August 8, 2023
What is the Gold Standard for determining Body Fat?
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This question really depends on what we mean by the gold standard. The “gold standard” refers to a benchmark, criterion, or method that is widely recognized as the most accurate, reliable, and authoritative measure for evaluating or comparing something. In various fields, the gold standard represents the highest standard of quality, accuracy, or effectiveness against which other methods or approaches are compared. It’s important to remember that this may change over time with new technologies, methodologies, or research findings emerging.
Dual-Energy X-ray Absorptiometry (DXA) scan is often preferred due to its ability to offer a comprehensive analysis of the body’s composition, providing detailed measurements of fat distribution and bone density in various body regions. DXA is a medical imaging technique that uses two X-ray beams to measure the density of bone, fat, and lean tissue in the body. It is considered one of the most accurate and reliable methods for assessing body composition, including body fat percentage.
It still has some limitations:
|Regional Fat Distribution||DXA provides an overall body fat percentage and differentiates between fat and lean mass. It may not distinguish between visceral fat (deep abdominal fat) and subcutaneous fat (fat under the skin), which can be relevant for assessing health risks associated with central adiposity and fat accumulation.|
|Bone and Lean Mass Influence||Measures the attenuation of X-rays passing through the body, and both bone mineral content and lean mass can contribute to this measurement. In some cases, especially in individuals with higher bone density or significant muscle mass, the DXA may slightly overestimate the fat percentage due to interference from these tissues.|
|Sensitivity to Hydration Levels||Dehydration or excess water retention may affect the accuracy of the measurements.|
|Limited Data on Specific Populations||Accuracy may vary in specific groups, the elderly, certain medical conditions, or individuals with different ethnic backgrounds.|
|Radiation Exposure||Uses relatively low doses of X-rays. However, repeated scans over time can cumulatively increase radiation exposure, especially in cases where frequent monitoring is required|
|Cost and Accessibility||Specialized equipment and trained personnel are expensive and less accessible than simpler methods like BMI or bioelectrical impedance analysis (BIA).|
|Intra-observer and Inter-observer Variability||Results can be affected by observer variability and calibration issues, leading to minor discrepancies between different scans or operators.|
It’s important to remember that the gold standard doesn’t necessarily translate to the exam room. There are several alternative methods to Dual-Energy X-ray Absorptiometry (DXA). As with all areas of obesity medicine selection depends on factors such as cost, accessibility, and level of accuracy required.
Some common alternatives to DXA include:
Bioelectric impedance analysis (BIA) is a measurement of the impedance of the body to a small electric current. Different tissues (fat, muscle, bone) have different conductive properties, allowing BIA devices to estimate body fat percentage based on these measurements. A popular choice for body composition assessment in various settings as they are relatively inexpensive, easy to use, and widely available. Limitations include hydration status, age, gender, and physical activity level.
Skinfold Calipers utilize calipers to measure the thickness of skinfold folds at specific body sites. Measurements are used to estimate subcutaneous fat thickness, which is then used to calculate body fat percentage using various equations. They are a cost-effective method, but the accuracy of the results is dependent on the skill and experience of the person performing the measurements.
Magnetic Resonance Imaging (MRI) estimates the volume rather than the mass of adipose tissue. Again, limitations include cost and availability. MRI does have the ‘capacity for estimation of regional body composition, and it is currently an accurate and viable approach for the estimation of intra‐abdominal adipose tissue’ (Wells and Fewtrell, 2006). Many metabolically relevant body composition parameters including ectopic fat, in particular liver fat, can be evaluated with quantitative MRI or CT. MRI doesn’t require the use of ionizing radiation, expanding its utilization even in children and infants (Borga et al, 2018)
These techniques are of great value in research, but on a day-to-day basis, they are unlikely to have as much value in clinical management. This is why they haven’t found their way into the exam room and as such clinically have a way to go before they become the ‘Gold standard’ for my patients.
We are therefore left with Body mass index (BMI). Which remains a practical and widely used tool for population health and screening and is used daily in clinical practice. BMI, calculated as weight/height2 is an index of relative weight, often expressed as SDS to consider age and sex. Its relationship with body composition per se is controversial. It is easy to use, reproducible, and trackable but is unable to distinguish between fat and lean masses. As the CDC highlights in its publication ‘BMI: considerations for Practitioners’ BMI can’t provide an indication of the distribution of fat among individuals. It is important to remember and explain to our patients that BMI can be utilized as a part of a comprehensive health assessment rather than the sole determinant of obesity or body fat percentage.
Another commonly utilized and simple measurement is Waist circumference (WC). It has long been recognized in adults that waist–hip ratio is independently associated with morbidity after adjustment for relative weight, such that the use of relative weight and body shape simultaneously gives a better estimate of the risk of morbidity than either alone (Rimm 1988). There are limitations including inter-user variability something we have encountered in our office.
In summary, BMI and DXA serve different purposes in body composition assessment. BMI is a practical and widely used tool for population health and screening, while DXA scanning offers a more detailed and accurate evaluation of body composition in clinical and research settings. The choice between the two methods depends on the specific goals of the assessment and the level of precision required for the given context.
Rimm, A., Hartz A J, Fischer M E. (1988) ‘A Weight Shape Index for Assessing Risk of Disease in 44,820 Women’ Journal Clinical Epidemiology 41 (5) Pages 459-465 [online] available at: https://doi.org/10.1016/0895-4356(88)90047-9 CDC Body Mass Index: Considerations for Practitioners [online] available at: https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf#targetText=The%20clinical%20limitations%20of%20BMI,between%20BMI%20and%20body%20fat. Shepherd, J. Ng, B., Sommer, M. and Heymsfield, S. (2017) ‘Body Composition by DXA’ Bone 104 pages 101-105 [online] available at: doi: 10.1016/j.bone.2017.06.010 Wells, J and Fewtrell, M. (2006) ‘Measuring body composition’ Achieves of Diseases of Children 91(7) pages 612–617. [online] available at doi: 10.1136/adc.2005.085522 Borga M, West J, and Bell JD,(2018) ‘Advanced Body Composition Assessment: From Body Mass Index to Body Composition Profiling’ Journal of Investigative Medicine 66 pages1-9. [online] Available at: http://dx.doi.org/10.1136/jim-2018-000722
Article written by:
Kimberley Sampson, MD, FACOG, DABOM
Kimberley Sampson, MD, FACOG, DABOM, is a SCOPE-certified OB/GYN and Obesity Medicine Physician at Dartmouth Health. Chair of the Department of Obstetrics and Gynecology at SVMC, Chair of the Vermont Section of ACOG, and Clinical Assistant Professor in OBGYN, Geisel School of Medicine at Dartmouth. Member of the OMA Outreach and Advocacy Committees.