2012年11月8日星期四

Does green tea have caffeine? Seven things you need to know


If you want to completely eliminate caffeine from your diet, you will have to add green tea to your list of forbidden foods. However, if you merely want to reduce your caffeine intake, you may want to substitute green tea for coffee as your morning pick-me-up beverage. Consider these facts about green tea:

1. As long as the number of cups you drink remains the same, replacing your morning coffee with a cup of green tea will reduce your caffeine intake by about 70%. One cup of coffee contains 100-150mg of caffeine; a cup of green tea has only about 25mg of caffeine. However, there are many variables affecting these numbers. For example, the caffeine content of different types of green tea can vary; also a longer brewing period can result in more strongly caffeinated tea.


2. Green tea contains two other stimulants in addition to caffeine. These substances, theobromine and theophylline, may affect heart rate and the central nervous system in a way somewhat similar to caffeine. These substances are also found in chocolate.


3. The combined stimulant effects of caffeine, theobromine and theophylline in green tea may be balanced by another substance in the tea, the amino acid L-Theanine which simultaneously calms the nervous system and enhances concentration abilities.


4.Take some time to consider your reasons for wanting to eliminate caffeine from your diet. If you experience negative effects such as anxiety, irritability or insomnia after drinking coffee, consider whether these might be related to the number of cups you drink per day, the time of day when you consume coffee, and what you add to your coffee to sweeten it. You may want to try cutting down on the number of cups you drink per day, switching to another beverage after early afternoon and/or cutting down on the sugar you add to your coffee. There is increasing evidence that caffeine is not as much of a dietary culprit as experts previously thought. For example, some studies indicate caffeine intake may have a protective effect against Parkinson's disease as well as liver and colorectal cancers.


5. If you feel certain that the caffeine in coffee is having a negative effect on your health, or if your health goals include weight loss or better dental health, you may want to switch from coffee to green tea, either entirely or midway through the day. Green tea boosts metabolism, helping the body burn fat more efficiently. Unlike coffee, which gives people bad breath, green tea has a natural antibiotic effect, killing bacteria in the mouth, which not only combats bad breath but can contribute to better dental check-ups. Also, green tea can help protect against heart disease.


6. As with any foods, careful selection of the most natural product helps you receive more of the potential health benefits. Most prepared teas in cans or bottles are pre-sweetened, often with high fructose corn syrup. Also, Japanese green tea leaves are often treated with fluoride. Try to select tea bags or loose tea leaves which are not chemically treated. How you prepare the tea can also have an effect: many health experts believe boiling water destroys the flavonoids in green tea which give it its healing potency. You may want to heat the water without bringing it to a full boil to preserve the positive effects of green tea.


7. If you want to receive the healing benefits of green tea without any caffeine, you can purchase decaffeinated tea. Green tea which is labeled as "naturally decaffeinated" has been treated with the chemical solvent ethyl acetate. A healthier choice is green tea where the caffeine has been removed through a process of "effervescence" using carbon dioxide (CO2) and water.


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