DEXA vs BIA: Which Is the Best for Body Composition Analysis?

Exploring body composition is key for anyone interested in their health and fitness, from athletes to the general population.

Two of the most popular and advanced options available today are DEXA (Dual-Energy X-ray Absorptiometry) scans and Bioelectrical Impedance Analysis (e.g. InBody scans).

Each method has its pros and cons and varies in accuracy, therefore choosing between them may depend on your specific health goals and needs.

DEXA

DEXA scans have become the gold standard for measuring body composition. They work by using low-dose X-rays at two different energy levels to differentiate between tissues.

They utilize a 3-compartment model, which divides the body into three distinct components:

1. Bone Mineral Content: DEXA provides detailed measurements of bone density, which is used to assess bone health and the risk of conditions such as osteoporosis. This is a unique feature of DEXA scans, setting them apart from most other body composition analysis methods.
2. Lean Tissue: This compartment includes muscle mass, organs, and other non-fat, non-bone tissues.
3. Fat Mass: DEXA measures the amount of body fat, including both subcutaneous (under the skin) and visceral (around the organs) fat.

Its ability to measure bone density, which is not directly assessed in simpler two-compartment models, is one of the main differentiating factors between this method and the BIA.

The accessibility of DEXA scans is one of the biggest barriers to use, as they require specialized equipment, and technicians and are usually more expensive.

Although very low, DEXA scans involve radiation exposure, whereas BIA do not.

BIA

These work by sending small electrical currents through the body to measure the resistance these currents encounter, which varies between different types of tissue.

BIA devices use a 2-compartment model, dividing the body into:

1. Fat Mass: Fat tissue, which contains less water and is more resistive, can be quantified separately from lean mass.
2. Lean Mass: This compartment combines muscle and other non-fat tissues with the body’s water content. Since muscle and other tissues are conductive due to their water content, BIA can estimate the total lean mass. However, it’s important to note that changes in hydration can affect BIA measurements, as the method assumes a constant hydration level for lean mass.

DEXA VS BIA

Fat Mass

Research has consistently shown that DEXA scans are a more reliable method for predicting fat mass and body fat percentage.

BIA scans also tend to overestimate body fat when subjects are relatively lean and underestimate body fat when subjects are overweight or obese. Therefore, caution needs to be taken when measuring the body fat of those outside the healthy BMI range.

Similarly, BIA scans have been shown to be less accurate for predicting visceral fat compared to DEXA scans when correlated against that of an MRI. 

Lean Mass

DEXAs have a strong association with MRI-measured total body skeletal mass, with an R² value of 0.93. This is slightly higher to that of BIA scans, which have demonstrated an R² value of 0.83-0.89.

Many studies also use DEXA scans as the reference equipment when testing the validity of BIA at predicting lean mass, due to it’s known precision.

What to Choose

The biggest differentiating factor is the DEXA’s ability to measure bone mineral density. Therefore it will be the preferred choice if you are looking to gain insight into your bone health.

Due to the technology, it also has a higher degree of accuracy in measuring body composition components in comparison to BIA. Therefore for athletes looking to fine-tune their training and nutrition programs, DEXA scans would be the preferred choice.

For the general population interested in regular monitoring of their body composition to guide lifestyle changes or fitness goals, both options are viable, however BIA scans may be more affordable and accessible.

Summary

Ultimately, the decision between DEXA and InBody scans should be based on your specific health and fitness goals, as well as considerations of cost, convenience, and the level of detail you require from your analysis.

DEXA is the superior choice for the highest accuracy and precision. For a cheaper and more general outlook of your body composition, you could consider a BIA scan.