Green Tea and Weight Loss
What does the research suggest?
If you are one of the people wondering whether green tea boosts your metabolism and is consequently a great drink to add to your everyday menu for weight loss, you are certainly not alone. It is a very popular question these days, and depending on the source of information you consult looking for an answer you may have found anything from glowing reviews “confirming” green tea as a “fat burner”, to other completely conflicting conclusions on the issue.
With all of the hype regarding green tea and its potential as a weight loss tool, I’ve noticed that mainstream news, health, and entertainment magazines frequently seem to indicate or at least strongly suggest that the scientific research clearly confirms green tea promotes weight loss. I wanted to check the scientific literature independently to see if a general consensus has been reached by the scientific research community or not.
Here I will present to you a review of some of the relevant science on this subject, based solely on what I could find when searching the scientific MEDLINE database on PubMed (a large database maintained by the National Library of Medicine). The database accesses over “5600 biomedical journals published in the United States and worldwide” according to their website. I also used Google Scholar to look for additional studies.
It is a bit tricky to summarize results of a number of differing studies, and most people (I think) aren’t that interested in detail beyond the bottom line- does green tea help people lose weight or not? So- for the purposes of keeping this to the point, and not overwhelmingly burdensome and academic to read, I have briefly listed each study evaluated and what the researchers concluded for each study.
To go directly to study results, simply scroll down the page and click on each horizontal bar to open it and see the highlights of each study. At the bottom of this page is a summary of the conclusions.
This is not intended to be an exhaustive evaluation of the current scientific literature, or a replacement for medical advice from your own physician regarding the issue of green tea and weight loss. It is simply meant to be a helpful and informative resource that allows you to be a little more “in the know” when it comes to some of the research and conclusions on green tea as a weight loss tool.
Green Tea and Science
There are thousands of scientific journal articles that describe studies undertaken to evaluate some aspect of green tea and/or green tea supplements and the possible effects they exert on weight loss- and it isn’t possible to look at all of them. In order to broaden my search without having to look individually at thousands of studies, I included journal articles based on one of the two types of studies- either a systematic review or a meta-analysis approach.
Systematic Review
A systematic review is a research study in which multiple, quality studies relevant to a single question (for example, does green tea promote weight loss?) are identified based on specific criteria and then combined and analyzed together. The result is a summarization of results based on high quality evidence.
Meta-Analysis
A meta-analysis is a type of systematic review which allows for an even greater level of objectivity by mathematically (statistically) analyzing the combined results of multiple studies.
Can green tea preparations help with weight loss? Canadian Pharmacists Journal Revue Des Pharmaciens Du Canada, May (2014): 159-60.
Type of study: Cochrane Systematic review, including 14 Randomized controlled trials of at least 12 weeks duration evaluating weight loss as measured by reduction of at least one of the following: weight, body mass index (BMI), waist circumference, or hip to waist ratio.
Who was included in study? Participants were all overweight or obese adults, with a BMI of 25 or more.
What the study measured: Weight loss was measured for the group given green tea preparations, and compared to the control group who did not receive the green tea preparation.
Result: In the 14 controlled trials, those in the green tea group lost an average of 0.4 to 7.7 lb. (0.2-3.5 kg) more than those in the control group over 12 weeks. However, in most studies, the weight loss was not statistically significant (ie- the weight loss could have been attributed to chance and not the green tea).
Thoughts to consider: This study used “green tea preparations” and not cups of green tea. The trials used procedures to extract a higher concentration of active ingredients (catechins and caffeine) that were greater than in a cup of green tea the average person might steep at home. It would be difficult to determine how relevant this study is to an average overweight person who drinks green tea.
Effect of green tea or green tea extract consumption on body weight and body composition; systematic review and meta-analysis, Nutr Hosp 2014 Mar 1;29(3):479-90,
Type of study: systematic review and meta-analysis; all studies included in the analysis were published between 2000-2013
Who was included in study? participants were healthy adult men or women with a BMI of 25-40 kg/m2
What the study measured: the effect of green tea (or green tea extracts) on body weight, body mass index (BMI), fat mass, waist and hip circumference.
Result: No statistically significant effect of green tea on the weight of overweight or obese adults. There is a small effect on a decrease in fat mass but not “clinically relevant”.
Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men, Am J Clin Nutr 2005 Jan;81(1):122-9
Type of study: 12 week double blind study
Who was included in the study? 35 Japanese men divided into 2 groups- one of which ingested one bottle oolong (semi-green) tea per day containing 690 mg catechins (antioxidant flavonoids) and one group ingested a bottle of oolong with only 22 mg catechins.
What did the study measure? The body weight, BMI, waist circumference, and body fat mass of the men in the group given a higher level (690 mg) of tea catechins, compared to the same measurements in the group of men receiving the lower dose (22 mg) of catechins
Result: The men ingesting the higher level of tea catechins had significant decreases in body weight, BMI, waist circumference, and body fat mass.
Thoughts to consider: This is a small study including only Japanese men. Also, a typical brewed green tea beverage (about 8.5 oz or 250 ml) contains 50-100 mg catechins, so this is equivalent to the higher catechin dose group drinking about 6-7 cups of regular green tea, and the lower dose group dose would be equivalent to about a half cup of regular green tea.
The effects of green tea on weight loss and weight maintenance; a meta-analysis; International Journal of Obesity (2009)33,956-961
Type of study: meta-analysis
What did the study evaluate? does green tea (which contains an epigallocatechin gallate (EGCG)-caffeine mixture) have a function in body weight regulation?
Result: catechins in green tea were associated with significant decrease in body weight and a significant association with maintenance of body weight after a period of weight loss.
Thoughts to consider: Dosage of catechins did not have any significant effect on the size of the weight loss effect so based on this study one could suggest that all other things being equal, any consumption of green tea catechins might have a positive effect on weight loss. This is in contrast to the previously listed study where the Japanese men given the higher catechin dose had a greater decrease in body weight than the men at the lower dose. There are many possibilities of causes of the variation in the two studies.
Therapeutic Effect of high dose green tea extract on weight reduction: a randomized, double-blind, placebo controlled clinical trial; Clin nutr 2015 May 29, doi: 10.1016/j.clnu.2015.05.003.
Type of study: randomized, double blind, placebo clinical trial
Who was included in the study? 115 women with central obesity
What did the study evaluate? Is a high dose of a green tea extract (EGCG) at 856.8 mg per day safe and does it affect weight reduction and obesity related hormone profiles
Results: significant weight loss and decrease in BMI and waist circumference after 12 weeks of high dose EGCG treatment (856.8 mg per day). No side effects or adverse events occurred during the study.
Thoughts to consider: The study was limited to 115 obese women with no information on weight maintenance or follow up after the 12 week study. Also, it would be difficult to consume enough regular green tea daily to reach the same dose of epigallocatechin-3-gallate (EGCG) given to the study participants.
Efficacy of green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans; Am J Clin Nutr, 1999 Dec;70(6):1040-5
Type of study: 24-hr energy expenditure (EE), respiratory quotient (RQ) and urinary excretion of nitrogen and catecholamines were measured in a respiratory chamber
Who was included in the study? 10 healthy men who were given either green tea extract (50 mg caffeine and 90 mg EGCG), caffeine (50 mg), or a placebo, which they then ingested 3 times daily (breakfast, lunch, and dinner).
What did the study measure? Various measurements were taken and compared between groups to determine if the green tea extract which contains both caffeine and catechin polyphenols could increase fat oxidation (24hr energy expenditure(EE) or “fat burning”) in people.
Result: The group receiving the green tea extract had a significant increase in 24-h EE (energy expenditure compared to the other groups leading to the conclusion by researchers that green tea has “fat burning” capability that exceeds what could be explained by the amount of caffeine alone.
Thoughts to consider: This is a very small study including only 10 healthy, non-obese men.
Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin, and green tea; Am Journal of Physiology- Regulatory, Integratvive and Comparative Physiology Jan 2007 Vol 292 no1, R77-85
Type of study: A scientific review which examines the studies of thermogenic (fat burning/metabolism increasing) properties of green tea (as well as other supplements) in relation to regulation of body weight.
Result of review: There is evidence to show that green tea extract can increase the energy expenditure (EE) and fat oxidation in short term studies, and that the fat burning capability of green tea is above and beyond that of caffeine alone. Lab animal studies have shown that one of the primary and most active catechins in green tea (epigallocatechin 3-gallate, EGCG) can induce a reduction in food consumption and/or an increased metabolic (energy expenditure) rate. Some studies carried out over a 3 month (or longer) period of time show that consuming tea catechins is associated with a significant decrease in body weight and body fat. There is also some evidence to suggest that EGCG can play a role in obesity prevention.
Catechin- and caffeine-rich teas for control of body weight in humans; 2013 Am Society for nutrition(2013): 98(6 Suppl):1682S-1693S.
Type of study: meta-analysis and evaluation of interventional and observational studies to give detailed review of evidence of tea and its effect on body weight
Results: Catechin and caffeine rich teas (CCRTs) in most of the studies in this assessment showed a positive improvement in body weight, BMI, fat mass, and waist:hip ratio.
Thoughts to consider: The effects of green tea catechins on weight loss and other weight variables (BMI, etc.) are variable in effect depending on other factors such as habitual caffeine intake, ethnicity, genetics, etc. and as a result effects are not always present in every situation.
References
Baladia E., Basulto J., Manera M., Martínez R., Calbet, D. “Effect of green tea or green tea extract consumption on body weight and body composition; systematic review and meta-analysis.” Nutr Hosp (2014): 479-90.
Chen IJ, Liu CY, Chiu JP, Hsu CH. “Therapeutic effect of high dose green tea extract on weight reduction; a randomized, double-blind, placebo controlled clinical trial.” Clin Nutr (2015).
Diepvens K, Westerterp KR, Westerterp-Plantenga MS. “Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin, and green tea.” Am Journal of Physiology-Regulatory, Integrative and Comparative Physiology (2007): 77-85.
Dulloo AG, Duret C, Rohrer D, Girardier L, Mensi N, Fathi M, Chantre P, Vandermander J. “Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans.” Am J Clin Nutr (1999): 1040-5.
Hursel R, Viechtbauer W, Westerterp-Plantenga MS. “The effects of green tea on weight loss and weight maintenance; a meta-analysis.” International Journal of Obesity (2009): 956-961.
Hursel R, Westerterp-Plantenga MS. “Catechin- and caffeine-rich teas for control of body weight in humans.” Am Society for Nutrition (2013): 98(6 Suppl):1682S-1693S.
Nagao T1, Komine Y, Soga S, Meguro S, Hase T, Tanaka Y, Tokimitsu I. “Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men.” Am J Clin Nutr (2005): 122-9.
Tannis Jurgens, BSc(Pharm), MSc, PhDcorresponding author and Anne Marie Whelan, BSc(Pharm), PharmD, FCSHP. “Can green tea preparations help with weight loss?” Canadian Pharamacists Journal/Revue des Pharmaciens du Canada (2014): 159-60.
The bottom line
While the analysis and results of some of the available and reasonably current scientific literature on the subject of green tea and weight loss suggests there is a possible link between green tea consumption and weight loss, it does not seem strong enough to make definitive, broad based conclusions on the subject for any particular group of people.
What the National Institute of Health says
It seems (at least based on this sample of the scientific literature) that the current thinking is in agreement with what the NIH (National Institute of Health) website indicates in their “Natural Medicines Comprehensive Database”: Insufficient evidence to rate effectiveness (of green tea) for obesity.
A Ray of Hope
There are so many variables to try to control (ethnicity, current weight, genetics, habitual caffeine intake, etc.) and account for when trying to chase down specific cause and effect relationships, so research can take years to identify definitive and reproducible results. Having said that, there ARE studies linking weight loss to green tea consumption. It may work for you! But regardless of whether the catechins and other natural components of green tea induce weight loss or not, the simple fact that green tea (without sugar or other additives) is a low calorie drink means it can still be a part of any weight loss program- it is certainly more healthy and has lower calories than soft drinks, alcohol, juice drinks, or any other number of beverages. So hopefully you will still give it a try and find some varieties of green tea that you enjoy!
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