Onsen Tamago

“We found that habitual tub bathing was associated with a lower risk of cardiovascular disease (CVD) among middle-aged Japanese, suggesting a beneficial effect on the prevention of CVD.”[1]

This is certainly good news for cleanly middle-aged Japanese, but how about the rest of us? There are several details in this meticulously performed, extensive study which make fascinating reading. Let us look at three of them:

1. “Those who bathed in a tub bath almost daily accounted for the largest proportion of participants at 71.9% (n = 21,618).”[1]

2. “Vegetable, fruit and fish intakes tended to be lower among those who bathed in a tub less frequently.”[1]

3. “The typical Japanese style of bathing involves filling the tub to shoulder depth with hot water at approximately 40 to 42°C, while some prefer temperatures upward of 43°C.”[1]

One would hope that a similar percentage like the 71.9% could be found in the “Western” parts of the world if employed to the frequency of taking a shower – but that is certainly questionable. People who look after their body tend to lead a lifestyle which is considered to be “healthier.” That, at least, should be universally valid, although the problem of obtaining fresh fish remains unsolvable for many.

The exact way of taking a bath hides the most confounders. Whereas the temperatures are defined and seem to be a bit on the warm side, other potential influences are not mentioned. Does the average middle-aged Japanese use a cedarwood tub so typical in this country? Were any essences or salts added to the water which (with or without the characteristic vapors of cedarwood) could have had a beneficial effect on their own? Probably not, but this still leaves us with the wood aroma question. Be that as it may, the authors have produced a nice confirmatory study providing more data for the assumption that caring attention toward one's body should have positive effects in the long run. The results also suggest that a relaxing bath could, indeed, be preferable to a quick hop into the shower, but a randomized controlled comparison will never be done.

A follow-up study should definitely be designed, investigating the effect of another typical way of Japanese purification: the onsen. The hypothesis would be that this is bound to have an even greater impact, but the essential Material and Methods part is not readily available, not even in Japan. Onsen means a hot spring where the bathers immerse themselves into naturally heated water at, on average, around 42°C. An onsen can be found where the volcanic activity of the Japanese mountains comes close to the surface. In Beppu on the island of Kyushu, for instance, the whole town seems to be steaming. A traditional hotel, a ryokan, is often built around such a spring, offering the visitor complete relaxation: separated by gender one at first carefully cleans and rinses the body while sitting on a cedarwood stool which seems to have been designed for a child. Then one is ready to enter the steaming basin naked, only accompanied by a tenugui, a small towel, used for covering the head and to absorb the inevitable pearls of sweat. The tenugui should therefore not touch the onsen water. Afterwards, thorough drying with a bigger towel is mandatory before donning a wide-sleeved kimono (yakuta) to rest in a separate, quiet room, perhaps sipping some tea. Even writing or reading this description makes one feel incredibly comfortable. And no, an onsen has definitely nothing to do with a Jacuzzi.

The reader may have encountered the term onsen also in connection with eggs, and rightly so. An onsen tamago is an egg slowly heated in such a natural hot spring, specifically in its even hotter parts before the water is drained into the basins for bathing. Basically it is applied biochemistry. At around 64.0°C an important glycoprotein in the egg white called conalbumin or ovotransferrin starts to coagulate. Immersing a fresh egg into 64.0°C warm water for 45 to 60 minutes should provide you with a wobbly egg white and a creamy yolk: the longer the time, the firmer the yolk. It all depends on your water with an absolutely constant temperature (onsen or sous-vide heater), your atmospheric pressure (Beppu versus Bhutan) and your chicken (Leghorn versus New Hampshire Red). The temperature itself is also debated philosophically and vigorously: some say 63.7°C, some insist on 64.5°C. Again, it depends on your environment. The fun part is experimenting to achieve the perfect result, unpredictable before breaking the shell. No, an onsen tamago is definitely not just another poached egg. And, never mind the cholesterol.

Speaking of which, wouldn't it be lovely to have yet another study concluding that “habitual onsen tamago consumption was associated with a lower risk of cardiovascular disease (CVD) among elderly, slightly overweight Caucasian males, suggesting a beneficial effect on the prevention of CVD”? I am waiting for your submission.

• References

• 1 Ukai T, Iso H, Yamagishi K. , et al. Habitual tub bathing and risks of incident coronary heart disease and stroke. Heart 2020; 106 (10) 732-737