Green tea: benefits (what is a fact and what is a myth?)
Green tea has been brewed in China and Japan for over a thousand years, where it is prized for its natural, refreshing taste and supposed healing qualities. But here in the west, we’re a little late to the tea party, and it’s only been in the last few decades that we have started discovering the benefits of green tea for ourselves. But just what are those benefits? There have been a bewildering number of health claims, for everything from cancer to weight loss, and sometimes it’s difficult to know what to believe.
So is green tea really good for you? Most health claims concern certain plant compounds called catechins, which are present in all types of tea, but tend to be destroyed when the leaves are processed. Green tea, which undergoes the least processing, contains a greater concentration of catechins. Catechins are antioxidants, which means they bind to harmful free-radicals and neutralise them, preventing the inflammation and cell damage thought to contribute to various illnesses.
Scientists have been keen to test whether the cell-protecting catechins in green tea can help prevent disease, and there have been several studies comparing green tea drinkers to non green tea drinkers, but so far results have been mixed. Some studies show that people who drink green tea are less likely to contract certain types of cancer, including breast cancer and prostate cancer, but others show little or no difference, so we need more evidence to be sure. It is also important to be aware that any results we do have are about preventing cancer in the first place, rather than curing it, and results tend to be more successful in people who don’t already have a history of cancer.
Studies have also shown that green tea may lower LDL, or ‘bad’ cholesterol, and protect existing LDL particles from oxidation. This could lower the risk of various cardiovascular diseases, as oxidised LDL particles can cling to artery walls, causing high blood pressure, and can also cause blood clots that may lead to strokes or heart attacks. There is even some suggestion that green tea can reduce the risk of dementia, as it protects the blood vessels and neurons in the brain from damage. But here again, the evidence is mixed. Some studies suggest that green tea promotes healthy blood vessels, while others show no link at all.
Another major health claim is that green tea may improve insulin sensitivity and reduce blood sugar levels, helping to prevent type 2 diabetes. As with cancer, though, any evidence is for prevention rather than cure. There is no evidence that green tea can help to control blood sugar in people who already have diabetes.
As for weight loss, there have been a few studies showing a slight increase in metabolism, which in turn makes the body burn fat more quickly. These studies have led to an explosion of dieting products containing green tea, but unfortunately, most studies since have been unable to replicate the results. The good news is that green tea is relatively low in calories, so if you use it to replace high-sugar carbonated drinks, it can help with weight loss that way.
Overall, it seems that green tea may be useful for preventing a number of illnesses, but we need more evidence to be sure. If green tea does have health benefits, they are likely as prevention rather than cure, and there will be other factors, such as lifestyle and genetics, that determine how likely a person is to contract any disease. The effects of green tea often seem to be mild, and it should not be used as a replacement for conventional medicine. As always, you should consult a medical professional about any health concerns.
It is also worth noting that the amount of tea required varies widely between studies, from two to ten cups a day, and there can be negative effects to drinking too much green tea. Like all tea, green tea contains tannins, which can cause various side effects if consumed in high quantities, or by people with certain conditions. Tannins can lower levels of iron and folic acid in the body, making them unsuitable for pregnant women or people with iron deficiencies, and they can increase stomach acid, causing upset stomach, acid reflux and nausea. Green tea’s antioxidant properties can cause problems for some, too. It’s apparent ability to prevent blood clots can lead to over-thinning of the blood, meaning it is not recommended for people on blood-thinning medication, or those with bleeding disorders.
Green tea: is there caffeine in it?
Green tea does contain some caffeine, which is another reason to drink in moderation. Caffeine can make certain conditions worse, such as anxiety or migraines, and should also be avoided if breastfeeding. If consumed in high quantities, or by people with caffeine sensitivity, it may cause stomach problems, headaches, dizziness, trouble sleeping and in some rare cases, liver damage.
That said, most green tea contains less caffeine than the average cup of coffee, and is unlikely to cause issues if you drink a sensible amount. Experts recommend drinking no more than 4 or 5 cups a day, and you should also check the ingredients of any green tea powders or supplements, which may be highly concentrated.
Green tea also contains the amino acid L-theanine, which has anti-anxiety effects. If consumed in small quantities, it has been suggested that the combination of caffeine and L-theanine may help to stimulate brain activity without the jitteriness of high-caffeine drinks like coffee.
Different types of green tea
All green tea is made from the leaves of the Camellia sinensis plant, but there are different ways of growing and processing the leaves, which lead to different varieties with subtly different flavours.
Sencha is a Japanese green tea, made by infusing whole leaves in water. It is the most popular type of green tea in Japan, accounting for 80% of the green tea produced. Sencha has been a part of Japanese culture for hundreds of years, with entire rooms and buildings dedicated to the traditional art of Senchadō, which encompasses brewing, serving and drinking rituals.
Gyokuro, which translates as ‘jewel dew’ or ‘jade dew’ in the original Japanese, is one of the most expensive types of green tea. Unlike sencha, gyokuro is grown in the shade, increasing the concentration of theanine and caffeine and yielding a sweeter flavour. Gyokuro should be steeped at a lower temperature than other teas to preserve its distinctive sweetness.
Like gyokuro, tencha tea is grown in the shade for a sweeter flavour, but while gyokuro leaves are rolled to prepare them for steeping, tencha leaves are not. Tencha tea can be steeped, but is more often used in cooking or ground into matcha powder.
Matcha is a green tea powder made from ground tencha leaves, with the same high theanine and caffeine content as gyokuro and tencha, and the same distinctive sweet taste. It is prepared as hot tea in traditional Japanese tea ceremonies, but it’s concentrated green tea flavour and powdered form make it the perfect ingredient for a variety of recipes. Matcha is surprisingly versatile, and can be used in traditional Asian recipes like Japanese mochi cakes, or for a sophisticated twist on western classics, like a refreshing green tea ice cream or a mild and creamy green tea latte.
Funmatsucha is another powdered tea, made from ground sencha leaves. Sencha leaves are not sheltered from the sun, so funmatsucha has a bitter, but still pleasant taste. It is also more affordable than matcha powder, as it is easier to grow, making it an ideal substitute if you’re on a budget.