The four-compartment models in body composition: data from a study with dual-energy X-ray absorptiometry and near-infrared interactance on 815 normal subjects

Frequency of Metabolic Syndrome and Study of Anthropometric, Clinical and Biological Characteristics in Peri- and Postmenopausal Women in the City of Ksar El Kebir (Northern Morocco)

This study aimed to determine the frequency of metabolic syndrome and to identify its predictive factors in peri- and post-menopausal women in the city of Ksar El Kebir, in northern Morocco. A total of 373 peri- and post-menopausal women between 45 and 64 years old participated in the study. Metabolic syndrome was diagnosed according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) definition. Body mass index (BMI) was calculated to assess the degree of obesity in women; anthropometric, clinical and biological parameters were collected during interviews. The mean ages of peri- and postmenopausal women were 48.84 ± 2.4 years and 56.65 ± 4.29 years, respectively. Postmenopausal women had higher means of anthropometric and biological parameters than peri-menopausal women. We also noted a predominance of metabolic syndrome in postmenopausal women (n = 158) compared to peri-menopausal women (n = 81). Waist circumference was the predominant marker in the subjects studied, whereas triglycerides were the lower marker. In the overall population, the incidence of metabolic syndrome and its associated factors were higher in postmenopausal women than in peri-menopausal women, from which it can be concluded that post menopause may be a predictor of metabolic syndrome.

Imaging of the muscle-bone relationship

Muscle can be assessed by imaging techniques according to its size (as thickness, area, volume, or alternatively, as a mass) and architecture (fiber length and pennation angle), with values used as an anthropometric measure or a surrogate for force production. Similarly, the size of the bone (as area or volume) can be imaged using MRI or pQCT, although typically bone mineral mass is reported. Bone imaging measures of mineral density, size, and geometry can also be combined to calculate bone's structural strength-measures being highly predictive of bone's failure load ex vivo. Imaging of muscle-bone relationships can, hence, be accomplished through a number of approaches by adoption and comparison of these different muscle and bone parameters, dependent on the research question under investigation. These approaches have revealed evidence of direct, mechanical muscle-bone interactions independent of allometric associations. They have led to important information on bone mechanoadaptation and the influence of muscular action on bone, in addition to influences of age, gender, exercise, and disuse on muscle-bone relationships. Such analyses have also produced promising diagnostic tools for clinical use, such as identification of primary, disuse-induced, and secondary osteoporosis and estimation of bone safety factors. Standardization of muscle-bone imaging methods is required to permit more reliable comparisons between studies and differing imaging modes, and in particular to aid adoption of these methods into widespread clinical practice.

How can waist circumference predict the body composition?

BACKGROUND

Waist circumference (WC) is used as a risk assessment for metabolic syndrome, diabetes, and cardiovascular disease (CVD). WC consists of visceral fat area (VFA), subcutaneous fat area (SFA), muscle, intramuscular fat, viscera, and bone. Each component of the WC may differ between the sexes and generations, even if they have the same WC. However, this has not been measured in an epidemiological study.

METHODS

Between 2004 to 2009, employees and their spouses working at a Japanese company underwent a health examination after more than 12 hours of fasting. We analyzed the data of 11,570 subjects (9,874 men and 1,696 women), aged from 20 to 76 years, who underwent a computed tomography (CT) examination. VFA, SFA, WC, muscle, intramuscular fat, viscera, and bone were measured using a CT scanner. We conducted stratified analyses by generational age, and calculated the Pearson's correlation coefficients between the VFA and WC, BMI, and VFA plus SFA. To establish the equations for converting the WC to the corresponding VFA and VFA plus SFA, linear regression analyses were used to obtain the regression coefficients and intercepts.

RESULTS

As the generations increased in age, the VFA tended to increase. However, the differences in the WC values of each generation did not coincide with the VFA values in men (r = -0.275 and 0.979 for men and women, n = 5 generations), but did correlate with the difference in the sum of the VFA plus SFA for both sexes (r = 0.915 and 0.996 for men and women, n = 5 generations). Older generations had lower WC values when they had the same VFA values as the younger generations.

CONCLUSIONS

The WC value corresponding to a certain VFA value differed significantly by generational age. Thus, revised optimal cutoff values for the WC may be needed for each generation.

Bone mass increase in puberty: what makes it happen?

It is now thought that the critical property of bone is strength rather than weight, and that control of bone strength is mainly exercised through the effect of the mechanical loads brought to bear on bone. Muscle contraction places the greatest physiological load on bone, and so the strength of bone must be adapted to muscle strength (the functional muscle-bone unit). The Utah paradigm of skeletal physiology [J Hum Biol 1998;10:599-605] provides a model of bone development that describes how bone structure is regulated by local mechanical effects that can be adjusted by the effects of hormones. The DONALD (Dortmund Nutritional and Anthropometric Longitudinally Designed) study analysed the interaction between the muscle and bone systems in males and females before and during puberty. This study found that differences between the genders in bone adaptation during puberty are at least partly driven by the influence of oestrogen in females. Testosterone seems to have no direct relevant effect on bone during puberty, but may be implicated in the greater amount of muscle mass achieved in boys compared with girls.

A DXA study of muscle-bone relationships in the whole body and limbs of 2512 normal men and pre- and post-menopausal women

A whole-body DXA study of 1450 healthy Caucasian individuals [Bone 22 (1998) 683] found that mineral mass, either crude (BMC) or statistically adjusted to fat mass (FM-adjusted BMC), correlated linearly with lean mass (LM, proportional to muscle mass). The results showed similar slopes but decreasing intercepts (ordinate values) in the order: pre-MP women > men > post-MP women > children. This supports the hypothesis that sex hormones influence the control of bone status by muscle strength in all species. Now we further study those relationships in 2512 healthy Hispanic adults (307 men, 753 pre-MP women, 1452 post-MP women), including separate determinations in their upper and lower limbs. The slopes of the BMC or FM-adjusted BMC vs. LM relationships were parallel in all the studied regions. However, region-related differences were found between the ordinates of the curves. In the whole body, the crude-BMC/LM relationships showed the same ordinate differences as previously observed. In the lower limbs, those differences were smaller in magnitude but highly significant, showing the order: pre-MP women > men = post-MP women. In the upper limbs, the decreasing ordinate order was: men > pre-MP women > post-MP women. After fat adjustment of the BMC, order in both limbs was: men > pre-MP women > post-MP women. Parallelism of the curves was maintained in all cases. LM had a larger independent influence on these results than FM, body weight, or age. The parallelism of the curves supports the idea that a common biomechanical control of bones by muscles occurs in humans. Results suggest that sex-hormone-associated differences in DXA-assessed muscle-bone proportionality in humans could vary according to the region studied. This could be related to the different weight-bearing nature of the musculoskeletal structures studied. Besides the obvious anthropometric associations, FM would exert a mechanical effect as a component of body weight, evident in the lower limbs, while muscle contractions would induce a more significant, dynamical effect in both lower and upper limbs. Muscles seem to exert a larger influence than FM, body weight, and age on BMC in the whole body and lower limbs, regardless of the gender and reproductive status of the individual. The muscle-bone relationships studied may provide a rationale for a future differential diagnosis between disuse-related and other types of osteopenia.

Estrogen and bone--a reproductive and locomotive perspective

The primary function of the skeleton is locomotion, and the primary function of estrogen is reproduction. When the skeleton is considered within this locomotive context, the onset of estrogen secretion at puberty leads to packing of mechanically excess mineral into female bones for reproductive needs. Accordingly, the unpacking of this reproductive safety deposit at menopause denotes the origin of type I osteoporosis.

INTRODUCTION

According to the prevailing unitary model of involutional osteoporosis, female postmenopausal bone loss can be described as having an initial accelerated, transient phase (type I), followed by a gradual continuous phase (type II). Estrogen withdrawal is generally accepted as the primary cause of the type I osteoporosis. Thus, the quest to uncover the origin of type I osteoporosis has focused on the estrogen withdrawal-related skeletal changes at and around the menopause. However, considering that the cyclical secretion of estrogen normally begins in early adolescence and continues over the entire fertile period, one could argue that focusing on perimenopause alone may be too narrow.

MATERIALS AND METHODS

This is not a systematic review of the literature on the skeletal function of estrogen(s), but rather, an introduction of a novel structure- and locomotion-oriented perspective to this particular issue through pertinent experimental and clinical studies.

RESULTS AND CONCLUSIONS

When considering locomotion as the primary function of the skeleton and integrating the classic findings of the pubertal effects of estrogen on female bones and the more recent hypothesis-driven experimental and clinical studies on estrogen and mechanical loading on bone within this context, a novel evolution-based explanation for the role of estrogen in controlling female bone mass can be outlined: the onset of estrogen secretion at puberty induces packing of mechanically excess bone into female skeleton for needs of reproduction (pregnancy and lactation). Accordingly, the unpacking of this reproductive safety deposit of calcium at menopause denotes the accelerated phase of bone loss and thus the origin of type I osteoporosis.

Relation between body composition and age in healthy Japanese subjects

OBJECTIVE

To describe the relation between body composition and age measured by dual-energy X-ray absorptiometry (DXA) in healthy Japanese adults.

DESIGN

Cross-sectional study.

SUBJECTS AND MEASUREMENTS

The subjects were 2411 healthy Japanese adults (males 625, females 1786, age 20--79 y) who attended the Fukuoka Health Promotion Center, Fukuoka, Japan for health check-up. Body composition was determined by DXA (QDR-2000, Hologic) for the whole body and three anatomical regions of arms, legs and trunk.

RESULTS

The mean values of body mass index (BMI) and percentage fat mass (%FM) were 23.2+/-3.1 (s.d.) kg/m(2) and 21.8+/-6.8% for males and 22.1+/-3.3 kg/m(2) and 32.0+/-7.5% for females, respectively. For males, curvilinear relations with the peaks in their forties or fifties were seen for the variables associated adiposity, ie BMI, waist and hip circumference, waist-hip ratio, total or regional fat mass (FM), %FM and ratio of trunk FM to leg FM. For females, most of these variables increased linearly in older subjects. Lean mass (LM), bone mineral content (BMC) and bone mineral density (BMD) of the whole body and appendicular LM were relatively constant until the forties and then decreased in both sexes. The rates of decrease in the total or appendicular LM were larger for males than for females, whereas those in BMC or BMD were larger for females than for males.

CONCLUSIONS

This study presents the first detailed data on body composition in Japanese, which may be useful when comparing with populations of different racial and ethnic backgrounds and studying ill subjects.

Relation between body fat and age in 4 ethnic groups

BACKGROUND

Previous studies of the relation between age and body fat reached differing conclusions concerning the question of whether body fat is lower in the elderly than in middle-aged persons.

OBJECTIVE

The objectives of this study were to characterize the relation between age and body fat in 4 ethnic groups and test the hypothesis that body fat is lower in the elderly than in middle-aged persons.

DESIGN

Body fat was measured in a sample of 1324 volunteers aged 20-94 y by using a 4-component model of body composition. Four ethnic groups were studied: Asians, blacks, Puerto Ricans, and whites. Regression models were developed for fat mass and fat percentage as functions of age.

RESULTS

In all but one of the groups, a highly significant curvilinear relation between age and body fat was found, indicating a peak amount of body fat in late middle age and lower amounts of body fat at younger and older ages (P < 0.001). The age at which maximum body fat was predicted in the various groups ranged from 53 to 61 y for fat mass and from 55 to 71 y for fat percentage. In Puerto Rican men there was no significant relation between age and fat mass, and the relation between age and fat percentage was linear and positively correlated.

CONCLUSIONS

This study provided data on the relation between age and body fat in 4 ethnic groups and supported the hypothesis that body fat is lower in the elderly than in middle-aged persons.

Relationship of body water compartments to age, race, and fat-free mass

Water compartments were studied in 72 black and 128 white women, aged 20 to 70 years. Total body water (TBW) was measured by tritiated water dilution, and extracellular water (ECW) was measured by using delayed gamma neutron activation for the determination of total body chloride. Intracellular water (ICW) was assessed as the difference between TBW and ECW. Fat-free mass (FFM) was estimated by the measurement of total body potassium (TBK) and total body fat (TBF) by measurement of total body carbon (TBC). Total body protein was calculated from total body nitrogen (TBN). TBW was found to decline with age and to also be significantly influenced by body size. The extracellular water space was 41.5% of TBW. The decline of TBW with age is due primarily to a decline in ICW. The hydration of the FFM increased with age for the overall population because of a decline in TBK and TBN and an increase in ECW. Body composition models that have assumed constancy of hydration should be adjusted not only for gender but for age and body size.

Gender-related differences in the relationship between densitometric values of whole-body bone mineral content and lean body mass in humans between 2 and 87 years of age

The mineral, lean, and fat contents of the human body may be not only allometrically but also functionally associated. This report evaluates the influence of muscle mass on bone mass and its age-related changes by investigating these and other variables in both genders in the different stages of reproductive life. We have analyzed the dual-energy X-ray absorptiometry (DEXA)-determined whole-body mineral content (TBMC), lean body mass (LBM), and fat body mass data (FBM) of 778 children and adolescents of both genders, aged 2-20 years [previously reported in Bone 16(Suppl.): 393S-399S; 1995], and of 672 age-matched men and women, aged 20-87 years. Bone mass (as assessed by TBMC) was found to be closely and linearly associated with muscle mass (as reflected by LBM) throughout life. This relationship was similar in slope and intercept in prepubertal boys and girls. However, while keeping the same slope of that relationship (50-54 g increase in TBMC per kilogram LBM): (1) both men and women stored more mineral per unit of LBM within the reproductive period than before puberty (13%-29% and 33%-58%, respectively); (2) women stored more mineral than age-matched men with comparable LBM (17%-29%) until menopause; and (3) postmenopausal women had lower values of bone mineral than premenopausal women, similar to those of men with comparable LBM. Men showed no age effect on the TBMC/LBM relationship after puberty. Multiple regression analyses showed that not only the LBM, but also the FBM and body height (but not body weight), influenced the TBMC, in that decreasing order of determining power. However, neither the FBM nor body height could explain the pre/postpubertal and the gender-related differences in the TBMC/LBM relationship. Accordingly: (1) calculated TBMC/LBM and FBM-adjusted TBMC/LBM ratios were lower in girls and boys from 2-4 years of age until puberty; (2) thereafter, females rapidly reached significantly higher ratios than age-matched men until menopause; and (3) then, ratios for women and age-matched men tended to equalize. A biomechanical explanation of those differences is suggested. Sex hormones or related factors could affect the threshold of the feedback system that controls bone remodeling to adapt bone structure to the strains derived from customary mechanical usage in each region of the skeleton (bone "mechanostat"). Questions concerning whether the mineral accumulation in women during the reproductive period is related or not to an eventual role in pregnancy or lactation, or whether the new bone is stored in mechanically optimal or less optimal regions of the skeleton, are open to discussion.

Effects of the menopause transition on body fatness and body fat distribution

OBJECTIVE

The menopause transition increases cardiovascular and metabolic disease risk, partly because of the adverse effects of estrogen deficiency on the plasma lipid-lipoprotein profile and cardiovascular function. This increased cardiovascular and metabolic disease risk may also be partially mediated by increased body fat, increased intra-abdominal adipose tissue accumulation, or both. The objective of this mini-review is to summarize studies that have investigated the relationships among the menopause transition, body fatness, and body fat distribution.

RESEARCH METHODS AND PROCEDURES

A review of cross-sectional and longitudinal studies on menopause that examined body fatness and body fat distribution.

RESULTS

Cross-sectional reports show that the menopause transition is related to modest increases in body mass index or total fatness, although not all studies found significant effects. Increased central adiposity appears to be related to menopause, independent of advancing age, but these results are methodology dependent. An independent effect of menopause on central body fatness was noted by the use of techniques such as DEXA or computed tomography, whereas studies using circumference measures showed discrepant results. Longitudinal studies showed that the menopause transition accelerated the increase in central adiposity, although no studies quantified changes in intra-abdominal fat by imaging techniques.

DISCUSSION

Thus, additional longitudinal studies using more accurate measures of adiposity are needed to critically examine the effects of the menopause transition on total and central body fatness. Collectively, previous studies suggest that menopause is related to modest increase in total fatness and accelerated accumulation of central body fat that exceeds changes normally attributed to the aging process. These changes may increase the risk for cardiovascular and metabolic disease in aging women.

Influence of soft tissue (fat and fat-free mass) on ultrasound bone velocity: an in vivo study

RATIONALE AND OBJECTIVES

The authors determine the relative effect of soft-tissue compartments, body fat (percent [%Bfat] and weight [Bfat kg]) and fat-free mass (FFM kg), on measurements of ultrasound bone velocity (UBV m/second).

METHODS

The authors measured UBV in proximal phalanxes and body fat and fat-free mass by near infrared interactance in 40 healthy premenopausal women (mean age +/- standard deviation 28.2 +/- 3.8 years).

RESULTS

Correlation study (Fisher's r to z) showed that UBV correlated negatively with %Bfat (r = -0.61, P < 0.0001), Bfat kg (r = -0.56, P = 0.0001) and marginally with body weight (r = -0.33, P = 0.0403), but did not correlate with FFM kg or H2O L (both r = -0.08, P not significant). When the correlation test was adjusted for weight and age (partial correlation), the negative correlation between UBV and %Bfat persisted (r = -0.54, P < 0.0005; and r = -0.63, P < 0.0001, respectively) and the correlation with FFM kg, adjusted for weight, became positive and significant (r = 0.55, P < 0.0005).

CONCLUSIONS

These results, to our knowledge, are the first to be obtained by in vivo evaluation of UBV in relation to body fat and fat-free mass. Body fat, but not fat-free mass, was the main factor affecting UBV. This confirms the deficiency of UBV measurements, considering that obesity is a protective factor for bone mass.

Influence of weight and gonadal status on total and regional bone mineral content and on weight-bearing and non-weight-bearing bones, measured by dual-energy X-ray absosorptiometry

OBJECTIVE

To evaluate the influence of weight on total body bone mineral content (BMCTB) and regional body bone mineral content (head, arms, trunk and legs). This was studied in accordance with gonadal status and the weight-bearing or non-weight-bearing status of each region.

METHODS

The study included 94 postmenopausal women (mean age 60.6 +/- 10.5 years), 36 perimenopausal women (mean age 49.0 +/- 2.3 years) and 60 premenopausal women (mean age 36.1 +/- 6.9 years). Full-body bone densitometry (DXA), for measuring total body bone and regional bone mineral content, was carried out in all the women.

RESULTS

Among these groups, the influence of 1 kg of body weight on total and regional bone mineral content (percent) did not differ (paired test P ns). In the overall group of women, paired comparison showed differences between the head and other zones measured (P = 0.036-0.004). In the overall group of women, no differences were found in the percent influence of 1 kg body weight on bone mineral content in any study zone (by ANOVA, Fisher's PLSD post hoc test and the Kruskal-Wallis test). In the overall group of women, Fisher's r to z test revealed a non-significant relationship between weight and the bone mineral content of the head (r = 0.49, P ns) but in every other region the relationship between weight and bone mineral content was significant (r = 0.36-0.54, P < 0.0001 in all).

CONCLUSIONS

The effect of body weight on BMCTB and regional did not differ significantly with either gonadal status or weight-bearing (legs) and non-weight-bearing bones (arms).

Age-related changes in body composition of healthy and osteoporotic women

OBJECTIVES

The study was carried out to assess age-related changes of body composition and to evaluate the influence of lean and fat mass in bone mineral density of healthy and osteoporotic women.

METHODS

166 healthy women in premenopause (43.2 +/- 6.7 years), 591 healthy postmenopausal women (59.9 +/- 8.1 years) and 373 women with established involutive osteoporosis (66.2 +/- 7.8 years) were evaluated: bone mineral density (BMD) and soft tissue composition (fat mass, lean mass) were measured by a total body Lunar DPX device.

RESULTS

no difference in lean mass was appreciated between the groups. Fat mass was significantly lower in premenopausal women (19.5 +/- 6.5 kg) and osteoporotic patients (18.8 +/- 5.2 kg) than in postmenopausal healthy women (21.8 +/- 5.7 kg). In premenopause weight, soft tissue mass and fat mass increased with age (P < 0.05). In postmenopause, lean mass decreased significantly in healthy women (P < 0.05). Fat mass was lower in the osteoporotics than in normals. Total BMD correlated significantly with fat and lean mass in all groups (P < 0.01). BMD/height ratio correlated significantly with fat mass (P < 0.01), not with lean mass.

CONCLUSIONS

BMD is closely related to fat mass in healthy premenopausal and postmenopausal women, and in osteoporotic patients; osteoporotic patients and healthy premenopausal women are characterized by a lower fat mass than healthy postmenopausal women; fat mass may be considered one of the determinants of bone mass also in involutive osteoporosis.

Skeletal muscle mass and exercise performance in stable ambulatory patients with heart failure

The purpose of this study was to determine whether skeletal muscle atrophy limits the maximal exercise capacity of stable ambulatory patients with heart failure. Body composition and maximal exercise capacity were measured in 100 stable ambulatory patients with heart failure. Body composition was assessed by using dual-energy X-ray absorption. Peak exercise oxygen consumption (VO2peak) and the anaerobic threshold were measured by using a Naughton treadmill protocol and a Medical Graphics CardioO2 System. VO2peak averaged 13.4 +/- 3.3 ml.min-1.kg-1 or 43 +/- 12% of normal. Lean body mass averaged 52.9 +/- 10.5 kg and leg lean mass 16.5 +/- 3.6 kg. Leg lean mass correlated linearly with VO2peak (r = 0.68, P < 0.01), suggesting that exercise performance is influences by skeletal muscle mass. However, lean body mass was comparable to levels noted in 1,584 normal control subjects, suggesting no decrease in muscle mass. Leg muscle mass was comparable to levels noted in 34 normal control subjects, further supporting this conclusion. These findings suggest that exercise intolerance in stable ambulatory patients with heart failure is not due to skeletal muscle atrophy.

Circulatory status and response to cardiac rehabilitation in patients with heart failure

BACKGROUND

We recently reported that some patients with heart failure and exercise intolerance exhibit severe hemodynamic dysfunction during exercise, whereas others have normal cardiac output responses to exercise. We postulated that patients with preserved cardiac output responses to exercise are limited by deconditioning and would respond to exercise training, whereas patients with reduced cardiac output responses are limited by skeletal muscle underperfusion and would not improve with exercise training. The present study was undertaken to test this hypothesis.

METHODS AND RESULTS

Thirty-two patients with heart failure were studied. Hemodynamic response to maximal treadmill exercise was measured; then patients were enrolled in a standard 3-month cardiac rehabilitation program. Peak exercise VO2, lactate threshold, and quality-of-life questionnaires were assessed at 1, 2, and 3 months. Twenty-one patients had normal cardiac output responses to exercise. All 21 patients participated in the rehabilitation program without difficulty, and 9 (43%) responded to rehabilitation, defined as a > 10% increase in both peak exercise VO2 and the anaerobic threshold. Of the 11 patients with reduced cardiac output responses to exercise, 3 discontinued rehabilitation because of severe exhaustion, and only 1 qualified as a responder (9%; P < .04 versus preserved cardiac output).

CONCLUSIONS

Patients with heart failure and normal cardiac output responses to exercise frequently improve with exercise training. Patients with severe hemodynamic dysfunction during exercise usually do not improve with training, which suggests that they are limited primarily by circulatory factors.

Behavior of bone mass measurements. Dual energy x-ray absorptiometry total body bone mineral content, ultrasound bone velocity, and computed metacarpal radiogrammetry, with age, gonadal status, and weight in healthy women

RATIONALE AND OBJECTIVES

Bone mass as measured by dual energy x-ray absorptiometry varies with body weight. The authors studied the behavior of bone mass measurements made by ultrasound bone velocity and metacarpal radiogrammetry in relation to body weight.

METHODS

Eighty healthy women were studied: 40 post-menopausal and 40 premenopausal (mean age 60 +/- 6 and 38 +/- 8 years, respectively). The authors performed in every subject the following studies: a radiograph of the nondominant hand for metacarpal cortical thickness, a study of the 2nd to 5th proximal phalanges for ultrasound bone velocity, and total bone mineral content by dual energy x-ray absorptiometry.

RESULTS

The measurements obtained with the three methods correlated significantly with each other (P < 0.0001). The only parameter related significantly with weight were total bone mineral content (P < 0.0001). In the premenopausal women, age did not correlate with any measurement. In the postmenopausal women, age correlated significantly with the three measured parameters (P < 0.0058 to P < 0.0001).

CONCLUSIONS

Weight did not influence ultrasound bone velocity and metacarpal cortical thickness measurements.

Aging in women--the four-compartment model of body composition

The four-compartment model of body composition was examined in 155 white women through measurement of total body carbon (TBC), nitrogen (TBN), calcium (TBCa), and water levels. The age (mean +/- SD) of the population was 51.4 +/- 13.5 years, and values for the four compartments were as follows (in kilograms): protein 8.9 +/- 1.0, water 30.9 +/- 3.5, mineral 2.6 +/- 0.4, and fat 22.6 +/- 7.3. There was a linear change with age for protein and water, whereas mineral and fat were curvilinear. These latter two compartments also showed differences in premenopausal and postmenopausal rates of change. Various models were fit to the data to adjust for body size and age. Each of the four compartments (mineral, water, fat, and protein) changed with age, with fat increasing and the other compartments declining. The equation, y = age + age2 + height + weight, fit the data as well as the other models. Equations are provided to assess body composition in populations with disorders of nutrition, as well as other illnesses, using height, weight, and age as covariates. Since this was a cross-sectional study, longitudinal studies will have to be performed to confirm the accuracy of rates of change with age predicted with each compartment.