What is Green Tea?
Although tea is consumed worldwide, it is only grown in about 30 countries. All tea comes from the same plant, known as camellia Sinensis, which is an evergreen related to the magnolia. Depending upon how the leaves are processed, the leaves can become green tea, black tea, or oolong tea.
The taste of the tea can also differ depending upon the conditions and country in which the plant is grown. Green tea is the least processed of these teas; therefore, it retains most of the active compounds that provide its numerous health benefits.
These compounds are known as catechins, and they are strong antioxidants (scavage free radicals). Although there are several types of catechins within green tea, the most notable, researched, and probably the most powerful of these is epigallocatechin gallate (EGCG).
What are the possible uses or claims of Green Tea?
Most of the claims of green tea include weight management & thermogenic properties, reduced risk of cancer, cholesterol level management, hypertension, and coronary artery disease.
Free radicals are substances in the body that are produced as a byproduct of some metabolic processes. Free radicals are highly reactive, and therefore, they can damage molecules in the body by reacting with them. Excessive production of free radicals has been associated with the development of cardiovascular diseases, neurodegenerative disorders, and cancer.
Antioxidants are highly attracted to free radicals, and therefore, they can easily scavenge them to prevent them from reacting in a destructive manner. The fact that green tea contains some strong antioxidants (catechins, mainly EGCG) is one of the main reasons why it provides so many health benefits.
Weight Management & Thermogenic Properties
The management of weight is, in a large part, a function of how many calories one burns per day. Each person burns a certain amount of calories per day; this is known as Total Daily Energy Expenditure (TDEE). When one eats more than their TDEE, one will gain weight (this weight can be muscle or fat – although preferably muscle). When one eats less than their TDEE, one will lose weight (this weight can once again be muscle or fat – although preferably fat).
In addition to manipulating how much one eats per day to determine whether or not they will gain or lose weight, one can also influence their TDEE. The TDEE can be changed by things such as exercise, daily level of activity, frequency of meals, and stimulants (like caffeine).
One of the main components of green tea is caffeine; therefore, ingesting green tea will cause the TDEE to rise and make it more likely for there to be a caloric deficit, (side note: caloric deficits should not exceed about 20% of normal TDEE, otherwise, the metabolism will crash – that’s the topic for something else) therefore, causing weight loss to occur.
Caffeine mostly forms the basis for green tea’s weight management properties. In one study, green tea caused the TDEE to rise by about 180 calories.
There is more or less conflicting evidence as to whether or not there are additional components of green tea that stimulate the metabolism even further. In one study, it was theorized that EGCG could cause an additional increase in TDEE: Non-placebo groups were given 200mg of caffeine and variable doses of EGCG (90, 200, 300, 400) three times per day.
The caloric expenditure of tested groups increased by about 180 calories per day; however, this number did not change when the amount of EGCG given changed. Therefore, the increase in caloric expenditure is dependant upon the caffeine given to subjects.
In a study done by Dulloo and other authors, the researchers concluded that “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 (relating to the nervous system) activation of thermogenesis, fat oxidation, or both”.
Green Tea & Cancer
According to Lin and other authors, “excessive production of ROS (free radicals) has been implicated for the development of cardiovascular diseases, neurodegenerative disorders, and cancer”.
Therefore, it would make sense that antioxidants, which green tea is rich in, may lower the risk of cancer. In several analyses (more than are cited here), the authors have come to a conclusion that agrees with the fact that free radicals can cause damage to the body.
In their analysis of ovarian cancer risk, Larson and Wolk concluded, “These results suggest that tea consumption is associated with a reduced risk of epithelial ovarian cancer in a dose-response manner”. In an analysis of the relationship between breast cancer and green tea, Sun and other authors concluded, “The results of this meta-analysis indicate a lower risk for breast cancer with green tea consumption”.
Not many clinical trials involving humans have been done in regards to green tea’s effect on cancer, but one study using rats investigates green tea’s effect on breast cancer. Authors injected the mammary glands of female rats with DMBA to induce tumors. The tested rats were then placed on a diet containing 1%, 0.1%, or 0.01% green tea catechins for 35 weeks.
The authors concluded that the rats treated with green tea catechins had significantly smaller multiplicities of tumors compared to the control rats. However, they also concluded that “the effect is weak and not dose-dependent.” Unlike the meta-analyses, this study actually gauged the degree of effectiveness of green tea on breast cancer and revealed that its effect may be “weak”.
Green Tea and Cholesterol
There have been several studies involving the effects of green tea on cholesterol. Many have been done on rats, but a few have been done on humans. In a study done on humans by Erba and other authors, a group of healthy volunteers were split into two groups.
One group consumed green tea with a controlled diet and another group did not consume green tea but had a controlled diet (control group). The group consuming green tea had a moderate reduction in LDL cholesterol (from 119.9 to 106.6 mg/dL).
In a rat study done by Muramatsu and other authors, rats were fed a diet consisting of 15% lard and 1% cholesterol. “The liver weight, liver total lipids and cholesterol concentrations in rats fed the lard-cholesterol diet increased more than in the control rats, but the addition of tea catechins to the lard-cholesterol diet decreased those parameters.
” In other words, the addition of green tea decreased cholesterol in rats whose diets previously caused them to have a bad level of cholesterol.
In another rat study done by Yang and other authors, diet-induced hypercholesterolemic (the rats got high cholesterol because the authors modified their diet to do so) rats were administered Lung Chen Tea (a Chinese green tea).
The authors then monitored fecal bile acids and cholesterol excretions in these rats, which significantly increased. The authors concluded that Lung Chen Tea lowers cholesterol through these mechanisms (fecal bile acids and cholesterol excretion), but warranted that the exact way in which the tea accomplishes this needs to be further investigated.
Green Tea and Hypertension
Green Tea also may have positive effects on hypertension: In one analysis, in the Chinese population, drinking 120ml per day or more of moderate strength green tea or oolong tea significantly reduces the risk of developing hypertension.
In a rat study, the authors concluded that “both black and green tea polyphenols attenuate blood pressure increases through their antioxidant properties in SHRSP (rats)”.
Green Tea and Coronary Artery Disease
Green tea may also be beneficial for coronary artery disease. In one analysis, the authors assessed 203 patients for relationships between coronary artery disease and green tea. The authors concluded that green tea consumption is associated with a lower incidence of coronary artery disease.
Are there any Side Effects to Green Tea?
Green tea has been consumed for centuries around the world, one can draw their own conclusions from that. However, one may want to be aware of the caffeine content of green tea, because consuming too much caffeine can cause restlessness, insomnia, tachycardia, and (at extremely high doses) even death. Green tea contains about 24 mg of caffeine per 12 ounces.
What is the Proper Dosage of Green Tea?
Most of the research that has been done on green tea has used the amount that is usually consumed in the countries of Asia, which is about 3 cups. Supplementwatch.com recommends that typical dosage is “125-500mg/day – preferably of an extract standardized to at least 60% polyphenols and/or EGCG as a marker compound”.
Green tea shows possible benefits for weight management, cancer, cholesterol, and hypertension. However, many of the studies done with green tea involve rats or analyses of a population instead of direct studies involving humans. Even so, green tea is a cheap supplement (or simply a tea) with little risk of negative side effects in reasonable portions.