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Tea time discussion

Updated: Mar 18, 2021



We all have a tendency to lighten up at a dietary headline full of promise, especially if it doesn’t require any major alterations to our lifestyle. Get a handful of “superfood” berries, and you will cure everything from hypertension to constipation. As a bonus you will also magically loose extra weight, sleep better and look at least 10 years younger. We all fell into this trap, at least once in our life.

Social media does a great job to facilitate a rapid spread of new cure-all remedies. I have recently witnessed one interesting tweet posted by a medical doctor from the U.S. that became a “sensational event”. She brought an article with a catchy headline “Drinking oolong tea can help burn fat while you sleep, study shows”. Before you even have time to raise an eyebrow, thousands of people have already shared this news and stocked up on oolong tea. Obviously, I was intrigued. It was actually the first part of the headline that caught my attention. The second didn’t make much sense to me, given that we all burn fat while sleeping – you don’t need to be a researcher to understand the basics of human metabolism.



Article interpretation


So, the article starts with a brilliant introduction: “Want to lose weight but don’t have time to exercise all day? A new study finds a nice cup of tea can help do it for you — while you sleep!”

Isn’t it wonderful? Not only you don’t need to exercise, not to mention “all day”, but all you have to do is just to enjoy a nice cup of tea. Well, and fall asleep. The rest will be naturally taken care of by oolong tea bioactive ingredients which will transform you into a fat burning machine.





But what the study paper says?


I was interested enough to spend time finding and reading the original paper, published in a prestigious journal Nutrients in Dec 2020 by the group of Japanese researchers.

To my surprise, the study was actually well designed. For example, to control many variables such as physical activity or food intake, participants were locked in isolated special chambers (to measure how many calories they burn), allowed only to sit or to sleep for specific time periods. During the intervention days, when all metabolic parameters were measured, including at night, the reported time spent in bed was exactly 8h for all participants, not a minute more or less – very “a la Japanese”.



Participants and results


All participants were divided in 3 groups: placebo, caffeinated drink or oolong tea. They consumed it twice a day for breakfast and lunch for 14 days without knowing which one they got. Caffeinated drink and oolong tea were prepared with exactly the same amount of caffeine. It was intentional to assess whether there is another bioactive element in oolong tea other than caffeine affecting metabolism.

Study results were quite interesting but not really surprising. Compared with the placebo drink, ingesting caffeinated beverage and oolong tea did in fact increase fat oxidation during wake and sleep time.

However, there were no significant effects on energy expenditure (how many calories are used).

But before you all rush to order oolong tea, let’s have a look into details and methodology of this study. Researchers in Japan have enrolled only 12 men between 18 and 56 years old with a normal body weight. Obese or overweight people with chronic diseases were excluded from this study. Funny enough, the fat ratio of these 12 men was in the range of 17%. To give you a little reference, the fat percentage of men in a fitness category is 14-17%. Study participants also didn’t use any medication or dietary supplements, didn’t smoke, didn’t have issues with sleeping and were not coffee addicts. In summary, it’s a nice description of a healthy and metabolically flexible man. Not necessarily representative of an average middle-age man, reading the promising tweet and dreaming to lose weight without effort.



Results analysis


Now, we all know that caffeine, especially in large doses, does stimulate the amount of energy a person uses in the form of calories to a certain extent, although the mechanisms are still not understood. It’s already been demonstrated in many studies. Unfortunately, findings of this particular study did not confirm this fact. Proposed explanation to this was that caffeine amount in drinks was relatively small, and by the end of 2 weeks period our japanese volunteers developed caffeine tolerance, when the effect of caffeine decreased over time because of regular consumption. So the energy expenditure didn’t increase, but interestingly enough the fat oxidation did. And not just in oolong tea group, caffeine drinkers also did experience an increase in fat burning ratio, which is most likely explained by the same amount of caffeine content in both drinks.

However, the difference in fat oxidation between two groups was so small between 2 groups, that it’s hard to determine whether there is any other magic component in oolong tea stimulating fat burning.

In short, this study didn't really demonstrate any superiority of oolong tea over coffee on human metabolism.


What was really interesting in this study is that the heart rate and sympathetic (fight or flight) nervous system activity in the caffeine group were significantly lower than in the placebo group. And even more surprisingly, the parasympathetic (calm) nervous system activity in caffeine or oolong tea groups was higher than in placebo. Basically, it seems like caffeinated drinks have a massive calming effect on Japanese healthy men. That was something new and different from the original idea, probably worth investigating.


What have we learned?


The promising headline of the hyped news was actually based on a real and well designed study, but again, the reality is a bit more complicated.

As we have discovered, it’s very hard to generalise such information because this study was run in a controlled hospital-like environment on a small group of healthy Japanese men. It might not be the same for women, teenagers or overweight people. For insulin resistant people it’s even more complex, given that they are not metabolically flexible i.e. their metabolism can’t easily switch from burning carbohydrates to fat. And it’s not by drinking tea that this balance would shift in a significant way.


The conclusion of this study was well written and objective, saying that “2 weeks was not long enough to assess the effects of the intervention on body weight and body composition, and whether caffeine or oolong tea consumption actually reduces body fat remains to be evaluated.” Objective and professional!

But completely different from what’s been written in the newspaper and social media.


So, enjoy your morning cup of good quality coffee or free tea with a warming thought that it does slightly stimulate your calorie & fat burning engine. But keep in mind if you have been drinking your morning coffee for the last 20 years, your body is probably well adapted to the amount of ingested caffeine, and its effect has already diminished over time.






And finally, if you really need to lose weight, it’s not a “nice cup” of tea that will make these extra kilos of fat disappear in no time. Unless, of course, you sip only oolong tea all day long and sleep at least 8h a day ;)


There are more efficient and sustainable ways to lose these kilos, if you want to know more, get in touch.





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