Measuring Up: Can we rely on DXA and BIA to measure central adiposity?

When it comes to measuring changes in body composition, there are a plethora of techniques and tools available - ranging from the most expensive (and highly inaccessible) doubly labelled water to the simplest of measures, such as waist circumference. With advancements in technology, once-coveted techniques, like dual-energy X-ray absorptiometry (DXA) and bioimpedance analysis (BIA), are now available at our fingertips and for relatively little expense. There has been a dramatic increase in facilities offering DXA scans to measure body composition, with a scan costing as little as $80.00 nowadays. While commercially available BIA devices, typically in the form of scales, can be easily purchased for under $150.00. With these seemingly superior measurement tools now more accessible, as practitioners and clinicians, we need to ask ourselves questions about their appropriateness and relevance to what we are aiming to fundamentally achieve.

Measurements of body composition go beyond ‘vanity metrics.’ Indeed measurements are often related to how we look, however, the measurement of visceral adiposity (fat tissue that is located around the central organs such as the liver, and kidneys), is an important indicator used by allied health and medical practitioners to quantify an individual's risk of metabolic disease. Metabolic disease is a collection of conditions that often occur together and increase an individual's risk of diabetes, stroke and heart disease [1]. The main identifiers of metabolic syndrome include central adiposity, high blood pressure, high blood triglycerides, low levels of HDL cholesterol and insulin resistance [2]. As such, being able to accurately measure visceral adiposity can aid in the diagnosis, management and treatment of one of Australia’s most prevalent health concerns.

Despite their widespread use, DXA and BIA are still unable to obtain reliable visceral fat measurements - just ask researchers Dr Aimee Dordevic and Kaitlin Day from Monash University’s Department of Nutrition, Dietetics and Food, whose recent publications in the journal Nutrients explored this very issue.

“While DXA and BIA are continually increasing in their sophistication and capabilities, the technology has not yet reached a point where measures of visceral adiposity can be obtained with accuracy and reproducibility,” explained Aimee and Kaitlin. The duo state that it is not possible to confidently report whether changes over time as measured with DXA and BIA are an accurate reflection of biological (real) change or technical variability. They did note, however, that as the extent of an individual’s adiposity increases, so too does the confidence in the ability to track meaningful changes. Contributing to this problem is the fact that “both techniques rely on proprietary algorithms, and do not measure visceral adiposity directly” explained Aimee. These algorithms continue for the most part to remain secret - the intellectual property of the companies who produce them, meaning there is usually no way for researchers or clinicians to verify the results for themselves. This also raises the issue of variances in algorithms used by different companies, making it difficult to compare between pieces of equipment.

Additionally, Aimee and Kaitlin also urge practitioners and clinicians to consider the necessity of ordering a DXA for a client or patient. While radiation exposure from a DXA scan is low, it contributes to an individual's lifetime exposure and its use should not be taken lightly in the absence of a clinically indicated use (e.g. osteoporosis). This is particularly pertinent when there are other valid measures that do not expose individuals to radiation. “We'd like people to carefully consider all options before ordering DXA scans. If your outcomes rely on tracking change in different body compartments, then we believe DXA would be justified.”

Aimee and Kaitlin’s advice? When tracking changes in an individual's metabolic syndrome risk, waist circumference and waist to hip ratio measures are more than adequate measurements particularly if you don’t have access to more technical equipment. “They are easily accessible and are valid measures to track changes in adiposity and central adiposity.”

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Dr Aimee Dordevic is a Registered Nutritionist (Australia, UK) and works as a lecturer and researcher in the Department of Nutrition, Dietetics and Food at Monash University. Her current research focuses on investigating dietary strategies that improve metabolic outcomes in people with or at risk of chronic disease, with a particular interest in metabolic inflammation, and analysis of ‘omic’ data. Click here to access Aimee’s research profile. You can follow Aimee on Twitter via @AimeeDordevic.

Kaitlin Day is a PhD candidate in the Department of Nutrition, Dietetics and Food at Monash University. Her current research focuses on a big data/bioinformatics approach to obesity and understanding the factors that influence energy balance. Her current PhD work focuses on understanding the biological response during weight loss with the aim to help improve long-term outcomes for weight maintenance through individualised treatment options.. Click here to access Kaitlin’s research profile. You can follow Kaitlin on Twitter via @kaitlinjday.

Stay up to date with the Monash University Department of Nutrition, Dietetics and Food on Twitter via @MonashNutrition.

Publication information

Reference: Dordevic AL, Bonham M, Ghasem-Zadeh A, Evans A, Barber E, Day K, Kwok A, Truby H. Reliability of Compartmental Body Composition Measures in Weight-Stable Adults Using GE iDXA: Implications for Research and Practice. Nutrients. 2018;12;10(10). doi: 10.3390/nu10101484.

Link to publication: Click here to access the paper published in Nutrients.

Reference: Day K, Kwok A, Evans A, Mata F, Verdejo-Garcia A, Hart K, Ward LC, Truby H. Comparison of a Bioelectrical Impedance Device against the Reference Method Dual  Energy X-Ray Absorptiometry and Anthropometry for the Evaluation of Body Composition in Adults. Nutrients. 2018;10;10(10). doi: 10.3390/nu10101469.

Link to publication: Click here to access the paper published in Nutrients.

The journal Nutrients is ranked 18 out of 124 in the category Nutrition and Dietetics and has an impact factor of 4.196.  Nutrients is a Q1 journal.

References

1. Ford ES. Risks for all-cause mortality, cardiovascular disease, and diabetes associated with the metabolic syndrome: a summary of the evidence. Diabetes Care. 2005;28(7):1769-78.
2. Alberti KG, Zimmet P, Shaw J. The metabolic syndrome-a new worldwide definition. The Lancet. 2005; 24;366(9491):1059-62.