Let Greentealovers Help You Lose Weight! - This section provides some of the latest research on green tea's effect on diet & weight loss there are studies on. Our tea site is featured in this book.
Green Tea: Fat Fighter?
Black tea, oolong tea, and green tea come from the same Camellia sinensis plant. But unlike the other two varieties, green tea leaves are not fermented before steaming and drying.
Most teas contain large amounts of polyphenols, which are plant-based substances that have been shown to have antioxidant, anticancer, and antiviral properties.
However, green tea is particularly rich in a type of polyphenols called catechins. These substances have also been shown to have anti-inflammatory and anticancer properties, but recent research in animals show that catechins may also affect body fat accumulation and cholesterol levels.
In this study, researchers looked at the effects of catechins on body fat reduction and weight loss in a group of 35 Japanese men. The men had similar weights based on their BMI(body mass index, an indicator of body fat) and waist sizes.
The men were divided into two groups. For three months, the first group drank a bottle of oolong tea fortified with green tea extract containing 690 milligrams of catechins, and the other group drank a bottle of oolong tea with 22 milligrams of catechins.
During this time, the men ate identical breakfasts and dinners and were instructed to control their calorie and fat intake at all times so that overall total diets were similar.
After three months, the study showed that the men who drank the green tea extract lost more weight (5.3 pounds vs. 2.9 pounds) and experienced a significantly greater decrease in BMI, waist size, and total body fat.
In addition, LDL "bad" cholesterol went down in the men who drank the green tea extract.
The catechin content varies by amount of green tea used and steeping time. But general recommendations, based on previous studies on the benefits of green tea, are at least 4 cups a day. Green tea extract supplements are also available.
Researchers say the results indicate that catechins in green tea not only help burn calories and lower LDL cholesterol but may also be able to mildly reduce body fat.
"These results suggest that catechins contribute to the prevention of and improvement in various lifestyle-related diseases, particularly obesity," write researcher Tomonori Nagao of Health Care Products Research Laboratories in Tokyo, and colleagues.Reference
By Jennifer Warner
WebMD Medical News
Reviewed By Michael Smith, MD
on Wednesday, January 26, 2005
Results: Among the 1103 analyzed subjects, 473 adults (42.9%) consumed tea once or more per week for at least 6 months. The habitual tea drinkers were male-dominant, more frequently current smokers, and alcohol or coffee drinkers than the non-habitual tea drinkers. Habitual tea drinkers for more than 10 years showed a 19.6% reduction in BF% and a 2.1% reduction in WHR compared with non-habitual tea drinkers. The multiple stepwise regression models revealed that men, older age, higher BMI, and current smokers were positive factors for BF% and WHR. In contrast, longer duration of habitual tea consumption and higher total physical activity were negative factors for BF%. Longer duration of habitual tea consumption, higher socioeconomic status, and premenopausal status were negative factors for WHR.
Discussion: An inverse relationship may exist among habitual tea consumption, BF%, and body fat distribution, especially for subjects who have maintained the habit of tea consumption for more than 10 years.Reference
Chih-Hsing Wu, Feng-Hwa Lu, Chin-Song Chang, Tsui-Chen Chang, Ru-Hsueh Wang and Chih-Jen Chang Department of Family Medicine, National Cheng Kung University Hospital, Tainan, Taiwan. Address correspondence to Chih-Jen Chang, Department of Family Medicine, National Cheng Kung University Hospital, 138 Sheng-Li Road, Tainan 70428, Taiwan. E-mail: firstname.lastname@example.org
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.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.
GUPTA: You know [what] the second most common drink in the world is, Bill?
HEMMER: I would say tea.
GUPTA: Tea, yes, you're right.
GUPTA: Chai, exactly. There's been a lot of talk as you mentioned, Bill, about the health benefits of tea. Certainly that's something people have known about abstractly for quite some time. But now the first study showing a causal relationship, cause and effect relationship, between tea and cholesterol.
There was a lot of studies incidentally done on animals before, and that data was extrapolated to human beings, but this is the first study actually looking at tea and cholesterol, showing in fact that taking extracts from tea can actually lower your cholesterol.
Take a look at what researchers decided to do. They looked at over 200 people, actually close to 220 people, all of them Asian. This was done in China. People were already on a low-fat diet because they had a moderate to severely elevated cholesterol.
And what they found was over a 12-week period. They divided the people into two groups. One group got the pill, which was a soft gel capsule with the tea extract. The other group got just a placebo, a sugar pill, and they found that the capsule group, the people who are getting the tea, actually had an 11 percent increase in total cholesterol and a 16 percent decrease in the bad type of cholesterol. Again, that's just over 12 weeks. So pretty significant results there.
They're not quite ready to recommend tea for everybody to take all of the time. They still say that you need to see some of the long-term effects of taking tea every day, and taking these capsules every day. Two, is to find out how it interacts with some of existing medications. A lot of people with elevated cholesterols are already on medications. Would this capsule somehow interact with that?
So two questions out there still, Bill, but certainly a positive step for these tea extracts and lowering your cholesterol.
HEMMER: What about the arguments green tea, black tea? What should we know about that?
GUPTA: Yes, that's been a longstanding debate as well. Just a couple of things to keep in mind, green tea probably has more antioxidants than black tea. So the green tea [is] probably better. Both teas, if you're going to be making tea, you need to steep it for at least five minutes. That will release most of the antioxidant quality. But if you're looking for the antioxidants in general, green tea better than black tea.
And let me just tell you as well, Bill, as you mentioned at the top, there are a lot of different health benefits that have been attributed to tea for quite some time. Take a look at the list of possible health benefits that people have known about for some time.
Heart disease (is one). People are hearing a lot about that. Benefiting bone density, it's anti-inflammatory, anti-carcinogenic as well. All sorts of different benefits. They've been drinking it in China for thousands of years. They have lower rates of esophageal and stomach cancer among Chinese men as well, even after you control for other health considerations and societal considerations. There may be a lot of benefits to tea out there that we'll still figure out in the long run.
HEMMER: OK, Sanjay. Thanks. Next time we'll talk beer?
GUPTA: Third most common drink.
CNN Interview with Dr. Sanjay Gupta: Another benefit to tea-time (Courtesy of CNN)
In previous studies, EGCG was observed to reduce the size of breast and prostate tumors in mice, a result that led Shutsung Liao, PhD, Director of the Tang Center and professor in the Ben May Institute for Cancer Research and colleagues to study the effects of EGCG on the endocrine systems of rats.
The current study, published in the March issue of Endocrinology, reports that rats injected with EGCG for just a few days experienced significant changes in the blood levels of several hormones, including leptin. "This result was significant because previous research has shown that leptin is involved in controlling the appetite," says Liao, "but the result was very unexpected."
When Liao injected normal rats with EGCG, their leptin levels in the bloodstream went down. This should have caused the rats to eat more. Instead, they ate less.
Next, Liao injected rats whose leptin receptors had been desensitized. These rats were engineered to be immune to changes in leptin concentration. When these leptin- numb rats were injected with EGCG, the results were the same: the rats ate less.
"This reinforced the idea that leptin has nothing to do with the decrease in food intake. We suspect that EGCG may work through other hormonal systems that control appetite and body weight that we don't know about yet," says Liao. "We are currently investigating on a molecular level how EGCG works to suppress appetite."
In addition to decreased food intake and body weight, rats injected with EGCG had lower levels of testosterone (70 percent less in the bloodstream) and insulin. "These results may not have been a direct result of EGCG since food restriction could also cause these hormones to drop," said Liao.
To test whether the EGCG was the direct cause of the hormonal changes, Liao compared the EGCG-injected rats to controls who were fed a restricted diet. These rats showed similar decreases in testosterone and insulin levels, but some hormones changes were seen in the EGCG-injected rats that were not observed in the restricted diet rats.
"This means that some changes are directly due to EGCG," Liao said.
Because of the lower testosterone levels, the researchers also noticed that EGCG injections caused the prostate of healthy rats to decrease in weight. In some rats, the prostate lost 70 percent of its original weight. Lowering the testosterone level may be helpful in preventing the enlargement of prostate and the growth prostate cancer in older people, Liao said.
EGCG was less effective when rats were given the substance orally. "This may be because of poor absorption of EGCG or possibly because of an interaction with food," said Liao. The researchers also found that EGCG reduced abdominal and subcutaneous (just under the skin) fat, and blood levels of lipid, glucose and cholesterol, but did not appear to cause liver damage.
Although oral administration of EGCG was ineffective even after 14 consecutive days of large doses, Liao thinks that long term oral consumption may mimic some of the results obtained with injection.
"A person would have to drink green tea almost constantly to obtain these results," said Liao. "And since some of the hormonal changes we saw in the rats could have negative effects, especially in younger people, I don't recommend drinking large quantities of green tea for everybody. Much more research needs to be done," cautioned Liao.
Other researchers on this study included Yung-hsi Kao, PhD, research associate in the Ben May Institute for Cancer Research, and Richard Hiipakka, PhD, senior research associate in the Ben May Institute for Cancer Research.Reference
The University of Chicago Medical Center
Office of Public Affairs
5841 S. Maryland Avenue, MC6063
Chicago, IL 60637