Fat mass, but not fat-free mass, predicts increased foot pain with obesity, independent of bariatric surgery

Background: Foot pain is a common manifestation of obesity. Objective: To determine if bariatric surgery is associated with a reduction in foot pain and if body mass index (BMI) or body composition predict a change in foot pain. Setting: University hospital. Methods: Participants with foot pain awaiting bariatric surgery were recruited for this prospective study. Multivariable linear regression was used to determine predictors of change in foot pain between baseline and 6-month follow-up using body composition (fat mass index and fat-free mass index) or BMI, adjusting for, depression, age, sex, and group (surgery versus control). Results: Forty-five participants (38 female), mean standard deviation age of 45.7 +/- 9.4 years, were recruited for this study. Twenty-nine participants mean standard deviation BMI of 44.8 +/- 7.0 kg underwent bariatric surgery, while 16 participants mean standard deviation BMI of 47.9 +/- 5.2 kg were on the waiting list (control). One participant was lost to follow-up. The treatment group lost a mean of 24.3 kg (95% confidence interval [CI] 21.1-27.5), while the control group gained 1.2 kg (95% CI -2.5 to 4.9), respectively. In multivariable analysis, bariatric surgery was significantly associated with reduced foot pain at 6-month follow-up 32.6 points (95% CI -43.8 to 21.4, P <.001), while fat mass index was significantly associated with increased pain at follow-up 1.5 points (95% CI.2 to 2.8, P=.027), after controlling for fat-free mass index, age, sex, and depression. Conclusions: Bariatric surgery was significantly associated with reduced foot pain. Higher baseline fat mass index, but not fat-free mass index or BMI, was predictive of increased foot pain at follow-up. Foot pain may be mediated by metabolic, rather than mechanical, factors in bariatric surgery candidates. (C) 2018 American Society for Bariatric Surgery. Published by Elsevier Inc. All rights reserved.