Well it’s that time of year again when tea is peddled as a weight-loss product. Green tea is often the focus of this attention but a Cochrane review was published in December 2012. This work reviewed all the published experiments that had been done on green tea for overweight or obese adults. The conclusion was that “green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults”. The study also concluded that “green tea had no significant effect on the maintenance of weight loss”.
The full text of the review is available here and it is worth downloading for the appendices alone. The rationale for the systematic review was to provide healthcare providers and consumers with reliable information on the impact of green tea in weight loss and weight maintenance. The authors only looked at randomised controlled trials (the most thorough of investigations). The studies were all at least 12 weeks in duration and compared green tea preparations with a control in overweight or obese adults who had no other health problems.
A search was done across a very wide range of databases (MEDLINE, CINAHL, AMED etc) for studies that investigated weight-gain and green tea in humans. The search was not limited by language and around 919 studies were found. 72 of those were relevant and 18 met the criteria of this review (randomised control trial with just green tea, greater than 12 weeks, on participants who were overweight but had no other significant illness) . In total 2,076 people participated in these 18 studies (ranging from 19 to 270 for each). Half of the studies took place in Japan with the other 9 conducted in Netherlands, Australia, China, Taiwan, Thailand and the US.
Higher weight losses were reported in the Japanese studies with eight studies reporting weight losses that ranged from -3.5kg to -0.2kg but overall, the author concluded that green tea produced a “very small, statistically non-significant loss of weight, decrease in BMI, and decrease in waist circumference” compared to those who did not have the green tea. The role of caffeine is not clear but there are some indications that the catechins in green tea, and not caffeine, may have been responsible for the “modest effect on weight loss”.
It’s not very encouraging for people who have started drinking green tea to help with weight reduction but swapping a double-mocha for a green tea would obviously be a different story. And green tea does bring other health benefits so as the author says “even though the changes may be small, any small loss combined with minimal adverse effects may have an overall positive impact on an individual attempting to lose weight”.
Jurgens TM, Whelan AM, Killian L, Doucette S, Kirk S, Foy E. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database of Systematic Reviews. 2012 Dec 12.