Do early indicators of euthyroid sick syndrome predict longer-term post-bariatric weight loss? A hypothesis-generating preliminary study

Abstract

Background: Despite the success of bariatric surgery for most patients, up to 30 % do not experience optimal weight loss outcomes. Reasons remain incompletely understood. Thyroid hormones, due to their role in energy expenditure, have received study. Yet research to date is inconclusive regarding the impact of standard thyroid markers (e.g., thyroid stimulating hormone, or TSH) on weight regulation after bariatric surgery. This prospective observational study investigates whether the early development of euthyroid sick syndrome (ESS) predicts reduced longer-term post-bariatric weight loss. ESS develops during periods of stress (e.g., critical illness, severe infection, famine) and is thought to serve a protective function by suppressing metabolism and conserving weight. Levels of metabolically active free triiodothyronine (FT3) drop, levels of non-catabolic reverse 3, 3, 5-triiodothyronine (rT3) rise, and TSH levels remain euthyroid. Reductions in the ratio of FT3 to rT3 significantly predict outcomes in critically ill patients with ESS yet have been unexamined in intentional weight loss among post-bariatric patients. Hence this hypothesis-generating preliminary study investigated whether early changes in the FT3:rT3 ratio predict weight changes at 1-2 years post-bariatric surgery. Methods: Twenty-three adult patients undergoing Roux-en-Y gastric bypass (n=12) or sleeve gastrectomy (n=11) were recruited from a bariatric surgery clinic. The TSH, FT4, FT3, rT3, and self-reported hypothyroid symptoms were collected 2-weeks pre-surgery and between 2 weeks to 3 months post-surgery. Body mass index was measured pre-surgery and 1-2 years post-surgery. Results: Reductions in the FT3:rT3 ratio from pre- to early post-surgery significantly predicted reduced weight loss at 1 (p= 0.03) and 2 years (p= 0.02) post-surgery. No other thyroid-related markers nor hypothyroid symptoms were predictive. Conclusions: Although replication with larger samples is needed (especially given sizeable study attrition), this small exploratory study provides provocative support that early changes in the FT3:rT3 ratio associated with ESS predict longer-term reductions in post-bariatric surgery weight loss. Clinical implications are discussed.