Green Tea – Weight Loss Supplement?

Is green tea a weight loss supplement?  A surprising number of studies suggest that there is evidence to believe this to be the case.

First off, a couple of side notes.  Green tea has a huge number of health benefits far beyond mere weight loss, from antioxidant and anti-cancer properties to helping you keep your teeth.  I’ve discussed a few of them on this site in the past.  So I consider it a good addition to your health routine irregardless of any weight loss effects.  However, I also feel the need to point out that no weight loss supplement ever invented will beat good old fashioned diet and exercise habits for turning your bulging belly into a flat one.

At best…. at BEST… you can hope for a supplement to enhance your diet and exercise changes by MAYBE 10%.  If you’re trying to get more than that out of a supplement, you’re probably doing a mildly glorified version of smoking crystal meth.

In case you’re wondering, I do not advise smoking crystal meth for weight loss, or any other reason, really.

Okay, back to green tea and weight loss. A recent meta-analysis out of the University of Connecticut suggests that green tea catechins (these are the antioxidants in green tea) can indeed help with weight loss, but only if there’s caffeine involved.

First off, for those of you unfamiliar with the term “meta-analysis“, that just refers to taking a whole bunch of studies and sort of summing up their results into one bigger group study.  The researchers don’t actually perform a scientific study of their own; they just borrow other people’s data.

They’re nice because you get to pool data into a much larger pile than one study alone can hope to do.  And, they’re cheap and relatively easy, because hey, somebody else did all the hard work of finding subjects and measuring them and poking them with a pointy stick (okay, not that last one).

The bad news is, they are really, really vulnerable to researcher bias, in that if I’m a researcher and I really, really feel strongly that green tea is a super-fantastic weight loss supplement, I might (consciously or subsconsciously) only select those studies which will support my opinion.  This happens a lot more than you might think, so be aware of this particular limitation.

The Green Tea Weight Loss Meta-Study

In this case, the researchers found 15 studies that compared the use of green tea catechins with caffeiene to the use of the same green tea stuff without caffeine.  Added together, this provided a total of over 1,200 subjects, and when it comes to scientific analysis, more subjects is more better-er, as my Pappy used to say (not really).

What they found, was that you pretty much had to have green tea plus caffeine in order to see any effect.  Green tea catechins alone didn’t seem to do much, and while caffeiene had some effect, it worked far better if you had green tea added in.  The effects were measurable for body weight, BMI (body mass index), and waist circumference.

Here’s the bad news.  When you read the fine print, this study doesn’t seem quite as strong.  Not every study measured the same things.  The dosages varied (of green tea as well as caffeine), as did the length of time the subjects were followed.  Basically, this was a real patchwork quilt of studies that didn’t seem to fit well together into a meta-analysis.

Still, it gives a crude indication that there’s probably something going on in the whole green tea- weight loss arena.  So let’s look at some more evidence.

The Green Tea Air Chamber Study

One study measured acutal energy expenditure in ten subjects with either placebo, caffeiene, or green tea extract (with caffeine).  Each subject was tested on three seperate occasions under three different conditions.  The researchers found a 4% increase in energy expenditure in the green tea group.

How did they measure energy expenditure, you ask?  By sealing the subjects in a “respiratory chamber” for 24 hrs and measuring the changes in oxygen and cardon dioxide levels, and then using a fancy-schmancy equation to indirectly guess at how much energy the subjects were burning off.  Frankly, I’m not very familiar with that technique, so I can’t tell you how accurate it is or isn’t.

If we take it as a given that this technique is accurate for estimating energy expenditure, this is a nifty study, but ten subjects is a really small sample size.  This alone put this research more in the “pilot study” category, which is kind of a mini-study that checks to see if we should bother to make a bigger, more expensive study on the subject.  But by itself, it’s not too convincing.

The Bigger, More Expensive Green Tea Weight Loss Study

Okay, here’s a really good one.  A study published in the Journal of Nutrition in 2009 took a bunch of people, had them keep their caloric intake consistent, and had them exercise for three hours a week (some of it supervised).  Half of them got a caffeiene only supplement, the other had a green tea extract/caffeiene mix (the caffeiene level was the same as the other group).  Twelve weeks later, they checked the results.

What they basically found was that the green tea extract enhanced the exercise-induced weight loss.  Not a lot, but since they had over a hundred subjects, it was enough to be noticed.  What was most interesting was the effect on abdominal fat distribution.

You see, they didn’t just weigh these people.  They used CT scans to find out exactly how fat their bellies were before and after.  While the effects of green tea on body weight were only mildly noticeable, there was a much more obvious effect in abdominal fat distribution.  Specifically, the caffeiene only group had an average total abdominal fat area decrease of 0.3%, while the green tea group had a total abdominal fat loss of 7.7% on average.

I like this study because it directly measures what we really care about (does green tea make my big belly get smaller) rather than indirectly measuring something that maybe, kinda-sorta, somehow has something to do with what we want (like the energy expenditure air chamber thing).  Plus, they had a good sample size and simple-but-solid study design… the kind that’s harder to screw up.

And, they confirm what I told you up at the top of the page.  Supplements don’t do THAT much.  It’s the diet and exercise that will pull the heavy weight.  Even with large levels of green tea supplements (over 600 mg/day), there was only a small difference in fat loss over control… and these people were exercising, as well.

So, in the great green tea weight loss supplement debate, remember that supplements only nudge you in the right direction… diet and exercise are going to do the real work in fat loss.

Article citations:

Meta-Study:

Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis.Phung OJ, Baker WL, Matthews LJ, Lanosa M, Thorne A, Coleman CI.Am J Clin Nutr. 2010 Jan;91(1):73-81. Epub 2009 Nov 11. Review.

Itty-Bitty Respiratory Chamber Study:

Dulloo AG, Duret C, Rohrer D, et al 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;70:1040–5

Green tea catechin consumption enhances exercise-induced abdominal fat loss in overweight and obese adults.Maki KC, Reeves MS, Farmer M, Yasunaga K, Matsuo N, Katsuragi Y, Komikado M, Tokimitsu I, Wilder D, Jones F, Blumberg JB, Cartwright Y.J Nutr. 2009 Feb;139(2):264-70. Epub 2008 Dec 11.