Obesity, which involves an excess of adipose tissue, is recognized as one of the most prevalent and preventable health issues [1]. While the rates of obesity and overweight among Korean adults are lower than in many developed countries, the westernization and urbanization of lifestyles in Asia have contributed to a rise in obesity-related diseases [2]. The Korean Ministry of Health and Welfare reported that in 2019, 33.8% of Korean adults were obese, with men at 41.8% and women at 25.0%. Furthermore, the prevalence of obesity in women increased with age [3]. A linear relationship between age and obesity has been observed among Korean women, with 25.8% in their 40s, 29.6% in their 50s, and 34.9% in their 60s, based on the Korean obesity guidelines which define obesity as a Body Mass Index (BMI) of 25 kg/m² or higher [3, 4].

Obesity is widely recognized as a significant risk factor for Cardiovascular Disease (CVD) and metabolic disorders. However, not all forms of obesity are equally concerning. The specific type of obesity that poses a risk is determined by the distribution of body fat [5]. Central obesity, characterized by an excessive accumulation of visceral and subcutaneous fat in the abdomen, can lead to complications such as hypertension, abnormal serum lipid levels, heart disease, stroke, and elevated insulin levels [1]. Visceral fat is also linked to insulin resistance, hyperinsulinemia, Type 2 Diabetes Mellitus (T2DM), dyslipidemia, increased inflammatory levels, and blood clot formation. Moreover, it serves as an independent marker for increased risk of cardiovascular and metabolic morbidity and mortality [6].

Cardiometabolic risk involves assessing the combined risk factors associated with CVD and metabolic disorders [7]. Metabolic Syndrome (MS) is characterized by a cluster of conditions including abdominal obesity, elevated Blood Pressure (BP), reduced High-Density Lipoprotein-Cholesterol (HDL-C), and increased levels of triglycerides and blood glucose. Individuals with MS are five times more likely to develop T2DM and three times more likely to develop CVD than those without MS [8]. The identification of CVD in conjunction with MS has led to the concept of cardiometabolic syndrome [7]. Notably, in 2022, CVD was the second leading cause of death among Koreans, with the mortality rate for women being higher than for men, at 140.6 and 128.7 per 100,000, respectively [9].

Visceral adipose tissue is known to increase until the ages of 65~70, after which it decreases in both men and women [10]. In women, the onset of menopause typically leads to a gradual increase in body fat during their 40s, while decreases in estrogen and progesterone levels can accelerate the accumulation of visceral fat [11]. Although the distribution of body fat is influenced by various factors, previous studies primarily examined the effects of age [12] and Physical Activity (PA) [13] on the Visceral Fat Area (VFA). The objectives of this study were to 1) investigate the cardiometabolic risks associated with different types of obesity by comparing Visceral Fat Obesity (VFO) and Subcutaneous Fat Obesity (SFO) in terms of VFA, and 2) identify specific factors influencing VFO in middle-aged Korean women who are overweight or obese.

This study demonstrated an association between VFO and cardiometabolic risk in middle-aged women with excessive weight. Additionally, factors such as age, BMI, frequency of vigorous PA per week, and intake of animal-derived calcium were found to influence VFO in this demographic. These findings are consistent with previous research that identified aging as a risk factor for the accumulation of visceral fat [6, 12]. This relationship may be linked to hormonal changes that occur during menopause in middle-aged women. Estrogen significantly influences fat distribution, leading to a tendency for men to accumulate fat in the abdominal region and for women in the thighs. The perimenopausal period is characterized by a significant decrease in estrogen levels, which is accompanied by a redistribution of fat from subcutaneous to visceral areas [24]. Previous research has shown that VFA increased significantly by 8.2% and 5.8% annually, both two years before and after the final menstrual period, indicating that the prevalence of visceral adiposity increases with age [11].

Previous studies have demonstrated a positive association between BMI and visceral fat [25]. Although BMI does not distinguish between muscle and fat mass, nor does it consider the distribution of fat, it continues to be a practical tool for assessing obesity in clinical settings. Nevertheless, its limitations should be acknowledged, especially in situations where regional fat distribution is crucial for cardiometabolic health.

The frequency of vigorous PA has been shown to positively impact the reduction of VFO. This aligns with findings from a previous meta-analysis, which indicated that aerobic exercise of a certain intensity effectively reduces VFA [13]. High-intensity physical activity promotes the release of adiponectin, and studies have established a strong correlation between adiponectin levels and changes in visceral adipose tissue [26]. Research suggests that high-intensity exercise is more effective than moderate or low-intensity exercise in reducing visceral adipose tissue and improving insulin sensitivity, with intensity being more crucial than duration [27]. However, the relationship between exercise intensity and VFA requires further experimental research using more objective and accurate measurements, as the findings of this study were based on self-reported data, which are vulnerable to subjectivity.

The present study found that an increase in animal calcium intake was associated with a decreased risk of VFO. The exact mechanisms by which calcium intake affects visceral fat accumulation are not fully understood. However, potential pathways may include the suppression of calcitriol levels, which reduces fat deposition [28], and enhancements in insulin sensitivity [29]. A previous study [30] demonstrated that elevated visceral fat is associated with lower calcium intake. While prior interventional studies have explored the combined effects of calcium and vitamin D3 intake on visceral fat [31], there remains a scarcity of human intervention studies focusing solely on the effects of calcium. Additionally, this study revealed that calcium intake, particularly from animal sources, was significantly lower in the VFO group compared to the SFO group. Given the link between bone mass reduction and menopause, the importance of calcium intake is particularly critical for middle-aged Korean women, whose consumption often falls below the recommended levels for their age [32].

Dyslipidemia was the most common comorbidity observed in this study, occurring twice as frequently in the VFO group compared to the SFO group. Additionally, T2DM was exclusively found in the VFO group. Abnormal mean values of triglycerides, TC, LDL-C, and FBG in the VFO group further supported the link between visceral fat and both dyslipidemia and T2DM. Interestingly, the mean BP values for both groups were within the normal range, despite a 16.9% prevalence of hypertension. This can be partly attributed to the high adherence rate (80.0%) to antihypertensive medication. In contrast, only 47.3% of those diagnosed with dyslipidemia adhered to their prescribed lipid-lowering medication regimen. This underscores the critical importance of medication adherence, which cannot be overstated.

Although regular exercise was not considered a factor influencing VFO, a significant difference was observed between the two groups. Women with SFO engaged in regular and more vigorous exercise compared to those with VFO. However, regardless of the type of obesity, middle-aged women with weight issues generally exhibited low PA levels. This aligns with a national report indicating that the adherence rate to aerobic PA among Korean women aged 40 to 59 is lower than that of Korean men in the same age group and their younger female counterparts [3]. Given that muscle mass and SFA were similar in the two groups, an effective exercise program for women with excessive weight or obesity should include strategies to increase muscle mass and reduce fat tissue in a manner that is feasible for them to maintain.

Regardless of the type of obesity, 41.6% of all participants were found to have a high sodium diet, consuming almost 1.5 times more than the recommended amount of 2300 mg [32]. Although sodium intake was not identified as a factor influencing VFO in this study, previous research has reported a significant correlation between urinary sodium output and VFA, as confirmed by abdominal CT [33]. Therefore, reducing sodium intake is advisable not only for women with hypertension but also for those with VFO. According to the analysis of a 3-day food diary, the daily proportions of protein, fat, and carbohydrate intake appeared to be adequate overall. However, the frequency of fat intake was high, as evidenced by more than two-thirds of the participants, regardless of obesity type. Given that significantly higher values of TC, LDL-C, and triglycerides in the VFO group were associated with animal fat intake, and considering the significantly lower intake of plant fats in the VFO group than in the SFO group, an increased intake of plant fats over animal fats is recommended for middle-aged women with VFO.

Women with VFO exhibited higher body weight, BMI, body fat percentage, VFA, and V/S ratio compared to those with SFO. Additionally, the VFO group displayed metabolic syndrome characterized by three abnormal factors: WC, triglycerides, and FBG. The mean values of BMI, WC, and VFA in each group were indicative of obesity and abdominal obesity, aligning with previous studies that demonstrated a correlational relationship between BMI, WC, and VFA [34]. Furthermore, the VFO group had significantly higher abnormal values of TC and LDL-C, suggesting a higher incidence of dyslipidemia in women with VFO. This aligns with earlier research highlighting the negative impact of VFO on cardiometabolic risk in women [5]. Additionally, the average hs-CRP level in the VFO group indicated a moderate risk, with the number of women at moderate or high risk being more than double that in the SFO group. This finding further supports the link between VFA and inflammation, which may increase the risk of CVD [6]. Moreover, the 10-year CVD risk estimate for the VFO group was significantly higher than that for the SFO group, corroborating the findings of Neeland et al. [35]. In summary, middle-aged women with VFO are at an increased risk for cardiometabolic disorders; therefore, it is crucial to manage their VFO comprehensively before the onset of menopause.

By incorporating the relevant factors identified from this study, lifestyle intervention programs can be designed to improve cardiometabolic health by reducing visceral fat. In particular, as vigorous PA has been shown to reduce visceral obesity, it is anticipated that targeted exercise programs emphasizing high-intensity activities can be developed. However, the reliability of these study results is compromised by the use of self-reported questionnaires to assess physical activity and dietary behaviors, which introduces the potential for recall bias and responder bias. Future research should employ objective measures, such as wearable devices, to obtain more accurate assessments of health behaviors. Additionally, as all participants were recruited from Seoul, Korea, the generalizability of the findings to women in other regions may be limited. Including participants from a variety of regions would improve the broader applicability of the findings. While this study concentrated on exercise and dietary habits, the omission of other lifestyle factors such as smoking and alcohol consumption is a limitation. This suggests a need for future studies to more comprehensively explore their impact on visceral fat and cardiometabolic risk.

This study demonstrated a positive association between VFO and cardiometabolic risk, identifying key factors influencing VFO in middle-aged women who are overweight. Significant differences were observed in body weight, BMI, WC, cholesterol profile, hs-CRP, and the 10-year estimate for CVD risk between the SFO group and the VFO group. Since abdominal fat gradually increases with age and with the onset of menopause, managing visceral fat is crucial for the health of middle-aged women. Although aging and menopause are inevitable, modifiable health behaviors such as healthy eating and regular PA should be closely monitored to reduce the accumulation of visceral fat. In conclusion, there is an urgent need for weight management programs that focus on reducing visceral fat accumulation in abdominal obesity among middle-aged women.