Green tea has been consumed, mainly by Asian nations (having originated in China) for hundreds and hundreds of years. Over the course of history numerous and powerful heath effects have been attributed to frequent consumption of green tea.
In the modern day, green tea and green tea based products are major staples of health food and fitness shops with much emphasis placed on it’s ‘fat melting’ properties.
Green tea has also been linked to other extraordinary benefits…
- A cure for various cancers
- Decreases risk of cardiovascular disease
- Improves glycemic control
- Reduces ‘bad’ cholesterol
- A general reduction in risk of death
- Reduces inflammation
- Powerful weight loss aid
These are all extraordinary claims which of course require extraordinary evidence. Luckily a fair amount of research has looked more closely at these proposed benefits…
Is green tea beneficial to health: What does the science say?
I’ve gone through the major ‘health benefits’ of green tea and addressed them below. Where possible I’ve used meta-studies to support my arguments. These are large scale reviews of all the available data on the topic and can provide stronger evidence than individual studies alone.
Cancer: There are a few studies which make suggestive links between consumption of green tea and reduced risk of certain types of cancer in specific populations. A small decrease in esophageal cancer rates amongst the Chinese and slightly lower rates of oral cancers in Asian populations. (1, 2). However it is impossible to control for all variables in these sort of population studies and although overall cancer rates were very slightly lower in green tea drinkers, there are also many many other differences in lifestyle habits that could lead to this outcome. When all current data is taken together, there is no firm, conclusive evidence that green tea consumption prevents or treats cancer (3,4).
Cardiovascular disease: A recent meta-study which compiled a large amount of data on this subject concluded that daily intake of green tea was associated with a roughly 5% chance reduced risk of death from cardiovascular diseases (this includes things like heart attacks and stroke) (5). A well respected Cochrane review also compiled data from numerous randomised trials a few years previously and reported a small reduction in blood pressure associated with tea consumption (6). In fitting with these findings, a number of other studies have suggested green tea consumption may also be associated with a reduced risk of stroke (7).
Blood glucose control: Data here is a little bit messy. Green tea lowered fasting blood glucose in one trial but data generated on fasting insulin levels as well as glycated hemoglobin levels (used to determine longer term average blood glucose) was inconsistent (8,9). Both these references are large scale meta-studies so we can be fairly certain that green tea consumption has no real impact on glycemic control.
Cholesterol: In this area green tea does appear to have some small but clear benefits. Another Cochrane review (can’t get enough) of longer term trials over 3 months in duration, concluded that green tea consumption lowers total blood cholesterol concentrations in the blood including LDL (low density lipoprotein) cholesterol sometimes called ‘bad cholesterol’ (10).
General risk of death: Two separate meta-studies concluded that frequent consumption of green tea resulted in a small reduction in the percentage chance of death from any cause (11,12).
Inflammation: Green tea consumption is not associated with a significantly lower concentration of c-reactive protein in the blood. C-reactive protein is an acute phase protein from the liver that increases in response to macrophage and T cell activation so is used as a marker of inflammation (13).
Green tea and pills containing concentrated green tea extract (catechins being the most important component) are a multi-million dollar market. Although there is some suggestive evidence of small health benefits (see above), green tea is most commonly sold as a weight loss aid.
But does it actually help with weight loss?
Green tea is not a weight loss aid
If you can convince people that your product will help them lose weight then you will make a guaranteed profit. The population is getting fatter and more than ever, people are desperate for a quick fix for weight problems.
As you’ve guessed – there is no magic pill or easy fix for weight loss. It requires a maintained change to your eating and exercise habits.
Green tea is described on lots of product labelling as a ‘metabolic booster’ or ‘fat burner’. The main molecule that is often reported to be the ‘fat burner’ is a catechin called epigallocatechin gallate (EGCG) . So what sort of conclusions are drawn from study’s looking at the ‘fat burning’ properties of green tea?
Important point to bare in mind: Your average cup of green tea contains about 50-60 mg of EGCG
One study from 2009 looked directly at the effects of green tea on body composition, measuring things like intra-abdominal fat, waist circumference and total body fat in control subjects and subjects receiving a varying amount of EGCG and caffeine. The group receiving the highest daily dose of EGCG and caffeine saw a clear reduction in all three measurements (14).
.Sounds great right?
.Well not really.
.This group was receiving 900 mg of EGCG a day as well as 200 mg of caffeine on top.
That’s the equivalent of about 18 cups of green tea and 5 cups of coffee...
Neither of which can be described as ‘healthy’ in the long term.
Another study, published in 2008 approached from a different angle and looked at if green tea could enhance exercise-induced weight loss.
These participants were receiving over 600 mg of EGCG a day. The paper describes a ‘trend towards greater fat mass loss in the catechin group’ which is another way of saying there was no statistically detectable difference between the groups. (15).
What about claims that green tea ‘boost or increases metabolism’?
Short answer: It doesn’t.
A number of studies have shown that green tea consumption has no effect at all on the basal metabolic rate of healthy participants (16, 17). Importantly, these studies were measuring basal or resting metabolism . People peddling ‘fat burning’ green tea supplements want you to believe that green tea will simply burn away the extra calories all while you sit on the sofa. Impossible!
A more recent Cochrane meta-study, taking data from 18 separate studies and involving close to 2000 participants concluded that green tea does lead to small weight loss in obese people. However this is described as ‘non-significant and unlikely to be clinically important’. Additionally, green tea has no effect on weight loss maintenance (18).
All strong evidence that Green Tea or Green Tea Extract products are close to useless when it comes to weight loss.
Take home message
So what have we learned about green tea…
Commonly advertised attributes and the truth side by side:
- A cure for various cancers : No
- Decreases risk of cardiovascular disease: Small reduction
- Improves glycemic control: Currently inconclusive
- Reduces ‘bad’ cholesterol: Small but clear reduction
- A general reduction in risk of death: Potentially true but could be explained by many other variables
- Reduces inflammation: No
- Powerful weight loss aid: No
Although there is some evidence that green tea consumption can have health benefits such as a reduced risk of death from cardiovascular disease and a reduction in cholesterol, relying on supplements for this benefit isn’t necessary. Reducing your intake of trans fats and exercising more will provide you with these benefits plus many more.
In terms of the fat burning potential of green tea, it simply doesn’t exist.
If you enjoy green tea then by all means enjoy a hot brew every now and then. However if you are forcing yourself to drink green tea for the advertised benefits or paying through the nose for green tea extract pills then it’s not worth your time or money.
Thanks for reading,
I recommend using Google Scholar for quick access to these studies.
1) Zheng JS, Yang J, Fu YQ, Huang T, Huang YJ, Li D (January 2013). “Effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer: a systematic review and meta-analysis of observational studies”. Nutr Cancer (Systematic Review and Meta-Analysis). 65 (1): 1–16.
2) Wang W, Yang Y, Zhang W, Wu W (April 2014). “Association of tea consumption and the risk of oral cancer: a meta-analysis”. Oral Oncol (Meta-Analysis). 50 (4): 276–81.
3) Boehm K, Borrelli F, Ernst E, et al. (2009). “Green tea (Camellia sinensis) for the prevention of cancer”. Cochrane Database Syst Rev (Systematic review) (3): CD005004
4) Johnson R, Bryant S, Huntley AL (December 2012). “Green tea and green tea catechin extracts: an overview of the clinical evidence”. Maturitas (Review). 73 (4): 280–7.
5) Tang J, Zheng JS, Fang L, Jin Y, Cai W, Li D (July 2015). “Tea consumption and mortality of all cancers, CVD and all causes: a meta-analysis of eighteen prospective cohort studies”. Br J Nutr (Meta-analysis). 114: 1–11.
6) Zhang C, Qin YY, Wei X, Yu FF, Zhou YH, He J (February 2015). “Tea consumption and risk of cardiovascular outcomes and total mortality: a systematic review and meta-analysis of prospective observational studies”. Eur J Epidemiology(Systematic Review and Meta-Analysis). 30 (2): 103–13.
7) Khalesi S, Sun J, Buys N, Jamshidi A, Nikbakht-Nasrabadi E, Khosravi-Boroujeni H (September 2014). “Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials”. Eur J Nutr (Systematic Review and Meta-Analysis). 53 (6): 1299–1311
8) Liu K, Zhou R, Wang B, Chen K, Shi LY, Zhu JD, Mi MT (August 2013). “Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials”. Am J Clin Nutr (Meta-Analysis). 98 (2): 340–8.
9) Zheng XX, Xu YL, Li SH, Hui R, Wu YJ, Huang XH (April 2013). “Effects of green tea catechins with or without caffeine on glycemic control in adults: a meta-analysis of randomized controlled trials”. Am J Clin Nutr (Meta-Analysis). 97 (4): 750–62.
10) Zheng XX, Xu YL, Li SH, Liu XX, Hui R, Huang XH (August 2011). “Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials”. Am J Clin Nutr (Meta-Analysis). 94 (2): 601–10.
11) Tang J, Zheng JS, Fang L, Jin Y, Cai W, Li D (July 2015). “Tea consumption and mortality of all cancers, CVD and all causes: a meta-analysis of eighteen prospective cohort studies”. Br J Nutr (Meta-analysis). 114: 1–11.
12) Zhang C, Qin YY, Wei X, Yu FF, Zhou YH, He J (February 2015). “Tea consumption and risk of cardiovascular outcomes and total mortality: a systematic review and meta-analysis of prospective observational studies“. Eur J Epidemiology(Systematic Review and Meta-Analysis). 30 (2): 103–13
13) Serban C, Sahebkar A, Antal D, Ursoniu S, Banach M (September 2015). “Effects of supplementation with green tea catechins on plasma C-reactive protein concentrations: A systematic review and meta-analysis of randomized controlled trials”. Nutrition (Systematic review & meta-analysis). 31 (9): 1061–71.
14) Wang et al (August 2009). ”Effects of catechin enriched green tea on body composition” Obesity 18 (4):773-9
15) Maki et al (December 2008) ”Green tea catechin consumption enhances exercise-induced abdominal fat loss in overweight and obese adults” Journal of Nutrition 139(2):264-70.
16) Lonac et al (August 2010) ”Influence of short-term consumption of caffine-free EGCG supplement on resting metabolism and the thermic effect of feeding”. Obesity 19(2):298-304.
17) Gregersen et al (May 2009) ”Effect of moderation intakes of different tea catechins and caffeine on acute measures of energy metabolism under sedentary conditions”. Journal of Nutrition 102(8):1187-94.
18) Jurgens et al (December 2012) ”Green tea for weight loss and weight maintenance in overweight or obese adults”. Cochrane Library