Abstract
The rates of diabetes in the USA are rapidly increasing, and vary widely across different racial/ethnic groups. This paper explores the potential contribution of body composition, diet and physical activity in explaining diabetes disparities across women of different racial and ethnic backgrounds. For body composition, racial/ethnic groups differ widely by BMI, distribution of body mass and quantity and type of adipose tissue. Dietary patterns that vary across race/ethnicity include consumption of meat, added sugars, high-glycemic carbohydrates and fast food. Additionally, physical activity patterns of interest include aerobic versus muscle-strengthening exercises, and the purpose of physical activity (leisure, occupation, or transportation). Overall, these variables provide a partial picture of the source of these widening disparities, and could help guide future research in addressing and reducing diabetes disparities.
Type II diabetes (diabetes) is a largely preventable disease, yet the prevalence of diabetes in the USA has reached epidemic proportions. Recent studies estimate that 40% of the US adults have diabetes or prediabetes [1]. This constitutes an approximate 50% increase in diabetes in the past decade [1], and numbers are expected to rise. Based on current trends, it is projected that the prevalence of diagnosed diabetes will more than double by 2050 [2]. Those with diabetes experience increased risk of a number of complications, including cardiovascular disease, chronic kidney disease and reduced lifespan. People who are diagnosed before age 30 lose an estimated 15 years of life, and 24 years of quality-adjusted life [3]. Additionally, treatment for diabetes is extremely costly. Recent studies estimate that the cost of diabetes in the USA has increased by 41% in just 5 years, totaling US$245 billion in 2012, and is more than 20% of total US healthcare costs [4].
While diabetes is prevalent across racial/ethnic groups, it shows marked health disparities between individuals of different races and ethnicities. Age-adjusted rates of diabetes for non-Hispanic blacks (blacks) and Hispanics are nearly double those of non-Hispanic whites (whites) [1]. While these differences are large, disparities with other racial groups are even more extreme: prevalence for white adults is approximately 7.6% [5], yet rates as high as 18.3% for US-dwelling Asian–Indians [6] and 38% in US-dwelling Pima Indians [7] have been reported. Nationally collected data from the CDC show significantly higher rates of diabetes among Hispanics, blacks, Asian–Americans (Asians) and American Indians compared with whites, with only Chinese–Americans and Alaska Natives showing lower diabetes prevalence [5].
Additionally, these disparities are expected to increase. While the overall number of individuals with diagnosed diabetes is projected to increase by approximately 99% among whites by 2050, the increase is estimated to be over 200% for blacks and nearly 500% for Hispanics [2]. Rates of diabetes are expected to increase more in women (220%) than in men (174%) by 2050, particularly for women of racial and ethnic minorities. Given current trends, it is expected that 49% of black women and 52.5% of Hispanic women will develop diabetes in their lifetime, compared with 31% of white women [3].
A key component of addressing rising rates of diabetes in women, then, will be addressing disparities in this disease. However, the causes of these wide disparities at this point are not well understood. The causes of diabetes are varied, and include genetics, physiology (such as body composition), behaviors (such as diet and physical activity) and healthcare access. Differences in any or all of these factors could contribute to different rates of diabetes. In the current paper, we will explore potential sources of diabetes disparities by examining past research on differences in health behavior and physiology between women of different racial/ethnic backgrounds. Specifically, we will examine patterns of body composition, diet and physical activity across women of varying racial/ethnic groups in order to explore the potential role each of these may play in differential rates of diabetes between women of different racial/ethnic groups.
Literature search
We searched PubMed for papers comparing body composition, dietary patterns and/or physical activity variables between two or more racial/ethnic groups. In the case of body composition, this included BMI, percent body fat, body fat distribution and specific fat depots (such as visceral and subcutaneous fat). For dietary patterns, we searched for papers on specific dietary patterns that have been linked to diabetes such as sugar and sugar-sweetened beverage consumption; consumption of red and processed meats; fast food consumption; and low intakes of fiber, fruits and vegetables. Physical activity was considered any sort of measured bodily movement, and included both aerobic and muscle-strengthening activities. Whenever possible, we isolated data that were specific to women. We restricted our search to papers published since 1990.
We focused primarily on data from white, black and Hispanic women, simply because the greatest amount of data were available for these groups. The majority of large, nationally representative datasets generally have not provided more detailed racial/ethnic categories beyond these. Data were seldom available, particularly for behavioral variables, for Asian, Pacific Islander, or American Indian women. Additionally, data on different subgroups within racial/ethnic categories were scarce, though this data was included when available.
Racial/ethnic differences in women's body composition
BMI & obesity
The vast majority of research exploring the association between body composition and diabetes has centered on excess adiposity, marked differences in which have been noted across racial/ethnic groups. Obesity, classified as a BMI greater than 30, has been strongly tied to risk of diabetes in women. In the Nurses’ Health Study, women in the 90th BMI percentile had 11 times greater risk of developing diabetes over the 8-year follow-up than women in the 10th percentile [8]. Higher BMI even in women within a normal weight range has been linked to greater incident diabetes, as has weight gain in normal weight women [9].
Measures of BMI show that black and Hispanic women typically have higher overall BMI and higher rates of overweight and obesity than white women. Recent estimates show that approximately 82% of black women and 74% of Hispanic women are classified as overweight (BMI >25), compared with 61% of white women, while obesity is seen in 58 and 41% of black and Hispanic women, respectively, compared with 33% of white women [10]. Few nationally representative studies have included racial/ethnic breakdowns beyond these, but those that have consistently show that Asian–Americans, particularly women, have a markedly lower prevalence of overweight and obesity, while obesity in Native American women is similar to rates in blacks and Hispanics [11].
However, there are drawbacks to using BMI to compare body composition across racial/ethnic groups. Actual body composition, such as percent body fat, appears to differ across different racial/ethnic backgrounds such that two women with identical BMIs may have very different physiology. Articles examining BMI and body fat percentage consistently show higher body fat percentage in South East Asians than whites at the same BMI [12]. For example, at a given percent body fat, BMI in whites is approximately three BMI points higher than in Singaporeans [13]. More extreme differences were shown when comparing body fat percentages in Asian Indian women and Pacific Island women, who had the same percentage of fat, but BMIs of 26 and 35, respectively [14]. One meta-analysis examined the association between percent body fat and BMI in American black, white, Chinese, Ethiopian, Indonesian, Polynesian and Thai women, and found that predictions of body fat percentage using standard BMI, age and gender-centered equations erred by a range of −3.9% (Polynesians) to +10% (Ethiopians) [15]. These racial/ethnic differences in body fat–BMI relationships also appear to be more pronounced in women than men [12,16].
Body fat distribution
In this respect, exploring overall rates of overweight and obesity between racial/ethnic groups is likely less useful to the discussion of disparities in diabetes than examining differences in more specific measures of body composition. While more exact measures of percent body fat are useful, a large body of research suggests that the distribution of body fat may be more important than the quantity. Fat in the abdominal region in particular has been shown to be strongly associated with diabetes. Among the most common measures of abdominal distribution of fat are waist circumference, which offers a crude measure of abdominal adiposity, and the ratio of the waist and hip circumference (waist–hip ratio), which compares distribution of fat in the abdomen and hip region. Waist circumference (WC) has been shown to be a markedly better predictor of prevalent and incident diabetes than overall weight or BMI [17]. Longitudinal data in the Nurses’ Health Study showed that, even after adjusting for BMI, risk of incident diabetes over an 8-year period was more than five times higher in the 90th percentile for WC than those in the 10th percentile, and more than three times higher in the 90th versus 10th percentile for waist–hip ratio (WHR) [8]. Similarly, in the Normative Aging Study, WHR in men was more strongly associated with diabetes than overall BMI and was positively associated with blood glucose independent of overall adiposity [18].
There is some evidence that distribution of fat differs between racial/ethnic groups. There are somewhat consistent findings showing that Hispanics have greater abdominal adiposity than white women [19]. For example, one study found relatively modest differences in average BMI (25.2 vs 23.9) and body fat percentage (38.4 vs 34.9) in Hispanic versus white women, yet found that abdominal adiposity was 30–40% greater in Hispanics [19]. In fact, waist circumference was identified as the best predictor of incident diabetes in a cohort of Mexican–Americans, with those in the highest quartile showing 11 times greater risk than those in the lowest quartile [20]. There is also evidence that Asian women (Filipino), who generally have lower BMIs than white women, have higher WHR [21], and black women generally have higher WC measurements than white women [22].
While mass and distribution of body fat clearly vary across women of different racial/ethnic backgrounds, it appears the story is even more complicated than that. Several studies have shown that these differences appear to change at different levels of BMI/WC [16,23], and also appear to change with age [24]. Thus, while BMI may be an equally good predictor of fat mass for both Chinese women and white women, this may only be true for middle aged, normal weight women. One study showed that accounting for both age and skinfold thickness improved correlations between BMI and percent body fat for white and Asian (primarily Chinese) women [12].
Abdominal fat deposits
While abdominal obesity is a superior predictor of diabetes than overall body fat or BMI, this measure is limited in that it cannot distinguish between types of fat in the abdomen. Fat in the abdominal region is generally deposited either outside of the abdominal wall (subcutaneous adipose tissue [SAT]) or within the abdominal wall (visceral adipose tissue [VAT]). Both of these fat depots are captured simultaneously when relying on WC or WHR, yet they differ markedly in their physiology and association with metabolic dysfunction. VAT in particular is robustly predictive of metabolic risk factors such as fasting glucose, metabolic syndrome, insulin sensitivity and diabetes [25]. SAT, on the other hand, often shows no association with metabolic markers, and has even been shown to be protective against diabetes [25]. Distribution of fat in these locations in the abdomen may vary across race/ethnicity, which could contribute to differential rates of diabetes beyond simple measures of overall abdominal obesity.
Research examining racial/ethnic differences in VAT and SAT distribution have shown remarkably consistent results
Measures of visceral adipose tissue and subcutaneous adipose tissue in women of different racial/ethnic backgrounds.
CT: Computed tomography; SAT: Subcutaneous adipose tissue; VAT: Visceral adipose tissue; WC: Waist circumference.
The vast differences in body composition between racial/ethnic groups suggest that racial/ethnic-specific anthropometric targets, like BMI or WC, be established [33,34]. This may be particularly appropriate for Asians, given the large discrepancy between BMI/overall body size and body fat, especially VAT in the abdomen. Accordingly, the American Diabetes Association has recently released new BMI cut points specifically for Asian–Americans, identifying 23 as an appropriate BMI cut point for diabetes screening rather than 25, as is used for other racial/ethnic groups [35,36].
Muscle mass across racial/ethnic groups
Despite the fact that muscle plays a crucial role in glucose metabolism, very little data exist on how muscle quantity or quality relates to the risk of metabolic disorders. There is some evidence suggesting that lower ratios of muscle-to-total body weight is associated with greater insulin resistance [37], and lower abdominal muscle mass in ethnically diverse women has been associated with higher diabetes prevalence [38].
Few studies have examined differences in muscle mass between racial and ethnic groups. One examination of abdominal muscle in an ethnically diverse sample showed that Asian–Indians had less lean mass and skeletal muscle than European or Pacific Island individuals [14]. Similarly, one study examining fat and muscle mass in white and Hispanic women found that Hispanics not only had more abdominal fat mass, they also had less fat free mass in the trunk region [19].
Body composition & disease risk across diverse populations
Clearly there are differences in body composition in women of different racial/ethnic backgrounds; whether these differences translate to differences in disease risk is an important question that has received relatively little attention. Black women, for example, have relatively high rates of diabetes, but consistently had the lowest levels of VAT, thus the influence of body composition may differ by racial/ethnic group. In the Nurses’ Health Study, each 5-unit increment in BMI at baseline was associated with the greatest increase in risk of incident diabetes in Asian (RR: 2.36) and Hispanic women (RR: 2.21), and the lowest increase in risk in black women (RR: 1.55) [39]. Similarly, weight gain over the 20-year period increased the risk of diabetes most strongly for Asian women: each 5-kg gain increased risk by 84% in Asian women, compared with just 38% for blacks and 37% for whites. In a study of South Asians and Europeans, increasing WHR was associated with greater diabetes prevalence in both racial groups. However, this association was stronger for South Asians, with each increase in WHR being associated with more than double the prevalence of diabetes [40]. Additionally, higher rates of VAT appear to be only part of the explanation for the higher rates of diabetes in South Asians. While Filipino women had the highest rates of diabetes and the highest levels of VAT in the Rancho Bernardo cohort, the odds of diabetes in Filipinos were still more than twice that of black women and more than seven-times that of white women even after adjusting for VAT area [22]. Similarly, an examination of anthropometrics and metabolic markers in white and black women showed that, despite similar BMI and WHR between the two groups, insulin sensitivity was 36% lower in black women [27].
Finally, one study did directly assess the extent to which differences in body composition contributed to disparities in diabetes across women of different racial/ethnic groups. The authors found that differences in abdominal obesity specifically accounted for 12.1% of the difference in diabetes between white and black women and 9.8% of the difference between white and Hispanic women [41]. Differences in abdominal obesity, then, do play a role in diabetes disparities, yet clearly there are other factors responsible as well.
Racial/ethnic differences in diet
Dietary patterns have been strongly related to diabetes risk. While consumption of sugars [42–46], foods with high glycemic indexes [47,48], red and processed meats [49–53] and saturated fat [54] are associated with increased risk of diabetes, other foods such as green leafy vegetables [55,56] and whole grains [57,58] constitute protective factors. Thus, differences in food consumption among women of various ethnicities may partially account for disparities in their risks of diabetes. According to national data, for example, blacks are less likely to meet nutrition guidelines, compared with whites and Mexican–Americans [59]. A closer inspection of dietary practices among different racial/ethnic groups, detailed below and summarized in
Dietary behaviors among women of different ethnic/racial backgrounds.
CSFII: Continuing Survey of Food Intake by Individuals; DHKS: Dietary Health and Knowledge Survey; MA: Mexican–American; NHANES: National Health and Nutrition Examination Survey; WIC: Women Infant Children.
Added sugars & sugar-sweetened beverages
Intake of added sugar is positively associated with incidence of diabetes, not only through weight gain but also through glycemic and metabolic processes [42–46,67]. Additionally, increased consumption of sugar-sweetened beverages, which comprise the largest (42%) source of added sugar intake [67], has been associated with increased incidence of diabetes in various cohort studies [43–46]. Multiple studies analyzing racial/ethnic differences in added sugar and sugar-sweetened beverage consumption yield that blacks consume significantly more added sugars than whites, and whites consume the least amount of added sugars of racial/ethnic groups [68–70]. A study that used 2009 California Health Interview Survey data found Hispanic women to be more likely to consume larger quantities of sugar-sweetened beverages, compared with non-Hispanic women [60]. On the other hand, a comparison of black and Hispanic mothers enrolled in the Women, Infants and Children (WIC) program in Chicago found Hispanics to consume significantly less added sugars and sweetened beverages than blacks [61]. While there is less research regarding the consumption of sugar and sugar-sweetened beverages among Asian populations compared with other ethnicities, there is some evidence that acculturation plays a role in sugar consumption among Asians. In a sample of Korean Americans in New York [71], acculturation was positively associated with consumption of sweet foods, such as candies or chocolates. Less acculturated individuals ate fewer sweet foods, although they were more likely to add sugar to coffee or tea.
Carbohydrates & fiber
Carbohydrates are classified according to their glycemic index, which measures the rate at which a carbohydrate raises blood glucose after ingestion [48]. Highfiber, low-glycemic foods, such as whole grains, leafy greens and legumes, are associated with reduced risk of diabetes [47,57,72]. Conversely, consumption of low-fiber, high-glycemic foods, such as refined grains and white bread, is associated with an increased risk of diabetes [47,48].
Storey and Anderson [62] revealed that dietary fiber consumption is below adequate for women of all ethnicities in their analysis of NHANES data for white, black, Hispanic and ‘other race’ women. Women of ‘other races’ were found to have the highest intake of dietary fiber, followed by Hispanic women and white women, while black women had the lowest. Studies have consistently found blacks to have lower intake of dietary fiber compared with whites and Mexican–Americans, while Mexican–Americans have been found to have the highest intake of dietary fiber [73,74]. In their study of WIC mothers in Chicago, Kong and colleagues [61] found significantly higher consumption of fiber among Hispanic women, compared with black women; whole grain and fruit consumption was also significantly higher among Hispanic women, compared with black women. Nationwide, blacks have lower intakes of fruits and vegetables, compared with whites and Mexican–Americans [59]. Drewnowski and Rehm [63] also suggested that black women are less likely to consume an adequate amount of fruit than white, Mexican–American and other Hispanic women.
Red & processed meat
Positive associations have been found between meat consumption and diabetes, particularly processed and red meat [49–53]. Nevertheless, more research is necessary to understand why consumption of red and processed meat is associated with an increased risk of diabetes. Saturated fat, found in meat products, and trans fatty acids from hydrogenated oils have also been associated with increased risk of diabetes [54]. These types of fat are believed to increase insulin resistance [54]. Conversely, certain types of unsaturated fats, like linoleic acid, decrease risk of diabetes through improved insulin sensitivity [54].
NHANES data from 1999–2004 show that black women consumed more red meat and other meat products, and Mexican–American women consumed more red meat, compared with white and ‘other race’ women [64]. However, a study comparing white and black women in New York and New Jersey found that red meat consumption was higher for white women, while processed meat consumption was higher for black women [65]. Additionally, a comparison of black and Hispanic mothers enrolled in WIC programs in Chicago revealed that Hispanic women consumed significantly less saturated fat than black women [61].
Fast food consumption
Various studies have documented periodic increases in fast food consumption throughout the years, which is correlated with increased consumption of saturated fat, carbohydrates, added sugars, soft drinks and meats, and with decreased intake of fruits, nonstarchy vegetables and fiber [75–77]. Nationwide, fast food consumption has been found to be higher among blacks compared with all other ethnicities [75]. A comparison of blacks and whites in a multicenter cohort study revealed fast-food consumption to be higher among blacks at all time points [66]. White women had the lowest consumption of fast food compared with black women, white men and black men; additionally, white women's consumption of fast food decreased over time, while for black women it increased [66]. Hispanic women appear to be at increased risk for fast-food consumption compared with other ethnicities, as revealed by O'Brien and colleagues [60] in their study comparing Hispanic women with non-Hispanics in California.
Overall, a recommended diet for the prevention of diabetes includes a low intake of sugars, starches and saturated fats, and favors consumption of fiber-rich fruits, vegetables and whole grains. National data reveal disparities in diabetes-related eating behaviors among different ethnicities. Black women particularly are more likely to engage in unhealthy eating practices compared with whites and Hispanics. Nevertheless, certain regional studies obtained different results, as demonstrated by Chandran and colleagues’ study of women in New York and New Jersey [65], where red meat consumption was higher for white women. Newby and colleagues [78] suggested that research should focus not only on ethnicity but also on region when analyzing dietary habits; in their study of white and black men, they found an interaction between race and region for consumption of trans fat. In our review of literature, we found no epidemiological research that compared women's eating behaviors across regions, in addition to race/ethnicity.
Racial/ethnic differences in physical activity Benefits of physical activity
Physical activity is associated with a decreased likelihood of developing Type 2 diabetes. In the Women's Health Study, women who walked 5 h per week were 33% less likely to develop diabetes than women who did not walk regularly [79,80]. One longitudinal study of women at risk for developing diabetes found physical activity to be associated with risk for diabetes independently from BMI – with each 100-minincrement of moderate physical activity per week being associated with a 9% decreased risk for diabetes [81].
Both aerobic and muscle-strengthening exercises are protective against diabetes, and can improve glycemic control in people with diabetes. Combined exercise regimens include both aerobic and muscle-strengthening exercise, and are effective in improving insulin sensitivity and decreasing insulin requirement [82]. The CDC recommends that adults get at least 150 min of aerobic activity per week and that they engage in muscle-strengthening exercise at least 2 days per week [83]. Aerobic exercise is recommended to be spread between multiple days throughout the week, and to be at least moderate intensity [83].
Engagement in physical activity
Less than half of all women in the USA meet physical activity (PA) guidelines [84]. Engagement in PA varies markedly by racial/ethnic group. National level surveys have primarily focused on measuring aerobic PA, some through self-report and some through objective measures such as accelerometers. Those relying on self-report measures have typically found higher rates of PA and meeting guidelines in white women compared with black and Hispanic women. A comparison of the self-report measures included in NHANES, the National Health Interview Survey (NHIS), and the Behavioral Risk Factor Surveillance System (BRFSS) all showed a higher percentage of whites meeting PA recommendations compared with blacks and Hispanics, and whites being less likely to be classified as ‘inactive’ [85]. According to the 2011 version of the NHIS, 50% of white women reported meeting aerobic exercise guidelines, compared with just 34.6% of black women and 36.2% of Hispanic women. Black and Hispanic women were also much more likely to be classified as inactive (41.8 and 41.6%, respectively) compared with white women (26.7%) [86]. Similarly, the 2001 version of the BRFSS showed that, compared with white women, odds of meeting PA guidelines were 37 and 27% lower in black and Hispanic women, respectively [87]. Similarly, the National Physical Activity and Weight Loss Survey, conducted in 2002, found that only 12% of white women reported doing no PA, compared with 25.2% of black women and 27.3% of Hispanic women [88].
Data derived from accelerometers has generally shown much lower rates of PA, as well as different pat terns between racial/ethnic groups, than self-reported PA. Accelerometer data from NHANES compiling total PA per day (not in 10-min bouts) show that Hispanic women engaged in 21.7 min per day of moderate PA, compared with 19.4 min in black women and 18.6 min in white women [89]. When looking at the same data for 10-min bouts of exercise, Troiano et al. found that black women engaged in the most PA, followed by Hispanic women, and then white women [89]. Accelerometer data from the CDC show that white women are more likely to engage in vigorous activity, with 10% of white women engaging in five or more 10-min bouts of vigorous activity per week compared with 6% of black women, and 7% of Hispanic women [90].
The discrepancy between self-report and accelerometer-derived data could reflect less overreporting bias on the part of black and Hispanic women, and/or an emphasis in self-report measures on leisure time physical activity (LTPA), rather than occupational (OPA) or transportation activity (TPA; see
Measures of leisure-time physical activity, occupational physical activity and transportation-related physical activity in women of different ethnic/racial backgrounds.
BRFSS: Behavioral Risk Factor Surveillance System; CHIS: California Health Interview Survey; LTPA: Leisure time physical activity; OPA: Occupational physical activity
PA: Physical activity; TPA: Transportation activity.
Engagement in different types of activity has also changed over time. From 2000–2012, whites and Chinese significantly increased their amount of LTPA, while Hispanics significantly increased their engagement in TPA [94]. In the 2001 California Health Interview Survey, Asian–American women reported engaging in 11.6 min of TPA per day, compared with whites, blacks and Hispanics, who reported an average of 8.1 min per day [93]. Although Asian–American women were more likely to engage in TPA, Asian–American women were 52% less likely than other women to meet LTPA guidelines and were twice as likely to be physically inactive [93].
Similar to PA differences between racial groups, significant PA differences exist between racial subgroups. For example, Japanese are 4% less likely than Chinese to meet LTPA recommendations, while Filipinos are 51% more likely [93]. South Asians are 38% more likely, Koreans 42% more likely and Vietnamese 23% more likely to meet LTPA recommendations than are Chinese [93]. Among Hispanic women, Puerto Ricans are 33% less likely to meet LTPA recommendations than whites, Mexicans are 28% less likely, Mexican–Americans are 22% less likely, Cubans are 67% less likely, Dominicans are 62% less likely and Central or South Americans are 34% less likely [92]. Similarly, a study comparing PA between racial groups found a significant difference in OPA among English-speaking and Spanish-speaking Hispanic women. Only 11.6% of English-speaking Hispanic women reported engaging in OPA three or more times per week, compared with 27.7% of Spanish-speaking Hispanic women [88]. It is likely that women within the same ethnicity vary in PA engagement by other factors, such as age, education level and socioeconomic status.
Muscle-strengthening physical activity
It is also important to understand how adherence to muscle-strengthening guidelines varies by ethnicity. The 2012 NHIS reported that 30.9% of white women met aerobic guidelines only, compared with 24.5% of black women and 26% of Hispanic women [86]. Fewer women met both muscle-strengthening and aerobic guidelines: 19.9% of white women, 10.8% of black women and 12.2% of Hispanic women [86]. Additionally, women were less likely to engage in both aerobic and muscle-strengthening exercises than men: 19.9 versus 26% in whites, 10.8 versus 23.7% in blacks and 12.2 versus 19.3% in Hispanics, respectively [86]. NHIS data from 1998 through 2004 indicate that muscle-strengthening exercises are becoming more common in women: among white women, 16.2 compared with 20.4% (1998, 2004, respectively); among black women, 9.4 compared with 11.3%; and among Hispanic women, 8.9 compared with 9.1% [95]. Women's adherence to muscle-strengthening exercises also varies by age. In 2004, 20.1% of women aged 18–24 years engaged in muscle-strengthening exercises at least twice a week, compared with only 10.7% of women aged 65 and older [95]. Information regarding muscle-strengthening adherence in Asians, American Indians/Alaskan Natives (AI/AN) and Native Hawaiian/Pacific Islanders (NH/PI) are only available for men and women combined: 18.7% of AI/ANs, 17.1% of Asians and 31% of NH/PIs, compared with 21.4% of whites and 16.8% of blacks, meet both aerobic and muscle-strengthening guidelines [86].
Overall, women of different racial groups vary significantly in their engagement in physical activity. Further differences exist between engagement in LTPA, OPA and TPA. When examining percentages of people engaged in muscle-strengthening exercise compared with aerobic exercise, it is clear that few people engage in muscle-strengthening exercise. There was very little data on women-specific muscle-strengthening exercise, despite the importance of resistance training to metabolic health.
Discussion
Overall, data from body composition and behavioral studies showed patterns consistent with patterns of diabetes prevalence. Women from racial/ethnic groups with higher prevalence of diabetes – namely, black, Hispanic, Pacific Islander and Native American – tended to have higher rates of obesity, with the most notable exception being Asian women, who consistently had lower BMI and WC despite a higher prevalence of diabetes. More specific measures of body composition were less consistent with trends in diabetes prevalence, and there was marked variation in body composition measures between racial/ethnic groups. While black women generally had higher BMIs, WCs and overall body fat, they consistently had the lowest amount of visceral fat. Asian women, conversely, despite small body size, had the highest amounts of visceral fat, followed by Hispanics.
Data on diet were somewhat more consistent, though largely limited to whites, blacks and Hispanics. Though there were some regional differences, generally black women in particular showed more metabolically unhealthy dietary practices compared with white women. Data comparing dietary practices in other racial/ethnic groups was extremely limited. Findings from physical activity studies varied greatly depending on the measures used. Virtually all self-report studies showed greater activity and lower inactivity in white women compared with black and Hispanic women, while accelerometer data showed the opposite. Leisure time physical activity was highest among white women, while Hispanic women reported the most occupational activity. Given the variations in findings for physical activity, it is difficult to comment on how these may contribute to differential rates of diabetes. Overall, however, physical activity was quite low, which could contribute to rising rates of diabetes across racial/ethnic groups.
Of course, commenting on the contribution these variables may make to diabetes disparities in complicated by the fact that they are not independent of one another. Body composition can be directly influenced by both diet and physical activity, beyond simple associations with overall adiposity. Physical fitness has been associated with less VAT [96], and increasing physical activity appears to selectively reduce VAT deposits rather than SAT [97]. Weight loss strategies relying on dietary change, however, do not show this selective reduction [98], though dietary patterns, such as fiber intake, fast food intake, a ‘southern’ diet, sugar-sweetened beverages and overall calorie consumption have all been associated with specific fat depots [99–101]. These relationships are further complicated by the fact that they may differ by racial/ethnic group. For example, a weight loss study with black and white women showed that, with similar overall weight loss, black women selectively reduced SAT while white women selectively reduced VAT [102].
The physical environment may play a key role in differences in health behavior. A review found evidence (although not always consistent) of positive associations between engagement in physical activity and different characteristics of the built environment, including aesthetics, safety and access to trails, parks and walkable destinations [103]. Moreover, studies have found associations between various traits of the built environment and neighborhoods’ racial composition. Moore and colleagues analyzed North Carolina, New York and Maryland census data and found an increased likelihood of availability of recreational facilities and parks in predominantly white neighborhoods, compared with ethnic minority neighborhoods (i.e., predominantly black and Hispanic neighborhoods) 104].
Likewise, there is scientific evidence regarding racial/ethnic disparities in access to healthy and unhealthy food. Neighborhoods consisting of ethnic minority populations generally have increased concentrations of fast-food outlets and decreased access to healthy food outlets, although these results have not been completely consistent [105–108]. There is also evidence regarding associations between increased availability of healthy food through neighborhood outlets and increased consumption of healthy food [106,107]. For example, in one study higher availability of dark green and orange vegetables in the neighborhood led to increased intake of these vegetables [109]. Understanding determinants of behavior, such as physical environment, will better equip researchers to address health disparities in diabetes among different racial/ethnic groups.
Conclusion & future perspective
This review revealed important gaps in the literature regarding availability of data beyond the major racial/ethnic groups (i.e., whites, blacks and Hispanics, and in lesser degree Asians and Mexican–Americans). For example, not until 2011–2012 did NHANES include a category for Asians (previous racial/ethnic categories included whites, blacks, Mexican–Americans, other Hispanic and other races). The need for data specific to subgroups is emphasized by the fact that diabetes prevalence itself varies remarkably across subgroups, often showing a larger range within than between racial/ethnic groups. Rates in Alaska Natives/American Indians, for example, range from 6% in Alaska Natives to 24.1% in American Indians in Southern Arizona, and within Asian subgroups prevalence ranges from 4.4% in Chinese to 13% in Asian–Indians [110]. Given these vast differences in diabetes prevalence between subgroups, it is likely that data on risk factors is similarly misleading when generalized across racial/ethnic groups.
Continued investigation of ethnic differences by subgroups and by region is necessary; this type of data reveals important distinctions that are not captured by more general national data, which is limited in its treatment of race/ethnicity. In the nutrition realm, for example, national data identifies black women as having higher odds of most risk factors (e.g., higher consumption of added sugars, red meat, processed meat, etc); however, smaller regional studies might contradict these findings. For example, Chandran and colleagues studied differences between white and black women in New York and New Jersey, and found white women to have higher consumption of red meat [64].
Another large gap revealed in the literature was in muscle and strength training measures. Although muscle is highly active in glucose metabolism, and muscle-strengthening exercise increases insulin sensitivity, both the body composition literature and the physical activity literature lack information on the association between muscle and diabetes. Future research should focus on racial/ ethnic differences in muscle quantity and type, in conjunction with insulin sensitivity and diabetes risk. In the physical activity literature, there is scant data regarding adherence to muscle-strengthening guidelines between women across ethnic/ racial groups. Exercise physiology studies illustrate improvements in insulin sensitivity from muscle-strengthening exercise and combined aerobic/ muscle-strengthening exercise regimens [111]. However, NHIS data report that very few women participate in muscle-strengthening exercises [112]. Promoting strength training, therefore, may be a key future area of health behavior research, particularly for women from racial/ ethnic groups at high risk for diabetes.
Executive summary
In addition to BMI, distribution of adipose tissue is associated with risk of diabetes.
Correlations between BMI and more specific body composition measures, such as percent body fat and waist circumference, vary widely across racial/ethnic groups.
Women of different races/ethnicities vary greatly in accumulations of visceral versus subcutaneous adipose tissue. Asian women are most likely to have a high amount of visceral adipose tissue at lower BMI cut points, and therefore have the highest risk of diabetes at the lowest BMIs when comparing across ethnicities.
Added sugar consumption is correlated with increased risk of diabetes. Black women consumed the highest amount of added sugars, and Hispanic women consumed the highest quantity of sugar-sweetened beverages, when comparing blacks, Hispanics and whites.
Red and processed meat consumption is correlated with increased risk of diabetes, while fruit and vegetable intake is correlated with reduced risk of diabetes. Measures of meat, fruit and vegetable intakes across ethnicity vary by study.
Self-report physical activity data yield that white women engage in the most physical activity, followed by Hispanics and blacks.
Accelerometer data yield that black and Hispanic women engage in the most physical activity, followed by whites.
Less than 50% of women in the USA meet government-recommended physical activity guidelines; even fewer women engage in muscle-strengthening exercises.
Hispanics are most likely to engage in occupational physical activity, while whites are most likely to engage in leisure time physical activity, and Asians are the most likely to engage in transportation-related physical activity.
Future research should include more racially/ethnically-specific data beyond typical broad categories (white, black and Hispanic), including data specific to subgroups within racial/ethnic groups and regionally-specific data.
Future interventions should consider environmental determinants of behavior, and should shift a greater focus to muscle and strengthening exercises in order to prevent and manage diabetes in diverse women.
Footnotes
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.