Validity of weight loss to estimate improvement in body composition in individuals attending a wellness center.

The accuracy of weight loss in estimating successful changes in body composition (BC), namely fat mass (FM) loss, is not known and was addressed in our study. To assess the correlation between change in body weight and change in FM, fat% and fat-free mass (FFM), 465 participants (41% male; 41 ± 13 years), who met the criteria for weight change assessment at a wellness center, underwent air-displacement plethysmography (ADP). Body weight and BC were measured at the same time. We categorized the change in body weight, FM and FFM as an increase if there was >1 kg gain, a decrease if there was >1 kg loss and no change if the difference was ≤1 kg. We estimated the diagnostic performance of weight change to identify improvement in BC. After a median time of 132 days, there was a mean weight change was 2.4 kg. From the 255 people who lost >1 kg of weight, 216 (84.7%) had lost >1 kg of FM, but 69 (27.1%) had lost >1 kg of FFM. Of the 143 people with no weight change, 42 (29.4%) had actually lost >1 kg of FM. Of the 67 who gained >1 kg of weight at follow-up, in 23 (34.3%) this was due to an increase in FFM but not in FM. Weight change had a NPV of 73%. Our results indicate that favorable improvements in BC may go undetected in almost one-third of people whose weight remains the same and in one-third of people who gain weight after attending a wellness center. These results underscore the potential role of BC measurements in people attempting lifestyle changes.