Purpose of reviewBody composition analysis allows division of the body into different compartments on the basis of differing physical properties. A variety of techniques are available for measuring body composition. This review describes the changes that occur with increasing age, their significance

Body composition analysis techniques in the aged adult: indications and limitations.

BACKGROUND It has been hypothesized that insulin resistance plays a role in the development of the loss of skeletal muscle; however, no cohort studies on insulin resistance and low relative appendicular skeletal muscle mass (ASM) have been published to date. Thus, we examined whether insulin resistance is associated with low relative ASM after a 4.6-year follow-up period among apparently healthy older men and women participants. METHODS This is a combined retrospective-prospective cohort study, which includes 147 community-dwelling older men and women participants. ASM was measured by dual-energy x-ray absorptiometry at baseline and follow-up. Participants with a relative change in ASM below the sex-specific 15th value were classified as the low relative ASM group. Homeostatic model assessment was used to quantify insulin resistance. Logistic regression calculated odds ratios and 95% confidence intervals for development of low relative ASM, adjusted for covariates. RESULTS The loss of ASM in the low relative ASM and normal groups was -1.8kg and -0.35kg, respectively (p ≤ .05). The low relative ASM group was older and had higher insulin and homeostatic model assessment of insulin resistance values at baseline. The risk of developing low relative ASM at 4.6-year follow-up was 2.9 times higher (95% CI, 1.00-7.8; p = .04) among the participants with homeostatic model assessment of insulin resistance levels more than 2.3. After adjusting for age, the risk increased to 3.9 times higher (95% CI, 1.3-11.5; p = .03). CONCLUSION Insulin resistance was associated with low relative ASM at 4.6-year follow-up after accounting for several covariates in a cohort of apparently healthy, well-functioning young older men and women.

Association Between Insulin Resistance and Low Relative Appendicular Skeletal Muscle Mass: Evidence From a Cohort Study in Community-Dwelling Older Men and Women Participants

The study of body composition in specific populations by techniques such as bio-impedance analysis (BIA) requires validation based on standard reference methods. The aim of this study was to develop and cross-validate a predictive equation for bioelectrical impedance using air displacement plethysmography (ADP) as standard method to measure body composition in Mexican adult men and women. This study included 155 male and female subjects from northern Mexico, 20–50 years of age, from low, middle, and upper income levels. Body composition was measured by ADP. Body weight (BW, kg) and height (Ht, cm) were obtained by standard anthropometric techniques. Resistance, R (ohms) and reactance, Xc (ohms) were also measured. A random-split method was used to obtain two samples: one was used to derive the equation by the "all possible regressions" procedure and was cross-validated in the other sample to test predicted versus measured values of fat-free mass (FFM). The final model was: FFM (kg) = 0.7374 * (Ht2 /R) + 0.1763 * (BW) - 0.1773 * (Age) + 0.1198 * (Xc) - 2.4658. R2 was 0.97; the square root of the mean square error (SRMSE) was 1.99 kg, and the pure error (PE) was 2.96. There was no difference between FFM predicted by the new equation (48.57 ± 10.9 kg) and that measured by ADP (48.43 ± 11.3 kg). The new equation did not differ from the line of identity, had a high R2 and a low SRMSE, and showed no significant bias (0.87 ± 2.84 kg). The new bioelectrical impedance equation based on the two-compartment model (2C) was accurate, precise, and free of bias. This equation can be used to assess body composition and nutritional status in populations similar in anthropometric and physical characteristics to this sample.

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Body fat measurement by bioelectrical impedance and air displacement plethysmography: a cross-validation study to design bioelectrical impedance equations in Mexican adults

Objective
Several limitations of published bioelectrical impedance analysis (BIA) equations have been reported. The aims were to develop in a multiethnic, elderly population a new prediction equation and cross-validate it along with some published BIA equations for estimating fat-free mass using deuterium oxide dilution as the reference method.

Prediction of fat-free mass by bioelectrical impedance analysis in older adults from developing countries: a cross-validation study using the deuterium dilution method.

Four-compartment model and validation of deuterium dilution technique to estimate fat-free mass in Mexican youth

The aims of this study were to validate BOD POD in a wide sample of healthy and independent Mexican elderly men and women subjects using the 4 compartment (4C) model as the reference method, and to evaluate the assumptions of the densitometric two-compartment (2C) model. Cross-sectional study designed to assess body composition and validation of a method based on 2C model (BOD POD). Urban and rural regions of Sonora, Mexico. Two hundred and two free-living subjects ⩾60 years old were completed in this study. Body density and body fat were measured by the BOD POD, total body water by deuterium dilution and total body bone ash by dual energy X-ray absorptiometry. Body composition was determined using Baumgartner's equation. Percent body fat by the 4C model was 31.2 and 42.5% in men and women, respectively (P<0.001). Group mean accuracy of body fat by BOD POD against that of the 4C model showed an effect of sex (P<0.001), but not the method (P=0.27). Results of individual accuracy showed no significant difference with the identity line and the slope was significantly different from zero or a slope similar to one. Precision assessed by model R2 was high for all subjects and for men and women by separate. The standard error of the estimate was low for all and for men and women by separate. Bland and Altman analysis showed no significant bias. The BOD POD technique is a valid and reliable method compared to the 4C model and it could be applied in subjects with similar physical and anthropometric characteristics to subjects of this study. The study was funded by CONACYT, Mexico (J37891-M) and IAEA (Research contract no. 12694/R0).

R H Huerta

Papers

Body composition by the four-compartment model: validity of the BOD POD for assessing body fat in Mexican elderly.