Prevalence and associated factors of normal-weight central obesity among community-dwelling adults 18 years and older in Mongolia

Abstract

Background

This study investigated the prevalence of and factors associated with normal-weight central obesity (NWCO) among adults aged 18–64 years in Mongolia.

Methods

Data were pooled from 5,287 participants aged 18–64 years who took part in repeated cross-sectional Mongolia STEPS surveys conducted in 2005, 2009, 2013, and 2019. Anthropometric and independent variables were measured using standard procedures. Factors associated with NWCO were examined using logistic regression analysis.

Results

Among individuals with normal weight (BMI 18.5–24.9 kg/m²), the prevalence of NWCO across the four surveys was 34.0%, increasing from 8.7% in 2005 to 37.0% in 2019. Adjusted logistic regression analyses showed that, compared with 2005, survey year 2019 (AOR = 3.07, 95% CI: 2.29–4.12), middle age (45–64 years) (AOR = 2.14, 95% CI: 1.65–2.79), low physical activity (AOR = 1.31, 95% CI: 1.05–1.64), and hypertension (AOR = 1.44, 95% CI: 1.09–1.90) were positively associated with NWCO. In contrast, male sex (AOR = 0.06, 95% CI: 0.01–0.27) and higher education (AOR = 0.68, 95% CI: 0.52–0.85) were negatively associated with NWCO.

Conclusions

Approximately one in three normal-weight adults in Mongolia had central obesity. To prevent NWCO, healthcare providers should emphasize the importance of maintaining a healthy lifestyle, including adequate physical activity and other weight-related behavioural changes.

Background

Mongolia is undergoing a rapid epidemiological transition [1]. The prevalence of underweight has declined, whereas the prevalence of overweight and obesity has increased steadily across all age groups [2]. National data from 2014 to 2015 indicate that 54.1% of adults in Mongolia were overweight or obese (body mass index [BMI] ≥ 25 kg/m²) [2]. Findings from four cross-sectional WHO STEPS surveys in Mongolia show that the prevalence of overweight and obesity (BMI ≥ 23.0 kg/m²) rose from 49.6% in 2005 to 64.0% in 2019 [3]. An earlier analysis of three cross-sectional STEPS surveys in Mongolia reported substantial increases in obesity prevalence by different anthropometric definitions. Specifically, the prevalence of obesity defined by waist circumference (WC) alone (BMI < 27.5 kg/m²; WC ≥ 88 cm for women and ≥ 102 cm for men) increased from 3.5% in 2005 to 7.2% in 2013. During the same period, the prevalence of obesity defined by both BMI and WC rose from 9.0% to 10.0%, while obesity defined by BMI alone increased from 17.4% to 28.3% [4]. Furthermore, among individuals with normal weight (BMI 18.5–24.9 kg/m²), pooled data from four STEPS surveys conducted between 2005 and 2019 showed that the prevalence of central obesity (WC ≥ 80 cm for women and ≥ 94 cm for men) was 17.8% in Mongolia [5].

However, data on the prevalence, trends, and associated factors of normal-weight central obesity (NWCO) in Mongolia are lacking. NWCO—defined as the presence of excess abdominal fat in individuals with a normal body mass index (BMI)—is increasingly recognized as a significant public health concern among adults. It is well established that general obesity increases the risk of diabetes, hypertension, and hypercholesterolemia [6, 7]. However, adults with NWCO also exhibit a higher prevalence of diabetes [5], hypertension [5, 8, 9], hypercholesterolemia [5], cardiovascular disease [10], and all-cause mortality [11] compared with individuals of normal weight without central obesity. Among adults with normal weight, the prevalence of central obesity was 26.7% in Peru in 2018–2021 [12], 7.7% in Jilin Province, China [13], and 21.7% globally [5].

Factors associated with NWCO among adults include female sex [12–14], older age [12–15], higher wealth status [12], full-time employment [15], retirement or unemployment [13], hypertension [12, 14], diabetes [12], dyslipidemia [14], non-daily cigarette smoking [14], physical inactivity [12] and low fruit intake [12]. These findings underscore the importance of routine assessment of central adiposity and the limitations of BMI alone in identifying obesity-related health risks, particularly among older adults. Therefore, this study aimed to examine the prevalence, trends, and associated factors of NWCO among adults aged 18 years and older in Mongolia using nationally representative data from 2005, 2009, 2013, and 2019.

Methods

We analysed secondary data from four nationally representative cross-sectional WHO STEPS surveys conducted in Mongolia in 2005, 2009, 2013, and 2019, which included comprehensive anthropometric measurements; pregnant women were excluded from all surveys [16–20]. The overall response rates were 95.0% in 2005, 95.0% in 2009, 97.4% in 2013, and 98.1% in 2019 [16–19]. Participants were randomly selected using a multistage stratified sampling design, targeting individuals aged 15–64 years in the 2005–2013 surveys and 15–69 years in the 2019 survey. For the present analysis, we restricted the sample to participants aged 18–64 years across all survey waves. In the 2005, 2009, and 2013 surveys, approximately one-third of selected participants completed STEP 3 laboratory measurements, whereas all participants underwent STEP 3 assessments in 2019 [16–19].

Data were collected using the WHO STEPwise approach to Surveillance (STEPS). Step 1 involved interviewer-administered questionnaires collecting sociodemographic characteristics, medical history, and health-risk behaviours; Step 2 included anthropometric measurements and blood pressure assessment; and Step 3 comprised biochemical measurements of blood glucose and blood lipids [20]. Blood pressure was measured using an OMRON Model M5 automatic blood pressure monitor, with three readings taken and the mean of the last two readings used for analysis [20]. At the survey sites, blood glucose and total cholesterol were measured in peripheral (capillary) blood using dry chemical methods and biochemical analysis with an automated analyser [16–19].

Measures

Outcome variables

Anthropometric measurements were obtained using standardized procedures by trained personnel across all four survey waves. Body weight was measured to the nearest 0.1 kg using an electronic scale, with participants barefoot and wearing light clothing (Gima professional scale, Italy). Height was measured without shoes to the nearest 0.1 cm using a Somatometre-Stanley 04-116 stadiometer (range up to 2 m). Waist circumference (WC) was measured to the nearest 0.1 cm using a non-stretchable tape at the midpoint between the upper margin of the iliac crest and the lower border of the rib cage (Gima waist meter, Italy) [16–19].

Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m²). Normal weight was defined as a BMI of 18.5–24.9 kg/m², in accordance with the Mongolian national nutrition guidelines for adults, which are aligned with World Health Organization criteria [21]. Central obesity was defined as a waist circumference ≥ 80 cm for women and ≥ 90 cm for men, based on cut-offs recommended for Asian populations [22]. Normal-weight central obesity (NWCO) was defined as having a normal BMI in combination with central obesity [8]. Participants who were underweight (BMI < 18.5 kg/m²) or overweight/obese (BMI ≥ 25 kg/m²) were excluded from the analysis.

Independent variables

Sociodemographic variables included age (years), educational attainment (total years of schooling and full-time study, excluding pre-school), sex (female or male, as observed), ethnicity (Khalkh, Kazakh, Dörvöd, Buriad, and others), employment status (yes/no), place of residence (urban or rural), and marital status (never married, currently married, cohabiting, separated, divorced, or widowed) [16–19].

Inadequate fruit consumption (< 2 servings/day) and inadequate vegetable intake (< 3 servings/day) were defined based on the total number of servings of fruits and vegetables consumed per day during a typical week [23].

Physical activity was assessed using the Global Physical Activity Questionnaire (GPAQ) and categorised as low (< 600 MET-min/week), moderate (600–1,500 MET-min/week), or high (> 1,500 MET-min/week) [24].

Smoking status was determined by the question, “Do you currently smoke tobacco products, such as cigarettes, cigars, or pipes?” and classified as yes or no.

Alcohol consumption was assessed by the frequency of consuming at least one standard alcoholic drink during the past 12 months and categorised as: never; less than once a month or 1–3 days per month; 1–2 days per week; and ≥ 3 days per week. Frequent alcohol use was defined as consumption on ≥ 3 days per week [16–19].

Diabetes was defined as fasting plasma glucose ≥ 7.0 mmol/L and/or current use of insulin or oral hypoglycaemic medications [20]. Hypertension was defined based on measured blood pressure (mean of the last two of three readings), with systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg, or current use of antihypertensive medication [25]. Raised total cholesterol was defined as fasting total cholesterol ≥ 5.0 mmol/L [20].

Statistical analysis

Descriptive statistics were used to summarise the study sample and estimate the prevalence of normal-weight central obesity (NWCO). Differences in proportions were assessed using chi-square tests. Binary logistic regression analyses were conducted to examine factors associated with NWCO. Variables that were statistically significant in univariable analyses—including survey year, age, sex, educational attainment, employment status, physical activity, hypertension, and raised total cholesterol—were entered into the multivariable model. The selection of independent variables was guided by previous literature [12–15].

All analyses accounted for the complex survey design using the svy commands in Stata, incorporating stratification, sampling weights, and primary sampling units. Variance estimation was performed using Taylor series linearisation. Multicollinearity was assessed using the variance inflation factor (VIF), with no evidence of collinearity observed. Statistical significance was set at p < 0.05. All statistical analyses were performed using Stata version 18.0 (StataCorp LLC, College Station, TX, USA).

Results

Sample characteristics

A total of 5,287 non-pregnant participants with normal body weight (BMI 18.5–24.9 kg/m²) from four survey waves (2005, 2009, 2013, and 2019) were included in the analysis. The mean age of participants was 36.1 years (SD = 12.3; range: 18–64 years), and 19.3% were men. The overall prevalence of NWCO among individuals with a normal BMI across all survey years was 34.0%, increasing from 8.7% in 2005 to 37.0% in 2019. The prevalence of NWCO differed significantly by age, sex, educational attainment, employment status, physical activity level, raised total cholesterol, and hypertension (Table 1).

Table 1.

Sample and normal-weight central obesity characteristics, STEPS survey Mongolia, 2005-2019

Variable	Sample	Normal-weight central obesity
	N (%)	No	Yes	P-valuea
		N (%)	N (%)
All	5287	3803 (66.0)	1484 (34.0)
Survey year
2005	1657 (31.3)	1479 (91.3)	178 (8.7)	<0.001
2009	1275 (24.1)	865 (70.8)	410 (29.2)
2013	1134 (21.4)	747 (64.9)	387 (35.1)
2019	1221 (23.1)	712 (63.0)	509 (37.0)
Sociodemographics
Age in years
18-29	1924 (36.4)	1539 (75.5)	385 (24.5)	<0.001
30-44	2011 (38.0)	1390 (59.5)	621 (40.5)
45-64	1352 (25.6)	874 (54.0)	478 (46.0)
Sex
Female	4264 (80.7)	2816 (64.9)	1448 (35.1)	<0.001
Male	1023 (19.3)	987 (96.9)	36 (3.1)
Education (in years)
0-9	1407 (26.6)	1020 (60.1)	387 (39.9)	0.003
10-11	1450 (27.4)	1258 (63.9)	392 (36.1)
≥12	2430 (46.0)	1725 (69.1)	705 (30.9)
Ethnic group
Other	823 (16.5)	611 (68.2)	212 (31.8)	0.345
Kalkh	4458 (83.5)	3188 (65.5)	1270 (34.5)
Employment status
No	2460 (47.0)	1825 (69.8)	635 (30.2)	<0.001
Yes	2826 (53.0)	1977 (62.6)	849 (37.4)
Residence
Rural	2396 (43.6)	1726 (64.2)	670 (35.8)	0.261
Urban	2891 (56.4)	2077 (67.2)	814 (32.8)
Current smoking	869 (5.9)	741 (59.9)	128 (40.1)	0.122
Frequent alcohol use (≥3 times/week)	144 (2.7)	129 (76.4)	15 (23.6)	0.437
Fruit intake (<2 servings/day)	4579 (86.1)	3281 (65.7)	1298 (34.3)	0.277
Vegetable intake (<3 servings/day)	4436 (79.6)	3240 (66.5)	1196 (33.5)	0.508
Physical activity
Low	801 (18.8)	514 (59.4)	287 (40.6)	0.008
Moderate	1019 (20.2)	731 (67.0)	288 (33.0)
High	3433 (61.0)	2539 (67.8)	894 (32.2)
Hypertension	1027 (12.8)	694 (53.9)	333 (46.1)	<0.001
Diabetesb	109 (4.3)	68 (56.7)	41 (43.3)	0.166
Raised total cholesterolb	633 (27.0)	372 (58.3)	261 (41.7)	0.029

^aBased on Chi-square, ^bone-third of the selected participants in 2005, 2009 and 2013, and all of selected participants in 2019

Associations with normal-weight central obesity

In adjusted logistic regression analyses, compared with the 2005 survey, participation in the 2019 survey was associated with significantly higher odds of NWCO (adjusted odds ratio [AOR] = 3.07, 95% confidence interval [CI]: 2.29–4.12). Middle-aged participants (45–64 years) had higher odds of NWCO compared with younger adults (AOR = 2.14, 95% CI: 1.65–2.79). Low physical activity (AOR = 1.31, 95% CI: 1.05–1.64) and hypertension (AOR = 1.44, 95% CI: 1.09–1.90) were also positively associated with NWCO. In contrast, male sex (AOR = 0.06, 95% CI: 0.01–0.27) and higher educational attainment (AOR = 0.68, 95% CI: 0.52–0.85) were inversely associated with NWCO (Table 2).

Table 2.

Associations with normal weight central obesity, STEPS survey Mongolia, 2005-2019

Variable	COR (95% CI)	P-value	AOR (95% CI)	P-value
Survey year
2005	1 (Reference)		1 (Reference)
2009	4.34 (3.30, 5.70)	<0.001	2.47 (1.82, 3.35)	<0.001
2013	5.70 (4.43, 7.33)	<0.001	2.28 (1.91, 3.50)	<0.001
2019	6.20 (4.96, 7.74)	<0.001	3.07 (2.29, 4.12)	<0.001
Age in years
18-29	1 (Reference)		1 (Reference)
30-44	2.09 (1.70, 2.58)	<0.001	1.80 (1.45, 2.24)	<0.001
45-64	2.63 (2.08, 3.33)	<0.001	2.14 (1.65, 2.79)	<0.001
Sex
Female	1 (Reference)		1 (Reference)
Male	0.06 (0.01, 0.28)	<0.001	0.06 (0.01, 0.27)	0.001
Education (in years)
0-9	1 (Reference)		1 (Reference)
10-11	0.85 (0.65, 1.11)	0.233	0.90 (0.68, 1.19)	0.461
≥12	0.67 (0.53, 0.86)	<0.001	0.68 (0.52, 0.85)	0.003
Ethnic group
Other	1 (Reference)		---
Kalkh	1.13 (0.88, 1.45)	0.345
Employment status
No	1 (Reference)		1 (Reference)
Yes	1.38 (1.14, 1.68)	<0.001	1.21 (0.98, 1.49)	0.076
Residence
Rural	1 (Reference)		---
Urban	0.87 (0.69, 1.10)	0.261
Current smoking	1.32 (0.93, 1.88)	0.123	---
Frequent alcohol use (≥3 times/week)	0.60 (0.16, 2.22)	0.442	---
Fruit intake (<2 servings/day)	1.15 (0.89, 1.48)	0.277	---
Vegetable intake (<3 servings/day)	0.91 (0.70, 1.19)	0.508	---
Physical activity (low)	1.43 (1.14, 1.78)	0.002	1.31 (1.05, 1.64)	0.017
Hypertension	1.79 (1.40, 2.30)	<0.001	1.44 (1.09, 1.90)	0.009
Diabetesa	1.43 (0.86, 2.37)	0.168	---
Raised total cholesterola	1.33 (1.03, 1.73)	0.030	1.27 (0.95, 1.70)	0.106

COR Crude Odds Ratio, AOR Adjusted Odds Ratio, CI Confidence Interval

^aone-third of the selected participants in 2005, 2009 and 2013, and all of selected participants in 2019

Discussion

The prevalence of NWCO observed in Mongolia over the period 2005–2019 (34.0%) was higher than that reported in Peru (26.7%) during 2018–2021 [12] and the global estimate (21.7%) [5]. A marked increase in NWCO prevalence was observed in Mongolia, rising from 8.7% in 2005 to 37.0% in 2019. This rapid increase may reflect changes in body fat distribution among Mongolian adults, potentially driven by epidemiological and lifestyle transitions [4, 26]. These findings highlight the need for strengthened public health interventions targeting central adiposity, even among individuals with normal body mass index.

Multivariable analyses indicated that more recent survey year, female sex, older age, lower educational attainment, low physical activity, and hypertension were associated with higher odds of NWCO. Consistent with previous studies, female sex and older age were strong correlates of NWCO [12–15]. Sex differences in body composition may partly explain these findings, as men generally have lower total body fat and greater lean mass and bone mineral density than women [8, 27]. Age-related changes in body fat distribution include reductions in appendicular fat, increases in trunk and abdominal fat, and greater fat infiltration into ectopic sites such as the liver and skeletal muscle, all of which contribute to increased metabolic risk with advancing age [12, 28].

In line with a previous study [15], employment status was marginally associated with increased odds of NWCO. While a multicountry study reported higher wealth status to be associated with NWCO [12], our findings indicate that lower educational attainment was associated with NWCO. Employment, particularly in certain occupational settings, may increase the risk of normal-weight central obesity due to sedentary work patterns, occupational stress, and adverse working conditions [29, 30].

Consistent with earlier research, physical inactivity was associated with NWCO in the present study [31]. Physical inactivity contributes to metabolic dysregulation, including reduced insulin sensitivity and increased visceral adiposity, even in the absence of overall weight gain [32]. Although a study from Peru reported a protective effect of fruit intake against NWCO [12], we did not observe significant associations between inadequate fruit or vegetable intake and NWCO. Similarly, while non-daily cigarette smoking has been associated with NWCO in previous research [14], no significant association was found between current smoking and NWCO in this study.

In agreement with prior studies, hypertension and raised total cholesterol (the latter in unadjusted analyses) were associated with NWCO [12, 14]. However, unlike some previous studies, no association was observed between diabetes and NWCO [5, 12]. Visceral fat accumulation is known to promote oxidative stress, insulin resistance, and systemic inflammation, which contribute to the development of cardiometabolic diseases and may explain these observed associations [33].

Because reliance on BMI alone may misclassify individuals and underestimate cardiometabolic risk, the high prevalence of NWCO observed in this study underscores the importance of incorporating additional anthropometric indicators beyond BMI when assessing excess adiposity. In particular, combined use of waist circumference and BMI is critical for identifying individuals with NWCO who may otherwise be overlooked [14]. Targeted health education and timely interventions are essential for preventing and managing cardiometabolic complications in this population. Furthermore, these findings highlight the value of monitoring waist circumference even among individuals with normal BMI. For individuals with NWCO, integrated interventions combining increased physical activity and dietary modification may be effective in reducing central obesity and associated health risks [34].

Strengths and limitations

A key strength of this study is the use of standardized measurement protocols and nationally representative samples across four survey waves conducted between 2005 and 2019. However, several limitations should be acknowledged. Some variables, particularly health-related behaviours, were self-reported and therefore subject to recall and social desirability bias. In addition, the cross-sectional design precludes causal inference regarding the observed associations. Future longitudinal studies are needed to better elucidate temporal and causal relationships. Furthermore, important factors potentially associated with NWCO, such as other dietary behaviours, were not assessed and should be incorporated in future research [35].

Conclusion

Nearly one in three adults in Mongolia had normal-weight central obesity, with prevalence increasing by 27.0% points between 2005 and 2019. Multivariable analyses showed that more recent survey year, female sex, older age, employment status, low physical activity, hypertension, and raised total cholesterol were associated with NWCO. These findings highlight the importance of incorporating waist circumference alongside BMI in routine clinical and public health assessments. To prevent NWCO and its associated cardiometabolic risks, healthcare providers should emphasise the maintenance of a healthy lifestyle, including regular physical activity and appropriate dietary behaviours, even among individuals with normal BMI.

Conclusion

Almost one in three adults in Mongolia had NWCO, which increased by 27.0% from 2005 to 2019. Regressions showed that more recent survey year, female sex, older age, being employed, current smoking, low physical activity, having hypertension and raised total cholesterol were associated with NWCO. In order to prevent NWCO, health care providers can inform their patients about the significance of maintaining a healthy weight and lifestyle changes.

Authors’ contributions

All authors fulfil the criteria for authorship. KP and SP conceived and designed the research, performed statistical analysis, drafted the manuscript and made critical revision of the manuscript for key intellectual content. All authors read and approved the final version of the manuscript and have agreed to authorship and order of authorship for this manuscript.’

Funding

No funding was received.

Data availability

The data on which this analysis were based are publicly available at the World Health Organization NCD Microdata Repository: URL: https://extranet.who.int/ncdsmicrodata/index.php/catalog.

Declarations

Ethics approval and consent to participate

The Ethical Review Committee of the Western Pacific Regional Office of WHO (WRC-WPRO) and the Ministry of Health Medical Ethical Committee in Mongolia accepted the study protocols, in accordance with the Declaration of Helsinki, and study participants gave written informed consent.

Competing interests

The authors declare no competing interests.