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Oolong Tea May Aid Fat Breakdown While You Sleep, Research Suggests

oolong tea in tea cups with tea pot

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Key Takeaways

  • Caffeine has been shown to boost the breakdown of fat by 20%, which might aid weight loss.
  • A recent study found that oolong tea, which contains around 31 mg of caffeine per 100 ml, continues to boost metabolism after you fall asleep – unlike pure caffeine, which stops working during sleep.
  • However, the study has its limitations, and further research is needed to validate its findings.

Losing weight is a tricky subject, as different lifestyle changes work for different people, and there is certainly no magic pill (or tea) that will make you shed pounds. Still, new research is revealing the fascinating ways our bodies interact with what we eat or drink, and sometimes that interaction occurs in our fat cells.

Recent research from Japan, published in the journal Nutrients, focused on oolong tea and how it impacts weight loss. Like all teas, oolong contains caffeine, which has been shown to boost the breakdown of fat by 20%, but oolong tea may have something extra. It doesn’t stop working when the person falls asleep, and carries on firing up the metabolism during sleep. 

Study Details 

The research was carried out by a team at the University of Tsukuba, led by Professor Kumpei Tokuyama. They tested three groups of healthy volunteers, who drank either oolong tea, pure caffeine, or a placebo, over a period of two weeks.

Compared to the control group, the volunteers who drank oolong tea or caffeine increased their breakdown of fat by 20%. But out of all the beverages, only oolong continued to work during sleep. And despite caffeine’s reputation for keeping drinkers awake, the researchers found no difference in sleeping patterns between the control group and the oolong drinkers.

This meant that those who drank oolong tea didn't have disrupted sleep, which has been linked to weight gain.

Professor Kumpei Tokuyama

The stimulatory effects of oolong tea on fat breakdown during sleep could have real clinical relevance for controlling body weight.

— Professor Kumpei Tokuyama

“Like all teas, oolong contains caffeine, which impacts energy metabolism by increasing our heart rate,” says Tokuyama. “However, studies suggest that tea consumption may also increase the breakdown of fat, independent of the effects of caffeine."

Notably, neither the oolong tea group nor the pure caffeine group showed an increase in energy expenditure. This suggests that the volunteers became more tolerant to the stimulatory effects of caffeine over the two-week study period. 

The researchers also analyzed the volunteers’ sleep patterns, because caffeine is known to inhibit sleep, and a lack of sleep can directly impact energy metabolism. But they observed no noticeable difference in sleep patterns, or the time it took participants to fall asleep, between the treatment and placebo groups. This is another plus point for oolong tea as it suggests that drinking it is unlikely to stop you getting a good night’s sleep.

If this encourages you to reach for the oolong before bedtime to aid your weight loss efforts, Tokuyama is all for it. "The stimulatory effects of oolong tea on fat breakdown during sleep could have real clinical relevance for controlling body weight,” he says.

What Is Oolong Tea?

According to U.K.-based company Whittard, which has been producing tea and other hot beverages since 1896, oolong is produced predominantly in China’s Fujian and Guangdong provinces and Taiwan. All tea comes from the same plant (Camellia sinensis), but its specific type is determined by the degree of oxidation, a chemical reaction that turns tea leaves black.

Oolong is a partially oxidized tea, falling somewhere between unoxidized green and fully oxidized black tea (and may resemble one of these more closely, depending on the oxidation process during production).

Fun fact: The literal translation of oolong is "black dragon," which may be because the leaf "dances" like a dragon when immersed in water. Or it may get its name from the black snakes that sometimes wind around the branches of tea trees.

Like green tea, oolong contains around 31mg of caffeine per 100 ml—slightly less than black tea and a little more than white and yellow tea. However, Whittard notes that it’s important to know this can vary depending on the specific batch of tea you drink, as well as the time, temperature, and strength of your brew.

The health benefits of oolong tea go way back. “According to Chinese tradition, oolong tea is supposed to help with weight loss/management, reduce blood sugar and insulin levels, provide heart health benefits. and help with brain function,” says Vanessa Rissetto MS, RD, CDN, co-founder of Culina Health

Vanessa Rissetto MS, RD, CDN

According to Chinese tradition, oolong tea is supposed to help with weight management, reduce blood sugar and insulin levels, provide heart health benefits, and help with brain function.

— Vanessa Rissetto MS, RD, CDN

However, Rissetto says this is basically an inference because the tea is loaded with antioxidants, and high levels of antioxidants are believed to have these positive outcomes. “Oolong tea is not well researched, so these are all anecdotal and inferential,” she notes. 

Limitations of the Study

Rissetto points out that Tokuyama’s study is only over 14 days and limited to 12 participants. “We can use it as a hypothesis and research the tea over time in order to really validate the findings,” she says. 

Tokuyama acknowledges that the study has its limitations. “We need to determine whether the effects we observed in the two-week study translate into actual body fat loss over a prolonged period,” he says. “In addition, we want to trial a decaffeinated oolong tea to better distinguish the effects of caffeine from other components of tea, which will help us understand exactly how oolong helps with fat breakdown." 

What This Means For You

If you want to try oolong tea, it's widely available in stores and online. If you're sensitive to caffeine, it may be a more suitable option than black tea or coffee.

But drinking oolong tea alone isn't enough to lose weight if that's one of your health goals. Your first step should be talking to your primary care doctor or a registered dietitian, who can help you come up with healthy lifestyle changes that work for you.

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  1. Zhang S et al. Subacute Ingestion of Caffeine and Oolong Tea Increases Fat Oxidation without Affecting Energy Expenditure and Sleep Architecture: A Randomized, Placebo-Controlled, Double-Blinded Cross-Over Trial. Nutrients. 2020 Nov. doi:10.3390/nu12123671