Nuts are an important component of a healthy diet, but little has been known about their effects on muscle health. Therefore, this study examined the association between nut consumption and low muscle strength among Korean adults. This cross-sectional analysis was conducted using single 24-h recall and handgrip strength data from 3962 younger adults 19–39 years, 6921 middle-aged adults 40–64 years and 3961 older adults ≥65 years participated in the seventh cycle (2016–2018) of the Korea National Health and Nutrition Examination Survey. Low muscle strength was defined as handgrip strength <28 kg for men and <18 kg for women. Sex-specific OR were obtained for younger, middle-aged and older adults using multivariable logistic regression analyses. About one in four Korean adults were consuming nuts (using a culinary definition) with peanut being the most frequently consumed type. After adjustment for age, BMI, total energy intake, household income, alcohol consumption, smoking, resistance exercise, medical history and dietary protein intake, nut consumption was associated with the lower risk of low muscle strength among older adults ≥65 years (men: OR 0·55, 95 % CI (0·38, 0·79); women: OR 0·69, 95 % CI (0·51, 0·93)); however, this association was not observed among younger adults 19–39 years or middle-aged adults 40–64 years. Our results suggest that consuming nuts might be beneficial in lowering the risk of low muscle strength among Korean older adults.

The findings of studies investigating the relationship between coffee consumption and C-reactive protein (CRP) levels have been inconsistent, and few researchers considered the type of coffee. We examined the association between coffee consumption and high CRP levels, using data from the Korea National Health and Nutrition Examination Survey, 2016–2018, with 9337 adults aged 19–64 years. A 24-h diet recall was used to assess diet, including the amount and type of coffee consumed. We classified coffee into black coffee and coffee with sugar and/or cream (non-drinkers, or ≤ 1, 2–3, > 3 cups/d) and used multivariable logistic regression models with high CRP levels (≥ 2·2 mg/l). After the adjustment for potential confounders, 2–3 cups/d of coffee consumption were inversely associated with high CRP levels, compared with no consumption (OR = 0·83, 95 % CI 0·69, 0·99). By type of coffee, the inverse association was stronger in subjects consuming black coffee (OR = 0·61, 95 % CI 0·45, 0·84), while the inverse association was much weaker in those consuming coffee with sugar and/or cream (OR = 0·92, 95 % CI 0·74, 1·14). By sex, the inverse association of 2–3 cups of black coffee was found both in men (OR = 0·65, 95 % CI 0·41, 1·03) and women (OR = 0·55, 95 % CI 0·36, 0·83). More than three cups/d of heavy coffee consumption were not significantly associated with high CRP levels. Our findings indicate that moderate black coffee consumption of 2–3 cups/d is inversely associated with high CRP levels in Korean adults. Further prospective studies are warranted to provide definitive evidence.

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.

Vegetables are an important source for the essential vitamins and minerals that are necessary for optimal health. This research investigated changes in vegetable intake over time in the Korean population from 1998 to 2017, focusing on preparation methods of vegetables and location of consumption. This cross-sectional study is based on the Korea National Health and Nutrition Examination Survey (KNHANES) that was established in 1998 to assess the health and nutritional status of the South Korean population. This research utilised information from 1998 to 2017 which is the extent of all available KNHANES data. Vegetable consumption was grouped, according to preparation methods and common eating locations. Both crude and age-standardised means of vegetable intake were derived via a 24-h dietary recall. All participants who completed a 24-h dietary recall survey were selected for the analyses. This included 109 220 individuals (49 069 men and 60 151 women) over the course of 20 years of the KNHANES. Total vegetable intake decreased over time (Pfor trends < 0·001), specifically, steamed and salted vegetables (Pfor trends < 0·001). In contrast, Koreans consumed noticeably more raw vegetables from 1998 to 2017 (Pfor trends < 0·001). Vegetable intake at home significantly declined (Pfor trends < 0·001), while that eaten at restaurants or outside the home increased greatly (Pfor trends < 0·001). Over 20 years, Koreans have ingested decreasing amounts of vegetables, but the intake of raw vegetables has escalated. However, the location of vegetable consumption has changed, with an increase at both restaurants and outside the home (approximately 70·0 %).

No studies have investigated the associations between established plant-based diet indices and the metabolic syndrome (MetS). We evaluated the associations between an overall plant-based diet index (PDI), healthy PDI (hPDI), unhealthy PDI (uPDI) and the MetS in a nationally representative sample using data from 14 450 Korean adults (≥19 years) in the Korea National Health and Nutrition Examination Survey 2012–2016. Dietary intakes were assessed by a semi-quantitative FFQ. In the PDI, all plant foods received positive scores. In the hPDI, only healthy plant foods received positive scores. In the uPDI, only unhealthy plant foods received positive scores. All indices reverse scored animal food intake. Multivariable logistic regression models were used to examine the associations between three PDI and the MetS by sex, adjusting for potential risk factors. A total of 23·3 % of Korean adults had the MetS. In the overall study population, individuals in the highest quintile of uPDI had greater odds (OR 1·54, 95 % CI 1·28, 1·86, Ptrend < 0·001) of the MetS than those in the lowest quintile. Higher uPDI score was associated with higher odds of hypertriacylglycerolaemia in men and abdominal obesity, high fasting glucose and hypertriacylglycerolaemia in women. No significant associations were observed between PDI, hPDI and the MetS. Greater adherence to unhealthy plant-based diets was associated with greater odds of the MetS and its components suggesting the importance of the quality of plant-based diet in South Korean adults. Sex differences may be considered when recommending plant-based diets for the prevention and management of metabolic diseases.

We aimed to identify the association of hydration status with insulin resistance (IR) and body fat distribution. A total of 14 344 adults participated in the Korea National Health and Nutrition Examination Survey 2008–2010. We used urine specific gravity (USG) to indicate hydration status, and HOMA-IR (homoeostasis model assessment of IR) and trunk:leg fat ratio (TLR) as primary outcomes. In multivariate logistic regression, the OR per 0·01 increase in USG for high IR was 1·303 (95 % CI 1·185, 1·433; P < 0·001). In multivariate generalised additive model plots, increased USG showed a J-shaped association with logarithmic HOMA-IR, with the lowest Akaike’s information criterion score of USG 1·030. Moreover, increased USG was independently associated with increased trunk fat, decreased leg fat and increased TLR. In mediation analysis, the proportion of mediation effects of USG on TLR via IR was 0·193 (95 % CI 0·132, 0·285; P < 0·001), while the proportion of mediation effects of USG on IR via TLR was 0·130 (95 % CI 0·086, 0·188; P < 0·001). Increased USG, a sign of low hydration status and presumably high vasopressin, was associated with IR and poor fat distribution. Direct effect of low hydration status may be more dominant than indirect effect via IR or fat distribution. Further studies are necessary to confirm our findings.

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.

We investigated whether dietary and urinary Na is associated with adiposity in Korean children and adolescents (10–18 years), a population with a high salt intake. Study subjects were Korean children and adolescents who participated in the cross-sectional nationally representative Korea National Health and Nutrition Examination Survey (2010–2011). This study used measures of dietary (24-h dietary recall) and urinary Na (Na:creatinine ratio) and three methods to determine obesity (BMI, waist circumference (WC) and total body per cent fat (TBPF)). Higher Na intake was significantly associated with obesity, adjusting for the covariates. Subjects in the highest tertile of urinary Na excretion had a significantly higher OR for higher adiposity compared with those in the lowest tertile (multivariate-adjusted OR 3·13 (95 % CI 1·81, 5·50) for BMI, 2·15 (95 % CI 1·27, 3·66) for WC and 1·92 (95 % CI 1·29, 2·86) for TBPF, respectively). Na intake estimated by the 24-h recall method also showed significant association with adiposity (multivariate-adjusted OR 2·79 (95 % CI 1·66, 4·68) for BMI and 2·14 (95 % CI 1·25, 3·67) for WC, respectively). The significant associations between Na and adiposity remained significant after additionally adjusting for sugar-sweetened beverage (SSB) consumption. Our results revealed a significant positive association between urinary and dietary Na and adiposity in Korean children and adolescents, independent of SSB consumption.

Epidemiological studies have suggested that flavonoids exhibit preventive effects on degenerative diseases. However, lack of sufficient data on flavonoid intake has limited evaluating the proposed effects in populations. Therefore, we aimed to estimate the total and individual flavonoid intakes among Korean adults and determine the major dietary sources of these flavonoids. We constructed a flavonoid database of common Korean foods, based on the food list reported in the 24-h recall of the Korea National Health and Nutrition Examination Survey (KNHANES) 2007–2012, using data from the Korea Functional Food Composition Table, US Department of Agriculture flavonoid database, Phenol-Explorer database and other analytical studies. This database, which covers 49 % of food items and 76 % of food intake, was linked with the 24-h recall data of 33 581 subjects aged ≥19 years in the KNHANES 2007–2012. The mean daily intake of total flavonoids in Korean adults was 318·0 mg/d, from proanthocyanidins (22·3 %), flavonols (20·3 %), isoflavones (18·1 %), flavan-3-ols (16·2 %), anthocyanidins (11·6 %), flavanones (11·3 %) and flavones (0·3 %). The major contributing food groups to the flavonoid intake were fruits (54·4 %), vegetables (20·5 %), legumes and legume products (16·2 %) and beverages and alcohols (3·1 %), and the major contributing food items were apples (21·9 %), mandarins (12·5 %), tofu (11·5 %), onions (9·6 %) and grapes (9·0 %). In the regression analysis, the consumption of legumes and legume products, vegetables and fruits predicted total flavonoid intake the most. The findings of this study could facilitate further investigation on the health benefits of flavonoids and provide the basic information for establishing recommended flavonoid intakes for Koreans.

The objective of this study was to examine whether high serum 25-hydroxyvitamin D (25(OH)D) concentration was associated with high skeletal muscle mass, taking into account the effects of sex and age among the participants of the Korea National Health and Nutrition Examination Survey (KNHANES) aged 40 years or older. This was a cross-sectional study using data from the 2009 to 2010 KNHANES; a total of 8406 subjects (3671 men and 4735 women) were included. The appendicular skeletal muscle mass index (ASMMI, kg/m2) was estimated to measure the skeletal muscle mass. Hypovitaminosis was classified when the level of serum 25(OH)D was <20 ng/ml. The general linear model adjusted for confounding factors was used to determine differences in means of ASMMI by 25(OH)D status. The mean values of ASMMI were higher for men when compared with women. Women had a greater proportion of hypovitaminosis (71·1 %) compared with men (53·2 %). After adjusting for multiple factors, men were seen to have significant differences in ASMMI based on 25(OH)D status regardless of age, showing a lower mean value of ASSMI in those with hypovitaminosis. However, there was no difference in ASMMI by 25(OH)D status among women in both younger and older age groups. In conclusion, we found that there might be a positive relationship between 25(OH)D and skeletal muscle mass in men, indicating that interventions to improve 25(OH)D levels that are aimed at increasing muscle mass could be beneficial for men with more rapid decreased rate of skeletal muscle mass.