The assessment of body composition is one of the main components within the evaluation of nutritional status under the ABCDE model. Generally, the use of equations to estimate components is a frequent strategy since it represents a doubly indirect method that has good correlation with methods of higher sensitivity (i.e., NMR, DXA, etc.). In this sense, the waist girth or circumference (WC) represents a quick, simple and inexpensive tool to evaluate the excess of fat mass in the human being; however, this measurement does not provide information on body composition in isolation and has been used as an important independent variable in some recent equations (e.g., relative fat mass [RFM]). Considering the lack of formulas or external validation of RFM in the Colombian population, the aim of this STROBE-Nut-based cross-sectional study is to develop and validate simple equations that use WC as an independent variable to estimate fat mass and fat-free mass in a population with different physical activity levels.

This research aims to validate and develop WC-based equations due to the estimation potential to assess body composition in the athletic, physically active and sedentary Colombian population. We will follow the standardized reporting guidelines of the Strengthening the Reporting of Observational Studies in Epidemiology-Nutritional Epidemiology (STROBE-nut). Stratified probability sampling techniques will be used. Participants of >18 years old, residing in Medellín or its metropolitan area, with different physical activity levels, and that give consent to be evaluated by health professionals will be invited to participate. Anthropometry and DXA assessment will be carried out in the participants. Subsequently, validation of the RFM will be performed by comparing the estimation results with gold standard methods using correlation and agreement (Bland-Altman) analyses. Finally, several models will be developed to estimate fat mass and fat-free mass in the population subgroups (athletes, physically active individuals and sedentary people). The results of this research will improve professional practice in health, exercise and sports science.

The F20 project is developed by the Research Division of the Dynamical Business & Science Society-DBSS International SAS with the support of University CES, University de Córdoba, University Distrital Francisco José de Caldas, Exercise & Sport Nutrition Laboratory at Texas A&M University, the R&D department of ARTHROS IPS, Smart Fit, and IPS Diagnosticarte.

Inclusion Criteria:

1. +18 years old (under 60 years)
2. Sedentary, Physically active and Athletes of competitive level.
3. Residing in the city of Medellín or nearby municipalities of the metropolitan area.
4. Signed informed consent.
5. Assist to anthropometric and DXA measurements.

Exclusion Criteria:

1. People with a disease and/or special condition that limits exposure to radiation emitted by DXA.
2. Adults over 60 years of age
3. Pregnant women
4. Athletes with injuries
5. People with implants or prostheses.

According to previous recommendations (Knofczynski and Mundfrom,2007), 130 participants will be needed to obtain a coefficient of determination (R2) of 0.5 with an excellent level of prediction and with three independent variables. The subjects will be divided into three groups for validation and development of the new equations, the total number of participants will be divided into 3 strata following optimal allocation methods. Assigned a fixed cost for each stratum (sedentary people, C1; physically active subjects, C2; and sportsmen, C3, given that C3>C2>C1).The values obtained for the sedentary group were n=54, the physically active population group n= 43, and the sportsmen group n=33. In the new equation, the development/validation ratio will be 70/30 over the number of subjects.