Health-Supporting Effects of Green Tea – Tea 1

By Jason Fung, MD

Tea is one of the world’s most popular beverages. Tea drinking very likely originated in China and there are various legends surrounding the origins of tea drinking. One legend claims that Shen Nong in 2700 BC set out to find out about the effects of eating various plants, so he tasted over 100 plants in a single day. Luckily he had a transparent stomach so he could directly observe their effects. Tea leaves apparently were able to clear out poisons. Ummm…. yeah. A slightly more believable legend claims that Shen Nong was boiling some water in a pot, when some leaves fell in. After tasting over 100 plants that day, he discovered that tea, while bitter, could make him think quicker and see clearer.

Tea drinking went ‘viral’ and would have broken the internet had the internet only existed in 2700 BC. It spread throughout the world a little more slowly by the various ancient trade routes. Because unprocessed tea is quite bitter, the origins of the word come from ‘tu’ meaning bitter (like bitter melon). In the mid 7th century, a stroke was removed and the word became ‘cha’.  Virtually all the words for tea in all the different languages of the world are variations are either ‘tea’ or ‘cha’. The ancient Chinese Min Nan dialect of the Fujian province used the word ‘te’ so spread via sea trade translated into the English ‘tea’ to as far away as the Maori ‘tii’. The dialects in landlocked regions of China used the word ‘cha’ and spread via the ancient Silk Road led to the Swahili ‘chai’ and as far as the Russian ‘chay’.

Interestingly, much of the early writings about tea touted its health-supporting effects, particularly on digestion, rather than the (bitter, kind of metallic) taste. Tea is the leaf of the plant Camellia sinensis, and is consumed as green, black and oolong. Most of the health-supporting effects are focused on green tea because of the high concentration of polyphenols and a compound compound called catechins, the most abundant of which is epigallocatechin-3-gallate (EGCG). According to traditional Chinese beliefs, tea may help support a healthy body weight . This fascinates me, because our current research may only now be catching up with what those ancient Chinese people knew.

An estimated 2.5 million tons of tea leaves are produced annually, with some 20% becoming green tea. The oldest tea tree in existence is an estimated 3200 years old (pictured here) and lives in the Yunnan province of China where Pu-er tea is believed to have originated. China’s culture, along with tea drinking spread to Korea and Japan by 200AD.

In the 1500s, Portuguese traders brought tea to Europe and by the 1600s it spread to England, who spread their cultural tastes (and their famous stiff upper lip) to much of the rest of the world. The English bought so much tea from China that they developed a huge trade deficit as the Chinese didn’t really want any English stuff, other than their silver.

So, the English introduced opium for the express purpose of creating a nation of addicts, which would happily (for the English) balance their trade deficit. The Chinese government were not nearly as happy about their burgeoning opioid crisis and moved to ban the trade, but in true gangland, drug-pusher style, the English sent in their big gunships to make sure the opium flowed freely. Thus began the two Opium Wars that eventually won England the ports of Hong Kong, Shanghai and others. As if that were not enough, the English then proceeded to smuggle some trees out of China and set up plantations in India to break China’s 4000 year old monopoly. That’s the kind of ruthlessness that wins you a global empire and probably why the English are the bad guys in the movie ‘Pirates of the Caribbean’.

Different teas come from the same tree species but undergo difference processing. Freshly harvested leaves are immediately steamed, rolled and dried. This inactivates the enzymes responsible for breakdown of color so it becomes the stable green tea leaves you can buy anywhere. This also helps preserve the natural polyphenols in the leaves. If the leaves are fermented, they become Oolong tea, and further fermentation produces black tea. The polyphenols and catechins become changed to theaflavins, which may have their own beneficial effects.

Green tea contains much higher concentrations of catechins than black teas, accounting for up to 30% of the dry weight. However, standard brewing methods are insufficient to fully extract them so many studies use catechin enriched green tea extracts to examine their effects. Cold brewed green tea is another potential solution to that problem. These catechins are potent anti-oxidants, which may help support the body’s natural anti-inflammatory mechanisms. In addition, they may also help support healthy brain function, albeit mostly in animal studies.


Two human studies suggested that catechins in green tea may help support a healthy body weight. The first study gave healthy volunteers a beverage containing green tea catechins, caffeine and calcium 3 times per day and compared the 24 hour energy expenditure.

Heart rate and blood pressure did not differ between the groups, so there was no evidence of excessive sympathetic stimulation by the caffeine that could explain the increased energy expenditure.

This echoes the results of an earlier study (Dulloo AG 1999) that found almost identical results, even though this study used half the amount of caffeine, they also showed a similar increase in metabolic rate. NOTE: I am sharing these study results for educational purposes only.

In this study, caffeine given alone did not increase energy expenditure. Most studies support the combination of caffeine and catechins, which is found naturally in green tea, although the concentrations of both are much higher in the extracts compared to brewed tea. The 2011 meta-analysis, comparing all studies on green tea, came to similar conclusions.. Only the catechin-caffeine mixtures increased fat oxidation. It was noted during the Cochrane review that no study supported the use of brewed green tea, compared to the small but consistent effects seen with green tea preparations that contain higher levels of catechins. A potential solution for naturally enriching green tea was discussed in our last post.

In other words, green tea may support healthy body weight. Yes, the effect is not huge, but battles are always won on the margin. Even the most strident critic would be hard pressed to come up with a problem with green tea consumption. Thus the benefit/risk ratio is very heavily in favor of green tea.
So why wouldn’t you use it? I can’t think of a single reason.

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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