Age-related changes in body composition, including an increase in fat mass and a substantial reduction in muscle mass, exert adverse effects on the physiologic function and metabolism of the human body (1). Many studies have noted that body fat distribution is closely related to metabolic dysfunction and disease, including impaired fasting glucose, insulin resistance, type 2 diabetes mellitus (DM), and cardiovascular diseases (CVD) (2–5). In a 2-year prospective cohort study, Son et al. suggested that low muscle mass is significantly associated with the incidence of type 2 DM, independent of obesity, in the Korean population (6). Furthermore, prospective studies have demonstrated associations between low muscle mass and an increased risk of CVD and all-cause mortality (7–10). Using dual-energy X-ray absorptiometry (DXA), Baumgartner first defined sarcopenic obesity as the co-presence of two conditions: (1) obesity, defined as percent body fat values above the median for each sex, and (2) sarcopenia, defined as an age-related change in muscle mass to height squared, with values falling two standard deviations below the mean of a healthy, younger population (11).

Sarcopenic obesity poses a critical risk to public health worldwide (12). Lim et al. reported that individuals with sarcopenic obesity with low appendicular skeletal muscle mass (ASM) and high visceral fat mass are at higher risk of metabolic syndrome and insulin resistance compared to those with either sarcopenia or obesity alone in the Korean population (13). Furthermore, a 10-year follow-up cohort study showed that participants with sarcopenic obesity carried a 23% higher risk of CVD, regardless of the lack of association between CVD risk and obesity or sarcopenia alone (14). The significant risks to public health outcomes posed by sarcopenic obesity emphasize the importance of preventive measures against imbalances in body composition (15).

Dietary patterns are a principal contributing factor to body composition, including sarcopenia and obesity (15, 16). Nutritional strategies have been designed in consideration of their effects on the development of sarcopenic obesity (15). Several studies have suggested that high protein intake combined with resistance exercise increases skeletal muscle mass and strength in an older adult population with low muscle mass (17, 18). According to a 13-week randomized controlled trial (RCT) in the Netherlands (2011–2012), a high intake of whey protein, leucine, and vitamin D supplements preserved skeletal muscle mass while prompting weight loss, in conjunction with resistance exercise three times a week, in older adults with high body fat (19). However, an RCT conducted in Denmark (2019–2021) found that, while a high-protein diet enhanced satiety, it did not significantly affect body composition or cardiometabolic markers in young women with overweight (20). These findings indicate that the effects of protein intake may vary depending on age, metabolic status, and exercise habits. Another area of controversy lies in the impact of macronutrient distribution on metabolic health. Parvaresh et al. reported that a high-carbohydrate diet has a distinct adverse effect on metabolic responses in obese individuals with insulin resistance, whereas high-protein or high-fat diets do not elicit such effects (21). On the other hand, a cross-sectional analysis from the 2011–2014 National Health and Nutrition Examination Survey (NHANES) found a positive association between dietary fat intake (both saturated and unsaturated fatty acids) and skeletal muscle mass, suggesting the potential need for adequate dietary fat intake to prevent sarcopenia (22). Meanwhile, a 13-week trial study conducted in the United States reported that dietary fat intake influenced intramyocellular lipid accumulation in both healthy and older individuals, which, in turn, negatively affected muscle metabolism, contributing to sarcopenia (23). Previous studies on sarcopenia and sarcopenic obesity have reported inconsistent findings, largely due to variations in study populations, methods used for assessing body composition and metabolism, and dietary intake measurement tools (22, 24). These discrepancies highlight the need for further research to clarify the relationship between dietary patterns and body composition characteristics.

Therefore, in this study, we aimed to examine whether individuals with low muscle mass only (LMo), high body fat only (HFo), or both conditions (LMHF) demonstrate distinct dietary behaviors compared to those with normal body composition. We hypothesized that these groups would differ in both macronutrient intake and the frequency of consuming specific food categories, reflecting variations in overall dietary quality. Using nationally representative data from the Korea National Health and Nutrition Examination Survey (KNHANES), we aimed to explore potential associations between diet and body composition in the Korean adult population.

In this study, we found that participants in the LMHF and HFo groups consumed less CHOs and higher proportions of proteins and fats compared to the N group. However, despite this higher protein intake, these groups still exhibited adverse body composition outcomes, contradicting the widely held assumption that protein intake protects against sarcopenic obesity. Notably, those in the LMHF and LMo groups reported less frequent consumption of rice and vegetables and more frequent intake of ultra-processed foods, a trend that aligns with the increasing prevalence of Westernized dietary patterns in the Republic of Korea. Additionally, participants in the LMo and HFo groups consumed beverages more frequently than those in the N group, further indicating an increased reliance on sugar-sweetened drinks and processed food sources. While carbohydrate restriction is often suggested to improve metabolic health, our findings suggest that imbalanced macronutrient intake, particularly in the form of ultra-processed foods and excessive dietary fats, may contribute to poor body composition outcomes despite higher protein intake.

The shift from a traditional Korean diet to a Westernized dietary pattern is reflected in the LMHF and HFo groups, which showed increased ultra-processed food and beverage consumption and reduced intake of traditional staples such as rice and vegetables. Traditionally, Korean-style balanced diets, which emphasize grains, vegetables, and fermented foods, have been associated with a lower risk of metabolic disorders (31, 32). However, recent trends indicate a decline in rice and vegetable consumption and an increase in processed food intake, paralleling the increase in obesity and metabolic syndrome in the Republic of Korea (33, 34). Our findings align with this dietary transition, as participants in the LMHF and HFo groups consumed fewer carbohydrates, more proteins and fats, and a higher proportion of ultra-processed foods, especially hamburger, compared to the N group. Similarly, participants in the LMo group also exhibited significantly lower consumption of rice and vegetables while relying more on beverages and processed foods. These patterns suggest that dietary shifts toward a Westernized eating pattern may contribute to unhealthy body composition (32), particularly in groups with imbalanced macronutrient intake.

While previous research has emphasized the benefits of carbohydrate restriction and adequate protein intake in managing sarcopenic obesity (15, 35–37), these studies often overlooked the role of overall dietary quality. Our findings fill this gap by demonstrating that participants in the LMHF group—despite lower carbohydrate and higher protein consumption—still exhibited unfavorable body composition. This paradox suggests that nutrient composition alone is insufficient; instead, dietary quality and food source are crucial determinants. Increased intake of ultra-processed foods, rich in sugar, salt, and saturated fats, may undermine the benefits of higher protein consumption by promoting inflammation and impairing muscle protein synthesis (38). Furthermore, protein efficacy may vary depending on its source, with high-quality proteins such as whey or soy offering greater benefits than processed or animal-based alternatives (39). These insights underscore the importance of moving beyond macronutrient-focused approaches toward holistic dietary assessments when addressing sarcopenic obesity.

Our findings are consistent with global studies, such as a French cohort study (2009–2019) that reported a positive correlation between ultra-processed food consumption and obesity (40) and a UK Biobank study that demonstrated a link between ultra-processed food intake and increased body fat (41).

One possible explanation for this phenomenon lies in the source and quality of protein intake. Although previous studies supported protein’s role in preserving lean mass (42–44), emerging evidence suggests that plant-based or minimally processed proteins may have more favorable effects on metabolic health compared to animal-based or highly processed sources (45). A more detailed analysis distinguishing between protein sources or categorizing fats into saturated and unsaturated types could yield deeper insights. In addition, the role of specific food components in metabolic regulation warrants attention. A 3-week intervention study involving polyphenol-rich pomegranate juice and fermented soy showed improvements in plasma antioxidant capacity and a reduction in lipid peroxidation, as evidenced by lower levels of thiobarbituric acid reactive substances (46). Beyond physiological biomarkers, a follow-up nutrigenomic analysis from the same study revealed subtle but meaningful changes in miRNA expression related to oxidative stress and immune modulation, as detectable through melt curve profiling (47). These findings underscore the importance of considering not only dietary content but also the molecular responses it elicits when evaluating dietary interventions aimed at improving body composition and metabolic health.

The lower carbohydrate intake observed in the LMHF and HFo groups may reflect a broader shift toward Westernized dietary patterns, which are typically high in ultra-processed foods and refined fats and low in dietary fiber. These patterns not only lower dietary quality but also impact gut microbial composition, a key mediator of metabolic health (32). Unlike traditional Korean diets rich in plant-based foods and fermented products, Western-style diets have been associated with decreased microbial diversity and increased abundance of taxa such as Bacteroides, which are linked to proteolytic activity and reduced fermentation of complex carbohydrates. This microbial shift may lead to increased gut permeability and low-grade inflammation, contributing to unfavorable body composition, including visceral fat accumulation and muscle loss (32). Supporting this shift, De Filippo et al. demonstrated that children consuming Western diets showed greater proteolytic fermentation and reduced microbiota richness compared to those following traditional, fiber-rich diets. These findings illustrate how habitual dietary intake influences gut ecology, which in turn may affect nutrient utilization and host metabolism (48). Taken together, this suggests that dietary patterns shape not only macronutrient balance but also microbiome-mediated mechanisms that may influence the development of sarcopenic obesity.

Frequent beverage consumption, particularly sugary drinks, has also been linked to adverse body composition outcomes. A 6-month randomized intervention study in 2012 by Maria et al. reported that beverages, including soft drinks, sugar-sweetened tea, and coffee with cream and artificial sweeteners, are associated with ectopic fat accumulation and increased visceral fat (49). Other studies have found that fructose from sugar-sweetened beverages promotes de novo lipogenesis in the liver, leading to fat accumulation in both skeletal muscle and visceral adipose tissue (50–53). These mechanisms suggest that beverage consumption may contribute to the development of body composition imbalances, including low muscle mass and high body fat.

Our study had several limitations. First, as a cross-sectional study, it identifies associations between body composition and dietary patterns but cannot establish causality. A deeper exploration of how specific dietary components directly influence muscle mass and fat accumulation is needed. Second, although we applied propensity score matching (PSM) to reduce confounding, unmeasured variables such as meal timing, supplement use, or chronic inflammation status were not accounted for. These factors may influence both dietary behavior and body composition, leading to residual confounding. The PSM technique, while valuable for improving group comparability, may have excluded participants with atypical dietary patterns or rare phenotypes. This technique could reduce the diversity of the sample and potentially limit the external validity of our findings when generalizing to the broader population. Third, the nutritional data obtained from the 24-h recall method and FFQ may be subject to inaccuracies due to reliance on dietary recall rather than precise nutrient recording. Fourth, a sub-analysis distinguishing protein sources (animal vs. plant) and fat types (saturated vs. unsaturated) could have provided deeper insights into body composition imbalances; however, our dataset’s limitations precluded such analyses. Fifth, while our study utilized large-scale national data, the final sample size may have been insufficient to fully capture population-level trends. Future research with larger cohorts and more detailed dietary assessments is needed to further elucidate these associations.

Despite these limitations, our investigation possesses several notable strengths. To our knowledge, this is the first nationwide study to compare dietary behaviors among individuals with LMo, HFo, and both conditions (LMHF) in a Korean adult population. Unlike previous studies focusing on single outcomes or limited age groups, our study uses a large, representative dataset (KNHANES) and robust PSM to provide an integrated analysis across distinct body composition phenotypes. Our findings also reflect Korea’s dietary transition—declining rice and vegetable intake and rising ultra-processed food consumption, which may contribute to the increasing prevalence of sarcopenic obesity. By identifying phenotype-specific dietary patterns, this study offers direction for tailored nutritional interventions.

Taken together, our study provides compelling evidence that dietary quality—not just nutrient quantity—is a critical determinant of body composition. This study fills an important gap in the literature by highlighting how modern dietary transitions in the Republic of Korea, such as increased ultra-processed food consumption, may contribute to the dual burden of obesity and sarcopenia. These insights emphasize the need to move beyond nutrient-specific guidelines and develop comprehensive, personalized dietary strategies for clinical practice and public health policy. Given the increasing prevalence of obesity and sarcopenic obesity in the Republic of Korea, further research is warranted to elucidate the underlying mechanisms of these associations and to assess the long-term metabolic consequences of evolving dietary patterns.