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Carolina Population Center University of North Carolina University Square, CB no. 8120 123 W Franklin Street Chapel Hill, NC 27516-3997 E-mail: popkin{at}unc.edu
Dear Sir:
Kesteloot and Zhang raised several important questions about the healthfulness of the Korean diet. Their focus was on fatty acid intake and salt intake patterns, information not provided by the national nutrition survey report (1), on which our nutritional analysis was mostly based (2). Their comments also led us to an important question about tradeoffs in the promotion and selection of dietary patterns. Essentially, they questioned the high intake of salt and its effect on the South Korean diet and health status.
We would like to provide additional information from other sources in response to their questions. It is obvious from our article that the ratio of polyunsaturated to saturated fatty acids would be high in South Korea on the basis of the description of the transition provided (ie, we showed that fish and shellfish consumption accounted for more than one third of the total intake of animal food products) (2). The concept of a ratio of polyunsaturated to saturated fatty acids emphasizes the balance of intakes of the different types of fatty acid, recognizing that their ratio is related to the dynamics of the blood cholesterol concentration, which is considered to be an important factor in cardiovascular health. The ratio of polyunsaturated to monounsaturated to saturated fatty acids and even the ratio of n-6 to n-3 fatty acids have been emphasized more recently. The recommended ratio of polyunsaturated to monounsaturated to saturated fatty acids is 1:1–1.5:1 and 1:1.5:1 in Korea and Japan, respectively (3). Nationally representative data are lacking but individual studies in South Korea showed that the ratio of polyunsaturated to monounsaturated to saturated fatty acids in South Korea is in the range of 0.7–1.6:1–1.5:1 (4). In Japan, the ratio is similar, but in the United States, intake of saturated fatty acids exceeds that of polyunsaturated fatty acids. The ratio of n-6 to n-3 fatty acids has been reported to be in the range of 6–10:1 in adults in South Korea (4). We did show in Figure 4 in our article that the percentage of energy from fat has increased in South Korea. An increase in the percentage of energy from fat in the diet is a universal trend worldwide with the nutrition transition. The unique and most interesting point in the South Korean nutrition transition, however, was that the fat intake was still low despite the increase, and the rate of increase was lower than that of other nearby Asian countries, such as China and Japan.
Salt intake was not reported by the national nutrition survey report (4), and therefore, nationally representative information on salt intake is not available for South Korea. The fact that discretionary intake accounts for a major share of sodium intake makes an analysis of salt intake from dietary surveys very challenging. Information on salt intake, even from other individual studies, is very scarce, but there are some data showing very high salt consumption (high urinary excretion) among Koreans (5), probably mainly from consumption of pickled vegetables and fish. Vegetable intake is very high in South Korea but there is little evidence on the proportion that is pickled. A positive relation between salted and processed foods and the incidence of stomach cancer and hypertensive disease has been reported in epidemiologic studies (6). The purpose of our presentation of cause-of-death data was to illustrate the major shifts in disease patterns from infectious to chronic disease. Therefore, we did not go into detailed mortality patterns for individual diseases in our article. Stomach cancer is indeed the top cause of death among cancers in South Korea (7). However, the mortality figures provided by Kesteloot and Zhang are exaggerated because they were obtained only from individuals aged 55–74 y. Mortality for all age groups shows a very different pattern. Mortality rates from selected diseases for total populations of South Korea, Japan, Hong Kong, Singapore, and the United States are shown in Table 1.
Mortality from stomach cancer is very high in South Korea compared with that of many other countries, but it is not higher than that in Japan. Lifestyle factors other than salt intake, such as alcohol consumption and smoking, also play an important role in stomach cancer mortality. A high rate of Helicobacter pylori infection in Asia is another factor to be considered. Mortality from cerebrovascular disease is also very high, but again, it is not higher than that in Japan. Mortality from ischemic heart disease is very low in South Korea compared with the United States and even with Japan. Mortality from hypertensive disease is high in South Korea, but in recent years, a drastic decrease has been noticed, along with a decreasing trend in mortality from stomach cancer (7). The etiology of a disease is very complex and is related to more than a single dietary factor. Only a more thorough analysis, exploring a full set of determinants, can explain the pathway of diet-related noncommunicable disease, and we suggested that as the next agenda of the study. Salt intake is definitely an important factor to be considered to study the unique mortality patterns in South Korea, as Kesteloot and Zhang suggested. Their hypothesis that the introduction of refrigerators may have resulted in a decrease in salt consumption is a probable one but we could not find data to prove that hypothesis.
There is an important benefit of vegetable consumption in South Korea. Our article did not focus on the vegetable consumption patterns; however, it is important to note that the South Korean vegetable intake of >280 g per capita per day (2) is among the highest in Asia. This high consumption comes from a meal pattern that emphasizes traditional dishes with many vegetable side dishes. Although the use of salt in these dishes may contribute to the higher salt intake in South Korea and the high salt intake could be somewhat reduced by discouraging the consumption of these side dishes, we would not want to overreact to try to reduce the consumption of these dishes without further careful consideration of the data. A campaign against salt intake should focus on reversing a more recent increase in intake of processed foods and decreasing discretionary salt intake, which is known to be especially high among Koreans.
View this table:
TABLE 1.. Mortality rate from selected diseases in South Korea, Japan, Hong Kong, Singapore, and the United States1
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