An animal study published in 2009 in “Phytomedicine” found that green rooibos tea helped regulate glucose metabolism, preventing increases in fasting blood glucose levels during the course of the five-week study. This effect is a result of aspalathin, a compound found in green rooibos. Poor glucose tolerance and high fasting glucose levels are signs of type-2 diabetes and are common in obesity. The study suggests rooibos tea may help keep blood glucose levels in check, preventing sharp spikes and falls that can trigger symptoms of hunger and possibly leading to lower calorie consumption.

Generally, lower-quality green teas are steeped hotter and longer while higher-quality teas are steeped cooler and shorter, but usually multiple times (2-3 typically). Higher-quality teas like gyokuro use more tea leaves and are steeped multiple times for short durations. Steeping too hot or too long results in the release of excessive amounts of tannins, leading to a bitter, astringent brew, regardless of initial quality. The brew’s taste is also affected by the steeping technique; two important ones are to warm the steeping container beforehand to prevent the tea from immediately cooling down, and to leave the tea leaf in the pot and gradually add more hot water during consumption.[citation needed] 

Green tea, however, is considered to have originated in China. It is said that even today the word “tea” in China refers only to green tea, not to the general category of tea as it does in the West. China’s Yunnan province is considered to be the original home of the Camellia sinensis plant species. In fact, 260 of the world’s 380+ varieties of tea can be found in Yunnan.
Day 28: Honesty time — I took several days off. I went away for the long weekend, and I overindulged in Mexican food, wine tastings, and cherry ice cream. When I got home, I was nursing an exhausted body and a bad case of bloat. The solution? To drink my final cup of tea. After drinking it, I went to bed feeling refreshed and lighter, then woke up the next morning ready for a workout and a day back at work.
Green tea also seems to boost physical performance, increase exercise endurance, and decrease reaction time, and there are many, many such studies showing these effects from caffeine, although other ingredients in green tea may aid this effect. Caffeine, and green tea’s, ability to mobilize fatty acids in fat tissue to make them more easily available for use as energy also seems to aid physical performance. In one study, caffeine was shown to significantly increase physical performance (exercise endurance and exertion). The antioxidants in green tea may also help prevent tissue damage during physical exertion as well.
“Red tea” is the name the Chinese use for what we in the west call “black tea.” All true tea comes from the same plant, Camellia sinensis. The differences between types of tea result from different methods of processing the leaves. For green tea, the tea leaves are steamed, rolled and dried, a method that preserves the content of polyphenols, antioxidant compounds that confer the well-known health benefits of tea. For black tea, the leaves undergo a process of oxidation that changes the color and flavor and reduces the content of polyphenols. Oolong is intermediate between green and black tea – in color, flavor and polyphenol content.
Unbeknownst to many, green tea actually comes from the same plant from where normal tea is obtained. Scientifically, it is known as Camellia sinensis. In fact, it is the same tea but it is processed differently. The normal black tea is obtained by fermenting the tea leaves. This fermentation changes its color and flavor while raising the level of caffeine and tannin in it. On the other hand, in the case of green tea, the tea leaves are dried or slightly steamed but not fermented. This is what makes it look green when it’s brewed.

Green tea contains significant amounts of flavonoids, antioxidants that protect against heart disease by slowing the breakdown of LDL cholesterol, preventing blood clots, and improving blood vessel function. The benefits of green tea also include associations with lower cholesterol and lower rates of artery blockages. People who drink a cup or two a day have a 46 percent lower risk of developing narrowed arteries. Upping that to three cups a day lowers the risk of having a heart attack by 43 percent and of dying from a heart attack by 70 percent. It can even help prevent a second heart attack. In a study of 1,900 patients recovering from heart attacks at Beth Israel Deaconess Medical Center in Boston, the death rate among patients who drank at least two cups of tea a day was 44 percent lower than among non-tea drinkers.
In January 2015, we wrote about the rapid rise of matcha on the American beverage landscape and posed the question, “Have we reached maximum matcha saturation?” Three years later, we're living amid matcha croissants, matcha custard pie, matcha face masks, matcha lifestyle guides and $50 cups of matcha itself. Clearly, the answer was "No." But what is this powder we're whisking into green lattes, baking into doughnuts, blending into smoothies, and adding to our fish fillets?
Dulloo, Abdul G., Claudette Duret, Dorothée Rohrer, Lucien Girardier, Nouri Mensi, Marc Fathi, Philippe Chantre, and Jacques Vandermander. “Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans.” The American journal of clinical nutrition 70, no. 6 (1999): 1040-1045.
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Matcha, like other green teas, contains a class of antioxidants called catechins. Matcha is high in a catechin called EGCG (epigallocatechin gallate), which is believed to have cancer-fighting effects on the body. Studies have linked green tea to a variety of health benefits, like helping to prevent heart disease, type 2 diabetes and cancer, and even encouraging weight loss. However, it’s important to note that much of this research isn’t from clinical trials that show green tea causes a benefit. Instead, it’s largely from population-based studies, where researchers look at groups of people who drink green tea and compare their health outcomes to groups that don’t drink it. Studies have shown associations between tea and better health, but causation is not yet proven. Matcha is even less studied than brewed green tea.
The polyphenols in green tea, especially EGCG, have been shown to have a particularly powerful effect in supporting skin cells and cellular DNA in the presence of UV radiation from sunlight. May different clinical studies have shown EGCG to help skin defend against UVA and UVB rays. And because these polyphenols can accumulate in the skin, regularly drinking green tea or taking a green tea supplement with EGCG can act as all-day supplemental protection.

Heat or boil water, but don’t let it completely boil and become too hot, as this can destroy some of the delicate compounds found in green tea leaves. The “ideal” temperature for brewing green tea is between 160 degrees Fahrenheit to 180 degrees F (traditionally standard Chinese green teas brew at a slightly higher temperatures). Pour hot water into the teapot to steep the leaves for only about 1–3 minutes. Larger leaves need more time to steep than finer, smaller leaves. At this point you can also add any fresh herbs you plan on steeping.
Scientists have also discovered that the antioxidants flavonoids may also protect the brain from oxidative stress. The scientists extrapolated that a human would need to drink about three liters of liquid infused with 0.5 percent of the catechins to get similar effects. However, because humans ingest other antioxidants in the form of vitamins and plant polyphenols, it’s likely that a much lower quantity could be effective in protecting memory.

Most detox teas contain caffeine, probably because this stimulant may suppress appetite, trigger your digestive system to let go of waste, and help you shed water weight. A caffeine-induced energy boost may also lead to working out a little longer or harder than usual. However, too much caffeine can also be risky (see above) and interfere with getting enough sleep–and catching too few zzzs may ultimately undo the tea's weight-loss effects. In fact, too little shuteye has been shown to trigger excessive eating and weight gain and even slow metabolism, which can make it easier to gain weight even if you don't eat extra calories. A good rule of thumb, regardless of where your caffeine is coming from, is to nix it at least six hours before bed. And if you're trying to shed pounds, commit to making adequate sleep a top priority.