Although a decrease in carbohydrate intake and an increase in fat intake among Koreans have been reported, investigations of changes in protein intake have been limited. Thus, this study aimed to explore trends in the dietary intake of total, plant and animal proteins overall and by socio-demographic subgroups in Korea over the past two decades. A total of 78 716 Korean adults aged ≥ 19 years who participated in the seven survey cycles of the Korea National Health and Nutrition Examination Survey 1998–2018 were included. Dietary protein intake, overall and by source, was calculated using a single 24-h dietary recall data. Changes in dietary protein over 20 years were estimated using multiple linear regression analysis after adjusting for potential covariates. For total protein intake, a significant decrease was reported from 1998 to 2016–2018 (P for trendlinearity < 0·001), whereas an increasing trend was observed from 2007–2009 to 2016–2018 (P for trendlinearity < 0·001). In terms of protein intake by source, plant protein intake decreased while animal protein intake increased over the past two decades, indicating steeper trends during the recent decade (P for trendlinearity < 0·001). These trends were more pronounced among younger adults and those with higher household income and education levels. These findings suggest that continuous monitoring of dietary protein intake overall and by source (plant v. animal) across socio-demographic group is needed.

Results from studies investigating the association between coffee consumption and the metabolic syndrome in Koreans have been inconsistent and remain controversial. We examined coffee intake in relation to the metabolic syndrome using data from the Korea National Health and Nutrition Examination Survey 2012–2015, with 8387 adults aged 19–64 years. Furthermore, we conducted a stratified analysis by obesity status (BMI <25 v. ≥25 kg/m2) to examine whether the association varied by obesity status. A 112-item FFQ was used to assess diet. Multivariable logistic regression models were used to determine the association of coffee consumption (<1, 1–2, 3–4 and ≥5 times/d) and the metabolic syndrome. Compared to people who consumed <1 time/d of coffee, the OR for the metabolic syndrome in those who consumed 3–4 times/d of coffee was 0·75 (95 % CI 0·58, 0·97). However, ≥5 times/d of coffee consumption was not significantly associated with the metabolic syndrome. By obesity status, in non-obese people, those consuming more coffee had lower odds of the metabolic syndrome, showing a significant linear trend (P-trend=0·0248). In obese people, the OR for the metabolic syndrome in people with 3–4 times/d of coffee consumption v. <1 time/d was 0·68 (95 % CI 0·50, 0·93), but ≥5 times/d of coffee consumption showed a non-significant positive association. Our findings suggest that moderate coffee consumption of 3–4 times/d is inversely associated with the metabolic syndrome in Korean adults. The association between heavy coffee consumption of ≥5 times/d and the metabolic syndrome varied by obesity status.

Prospective studies on the association between soft drink consumption and incident risk of the metabolic syndrome (MetS) have not been carried out in Asians. We explored the sex-specific association between soft drink consumption and incident risk of the MetS in Korean adults during 10 years of follow-up. A total of 5797 subjects who were free of the MetS at baseline were studied. Soft drink consumption was assessed using a semi-quantitative FFQ. Time-dependent Cox proportional hazard model was used to examine hazard ratios (HR) of incidence of the MetS and its components in relation to soft drink consumption. In women, the multivariable-adjusted HR for developing the MetS was 1·8-fold higher in frequent consumers of soft drinks (≥4 servings/week) compared with rare consumers (95 % CI 1·23, 2·64). The adjusted HR for elevated blood pressure increased by 2-fold (95 % CI 1·24, 3·14) and for hypertriacylglycerolaemia by 1·9-fold (95 % CI 1·19, 2·88) in frequent consumers of soft drinks compared with rare consumers. However, in men, there was no association between soft drink consumption and incident risk of the MetS or its components. Frequent soft drink consumption was associated with increased risk of developing the MetS and its components only in middle-aged Korean women, suggesting sex differences for the risk of the MetS related to diet.

The present study explored the relationships between fried food consumption and metabolic risk factors and hypertension in Korean adults. The study was based on the fifth Korean National Health and Nutrition Examination Survey between 2010 and 2011. A total of 9221 Korean adults aged ≥19 years were studied. Fried food consumption was assessed using a validated FFQ. Metabolic risk factors such as waist circumference, fasting plasma glucose (FPG), TAG, HDL-cholesterol and systolic and diastolic blood pressure (SBP and DBP) were measured. Hypertension was defined as SBP≥140 mmHg, DBP≥90 mmHg or current use of antihypertensive medication. Adjusted OR for elevated blood pressure significantly increased in men (OR 1·62; 95 % CI 1·11, 2·37; Ptrend=0·0447) and women (OR 2·20; 95 % CI 1·21, 4·00; Ptrend=0·0403) with a greater than twice a week consumption of fried food compared with those who rarely consumed fried food. However, fried food consumption was not associated with other metabolic risk factors (abdominal obesity, high FPG, hypertriacylglycerolaemia, low HDL-cholesterol and the metabolic syndrome). The adjusted OR for hypertension increased by 2·4-fold in women (OR 2·37; 95 % CI 1·19, 4·72; Ptrend=0·0272) with a greater than twice a week fried food consumption compared with those who rarely consumed it. No significant association was found between fried food consumption and hypertension in men. This study suggests that frequent fried food consumption is associated with hypertension in Korean women. Further studies are needed to investigate the effect of different types of fried foods on hypertension.