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Illinois State University

Regional Body Composition

Sex and Ethnic Variation

Chapter 18



Regional body composition refers to variation in the anatomical distribution of the major components of the body mass:

adipose tissue, skeletal muscle, and skeletal tissues.



The term distribution refers to the absolute or relative amount of a tissue in different regions or compartments of the body.

The term patterning is also used in discussion of regional body composition.


Variation in Body Composition

Two major sources of variation in body composition are the biological sex of the individual and population affinity (ethnicity).



Knowledge of age-, sex-, maturity-, and ethnicity-associated variation in regional body composition should contribute to the understanding of human variability.



A major portion of the variability in body composition has its origins during the years of growth and maturation.


Sex Differences

Biological difference between the sexes influence body composition per se and processes that affect body composition:– Rate of growth and maturation– The timing and tempo of the adolescent growth

spurt and sexual maturation– Body proportions and physique


Sex Differences

Sex differences in body composition are apparent early in life, are magnified during the adolescent growth spurt and sexual maturation, and present through adulthood.



Relatively greater accumulation of subcutaneous adipose tissue on the trunk compared to the extremities is often described as a central or truncal pattern.


Truncal Adiposity



A relatively greater accumulation over the abdomen compared to that over the hips is described as an android pattern, while the reverse is labeled a gynoid pattern.



Abdominal fatness is often indicated as a significant determinant of the relationship between obesity and morbidity, and as an independent risk factor for several degenerative diseases of adulthood, most notably some cardiovascular diseases and non-insulin-dependent diabetes.


Adipose Tissue

Adipose tissue can be differentiated into that which is visceral (internal or deep; VAT) and that which is subcutaneous (external or outer; SAT).


Age and Sex Differences

After young adulthood, T skinfold thickness increases more than E skinfold thickness in males, while both T and E skinfold thicknesses increase by similar amounts through the fourth decade in females.

Subsequently, T increases more than E in females.



The T/E ratio does not differ between the sexes from late childhood into early adolescence.

The ratio is rather stable in females, but increases considerably in males during adolescence and more slowly through the fifth decade.



Thus, males have proportionally more SAT on the T than E during adolescence and into adulthood.


Ethnic Variation

There are strong links between ethnicity, obesity, and disease.

Although individuals are labeled as belonging to a particular racial or ethnic group, variation within each of the categories is considerable.


Ethnic Variation

Certain ethnic groups have a relatively higher risk for obesity, predisposing them to cardiovascular disease, hypertension, non-insulin-dependent diabetes, certain cancers, and osteoarthritis.


Ethnic Variation

Because of this, African American women, Hispanic women, and American Indian women and men have been targeted for weight loss in nationwide health promotion and disease prevention initiatives.


Ethnic Variation

Among males, the T/E ratio does not consistently differ between White and Hispanic American children and adolescents.


Ethnic Variation

Subsequently, it is consistently larger in Hispanic Americans through adulthood.


Ethnic Variation

In contrast, the ratio is slightly but consistently larger in African Americans during childhood and adolescence.


Ethnic Variation

It is also larger in African Americans than in Whites during adulthood, but slightly smaller in African Americans than Hispanic Americans from the third through fifth decades.


Ethnic Variation

This suggests that, among males, African Americans have proportionally more SAT on the T than E during childhood through young adulthood than Whites and Hispanic Americans.


Ethnic Variation

The T/E ratio is thus, on average, consistently larger in African American and Hispanic American males than in White males throughout adulthood.


Ethnic Variation

During adulthood, African American women and Hispanic American women increase in both skinfold thicknesses more than White women, and these increases are larger at the subscapular site than at the triceps site.


Ethnic Variation

Hence the T/E ratio is consistently larger in women from these two ethnic groups, indicating proportionally more SAT on the T.


Ethnic Variation

The ethnic difference is greater in females than in males due especially to larger trunk skinfold thicknesses in Hispanic American women.


Ethnic Variation and Assessment

Ethnic differences in fat patterning and body composition place into question the applicability of generalized field method prediction equations derived primarily from Caucasian samples.



Because of differences in the proportions of the FFB composition among ethnic groups and inter-individual differences within ethnic groups, multi-component body composition assessment is recommended as a reference measure.



Unfortunately, most studies evaluating the applicability of methods and equations for specific ethnic groups have not used multi-component models.


Sex Variation

Adolescent girls have relatively little VAT, which suggests that abdominal VAT accumulates in later adolescence.


Sex Variation

During adulthood, abdominal VAT increases with age in each sex, more so in males than in females.


Sex Variation

Abdominal SAT also increases with age to about 60 years, and then decreases in each sex; females have, on average, more more SAT than males.


Sex Variation

Males have proportionally more abdominal VAT than females and the sex difference increases with age.

Women gain relatively more abdominal VAT after menopause.


Maturational Variation

Early maturing males have relatively more SAT on the T than average and late maturing males not only during adolescence but also in adulthood, which suggests persistence of maturity-associated variation into adulthood.



Thus, for the same size and mass, early maturing males have proportionally more SAT as adults.



There appears to be a gain in overall fatness and SAT during the transition from the premenarcheal to the postmenarcheal state.

Proportionally more SAT is accumulated on the T than on E at this time.



After menarche, proportionally more VAT is accumulated (lower SAT/FM ratio), while the relative distribution of SAT is unchanged (similar T/E ratios).


Skeleton

The dry, defatted skeleton weighs, on average, about 95g in infant boys and slightly less in girls.


Skeleton

In young adulthood, the skeleton weighs about 4.0 kg in men and 2.8 kg in women.


Skeleton

As a percentage of body weight, the dry, fat-free skeleton comprises about 3% of body weight in the fetus and newborn and about 6-7% of body weight in the adult.


Skeleton

Bone mineral, estimated from ash weight, comprises about 2% of body weight in infants and 4-5% of body weight in adults.


Skeleton

The skeleton is consistently heavier and has more mineral in American Blacks than in Whites from infancy through adulthood.


Skeleton

Long bones are more dense than vertebrae. Cervical vertebrae are more dense than the

other vertebrae in males but not significantly so in females.

Bones of males are more dense than those of females.


Skeleton

Bones of American Blacks are more dense than those of American Whites.

Densities of individual bones in males and females of both ethnic groups decrease with age.


Skeleton

The sex differences in density are related to bone mineral.


Skeleton

There is an absence of sex differences in BMC and BMD from childhood through mid-adolescence, except that the density of the upper limbs tends to be slightly larger in males.


Skeleton

In later adolescence, and especially in young adulthood, however, males have a greater BMC and BMD.

These trends persist into adulthood.


Skeleton

BMC and BMD of the normal older women are about 7% and 6%, relatively, less than in younger women, with relatively little variation among the different region/segments of the skeleton.


Skeleton

TBBM does not significantly differ between boys and girls in early puberty but is considerably higher in boys in later puberty when sex differences are significant.


Skeleton

Peak bone mass is achieved in 14-15 year- old females and 17 to 18- year-old males.


Skeleton

Vertebral BMD begins to decrease in young adulthood, and this decrease continues linearly with age, while reduction of radial BMD does not occur until 50 years of age, after which the rate of loss accelerates.


Skeleton

The estimated decline in BMD is greater in females than males at each site.


Skeletal Muscle Tissue

It is the component of body composition that is the most difficult to quantify in vivo.



Estimated muscle mass, derived from creatine excretion or potassium concentration, shows a growth pattern like that for body weight.



Sex differences are small prior to the adolescent growth spurt, but males gain considerably more muscle mass than females during adolescence and the sex differences persists throughout the life span.



Early dissection studies indicate that the head and trunk account for about 40% of the total weight of the musculature at birth but only 25-30% at maturity.



Muscles of the lower extremities increase their relative contribution from about 40% at birth to 55% of the total weight of the musculature at maturity, while muscles of the upper extremities have a relatively constant contribution of about 18-20%.



Thus, by 18 years of age, arm musculature of males is about 25% larger than of females, while the corresponding difference in calf musculature is only about 10%.



Males have proportionally more upper than lower extremity skeletal muscle than females.


Summary

Among the three tissues that constitute the body’s composition, variation in regional distribution is best documented for adipose tissue and then for skeletal (bone) tissue.


Summary

In the context of the available data, there is variation in the regional distribution of adipose, skeletal, and skeletal muscle tissues associated with age, sex, and ethnicity.


Summary

Individuality in the timing and tempo of sexual maturation and the adolescent growth spurt adds to the variation.


Summary

Most of the information on regional distribution of adipose, skeletal, and skeletal muscle tissues is based on cross-sectional data.


Summary

Hence, the present state of knowledge of regional variation in body composition during the life span is based largely on differences between age groups and not on changes which accompany age.

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