3. Physiological differences between the sexes and the characteristics of reproductive life in women

Among the physiological factors related to sex differences, there is a hormonal issue: Sex hormones strongly influence body fat distribution and adipocyte differentiation. Estrogens and testosterone differentially affect the physiology of adipocytes. Visceral fat is higher in men than in premenopausal women. In men, visceral fat accrual generally increases with the amount of total body fat, whereas in women, visceral fat accumulation is less a function of total adiposity. Women had less visceral fat despite having a higher total body fat, BMI, and subcutaneous fat [24–27].

As women reach menopause, depot differences in adipocyte size are attenuated due to the express increase in omental cell size. The propensity of postmenopausal women toward visceral fat accumulation and presence of larger adipocytes suggests that the decline of estrogen may stimulate adipocyte hypertrophy in this depot. In men, adipocytes of the visceral and abdominal subcutaneous fat compartments have similar sizes across the range of adiposity values [24, 28].

In men, a meta-analysis found that those with low concentrations of total testosterone (TT), sex hormone-binding globulin (SHBG), and free testosterone (FT) were more likely to develop metabolic syndrome compared to those having high sex hormone concentrations. The revealed associations were independent of age and lifestyle factors. Associations with TT were strongest for prevalent AO [OR (odds ratio) per quartile decrease = 1.58] (95% CI 1.51–1.66). Low FT concentrations were associated with incident AO [HR (hazard ratio) = 1.13] (95% CI 0.98–1.29), although the latter was not statistically significant [29].

Studies show that the prevention of AO should be focused on lifestyle. However, there are different hormonal factors between the sexes that must be considered, especially for women, whose menopausal transition goes through hormonal changes that favor the redistribution of body fat, being more susceptible to abdominal fat accumulation. Moreover, the life expectancy of women generally exceeds that of men, with a significant increase in the number of women experiencing the menopausal transition phase, which makes this an increasingly relevant issue in terms of public health.

To better understand this topic, it is important to elucidate the differences between sex (biology) and gender (the social). According to Annandale and Hunt [21], this distinction was essential to make it clear that gender inequalities in health were, in the most part, socially produced, rather than biologically given. Olinto [22] also called attention to the operationalization of the gender category in epidemiological studies. Sex only means the genetic, anatomical, and physiological characterization of human beings. However, gender roles are socially constructed and usually framed as an extension of biologically determined social functions. The pioneering feminist Simone de Beauvoir said in her famous quote: "One is not born, but rather becomes, a woman." Though the positions of women and men are not simply parallel, the principle is also true for men: One is not born masculine, but has to become a man [23]. Thus, gender is related to differences in patterns of employment, education, family, and household structure, leisure and consumption at the societal level, and in the everyday experience of individual men and women [21]. In this sense, we describe the possible biological and

>102 cm (males) and >88 cm (females); <sup>3</sup>

>90 cm

Author Country (year) Prevalence (%) Men (%) Women (%)

Beltrán-Sánchez et al. [10] USA (2009–2010)1 56.0 46.4 65.4 Gutiérrez-Fisac et al. [11] Spain (2008–2010)2 36.0 32.0 39.0 Riediger and Clara [12] Canada (2007–2009)<sup>1</sup> 35.0 29.1 40.0 Schienkiewitz et al. [13] Germany (1997–1999)<sup>1</sup> 33.9 29.7 38.0 Sardinha et al. [14] Portugal (2008–2009)<sup>2</sup> – 19.3 37.9

Barquera et al. [15] Mexico (2010–2012)<sup>3</sup> 74.0 64.5 82.8 Misra and Shivastava [16] South Asians (2011–2012)<sup>4</sup> 68.9 17.6–62.2 23.7–74.8 Xi et al. [17] China (2009)3 37.4 27.8 45.9 Linhares et al. [18] Brazil (2010)1 30.0 19.5 37.5 Chukwuonye et al. [19] Nigeria (2013)1 21.8 3.2 39.2

≥102 cm (males) and ≥88 cm (females); <sup>2</sup>

≥90 cm (males) and ≥80 cm (females).

Table 2. Prevalence of AO according to gender in selected high- and low-middle-income countries.

social factors associated with AO according to gender differences.

of reproductive life in women

High-income countries

74 Adiposity - Epidemiology and Treatment Modalities

Low-/middle-income countries

Cutoffs of WC for AO = <sup>1</sup>

(males) and >80 cm (females); <sup>4</sup>

3. Physiological differences between the sexes and the characteristics

Among the physiological factors related to sex differences, there is a hormonal issue: Sex hormones strongly influence body fat distribution and adipocyte differentiation. Estrogens and testosterone differentially affect the physiology of adipocytes. Visceral fat is higher in men than in premenopausal women. In men, visceral fat accrual generally increases with the Menarche and menopause set the beginning and the end of women's reproductive life and are important risk factors for chronic diseases, including obesity and cardiovascular disease. Early menarche, before the age of 12, has been associated with a higher prevalence of AO [30–33]. Both early menarche and early menopause can be considered as increased risk factors for cardiovascular disease.

The association between early menarche and obesity is still controversial in the literature. However, some longitudinal studies demonstrated that childhood obesity is the trigger to early pubertal development because of increased exposure to reproductive steroids [estradiol level] [30, 32, 34–36]. Furthermore, many genetic variants associated with the timing of menarche are in or near genes associated with childhood and adulthood obesity, so this fact should be considered [32].

Reproductive life characteristics are directly associated with AO. For example, a cross-sectional study with a sample of 617 women from southern Brazil observed that women with a history of three or more pregnancies and menarche at the age of 11 or earlier had a 25% higher prevalence of AO compared to nulliparous or primiparous women with menarche at 14 years or older [31]. Studies show that the number of parturitions leads to a tendency of decreased hip circumference and increased WC [37–39].

Pregnancy was associated with visceral adiposity gains and central obesity in the study with 122 premenopausal women monitored for 5 years. Throughout the monitoring period, nulliparous women had a 14% increase in the visceral adipose tissue, while those with at least one parturition increased by 40%. Parturition was associated with increased WC. It is suggested that after pregnancy, there is a preference for fat accumulation in the visceral adipose tissue [40]. Similarly, in a sample of 170 American women aged 18–76 years, it has been found that the intra-abdominal fat tissue increased as the number of parturitions increased, regardless of age, body fat percentage, physical activity, and smoking [41].

Changes in the distribution of body fat and AO as a consequence of pregnancy require further investigation. As a modifiable risk factor, weight gain during the pre- and postpartum periods can provide a critical window for performing interventions to prevent substantial weight gain and the development of obesity in women [42].

Epidemiological studies are consistent in the sense that characteristics of reproductive life may have a strong influence on body fat buildup in women during the menopausal transition. The transition from the reproductive phase to the nonreproductive phase is characterized by endocrine changes due to the decline of ovarian activity, biological changes due to decreased fertility, and consequent clinical changes due to menstrual cycle changes, as well as a variety of symptoms [43].

The change in metabolism that accompanies menopausal transition occurs at the expense of a reduction in lipoprotein lipase, responsible, along with estrogen, for regulating fat accumulation and distribution in tissues [44]. Testosterone seems to be a factor influencing the accumulation of visceral adipose tissue, and it seems to be related to the state of hyperandrogenism in women. The accumulation of visceral fat was higher in women after menopause compared to premenopausal women [45].

Several studies have shown a high prevalence of AO in postmenopausal women, ranging from 50 to 85% [31, 46–49]. A systematic review by Mendes et al. [49] found a high prevalence of AO in the menopausal transition, mainly in studies performed in clinics. Among these, the highest prevalence rates were reported in a study based on the Northeast region of Brazil, with 76.6% of premenopausal women and 85.2% of postmenopausal women. The lowest prevalence was found among Asian women, who had prevalence of 16.4% among premenopausal women and of 29.1% among postmenopausal women, suggesting that ethnicity is an outlier factor as far as the accumulation of fat in the abdominal region is concerned, once Western women have a higher prevalence than Eastern women.

The relationship involving women's experience in their reproductive period, their individual characteristics, such as age of menarche and number of parturition, hormonal changes during the menopausal transition, and the accumulation of fat in the abdominal region deserves more attention from health professionals.

## 4. Socioeconomic status and gender

Gender, as a social construct, plays an important role in the association between socioeconomic characteristics and AO. Socioeconomic status (SES) is a complex and multidimensional construct, in which individuals are classified by being compared to other individuals, based on material and nonmaterial attributes [50]. SES influences the individual access to goods and services regarding nutrition, physical activity, and other healthy practices and environmental conditions, which influence the relationship between socioeconomic position and AO.

nulliparous women had a 14% increase in the visceral adipose tissue, while those with at least one parturition increased by 40%. Parturition was associated with increased WC. It is suggested that after pregnancy, there is a preference for fat accumulation in the visceral adipose tissue [40]. Similarly, in a sample of 170 American women aged 18–76 years, it has been found that the intra-abdominal fat tissue increased as the number of parturitions

Changes in the distribution of body fat and AO as a consequence of pregnancy require further investigation. As a modifiable risk factor, weight gain during the pre- and postpartum periods can provide a critical window for performing interventions to prevent substantial weight gain

Epidemiological studies are consistent in the sense that characteristics of reproductive life may have a strong influence on body fat buildup in women during the menopausal transition. The transition from the reproductive phase to the nonreproductive phase is characterized by endocrine changes due to the decline of ovarian activity, biological changes due to decreased fertility, and consequent clinical changes due to menstrual cycle changes, as well as a variety of

The change in metabolism that accompanies menopausal transition occurs at the expense of a reduction in lipoprotein lipase, responsible, along with estrogen, for regulating fat accumulation and distribution in tissues [44]. Testosterone seems to be a factor influencing the accumulation of visceral adipose tissue, and it seems to be related to the state of hyperandrogenism in women. The accumulation of visceral fat was higher in women after menopause compared to

Several studies have shown a high prevalence of AO in postmenopausal women, ranging from 50 to 85% [31, 46–49]. A systematic review by Mendes et al. [49] found a high prevalence of AO in the menopausal transition, mainly in studies performed in clinics. Among these, the highest prevalence rates were reported in a study based on the Northeast region of Brazil, with 76.6% of premenopausal women and 85.2% of postmenopausal women. The lowest prevalence was found among Asian women, who had prevalence of 16.4% among premenopausal women and of 29.1% among postmenopausal women, suggesting that ethnicity is an outlier factor as far as the accumulation of fat in the abdominal region is concerned, once Western women have a

The relationship involving women's experience in their reproductive period, their individual characteristics, such as age of menarche and number of parturition, hormonal changes during the menopausal transition, and the accumulation of fat in the abdominal region deserves more

Gender, as a social construct, plays an important role in the association between socioeconomic characteristics and AO. Socioeconomic status (SES) is a complex and multidimensional construct,

increased, regardless of age, body fat percentage, physical activity, and smoking [41].

and the development of obesity in women [42].

76 Adiposity - Epidemiology and Treatment Modalities

symptoms [43].

premenopausal women [45].

higher prevalence than Eastern women.

attention from health professionals.

4. Socioeconomic status and gender

Studies have used different SES indicators; nonetheless, we focus primarily on individual characteristics, such as income, education and occupation, and economic development of countries, because they may have greater importance regarding interpretations of linkages between SES and AO which emphasize behavior.

Classic studies showed the direction of association between SES and obesity varied by population and economic status of countries. In developed countries, individuals with lower socioeconomic status were more likely to be obese than those in the higher socioeconomic group. However, in some LMIC the prevalence of obesity has increased among low SES groups, mainly among women. However, Is the association between SES and obesity similar to the association between SES and AO?

Most of these global analyses did not evaluate AO as outcome. This paper aims to show findings on the association between SES and WC in HIC and LMIC. In HIC, a recent study analyzed 50 years of socioeconomic inequities in WC among US-born black and white Americans, using data from the National Health Examination Surveys (NHES) I-III (1959–1970), National Health and Nutrition Examination Surveys (NHANES) I-III [1971–1994], and NHANES 1999–2008. WC increased in socioeconomic strata among both black and white Americans. Regarding income, white people in the 20th [low] income percentile have greater mean WC compared with people in the 80th [high] income percentile [51]. In the same direction, a cross-sectional study carried out with 12,883 individuals representing the Spanish population found that the frequency of obesity and AO decreased as the educational level increased [11]. In addition, a prospective study in the United Kingdom with 8312 subjects and three follow-ups over ten years showed that a lower adult occupational position predicted adverse changes in WC [52]. Finally, 56,556 participants from seven population-based German cohort studies (CARLA, SHIP, KORA, DEGS, EPIC-Heidelberg, EPIC-Potsdam, PopGen) were analyzed by meta-analysis. Men and women in the low education group had a 0.1% point greater annual increase in WC than participants in the high education group. Women with low income had a 0.1% point higher annual increase in WC than women with high income [53].

On the other hand, in LMIC, associations of risk factors with AO differ between men and women. The Thai National Health Examination Survey investigated this association in 64,480 adults. Compared with primary education, the odds of obesity [range I] were higher in men with university education. For women, the association was inverse, the odds of obesity ranges I and II were higher in those with primary education [54]. In Northeast China, a representative sample of 25,196 adults was evaluated. Analysis stratified by gender showed that men with a higher educational level, white-collar job, or cadre job were part of the high risk group, and women with a higher level of education or higher family income were in the low risk group [55]. Finally, in Brazil, a cross-sectional study with 1,720 Brazilian adults found results that point to the same direction. The WC was 4.67 cm higher in women who live in low education neighborhoods compared to the residents of high education areas. In the same group, the chance of AO was 2.05 times higher [56].

Thus, the findings suggest that the association between SES and AO is similar to the association with overall obesity. Separate studies of individual nations showed that high status people tend to have a smaller WC than others, in HIC, and this association is the same for women, in LMIC. On the other hand, among men from LMIC, the association between SES and AO is positive. First, this reversal in the relationship of SES and AO across levels of economic development highlights the importance of the national socioeconomic context of AO. Second, the high prevalence of AO among low SES women, in LMIC, shows an important health inequality. In some LMIC countries, low SES groups may now have sufficient access to cheap, calorie-dense, and processed food, as a consequence of the globalization of the fast food industry and agriculture.
