I didn't have to spend too much time talking with Dr. Oz's followers (told you this was a gold mine of blog material!) before the supposed "metabolic boosting" properties of Green Tea Extract came up. But is there any evidence to support this or are you just back to spending your money? Let's find out.....
First, let's make sure we are all on the same page when it comes to the word "metabolism." If you ask for a definition from those of us who work in a medical related field what the definition of metabolism is, you will likely see something similar to this one from the National Institutes of Health: Metabolism refers to all the physical and chemical processes in the body that convert or use energy to keep you running. So your ability to breathe, have a heart beat, contract a muscle to pick up a fork to pierce that steak, process that steak, poop out the steak, etc is all the result of your metabolism. Now, usually when all the non-medical people talk about metabolism, they are usually wondering how they can burn off extra body fat/increase their ability to burn calories. (Usually with minimal effort; you know who your are.) So if you ask your provider about how to "boost your metabolism," and they wince a little bit, it is because sarcasm took over and she probably thought "Really? You want to increase muscle contractions and cause cramps?" before she remembered you were talking about burning fat/losing the extra poundage.
Now that my sarcasm bout is temporarily over, let's talk about metabolism as your ability to burn calories, and whether or not green tea/green tea extract increases it. And in this situation, somebody might actually be on to something. I had already been doing some research this week, but a Pharmacist co-worker gave me a very helpful website called Natural Standards that covers a lot of alternative therapies including dietary supplements. When you type in "green tea extract" you will, um, probably see a listing for an article about genital warts (sorry about that), but if you click on "evidence table" you should get to a table with all the different conditions that green tea extract is supposed to help, and if you keep scrolling you will find "obesity." (Link) You will see that 1) while some studies showed modest weight loss, there wasn't much indication that there was a change in metabolism, 2) where there was change the researchers manipulated the levels of catechins (also called flavanoids) so there was more than the caffeine in the tea at work, and 3) if you were able to go in and read some of those studies that looked more positive you would notice that they are pretty small and/or done in one segment of the population (Link), so we don't know if there will be the same effect in women as in men, elders vs. children, etc. So the end result is, if you think that taking green tea extract might "boost your metabolism" there is a very qualified maybe.
And of course this type of supplement will usually appeal to those of you are have actually reduced your intake and exercised more but you just....can't....lose...that...last...ten...pounds. Even if you consider yourself pretty rational and skeptical you might be tempted, so I am going to leave these other considerations here:
1) My new favorite website does give an overview of products studied (here), as it is tough to know whether or not your product actually contains the catechins in the amount that you might want to try.
2) Make sure you look at the amount of caffeine that is in the product and think about what other sources of caffeine you might consume. Caffeine consumption over 500-600 mg per day could up your risk for dehydration, insomnia, heart rhythm problems, etc. In other words, it is a drug, even if it is "natural" and can cause problems if you consume too much. And if you already have a condition, like Irritable Bowel Syndrome, that is aggravated by caffeine, the capsules will likely aggravate that too.
2a) Keep in mind that the studies that showed promise indicated that the combination of the catechins and the caffeine were what helped the weight loss, not just the caffeine itself.
3) Make sure that you are not taking any medications that could interact with this supplement (Link).
4) Do not overestimate how many more calories you might be burning. In the study I linked above the participants burned about 180 more calories a day, which might sound like a lot. Until you realize that 180 calories equals a little over half a cup of ice cream or one of my dairy free desserts. So if you've got the spoon and that pint out and you think that the green tea extract is going to help, think again. (You know who you are).
Take home message--green tea extract might have modest impact on weight loss if you have already been following a satisfactory weight loss plan including change of diet and exercise.