The increased prevalence of childhood obesity worldwide is associated with serious health risks, such as insulin resistance (IR), type two diabetes (T2D), and cardiovascular disease (CVD) in childhood and later life [1]. The etiology of obesity and its metabolic consequences are complex and involve environmental factors that are challenging to modify. It is therefore crucial to identify modifiable risk factors involved in the early development of metabolic disorders to facilitate prevention and treatment.

In recent years, the gut microbiota has emerged as an important environmental factor associated with host health. The gut is home to trillions of microbes, and plays a major role in energy metabolism and the immune system [2, 3]. Several studies in animal models and humans have suggested that the gut microbiota is linked to complex disease phenotypes such as obesity and insulin resistance [4, 5]. A balanced gut microbiota composition confers benefit to the host, whereas microbial dysbiosis is implicated in various diseases, including obesity, T2D, and CVD. These studies imply that the effects of environmental factors on the development of metabolic-related disorders are mediated in part by altered gut microbial composition and function.

Therefore, research into factors affecting the gut microbiota has become an area of growing scientific interest. The gut microbiota is influenced by various factors, including the microbial species acquired at birth, age, host genotype, geography, and diet [6–9]. Of these, diet is considered a key contributor to the diversity of the gut microbiota, explaining 57% of the total structural variation, while only 12% is related to genetic differences [10]. Therefore, many studies have focused on the relationship between the gut microbiota and dietary factors, such as dietary pattern (vegetarian and Western) [11, 12], specific foods (whole grain products, fruits, and vegetables) [13–17], and food constituents (dietary fiber, fat, and protein) [8, 18–20]. Interestingly, a recent study showed that European children who consumed a typical Western diet had a microbiota enriched in Firmicutes and Enterobacteriaceae, whereas rural African children, who consumed a diet low in fat and animal protein and rich in plant-based foods, had greater abundances of the genera Bacteroidetes and Prevotella [7]. Another study demonstrated that microbiota composition was strongly associated with long-term diet [8]. Bacteroides abundance was found to be associated with a diet enriched in animal products, whereas that of Prevotella was correlated with diets that contained more plant-based foods.

Dietary factors can vary widely according to ethnicity and geographical location; however, few studies have focused on Korean populations. Therefore, we performed an in-depth analysis of the association between the fecal microbiota and dietary factors in Korean adolescents. Because dietary intake is a complex exposure variable, we used a total diet approach to identity the overall dietary patterns of Korean adolescents and then examined their associations with the gut microbiota composition and levels of biochemical markers. Assessment of food intake as a whole using dietary pattern analysis yielded useful information regarding the link between diet and the gut microbiota that will facilitate formulation of dietary guidelines to prevent disease.

There has been increasing interest in analyzing dietary factors associated with chronic disease. The analysis of dietary patterns has advantages over nutrient-based or food-group-based dietary assessment approaches because people consume foods in the form of meals, which are combinations of various foods and nutrients. Therefore, we analyzed dietary patterns in Korean adolescents using a combination of factor and cluster methods and compared the fecal microbiota and host phenotype across these dietary pattern groups.

In this study, we identified two major dietary patterns: traditional (Korean) and modified Western diets. The traditional diets were characterized as comprising predominantly plant-based and fermented foods because they included higher proportions of oriental sauce, sweet potatoes, vegetables, seaweeds, and whole grains, which are naturally high in fiber and undergo minimal processing. In contrast, the modified Western diets were characterized as comprising animal-based foods with intake of red meats, fishes, oils, and fats. Although the two dietary patterns were statistically independent as determined by the orthogonal rotation procedure, it would be possible for one individual to have high or low scores for both dietary patterns simultaneously [29]. In our study, white rice had high loadings in both the traditional and modified Western diets, as rice is the staple in the Korean diet.

Many studies have attempted to identify an association between dietary patterns and the composition of the gut microbiota. Here, we examined bacterial composition at the genus, family, and phylum levels according to dietary pattern group. We found that adolescents who consumed traditional diets showed a higher proportion of Bacteroides (Bacteroidaceae), Clostridium XlVa, Roseburia, Bifidobacterium (Bifidobacteriaceae–Actinobacteria) and Ruminococcaceae and a lower proportion of Prevotella (Prevotellaceae), whereas inverse associations were found for those who consumed modified Western diets. In our study, traditional diets comprised predominantly plant-based and fermented foods, which are low in fat and rich in carbohydrate, plant protein, vitamin, mineral, and fiber; in contrast, modified Western diets comprised greater proportions of animal-based foods and were high in fat and low in fiber. In support, previous studies have reported that vegetarian diets were associated with Bacteroides [11], and fat-restricted diets, together with higher carbohydrate intake, were linked to increased proportions of Bacteroides and Bifidobacterium [30]. However, Cani et al. reported a reduction in Clostridium cluster XIVa and lower Bifidobacterium and Bacteroides levels [31] and Kim et al. found the enrichment of Ruminococcaceae [32] in mice fed a high-fat diet.

Meanwhile, Wu et al. [8] reported that diets high in animal protein and fats, similar to a Westernized diet, were associated with a Bacteroides enterotype. By contrast, the Prevotella enterotype was associated with diets high in carbohydrates that contained more plant-based foods. Similarly, De Filippo et al. [7] found that children in rural Africa showed a higher abundance of Prevotella, whereas European children had a higher abundance of Bacteroides. The authors speculated that the abundance of Prevotella in rural African children was a consequence of their higher fiber intake because the traditional rural African diet is primarily vegetarian, being low in fat and animal protein and rich in starch, fiber, and polysaccharides. In contrast, the Western diet of the European children was high in animal protein, sugar, starch, and fat, and low in fiber. We assume that the inconsistencies with our findings are due to the complex relationships among genetic, geographical, environmental, technical, and/or clinical factors. The diet of people living in Korea, even those who consuming modified Western diets, is usually rather low in fat and provides a high amount of carbohydrate and fiber compared with the diet of people living in Western countries. Several studies showed that the microbiota composition clustered according to country in spite of a cultural area similar to the Western diet and quantity of Prevotella was greater in people from geographical regions where plant-based dietary pattern dominated [6, 33]. Furthermore, some reports suggested that the genus Prevotella was underrepresented in Americans probably due to discriminatory taxon, which is the enrichment in Prevotella in African children compared with European children, in Africans compared with African Americans, in the Hadza hunter-gatherers (from Tanzania) compared with Italian people, and in Succinivibrio and Treponema in several African populations [6, 34]. Therefore, more integrated approaches are needed to enhance our understanding of these complex associations.

It has been reported that the gut microbial communities of Koreans individuals differed from those of US, Japanese, and Chinese subject, but tended to vary less between individual Koreans, suggesting that diet type affects the gut microbiota [35]. They also found the core gut microbiota in Korean individuals and many of these are related to butyrate-producing bacteria. Koreans have high intakes of carbohydrate and fiber [36, 37], which are related to production of short-chain fatty acids (SCFA) such as acetate, propionate, and butyrate. SCFA, especially butyrate, have been suggested as important in maintaining gut health. Most subjects in our study were in the traditional diet group (73.2%), which was associated with a greater proportion of butyrate-producing bacteria, including Bacteroides, Clostridium XlVa, and Roseburia. Although we could not evaluate the subsequent effects of the gut microbiota related to dietary pattern and fecal metabolite in the current study, we believe that this should be taken into consideration in future in-depth studies.

Several studies have reported an association of major dietary patterns with obesity and metabolic disease. In this study, we found that subjects who consumed a modified Western diet had a higher prevalence of obesity and metabolic syndrome than those who consumed a traditional diet. In support of this, previous cross-sectional studies reported that Western dietary patterns were positively associated with obesity [38, 39]. Two large prospective cohort studies, the Nurses’ Health Study and the Health Professionals Follow-up Study, also reported that adoption of a Western dietary pattern was associated with greater weight gain [40], whereas reduction of weight gain was linked to diets rich in plant-based foods [41]. Furthermore, these studies reported that a Western diet was significantly related to metabolic diseases such as CVD [42, 43] and T2D [44, 45] and to all-cause mortality [43]. The Western dietary pattern was associated with increased risks of these diseases, whereas a prudent dietary pattern, diet high in unprocessed foods and fiber and low in salt, fat, and sugar, was associated with beneficial effects on host health [42–45]. In our study, we found that several important components of metabolic disorder were associated with dietary pattern. Subjects who consumed a modified Western diet had higher levels of liver enzymes, TC and TG, hs-CRP, insulin, and HOMA-IR than those who consumed a traditional diet, and these values were associated with increased risk of CVD and T2D. Also, we investigated that high consumption of whole grain and fiber or low consumption of fats is positively associated with Bacteroides, but not Prevotella (data not shown). However, the association disappeared after adjustment for BMI, because most obese adolescents consumed modified Western diet characterized with low intake of fiber and high intake of fat in the current study. This indicates the effects of fiber and fat intakes on gut microbiota composition including Bacteroides and Prevotella, which is associated with the pathogenesis of metabolic disease.

Many studies have attempted to identify an association between the composition of the gut microbiota and metabolic disease. In this study, we found that increased in prevotella (Prevotellaceae) and decreased in Bacteroides (Bacteroidaceae) and Ruminococcaceae had a higher risk of obesity. Theses tendency increased when they had with MS in genera and families of prevotella (Prevotellaceae) and Bacteroides (Bacteroidaceae). However, the evidence for an association between gut microbiota and metabolic disease is scarce. Recent studies suggested a potential role for diet in promoting a gut microbiome associated with the pathogenesis of metabolic disease. Koeth et al. [46, 47] found that microbial metabolism of choline, phosphatidylcholine and L-carnitine resulted in production of trimethylamine (TMA), which is further metabolized to the proatherogenic species, trimethylamin-N-oside (TMAO). Together, these findings suggested that individuals adhering to an omnivorous diet have higher fasting TMAO concentrations and produce more TMAO than do vegans or vegetarians after ingestion of carnitine through a microbiota-dependent mechanism. Furthermore, a correlation analysis of the fecal microbiota and plasma TMAO levels indicated that subjects with a Prevotella enterotype had significantly higher plasma TMAO concentrations than did Bacteroides enterotype subjects [47]. Interestingly, our study showed that subjects who consumed a modified Western diet had a greater abundance of Prevotella. Additionally, we recently reported that an increased Prevotella population was associated with increased TC, TG, and hs-crp levels, but negatively associated with HDL-C [4].

Due to the fact that QIAamp DNA Stool kit based on enzymatic DNA-extraction has the lower diversity of fecal microbiota comparing other DNA extraction kits [48] and is a insufficient method to lyse cell wall efficiently in detecting genes of various Gram-positive bacteria [49], caution must be used when interpreting these findings as regards to the general adolescent fecal microbiota. Additionally, short-term dietary data on 3-day food diaries maintained for three consecutive days (2 weekdays and 1 weekend day) were obtained from self-reported questionnaires which are not representative of the long-term dietary pattern of the subjects and may have resulted in an estimation bias. Finally, our study was cross-sectional in design. In this context, further studies with different methods using a prospective design and measurements before and after interventions are needed to determine core microbiota, the effects of dietary patterns, and the causal relationships among microbiota, dietary patterns, metabolic markers, and disease.

Nevertheless, we found that the proportions of the genera Bacteroides, Prevotella, Clostridium XlVa, Roseburia, and Bifidobacterium were markedly different in subjects who consumed traditional compared with those who consumed modified Western diets. Furthermore, a traditional (Korean) dietary pattern was associated with reduced risk of metabolic disease, whereas opposite associations were found for a modified Western dietary pattern. These findings suggest that dietary habits affect both the gut microbiota composition and host health.

We found that traditional dietary patterns were associated with higher proportions of Bacteroides (Bacteroidaceae) and Bifidobacterium (Bifidobacteriaceae-Actinobacteria) and a lower proportion of Prevotella (Prevotellaceae) relative to modified Western dietary patterns. Specifically, the proportion of Bacteroides (Bacteroidaceae) was associated with intake of plant-based nutrients such as fiber; however, that of Prevotella (Prevotellaceae) was negatively associated with these factors. Also, we found that prevotella (Prevotellaceae) increased and Bacteroides (Bacteroidaceae) and Ruminococcaceae decreased in higher risk group of obesity. The risk had a tendency to increase in obesity subjects with MS in genera of prevotella and Bacteroides and families of Prevotellaceae and Bacteroidaceae. We also found that the traditional dietary pattern was negatively associated with general and central adiposity and levels of clinical biomarkers, including AST, ALT, total cholesterol, triglyceride, hs-CRP, insulin, and HOMA-IR, whereas the positive associations were found for a modified Western dietary pattern. These findings suggest that dietary habits affect both the gut microbiota composition and host health.