Cholesterol Lowering Properties of Green Tea
Some very exciting results were found when rats were fed 2.5% green tea leaves in their diet. The experimental group showed a drop in total cholesterol, low-density cholesterol, and triglycerides. The body weight of green tea-fed rats was 10 to 18% lower than that of rats not consuming green tea. In addition, the activity of antioxidant enzymes superoxide dismutase (SOD) and catalase, and of anti-carcinogenic phase-II enzyme glutathione S-transferase (GST), were significantly higher in the green tea group, as was the glutathione level in the liver. There was no liver or kidney toxicity. Thus, the study demonstrated combined cardiovascular and anticancer effects of green tea.
The cholesterol-lowering (hypocholesterolemic) effects of green tea (as well as black tea) have been confirmed by both animal and human epidemiological studies. In addition to lowering the atherogenic index as expressed by the HDL/total cholesterol ratio in rats, green tea and jasmine green tea also reduced the increase of liver weight that results from fat deposition. High consumption of green tea by humans, especially more than 10 cups a day, was found to be associated with higher HDLs and lower LDL and VLDL cholesterol, as well as with various bio-markers indicating better liver health. Lower levels of lipid peroxides in the liver are one well-confirmed benefit of green tea supplementation, found in study after study. The pancreas is another organ that is protected by green tea.
Green tea may also lower intestinal fat absorption. One animal study found that rats fed a diet containing a significant amount of catechin had a higher excretion of fat in the feces compared to the control group on a polyphenol-free diet. If this holds for humans who take the green tea extract, then it's good weight-loss and cardiovascular news.
Supplementation with antioxidants is important in part because by protecting cholesterol from oxidation, antioxidants help protect against atherosclerosis. In an animal study comparing the effectiveness of various antioxidants in preventing the oxidation of VDL and LDL cholesterol, vitamin E, genistein (phytoestrogen found chiefly in soy products) and green tea were found to be effective antioxidants, with genistein being particularly effective (oxidation lag time of 49% on the high-genistein diet), but green tea also exerting considerable activity (lag time of 33%). It would be interesting to see the results of combined genistein and green tea supplementation, particularly in humans. On the other hand, it could be argued that this is precisely the case of the Japanese diet. Japan enjoys the longest life expectancy in the world, and the lowest cardiovascular mortality for men, in spite of heavy smoking.
Green Tea Increase Metabolism, May Aid In Weight Loss
Green tea extract has been the focus of several weight loss studies recently. In addition to its healthful benefit of strong antioxidant activity and its ability to burn more calories, green tea is now being studied for another weight loss benefit, reducing appetite.
Leptin is a protein produced by fats that appear to play an important role in how the body manages fat storage through brain signals. Years ago it was thought by scientists that lower leptin levels would increase appetite. Current research has now found that it does just the opposite and decreases appetite. There is clear evidence that green tea's polyphenols (EGCG) are a factor in depressing leptin as well as affecting other hormone levels important in regulating appetite.
Green tea is now holding promise in many areas of weight loss. Besides affecting leptin levels, green tea also increases noradrenaline levels. Noradrenaline is a chemical neurotransmitter in the nervous system that plays a major role in activation of brown fat tissue (BAT), which is the only metabolically active fat in the human body. Activation of brown fat by increased noradrenaline levels is significant because it burns calories from the white fat located around our waistline, hips and thighs.
In a study reported on in the American Journal of Clinical Nutrition, it was found that green tea extract resulted in a significant increase in energy expenditure (a measure of metabolism), plus also had a significant effect on fat oxidation. While some of the effects were originally theorized to be due to the caffeine content of green tea, the researchers discovered that the tea actually has properties that go beyond those that would be explained by the caffeine.
Green tea appears to speed up calorie burning, including fat calorie burning. The green tea extract may play a role in the control of body composition. Researchers studied the effects of green tea on 10 healthy young men, average age 25, who ranged from lean to mildly overweight. For 6 weeks, the men took two capsules at each meal: green tea extract plus 50 milligrams of caffeine; 50 milligrams of caffeine; or a placebo (inactive capsule).
The study participants were on a weight maintenance diet of about 13% protein, 40% fat, and 47% carbohydrates, a "typical Western diet." Three times during the study, the men spent 24 hours in a special room where the investigators measured their respiration and energy expenditure. Energy expenditure, the number of calories used during a 24-hour period, was higher for men taking green tea extract than for those taking caffeine or placebo. They also found evidence that men taking the green tea extract used more fat calories than those taking the placebo.
There was no difference between the caffeine users and the placebo users in terms of either overall calorie burning or fat calorie burning. The researchers therefore conclude that the increased calorie burning in the green tea group cannot be explained by caffeine intake alone. The investigators suggest that the caffeine interacted with natural substances in green tea called flavonoids to alter the body's use of norepinephrine, a chemical transmitter in the nervous system, and increase the rate of calorie burning. The researchers point out that, unlike some diet products, green tea does not contain high doses of caffeine, and it did not affect the heart rate in the study participants.
The researchers indicated that their findings have substantial implications for weight control. A 4% overall increase in 24-hour energy expenditure was attributed to the green tea extract, however, the research found that the extra expenditure took place during the daytime. This led them to conclude that, since thermogenesis (the body's own rate of burning calories) contributes 8-10% of daily energy expenditure in a typical subject, that this 4% overall increase in energy expenditure due to the green tea actually translated to a 35-43% increase in daytime thermogenesis.
Of critical importance to thyroid patients is the fact that none of the research subjects reported any side effects, and no significant differences in heart rates were noticed. In this respect, green tea extract is different from some of the prescription drugs for obesity, and herbal products like ephedra, which can raise heart rates and blood pressure, and are not recommended for many individuals, in particular, those with thyroid disease who may be particularly sensitive to stimulants. (For more about green tea and weight loss click here)
Reference
American Journal of Clinical Nutrition November 1999;70:1040_1045.
Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans1,2,3 Abdul G Dulloo, Claudette Duret, Dorothée Rohrer, Lucien Girardier, Nouri Mensi, Marc Fathi, Philippe Chantre and Jacques Vandermander.
