Critical analysis of dual-energy x-ray absorptiometry-measured body composition changes with voluntary weight loss

When treated with a macronutrient-balanced hypocaloric diet, do male individuals who have overweight and obesity lose relatively more dual-energy x-ray absorptiometry (DXA)-measured lean soft tissue (LST) mass than female individuals? Are there changes in bone mineral content (BMC), and if so, how do they impact relative reductions in LST compared to fat-free mass (FFM; LST plus BMC)? Are decrements in fat, LST, and FFM predictable from the magnitude of weight loss or baseline body composition?

To answer these questions, DXA studies were conducted before and after a 9- to 12-week calorie-restriction period in 43 male and 97 female individuals who lost a mean (SD) of 10.8% (2.2%) and 10.7% (1.6%) of their baseline weight, respectively.

The proportion of weight loss as LST was significantly (p < 0.001) larger in male (mean [SD], 0.33 [0.11] kg) than female individuals (0.25 [0.11] kg); BMC paradoxically increased, thereby leading to a significantly smaller reduction in FFM than LST in the male (-3.87 [1.73] kg vs. -3.92 [1.74] kg; p < 0.001) and female individuals (-2.22 [1.18] kg vs. -2.24 [1.18] kg; p < 0.001), and three different analyses showed that the composition of weight loss tracked as predicted a priori from weight change and baseline body composition.

These observations provide insights into and future guidance for analyzing the DXA-measured body composition changes associated with newer pharmacotherapies for weight loss.