Monday, May 6, 2013

Trip to South Korea: Hidden reasons for the leanness of its people


In September last year (2012) I went to South Korea to speak about nonlinear data analysis with WarpPLS (), initially for business and engineering faculty and students at Korea University in Seoul, and then as a keynote speaker at the HumanCom 2012 Conference () in Gwangju. Since Seoul is in the north part of the country, and Gwangju in the south, I had the opportunity to see quite a lot of the land and the people in this beautiful country.


(Korea University’s main entrance, Anam campus)


(In front of Korea University’s main Business School building)

Korea University is one of the most prestigious universities in South Korea. In the fields of business and engineering, it is arguably the most prestigious. It also has a solid international reputation, attracting a large number of highly qualified foreign students.

I wanted to take this opportunity and try to understand why obesity prevalence is so low in South Korea, which is a common characteristic among Southeast Asian countries, even though the caloric intake of South Koreans seems to be relatively high. Foods that are rich in carbohydrates, such as rice, are also high-calorie foods. At 4 calories per gram, carbohydrates are not as calorie-dense as fats (9 calories per gram), but they sure add up and can make one obese.

Based on my observations, explanations for the leanness that are too obvious or that focus on a particular dietary item (e.g., kimchi, green tea etc.) tend to miss the point.

Let us take for example a typical South Korean meal, like the one depicted in the photos below, which we had at a restaurant in Seoul. If you are a foreigner, this type of meal would be difficult to have without a local accompanying you, because it is not easy to make yourself understood in a traditional restaurant in South Korea speaking anything other than Korean.


(Main items of a traditional South Korean meal)


(You cook your own meal)

The meal started with thin-sliced meat (with some fat, but not much) and vegetables, with the obligatory side dishes, notably kimchi (). This part of the meal was low in calories and high in nutrients. Then we had two high-calorie low-nutrient items: noodles and rice. The rice was used in the end to soak up the broth left in the pot, so it ended adding to the nutrition value of the meal.

Because we started the meal with the low-calorie high-nutrient items, the meat and vegetables, our consumption of noodles and rice was not as high as if we had started the meal with those items. In a meal like this, a good chunk of calories would come from the carbohydrate-rich items. Still, it seems to me that we ingested plenty of calories, enough to make one fat over the long run, eating these types of meals regularly.

A side note. As I said here before, the caloric value of protein is less than the commonly listed 4 calories per gram, essentially because protein is a multi-purpose macronutrient.

In our meal, the way in which at least one of the carbohydrate-rich items was prepared possibly decreased its digestible carbohydrate content, and thus its calorie content, in a significant way. I am referring to the rice, which had been boiled, cooled and stored, way before it was re-heated and served. This likely turned some of its starch content into resistant starch (). Resistant starch is essentially treated by our digestive system as fiber.

Another factor to consider is the reduction in the glycemic load (not to be confused with glycemic index) of the rice. As I noted, the rice was used to soak up the broth from the pot. This soaking up process significantly reduces the rice’s glycemic load, because of a unique property of rice. It has an amazing capacity of absorbing liquid and swelling in the process.

This was one of several traditional Korean meals I had, and all of them followed a similar pattern in terms of the order in which the food items were consumed, and the way in which the carbohydrate-rich items were prepared. The order in which you eat foods affects your calorie intake because if you eat high nutrient-to-calorie ratio foods before, and leave the low nutrient-to-calorie ones for later, my experience is that you will eat less of the latter.

Another possible hidden reason for the low rate of obesity in South Korea is what seems to be a cultural resistance to industrialized foods, particularly among older generations; a sort of protective cultural inertia, if you will. Those foods are slowly being adopted – my visit left me with that impression – by not as quickly as in other countries. And there is overwhelming evidence that consumption of highly industrialized foods, especially those rich in refined carbohydrates and sugars, is a major cause obesity and a host of other problems.

Cultural resistance to, or cultural inertia against the adoption of, highly industrialized foods among pregnant mothers limits one’s exposure to those foods at a particularly critical time in one’s life – the 9-month gestation period in the mother’s womb. This could have a major impact on a person’s propensity to become obese or have other metabolic derangements later on in life. Some refer to this phenomenon as a classic example of modern epigenetics, whereby acquired traits appear to induce innate traits across generations.

Another reason I was excited about this trip to South Korea was my interest in table tennis. I wanted to know more about their table tennis “culture”, and how it was influenced by their general culture. China dominates modern table tennis, with such prodigies as Ma Lin, Ma Long, Wang Hao, Wang Liqin, and Zhang Jike. South Korea is not far behind; two of my all-time favorite South Korean players are Kim Taek-Soo and former Olympic champion Ryu Seung-Min.

Another side note. The best table tennis player of all time is arguably Jan-Ove Waldner (), from Sweden. I talked about him in my book on compensatory adaptation (). Waldner has been one of the few players outside China to be able to consistently beat the best Chinese players at times when they were at the top of the games, including Ma Lin ().

But, as I soon learned, as far as sports are concerned, it is not table tennis that most South Koreans are interested in these days. It is soccer.

A nice surprise during this trip was a tour in Gwangju in which we visited a studio that converted standard movies to stereoscopic three-dimensional ones (photo below). These folks were getting a lot of business, particularly from the USA, in a market that is very competitive.


(A standard-to-3D movie conversion studio in Gwangju)

Let’s get back to the health angle of the post. So there you have it, two possible “hidden” reasons for the low prevalence of obesity in South Korea, and maybe in other Southeast Asian countries. One is the way in which foods are prepared and consumed, and the other is cultural inertia. These are not very widely discussed, but future research may change that.

31 comments:

Andrea said...

This is fascinating and tremoundously helpful.

I routinely pre-cook and refrigerate the starchy foods I prepare for my husband-rice, buckwheat noodles, sweet potatoes, winter squash, white potatoes and starchy roots. This is a method of convenience for me but it's interesting to read that this changes the nature of those foods in a helpful way.

I will likely alter the way I serve supper to get those nutrient dense, non-starchy foods into him first.

Thanks so much.

shtove said...

Bit of noodling around on retrogradation for potatoes gives this recipe for puree:

http://www.kayahara.ca/2011/04/retrograde-redux/

Kim said...

Fascinating, eye opening, and, personally, very helpful. I can't believe how much we've wrecked our nutrition in this country. Thank you for a good read!

Chuck Currie said...

What did they use for the broth? Was the meat cooked in the broth or grilled first? What was the cooking time for the entire meal?

@shtove - "noodling" around - haha

Great post - thanks

Cheers

Suzie_B said...

"Still, it seems to me that we ingested plenty of calories, enough to make one fat over the long run, eating these types of meals regularly."

This just points out quality trumps quantity - that eating nutrient dense real foods for life won't make you fat while eating the western diet of processed flour and sugar will. Great post - Thanks.

Larry Eshelman said...

It is my understanding that most of the resistant starch is lost when the rice is reheated. On the other hand, sushi rice (or potato salad) would be high in resistant starch.

Jack C said...

Another factor that may contribute to the leanness of South Koreans is low intake of vegetable oils high in linoleic acid (LA).

A search for per capita intake of LA in south Korea was unsuccessful, but I did run across an interesting article which supports your conclusion that the traditional South Korean diet is very healthful.

http://www.cpc.unc.edu/projects/nutrans/research/bellagio/papers/PHNSKorea-Min-Jun.pdf

The article notes that nutritionists, government agencies and private companies are making an effort to educate the population about the health benefits of the traditional South Korean diet.

Nigel Kinbrum said...

Larry Eshelman said...
"It is my understanding that most of the resistant starch is lost when the rice is reheated. On the other hand, sushi rice (or potato salad) would be high in resistant starch."
In International table of glycemic index and glycemic load values: 2002, refrigerated & re-heated rice (275) has a GI of 53, which is moderate when compared to some of the other rices in that list.

Refrigerated & re-heated potatoes (605) has a GI of 23, which is low.

Larry Eshelman said...

Since I eat a lot of reheated rice and boiled potatoes, it would be nice to know to what extent the resistant starch is retained. When I did a search on this issue, before posting my comment, I consistently found statements to the effect that MOST of the resistance starch was lost on reheating. (But with multiple cooling and re-heating the level retained was higher.)

The table that Nigel cites shows that the GI for reheated rice was 53 and that the mean GI for 12 studies of the same type of rice was 64 with a std of 7. This is compatible with MOST of the resistance starch being lost. On the other hand, the contrast for potatoes is much larger: 23 for reheated versus a mean of 50, std of 9 for five studies.

Does anyone know of studies which actually compared the resistance starch levels pre and post heating?

Ned Kock said...

Thanks everybody for your comments. I would have thought that retrogradation was a sort of chemical degradation process, which was not easily reversible. So I’ve done some research, and it seems that retrogradation is not actually reversible.

Given this, the table of GIs linked by Nigel is a little surprising (Foster-Powell et al. article). Yes, cooked-cooled-reheated rice seems to have a much lower GI than what they call “boiled 13 min, then baked” (page 22 of the Foster-Powell et al. article), but that GI is not much lower than those of the other rice items.

Ned Kock said...

Still on retrogradation, the starch in rice would seem to be particularly well suited for starch gelatinization, which is an intermediate stage of retrogradation.

This is compatible with the difference in GI between the cooked-cooled-reheated rice in the Foster-Powell et al. article (53, compared with glucose) and the “boiled 13 min, then baked” rice (104).

Still, the GI of 53 is comparable with the other rice items in the table, which I presume are not a result of retrogradation.

I’ll do a bit more research on this. If someone finds an explanation, please post it here. My fist inclination is to look at what I think is a more important number than the GI, namely the GL, or glycemic load.

Larry Eshelman said...

Quote I found on the web:

"RS3 is present in most starchy foods, which have been cooked then cooled and stored for several hours, up to several months. Retrogradation is a recrystallisation of starch chains, which occurs after gelatinisation when the product has not been immediately dried. Single chains form double helixes. Mainly the linear fraction of the starch, the amylose, is involved; amylopectin, however, can also retrograde, although a much longer time is needed. Cooked and cooled potatoes have been shown to contain RS3 in significant amounts (Englyst & Cummings, 1987). Reheating of starch reduces the RS3 content of the potato, showing that the retrogradation is partly reversible. Several cycles of heating and cooling, however, allow an increase in the RS3 levels."


Reference:
Champ, M., A.-M. Langkilde, F. Brouns, B. Kettlitz, and Y. L. Bail-Collet, 2003: Advances in dietary fibre characterisation. 2. Consumption, chemistry, physiology and measurement of resistant starch; implications for health and food labelling. Nutrition Research Reviews, 16, 143–161.

Andrea said...

I tend to think the GI & GL numbers aren't very useful in real world situations.

The only way to really know is to see what your own blood sugar level is after ingesting a particular food.

Glucometers and testing strips are cheap and readily available. There's no reason a non-diabetic can't use them to suss out how our food affects us.

BigWhiskey said...

Great news that you had a great trip! I am not too sure feasting in a restaurant would explain the current diabetes rate among the Koreans, though. I will "second the motion" on Andrea's scientific method.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3178689/

Ned Kock said...

Both the glycemic index (GI) and glycemic load (GL) are blood glucose response measures. The GL is an adjusted version of the GI that takes into account the relative amount of carbohydrate present in a food item.

Ned Kock said...

As I thought, it seems that we should be looking at the glycemic load (GL) of the rice in the example discussed in this post. Note that I mentioned in the post that the rice was used to soak up the broth from the pot. The rice was the last item in that meal.

This soaking up process significantly reduces the rice’s GL, because of a unique property of rice. It has an amazing capacity of absorbing liquid and swelling in the process. This property is shared by another food item, namely bread. However, bread’s GI and GL are generally much higher than rice’s.

Still, I was wondering about the GIs reported in the Foster-Powell et al. article, and ran across some articles (e.g., linked below) that suggest that the GI is a measure that seems to be very prone to measurement error.

http://www.nature.com/ejcn/journal/v61/n1s/full/1602942a.html

This may be in part due to an interesting phenomenon. The GIs of foods seem to vary significantly when those foods are consumed at different times, a property that Björck and colleagues discuss in more detail (link below).

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=883932

In fact, Björck and colleagues put forth an interesting hypothesis, which is that “certain low-GI foods may be more efficient in modulating metabolism in the long term”.

Ned Kock said...

Here is a previous post on the GL of rice:

http://healthcorrelator.blogspot.com/2012/05/rice-consumption-and-health.html

Ned Kock said...

Speaking of GI variability, here is another interesting paper:

http://informahealthcare.com/doi/abs/10.1080/09637480802516191

dearieme said...

This is fascinating stuff. How about going beyond refrigeration: what happens if you put, for example, rice in the freezer for a while?

Stipetic said...

Hi Ned, interesting post (and some similar experiences to mine when I visited China). I've been under the impression that conversion of the native starch to resistent starch was of a low order (maybe 3-5%). Do you have anything suggesting a significant conversion rate?

Ned Kock said...

Hi dearieme. Do you think that freezing has an effect on retrogradation?

Ned Kock said...

Hi Stipetic. I think what we have here is a combined effect of retrogradation and GL reduction, with the latter possibly playing a key role. In fact, I’ll revise the post to reflect that.

Anonymous said...

Hi,

I was born in Korea, and happened to return to my home-country for a year recently. And to be honest, I don't find the people in our country that lean. The people there are definitely getting fatter. I don't agree with the resistance to processed food. If at all, Korea is really leaning towards processed food at the moment. Nobody in the younger generation is cooking. Take my grandma. My grandma was an amazing cook, who made every single ingredient, snack, meal, you name it, all by herself. But nowadays, nobody makes soy sauce by themselves. Nobody ferments anything by themselves (maybe except for some people, kimchi) except for the more elderly women. Everyone buys premade paste, etc all from the supermarkets. So many young workers eat out everyday. They never make their own food. And did you see the obsession with fried chicken in Korea? It is literally driving people to excessive weight gain! And I don't blame them...it tastes darn good.

As for food order, it's not reliable to judge how Korean people ACTUALLY eats from restaurant food. It's like in any other country. Restaurant meals are not representative of home-cooked meals or the meal order. Korean people do not eat meat and vegetables like that everyday, definitely not. Many Korean people also tend to eat nutritious parts of animals, but much much less of it, and as a condiment. Korean, home-cooked meals, are mainly rice-based. We eat little little bits of salty, sweet, ect side dishes accompanied by rice to buffer the strong taste of the side dishes. We share a little bit of meat or a whole fish (for a family, not one person) as a family. We usually have a bowl of soup. It is a treat to eat "meat and vegetables." Our family has it once a week or once every two weeks. Basically, we eat however much rice we think we need to eat, and finish that along with the side-dishes. People will give you strange looks if you eat all the side-dishes, and not the rice. We save rice for last only for huge course meals in restaurants. We want to eat the good stuff, not the bland rice, in restaurants!

I think the leanness has more to do with more movement (the transportation from Gangnam to your place of living will keep you fit!), eating less food, much smaller portions, and the lower reward of Korean food in general. Rice is more filling than bread, and the idea of having rice everyday with a little bit of side dishes is definitely much more monotonous than the Western dishes cooked at most homes. Asians seem to be also more protected from obesity than Westerners, and there is also immense pressure to look your best in Korea. The older generations are still quite lean in Korea, but I don't expect that same level of leanness in the future generations, with the kind of processed food they are eating combined with the Koreans' love of good food (we are all foodies at heart)!

Stipetic said...

Hello again Ned,

I looked into resistant starch a bit more. It turns out that the content is as I suspected, very low, in the vicinity of 2% for boiled potatoes, as an example, increasing to about 6% upon cooling. Rice is a bit lower. The effect on glycemic index is directly related to the amount of resistant starch produced. So, in my example you will have 4% less digestible starch after eating the cooled potato than you would have pre-cooling. This 4% difference is unlikely to have much of an effect on GI and why you see similar GI regardless of the formation of resistant starch after cooling. Milage may vary with other species of plants.

Resistant starch content in a selection of starchy foods on the Swedish market.Liljeberg Elmståhl H.Eur J Clin Nutr. 2002 Jun;56(6):500-5.

Digestion of polysaccharides of potato in the small intestine of man.Englyst HN, Cummings JH.Am J Clin Nutr. 1987 Feb;45(2):423-31.

Measurement of resistant starch: factors affecting the amount of starch escaping digestion in vitro. Muir JG, O'Dea K.Am J Clin Nutr. 1992 Jul;56(1):123-7.

Ned Kock said...

Thanks for sharing your experience Anon. You brought up another interesting factor: “… there is also immense pressure to look your best in Korea”.

Ned Kock said...

Hi Stipetic. As far as rice is concerned, I believe the GL is a much more important factor than the GI, because of rice’s “spongy” nature. I added this to the post:

Another factor to consider is the reduction in the glycemic load (not to be confused with glycemic index) of the rice. As I noted, the rice was used to soak up the broth from the pot. This soaking up process significantly reduces the rice’s glycemic load, because of a unique property of rice. It has an amazing capacity of absorbing liquid and swelling in the process.

Ned Kock said...

Btw, Anon, Koreans seemed to be much more knowledge about Brazilian soccer players than their own national table tennis team players. For example, Ronaldinho seemed to be better known than Ryu Seung-Min. This was a bit puzzling to me, given that the Korean team is an international table tennis powerhouse.

Stipetic said...

Good point, Ned. I'm strictly low-carb, but when we make rice for the kids we use homemade chicken broth instead of water (to get the micronutrient content of rice in a decent range). That probably drops the GL quite a bit.

A thing I noticed while in China is that all "entrees" were eaten above the rice dish--with drippings falling in the rice--and only after these entrees were eaten would anyone dip their chopsticks into the rice bowl. The only empty bowls were those of the visitors (mine included; I eat whatever I'm given when on business trips). The locals always left some rice in their bowl.

Justin Bieber said...

I tend to think the GI & GL numbers aren't very useful in real world situations.

The only way to really know is to see what your own blood sugar level is after ingesting a particular food.

Glucometers and testing strips are cheap and readily available. There's no reason a non-diabetic can't use them to suss out how our food affects us.

Brian said...

Interesting take on things. As someone who's lived in Korea for a cumulative time adding up to a number of years I feel the other side of the equation should also be pointed out--physical activity. Even using public transportation, there is much, much walking involved in getting around. In general the country, certainly including Seoul, is very hilly and mountainous. Observationally, I'd say the average Korean does the equivalent of spending 2 hours a day on a stairmaster.

wheelchair to bed transfer said...

Its interesting to know about Korean food, are they similar to Japanese food that some says are healthy?