Total body protein mass: validation of total body potassium prediction model in children and adolescents

The usefulness of total body protein mass models for adolescent athletes

The present study aimed to assess the utility of a less laborious technique for estimating total body protein (TBPro) in young athletes, using a multicomponent model as the criterion method. A total of 88 (49 boys and 39 girls) adolescent athletes (age: 15.2 ± 1.5 years; body mass index: 21.2 ± 2.7 kg/m2) participated. A 6-compartment model was used as the reference method (TBProReference) involving air displacement plethysmography for body volume, dual-energy X-ray absorptiometry (DXA) for bone mineral content, and deuterium dilution for total body water (TBW). Alternatively, DXA TBPro models were used as TBPro = lean-soft mass (LSM) - HFFFM × fat-free mass (FFM) - Ms. - G, where LSM and FFM were assessed using DXA, HFFFM is the hydration fraction of the FFM using measured TBW or assumed TBW (adult fraction of 0.732; Lohman's constants or mean observed HFFFM), Ms. is soft tissue minerals (Ms = 0.0129 × HFFFM × FFM), and G is glycogen calculated as 0.044 × (LSM - HFFFM × FFM - Ms). The maturation level was determined by self-assessment. TBPro obtained from DXA using the assumed HFFFM explained 73% to 77% of the variance compared to TBProReference. Meanwhile, using the mean values of measured HFFFM, the DXA model explained 53 and 36% for boys and girls, respectively. Larger bias (8.6% for boys and 25.8% for girls) and limits of agreement were found for the DXA model using measured HFFFM (boys for 66.9% and girls for 70%) compared to an assumed HFFFM (bias ranged from 1.5% to 22.5% and limits of agreement ranged from 31.3% to 35.3%). Less complex and demanding TBPro DXA models with the assumed HFFFM are valid alternatives for assessing this relevant FFM component in groups of adolescent athletes but are less accurate for individual results. Though future studies should be conducted to test the usefulness of these models in longitudinal and experimental designs, their potential to provide an estimation of protein mass after exercise and diet interventions in young athletes is anticipated.

Body composition techniques

Body composition is known to be associated with several diseases, such as cardiovascular disease, diabetes, cancers, osteoporosis and osteoarthritis. Body composition measurements are useful in assessing the effectiveness of nutritional interventions and monitoring the changes associated with growth and disease conditions. Changes in body composition occur when there is a mismatch between nutrient intake and requirement. Altered body composition is observed in conditions such as wasting and stunting when the nutritional intake may be inadequate. Overnutrition on the other hand leads to obesity. Many techniques are available for body composition assessment, which range from simple indirect measures to more sophisticated direct volumetric measurements. Some of the methods that are used today include anthropometry, tracer dilution, densitometry, dual-energy X-ray absorptiometry, air displacement plethysmography and bioelectrical impedance analysis. The methods vary in their precision and accuracy. Imaging techniques such as nuclear magnetic resonance imaging and computed tomography have become powerful tools due to their ability of visualizing and quantifying tissues, organs, or constituents such as muscle and adipose tissue. However, these methods are still considered to be research tools due to their cost and complexity of use. This review was aimed to describe the commonly used methods for body composition analysis and provide a brief introduction on the latest techniques available.

Evaluation of body composition in neonates and infants

A better understanding of the nutritional needs of both healthy and sick infants is important. Not only does too much or too little nutrition during early life have long-term effects on health, but periods of rapid growth during the first year of life also have long-term consequences. Knowledge of the changes in body composition in early life can help to better define nutritional needs at these ages. Several methods are available for measuring body composition of neonates and infants. Most focus on an assessment of either body fatness or bone mineralization; only a few can monitor the quality of the non-fat lean tissues. This paper provides an evaluation of the different approaches currently available to monitor infant body composition, identifying both their strengths and limitations.