Hydration affecting Body Composition Assessment

Recent Study on Hydration and Body Composition Assessment

Did you know? Hydration is a factor that affects the accuracy of many body composition methods.

Why? Many methods are affected by hydration status because they assume that the water content of the fat-free body is constant at a certain level (usually around 73%). If someone’s actual hydration level varies from this, the method will show a higher error rate.

In a recent study by Cataldi (2023)*, athletes were measured with several different body composition assessment methods. This study shows the important influence of hydration on the accuracy of body composition methods. The hydration level (water as a percent of fat free body) varied from 63 to 73% in 35 males and from 58 to 78% in 35 females.

In addition to making body water measurements, Cataldi and colleagues performed body composition measurements sing several other methods** — DXA, several types of BIA/BIS devices, a 3D optical scanner, ADP, UWW and BMI. To determine accuracy, they compared these measurements to the gold standard multicomponent model.

As expected, BMI was the worst predictor of fat mass. DXA and ADP showed the best performance with the lowest errors in predicting fat mass. In males, the 3D optical scanner showed higher errors but errors were lower in females. The BIA/BIS devices all showed higher errors for both men and women.

While many sources of error contribute to the accuracy of methods, hydration level can be a major contributor. In this study, many of the athletes measured varied considerably from the level that is typically assumed. This presumably impacted the error rates observed, especially for the BIA/BIS field methods. The lab-based methods tested performed well with low prediction errors. Therefore, hydration level is a key factor to consider when measuring different populations, including athletes. Measurement methods should be chosen with care.

_{**Cataldi D, et. al, Accuracy and precision of multiple body composition methods and associations with muscle strength in athletes of varying hydration: The Da Kine Study, Clinical Nutrition, 43 (2024) 284-294.}

_{*Abbreviations: DXA=dual-energy X-ray absorptiometry (Hologic Corp), ADP=air displacement plethysmography (BodPod by COSMED), BIA=bioelectrical impedance analysis ((InBody), BIS=bioimpedance spectroscopy (2 devices by ImpediMed), 3D Optical scanner (Fit3D), BMI=body mass index}