This corresponds with research of Zhang et al. (2006) who indicated too that (?)-CG (catechin gallate) was a potent inhibitor of FAS. Catechist too may be helpful due to the fact that catecholamines in the brain may play a major role in satiety [KaO ET AL, 2000].
A long-range of studies have concluded that green tea has obesity-reducing effects. Chung-Hua et al. (2008) however concluded otherwise indicating no effect through their double blind controlled study on 100 obese women. Nonetheless, most studies seem to show an impact. Properties of green tea that may be responsible for this FAS-inhibiting outcome have been variously said to be the (?)-CG (catechin gallate) that is a compound of the GTE (green tea extract).
If green tea does indeed have this affect that would be a huge discovery. Further studies…