Background No current treatment for obesity reliably sustains weight loss, perhaps because compensatory metabolic processes resist the maintenance of the altered body weight. We examined the effects of experimental perturbations of body weight on energy expenditure to determine whether they lead to metabolic changes and whether obese subjects and those who have never been obese respond similarly. Methods We repeatedly measured 24-hour total energy expenditure, resting and nonresting energy expenditure, and the thermic effect of feeding in 18 obese subjects and 23 subjects who had never been obese. The subjects were studied at their usual body weight and after losing 10 to 20 percent of their body weight by underfeeding or gaining 10 percent by overfeeding. Results Maintenance of a body weight at a level 10 percent or more below the initial weight was associated with a mean (±SD) reduction in total energy expenditure of 6±3 kcal per kilogram of fat-free mass per day in the subjects who had never been obese...

https://www.nejm.org/doi/pdf/10.1056/NEJM199503093321001

Changes in Energy Expenditure Resulting from Altered Body Weight

In vivo methods used to study human body composition continue to be developed, along with more advanced reference models that utilize the information obtained with these technologies. Some methods are well established, with a strong physiological basis for their measurement, whereas others are much more indirect. This review has been structured from the methodological point of view to help the reader understand what can be examined with each technique. The associations between the various in vivo methods (densitometry, dilution, bioelectrical impedance and conductance, whole body counting, neutron activation, X-ray absorptiometry, computer tomography, and magnetic resonance imaging) and the five-level multicompartment model of body composition are described, along with the limitations and advantages of each method. This review also provides an overview of the present status of this field of research in human biology, including examples of reference body composition data for infants, children, adolescents, and adults.

http://www.luzimarteixeira.com.br/wp-content/uploads/2009/09/composicao-corporal1.pdf

Human body composition: in vivo methods

Appendicular skeletal muscle mass: measurement by dual-photon absorptiometry.

The present study validates the use of dual energy X-ray absorptiometry (DEXA) for measurement of body composition. The precision error was expressed as the SD (CV%) for fat mass, FAT%, lean tissue mass, and total body bone mineral: 1.1 kg (6.4%), 1.6% (5.7%), 1.4 kg (3.1%), and 0.03 kg (1.2%), respectively. The accuracy study in vitro used (1) mixtures of water and alcohol, (2) mixtures of ox muscle and lard, and (3) dried bones. In the clinically relevant range of values there were only small influences on DEXA measurements of variations in amount and composition of the soft tissue equivalents. The accuracy study in vivo compared the components of body composition measured recently by DEXA and earlier by dual photon absorptiometry, counting of naturally occurring total body 40K, and body density by underwater weighing in 25 healthy adult subjects. We found agreement between fat percentage (and lean body mass) by DEXA and the three established measurements modalities; mean differences were (-5.3 to -0.4%) and (-0.7 to 2.5 kg) for fat percentage and lean body mass, respectively. We conclude that DEXA provides a new method of measuring body composition with precision and accuracy errors, which are compatible with the application of DEXA in group research studies and probably also in clinical measurements of the single subject.

Validation of body composition by dual energy X-ray absorptiometry (DEXA).

Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight

A chemical approach to establishing human body density in vivo was devel- oped by combining recently developed noninvasive methods. Four compartments were mea- sured: protein (P; prompt--y neutron activation), water (A; 3H2O dilution), mineral (M; dual- photon absorptiometry and delayed--y neutron activation), and fat (F; dual-photon absorpti- ometry). By this model body weight is equal to P + A + M + F. This approach was applied to 13 healthy adults (8 females and 5 males). The four compartments accounted for > 97% actual body weight. Calculated density based upon composition agreed within 0.6 ± 0.4% (1 ± SD) with density (D) measured by hydrodensitometry (calculated D (g/cc) = 0.86 measured D + 0. 15; r = 0.94, p < 0.00 1). The average calculated lean (P + A + M) density of 1.096 ± 0.007 g/cc agreed closely with three classic human cadaver studies (1 . 100 g/cc). This mubticompart- ment approach provides a new opportunity to estimate human body density in vivo and to refine body composition methods based upon an assumed but inadequately validated constant lean density. Am J C/in Nutr 1989;50: 1282-9.

Chemical determination of human body density in vivo

Francis D. Moore first recognized the essential need to know hidden aspects of the water phases of body composition when he cared for burn patients admitted to the Peter Bent Brigham Hospital after the Copacabana fire in wartime Boston in 1943. First, it was remarkable that a junior surgeon sensed that he needed to know the intracellular composition of “the body cell mass,” an entity that he defined in his book published 20 years later. Second, it is remarkable that he was able to find, in the superb academic community surrounding the Harvard Medical School, access to the radioactive isotopes of sodium, potassium, and bromide; the equipment to measure them; and the analytic concepts to establish a model for the body which we have only tuned up slightly in the years since his first studies and in those since his massive scientific and literary contribution (Moore 1963).

The Quality of the Body Cell Mass

Background: Bioelectrical impedance analysis (BIA) is an attractive method of measuring pediatric body composition in the field, but the applicability of existing equations to diverse populations has been questioned. Objective: The objectives were to evaluate the performance of 13 published pediatric BIA-based predictive equations for total body water (TBW) and fat-free mass (FFM) and to refit the bestperforming models. Design: We used TBW by deuterium dilution, FFM by dualenergy X-ray absorptiometry, and BIA-derived variables to evaluate BIA models in a cross-sectional study of 1291 pediatric subjects aged 4‐18 y, from several ethnic backgrounds, including 54 children with HIV infection and 627 females. The best-performing models were refitted according to criterion values from this population, cross-validated, and assessed for performance. Additional variables were added to improve the predictive accuracy of the equations. Results: The correlation between predicted and criterion values was high for all models tested, but bias and precision improved with the refitted models. The 95% limits of agreement between predicted and criterion values were 16% and 11% for TBW and FFM, respectively. Bias was significant for some subgroups, and there was greater loss of precision in specific age groups and pubertal stages. The models with additional variables eliminated bias, but the limits of agreement and the loss of precision persisted. Conclusion: This study confirms that BIA prediction models may not be appropriate for individual evaluation but are suitable for population studies. Additional variables may be necessary to eliminate bias for specific subgroups. Am J Clin Nutr 2002;76:991‐9.

Bioelectrical impedance analysis models for prediction of total body water and fat-free mass in healthy and HIV-infected children

Plasma Cell Myeloma in a Japanese Population: A Population-Based Cohort Study Association of Anthropometric Characteristics with the Risk of Malignant Lymphoma and

Skeletal muscle provides power to move body parts for life-maintaining routine physical functions, for exercise, and for survival. Skeletal muscle efficiency therefore directly influences the quality of life. Postmortem studies by Alexander (1964) in 17 healthy males dying suddenly of violence showed that skeletal muscle mass varied from 22 to 53% of body weight, varying as widely as the adipose tissue mass, based on age, gender, fitness, and nutrition.

Urinary Excretion of Creatinine and 3-Methylhistidine for Estimation of Skeletal Muscle Mass in Humans: An Overview

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