Ethnic Variations in Body Fat Storage

Research shows that ethnic groups exhibit varying patterns of fat distribution. Humans have two general patterns of fat distribution: androidal (commonly referred to as central or abdominal/truncal adiposity) and gynoidal (lower-body/peripheral adiposity), or described more colloquially by Marie Savard as “apple-shaped” or “pear-shaped,” respectively. While both patterns of fat distribution have potential health risks, research shows that abdominal (especially visceral fat) [Page 236]and truncal adiposity carry an increased risk for obesity-related complications such as glucose intolerance, hyperinsulinemia and the development of Type 2 diabetes, cardiovascular disease (CVD), and some types of cancer. Increased levels of central adiposity observed in some ethnic groups may explain the increased incidence of metabolic complications and CVD in these groups.

Ethnic groups, including non-Hispanic blacks, Mexican Americans, and some Native American groups in the United States, and black Caribbean and Irish groups in Britain, consistently show a higher prevalence of overweight and obesity according to body mass index (BMI) than the general population of the country. However, a growing body of evidence suggests that BMI alone may not adequately define overweight and obesity in adults or children for several reasons.

First, BMI does not distinguish between fat mass and lean (nonfat) mass. Therefore, a definition of obesity based on BMI alone might classify individuals with large central fat deposits as “normal” (defined as within the BMI range of 25–29.9), when that individual may be at greater risk for metabolic and cardiovascular complications.

Second, BMI also gives no indication of the distribution of body fat, and as mentioned above, fat distribution has been linked to several comorbidities. Simple anthropometric measures including waist circumference (WC), waist-hip ratio (WHR), and subscapular to triceps (STR) skinfold thickness ratio have been established as reliable measures of central adiposity. Among these, WC has been endorsed as the best surrogate measure of abdominal adiposity and cutoff points of over 102 centimeters in men and of over 88 centimeters in women are widely accepted as values representing risk for the development of obesity-related comorbidities. More sophisticated measurements such as computed tomography (CT) scans or magnetic resonance imaging (MRI) have also been used by some investigators because they can accurately distinguish between subcutaneous and visceral fat accumulation, but their usage is limited by their expense.

Certain ethnic groups exhibit a high prevalence of central obesity. When South Asians gain weight, they tend to accumulate fat in the abdominal and truncal regions of the body. This has been documented in several studies showing that they have larger waist circumferences, larger abdominal diameters, and thicker trunk skin folds for a given weight compared to other groups. South Asians also show a relationship between the onset of comorbidities such as Type 2 diabetes and CVD at much lower levels of BMI than has been documented in other groups. Japanese and Taiwanese Americans exhibit similar fat distribution as South Asians. Research in the United States shows that Mexican-American men and women have higher WC and STR than non-Hispanic Whites. Several studies demonstrate that abdominal adiposity in African Americans is characterized by a greater accumulation of subcutaneous fat than visceral fat, compared with other ethnic groups. Ethnic groups such as Pima Indians and Naruans do not show central fat distribution.

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