This study analyzed the lipid intake trends of Korean adults using the lipid intake data included in the KNHANES data spanning the 20-year period from 1998 to 2018. With this, factors related to the lipid intake of Korean adults over the 20-year period were investigated.
The study results showed that the lipid intake ratio contributed to energy ranged from 16–21% on average for all individuals, men, and women. This level was included in the proper range of the lipid ratio contributed to energy of 15–30% recommended by the 2015 KDRIs . Lipid intake increased significantly from the first to the seventh term for all individuals (+ 7.34 g), men (+ 9.71 g), and women (+ 4.93 g). The lipid intake ratio contributed to energy also rose significantly over the same period for all individuals (+ 3.52%p), men (+ 3.12%p), and women (+ 3.90%p). Song et al.  analyzed the lipid intake trends of Korean adults over an eight-year period (2007–2015) and reported that energy, total lipid, saturated fatty acids, unsaturated fatty acids, n-3 fatty acids, and n-6 fatty acids all increased steadily over the period. However, in a recent study that used the 2016–2017 KNHANES data , the intake ratio of polyunsaturated fatty acids remained unchanged, but that of saturated fatty acids increased. Overall, the lipid intake of Korean adults seems to be increasing. It is known that fats not only supply energy to the human body but are also used as a component of cell membranes and aid the absorption of fat-soluble vitamins . These fats can also be transformed into other fatty acids according to the body’s needs and serve a function in immune responses and as various chemical messengers . On the other hand, lipids can provide more than twice the energy of carbohydrates or proteins, and thus excessive lipid intake can increase the risk of obesity. Particularly, excessive intake of saturated fatty acids or trans fatty acids can increase the risk of cerebrovascular and cardiovascular disorders, dyslipidemia, diabetes, and hypertension . Therefore, it is considered that data are needed for dietary guidelines and nutrition education in the future to prevent increases in lipid intake.
Lipid intake by type of meal showed that intake via breakfast decreased continuously but increased through lunch, dinner, and snacks over the 20-year period. This is thought to be related to the significant increase in the proportion of people skipping breakfast, which increased from 11.8% in 1998 to 26.0% in 2016–2018, more than doubling over the 20-year study period. People who skip breakfast tend to eat more food at lunch or dinner, particularly high-fat meats. Studies have shown that skipping breakfast is highly correlated to obesity prevalence, high serum cholesterol, and high blood pressure. In this study, the group that consumed less energy at breakfast showed a higher fat-to-energy ratio and protein-to-energy ratio and lower carbohydrate-to-energy ratio [28–31].
The lipid intake by cooking location showed that intake increased significantly through meals prepared by commercial food services. Previous studies [32–34] also reported similar results of increased lipid intake from the meals provided by commercial food services. In a study conducted on the eating-out trends of Korean adults for the 14 years from 1998 to 2012, the lipid intake ratio of eating out increased from 19.2% in 1998 to 21.7% in 2012 . Also, a study on nutrient intake changes caused by eating out from 2010 to 2015 showed that carbohydrate and protein intakes decreased, while lipid intake increased continuously. The intake of refined processed foods and high-fat foods increases the more one eats out and consumes convenience foods. Moreover, food delivery has expanded due to the increased number of women in the workplace, reduced family size, and increased number of one-person households, in line with the social and economic changes in Korea .
Lipid intake by level of food security showed that the “enough food secure,” “mildly food insecure,” and “moderately food insecure” groups all increased significantly except “severely food insecure”. This trend may be related that most of meals and processed foods contain lipid.
According to the results of this study, total plant and animal lipid intake has increased over the 20-year period from 1998 to 2018. Specifically, the ratio of lipid intake from potatoes, sugars, seeds and nuts, seaweed, beverages, meats, eggs, dairy products, and other animal foods has increased, while that from grains, beans, vegetables, mushrooms, fruits, vegetable oils, fish and shellfish, and animal fats has decreased. Supporting this result, the survey of lipid intake from major foods conducted using the 2013 KNHANES data showed that total fats and fatty acids from pork were the major food source for lipid intake . Also, according to result of previous study , the foods that contributed most to the lipid intake of Koreans were pork, soybean oil, beef, eggs, and ramen, showing a high representation of animal foods. Because fats are present in various types and forms in foods, it is believed that the type of fatty acid, rather than the total lipid intake, has a greater effect on the blood lipid profile. In particular, monounsaturated fatty acids and n-3 fatty acids are largely contained in plant foods such as beans, seeds, and nuts, while polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are present in high concentration in fish. Thus, proper education on and intake of various types of fatty acids is recommended [11, 19].
Although it was not investigated in this study, the lipid intake might be different not only by type of meal but also diet. Recently, diets have emerged as an important factor, as diets such as the Mediterranean diet and USDA diet, which emphasize vegetables, fruits, whole grains, low-fat dairy products, fish, and fowl, are reported to reduce the risk of dyslipidemia and cardiovascular/cerebrovascular diseases [27, 37]. Also, it has been reported that diets affect obesity and thus are considered to be significantly related to genes associated with chronic disorders [27, 38, 39]. In the future, epidemiology and clinical intervention research should be performed on the basis of the results of this study on Koreans.
The proportion of individuals who had a proper fat ratio contributed to energy by the KDRIs (fat ratio range: 15–30%) increased by about 10.0%p (percentage points) over the 20-year period, rising from 43.9% in the first term (1998) to 53.0% in the seventh (2016 ~ 2018). This suggests that lipid intake has increased in the diets of Koreans compared to protein and carbohydrate intakes. However, several studies recently reported that groups with high carbohydrate intake, rather than lipid intake, were at higher risk of chronic diseases, including obesity [40, 41]. In this study, the group with high carbohydrate intake ratio contributed to energy was the group with less than proper fat ratio contributed to energy (< 15%), and the carbohydrate intake ratio was 75–78%. This exceeds the carbohydrate intake ratio by about 10–13% according to the 2015 KDRI (55–65%). The prevalence of obesity and abdominal obesity in this group, such as the obesity prevalence (38.3%) in men in the seventh term (2016 ~ 2018), was about 4.1–8.5% lower than that of the groups with proper (lipid intake ratio: 15–30%, obesity prevalence: 42.4%) or more than proper fat ratio contributed to energy (lipid intake ratio: over 30%, obesity prevalence: 46.8%) according to the 2015 KDRIs. This is slightly different from the results of previous studies on high carbohydrate intake. However, in the case of carbohydrates, a high-carbohydrate diet featuring foods with high dietary fiber content reportedly reduces blood lipid levels, including triglycerides, more than a carbohydrate diet with foods with low fiber content . Although the details should be checked further, it is believed that the obesity prevalence in men in this study might be explained by the results reported by such previous studies. Therefore, the type of carbohydrates ingested and their effects should be considered in future studies. Also, the difference in the obesity prevalence between this study and other previous studies should be confirmed in detail in the future, although there might be a difference due to the types of fatty acids. To support this, in-depth studies on the relationship between the intake of fats and fatty acids and chronic diseases, including obesity, will be needed, along with meta-analyses and systemic reviews that investigate disease prevalence more systematically and scientifically using long-term follow-up cohort study data such as the Korean Genome and Epidemiology Study (KoGES), which has been conducted since 2001 and recently completed its seventh follow-up study, and accumulated data.
As the association between the KNHANES data of the Ministry of Health and Welfare and the cause of death statistics of Statistics Korea  becomes possible in Korea, studies similar to the previous study on Americans, in which the mortality rates of high-fat diet groups and high-carbohydrate diet groups were compared , will be able to be conducted on Koreans.
This study has some limitations. First, we could not assess the actual intake of total lipid from the participants’ diet because of collecting the one-day 24-h recall data. However, the results of this study may be generalized to Korean adults due to KNHANES data is based on a large nationally representative sample.
Second, analysis of trends using data on various fatty acids data was not performed, as reported in the previous study by Song & Shim , and total lipid intake was analyzed according to general characteristics, dietary behavior, food groups, and KDRIs criteria. This is because fatty acid data have been collected since the 2016 KNHANES and the food code was the same as in the 2007–2015 KNHANES data, and fatty acid data seemed to be applied to the relevant years’ KNHANES data and used in the study. To enable detailed studies on various lipid intake trends to be conducted in Korea in the future, the food and meal codes should be standardized for the KNHANES data prior to 2007, and fatty acid data should be listed for all terms of the KNHANES data. In the future, lipid intake analysis should be performed for foods listed in the food frequency questionnaire conducted from 2012 to 2016, and thus studies on the annual lipid intake of Koreans, which cannot be deduced by the 24-hour recall survey, and comparative studies should be performed.