Validation of the Alterable Weight Loss Metric in Morbidly Obese
Patients Undergoing Gastric Bypass in Korea
Ji Yeon Park
Yong Jin Kim
Published online: 12 March 2018
Springer Science+Business Media, LLC, part of Springer Nature 2018
Background Percentage of excess weight loss (%EWL) is the most common metric used after bariatric surgery. However, there
has been consistent argument against its use since it varies significantly by initial body mass index (BMI). This study aimed to
validate the newly suggested percentage of alterable weight loss (%AWL) metric in Korean patients.
Methods A retrospective review of the prospectively established database at Soonchunhyang University Seoul Hospital identi-
fied 165 patients who underwent primary laparoscopic Roux-en-Y gastric bypass (RYGB) and had at least 2-year follow-up
weight loss results after surgery. Patients were classified into subgroups based on initial BMI, and their weight loss results
expressed as BMI, %EWL, %AWL, and percentage of total weight loss (%TWL) were compared in terms of nadir weight and
weight loss trajectory.
Results The study cohort included 27 male (16.4%) and 138 female (83.6%) patients with a mean baseline BMI of 38.1 ± 5.4.
Nadir weight was achieved at mean 24.1 ± 10.6 months postoperatively. Female patients required significantly longer to achieve
nadir weight than male patients (16.2 vs. 22.4 months, p = 0.001), and they achieved less weight loss expressed as nadir BMI,
%EWL, and %AWL. Of these metrics, only %AWL was not significantly influenced by preoperative BMI and showed the least
variation (25.2%) for reporting weight loss.
Conclusion The AWL metric can report weight loss regardless of baseline BMI in Korean patients undergoing RYGB; however,
it must be validated in a larger population involving multiple centers from the Asia-Pacific area before being used clinically.
Keywords Weight loss
Body mass index
Weight loss is one of the important outcomes of bariatric sur-
gery. The primary endpoint of bariatric surgery is clinically
significant and sustained weight loss, which is considered a
measure of efficacy following different surgical procedures
and the postoperative determinant of success or failure.
Therefore, it is paramount to establish a standardized metric
to report weight loss to facilitate easy communication between
different expert practitioners as well as provide an appropriate
method of comparing various weight control options.
Percent excess weight loss (%EWL) has long been used as
a comparative metric to evaluate weight loss outcomes follow-
ing bariatric surgery [1, 2]. This measure represents the pro-
portion of lost weight to the total amount of excess weight
over the ideal weight; the ideal weight corresponds to the body
mass index (BMI) of 25 kg/m
since Deitel et al. redefined this
metric in 2007 . However, there has been a consistent ar-
gument against the use of %EWL since it shows significant
variation by the baseline BMI of the patients and is rarely used
in non-surgical studies [1, 4–8]. Percentage of total weight
loss (%TWL) is the most commonly adopted method of
weight loss reported in the field of medical treatment for obe-
sity. Surgeons have recently advocated using %TWL after
bariatric surgery because it is less associated with preoperative
BMI and more intuitive than %EWL [8, 9]. It was recently
adopted as a mandatory measure for reporting weight loss
outcomes by leading bariatric scientific societies . Still,
* Yong J in Kim
School of Medicine, Kyungpook National University,
Daegu, Republic of Korea
Department of Surgery, Kyungpook National University Chilgok
Hospital, Daegu, Republic of Korea
Department of Surgery, Soonchunhyang University Seoul Hospital,
59 Daesagwan-ro, Yongsan-gu, Seoul 04401, Republic of Korea
Obesity Surgery (2018) 28:1704–1710