Truth or myth: Green tea and weight loss

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.

Bancha - Green TeaA 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.

Japanese Green Teas

I decided yesterday to taste two Japanese green teas together so I could compare them side by side. The first tea, a Sencha, is the most common type of Japanese Green Tea and would be drank on a daily basis in most Japanese homes.  Sencha is harvested in the Spring from the upper leaves of the tea plant that have been in direct sunlight.

The second tea, a Bancha, is also a common every-day tea in Japanese homes. It is made from later harvests of the tea plant or from the lower leaves and stems. It is therefore a coarser tea and it is considered to be a lower quality and less expensive tea than Sencha.

Although Sencha means roasted tea, both Sencha and Bancha are steamed and rolled soon after harvesting. The difference between the two teas is the quality of the leaves used. Where Bancha has come from lower, older leaves it will have less caffeine and less catechin (antioxidant) than sencha. However, where Bancha has come from a later harvest of upper leaves, it could have more catechins. Below is a short video from My Japanese Green Tea of the steaming, drying and rolling process at a Sencha plant

Sencha is considered a fussy tea in terms of preparation. While Bancha is can be prepared with boiling water for 30 seconds, boiling water on Sencha will bring out the bitterness and kill the flavor so Sencha needs a water temperature of ~80°C and a longer brewing time. For my comparison experiment, I decided to brew them both at 80°C for 2 minutes. If you don’t have a thermometer or a thermostatic kettle (I used my new Breville!), you can guess 80°C by waiting for small bubbles to appear on the inside of the kettle.  The bubbles need to be the size of shrimp’s eyes as opposed to crab eyes (85°C) or fish eyes (90°C)!

Looking at the dry leaf, both are flat leaf, emerald green. From the pictures below you can see that the Bancha includes stems. It probably isn’t obvious from the photos but it is clear when you have the leaves in front of you that the Bancha is also less regular and is more dusty. The Sencha has a deep musky aroma with some sweetness while the Bancha is more grassy with a malty sweetness.

Bancha leaves

Bancha leaves

Sencha Leaves

Sencha Leaves

To prepare these teas, I put 3g of tea in a warmed ceramic teapot and add 150ml of water at ~80°C. I steep for 2 minutes. Both give a yellow/green liquor and both are cloudy but the Bancha is noticeably more cloudy. The taste of the Sencha is bright and grassy with a background meaty taste (unami). There is a sweetness at the start that is matched by a bitterness and astringency that comes out later. The Bancha is grassy and malty sweet with less of the meaty flavor and noticeably less astringency. Both are light and refreshing but I would describe the Bancha as milder, gentler green tea.

I combined each with a small pinch of salt beforehand to see how it brings out the sweetness. For the Sencha it mutes the astringency and gives a rounder flavor but I didn’t notice a big difference with the Bancha. Both of these were samples so I don’t know the price but one of my local tea houses has a Sencha for €11/100g and a Bancha for half of that (€5/100g).