Is Bioimpedance Analysis Accurate in Transgender Males?

Gender incongruence is defined as a condition in which the gender with which a person identifies does not align with the gender assigned at birth. According to a recent population survey, 0.55% of the Danish population are gender incongruent, and 0.10% define themselves as transgender. There is an equal distribution between trans men and trans women. The treatments include gender-affirming hormone therapy and gender-affirming surgery. Exogenous treatment with sex steroids such as testosterone plays an important role in the distribution of body fat and lean body mass development, and thus induces masculinization of body composition in transgender males.

Body composition is a highly informative marker of an individual's nutrition-related condition and health. Furthermore, it contributes to the identification, diagnosis, and management of several medical conditions. In obesity, the body composition assessment improves the diagnosis and is useful in the monitoring of treatment response, which is central in the management of obesity-related chronic diseases and sarcopenic obesity. Maintaining muscle mass (MM) is important for longevity and health in humans as there is a natural increase in fat mass (FM) and a decrease in MM with age. This leads to an increased risk of cardiovascular disease, type 2 diabetes, several types of cancer, sarcopenia, and even early mortality. However, weight and BMI do not provide insights into the relative contributions of FM and MM on disease risk.

Body composition measured by bioimpedance analysis (BIA) includes FM and lean body mass estimates. The test is inexpensive, readily reproducible and suitable for outpatient clinic patients. Body fat percentage, measured by BIA, reflects body adiposity and is a superior indicator of obesity compared to BMI. Dual x-ray absorptiometry (DXA) is the gold standard distinguishing fat, lean tissue, and bone mineral, thus providing accurate estimates of bone mineral density, FM, and lean soft tissue/fat-free mass (FFM). The main limitations of DXA are that it is expensive, time-consuming, and exposes the subjects to radiation, which may hinder its use at a large scale. As body composition is more accurately assessed by fat percentage and FFM than BMI, it is relevant to consider which methods are most reliable for assessing body composition in transgender males.

We aim to investigate whether estimates of body composition by BIA in transgender males are significantly affected by the use of binary reference values. Furthermore, we aim to compare the body composition estimated by BIA to DXA scans.