Major clinical and nutrological findings of the relationship among obesity, metabolic syndrome, and bariatric surgery in the process of hair loss: a systematic review

Introduction: According to the World Obesity Atlas, overweight and obesity will affect nearly 3 billion adults (around 50%) by 2030. Bariatric surgery is an effective option for the treatment of obesity. However, nutritional deficiencies of vitamins, minerals, and trace elements can occur after bariatric surgery and are associated with hair loss (alopecia). Objective: It was to present the main clinical studies and meta-analyses on the relationship between obesity, metabolic syndrome, and bariatric surgery in the process of hair loss (alopecia). Methods: The PRISMA guidelines for systematic reviews were followed. Clinical studies and meta-analyses were included. The literature search process was conducted from July to August 2025 and developed based on Web of Science, Scopus, Embase, PubMed, Lilacs, Ebsco, Scielo, and Google Scholar, covering scientific articles from various periods up to the present day. Results and Conclusion: Seven studies with 9,940 participants were selected to comprise this systematic review. According to the GRADE instrument, most studies showed homogeneity in their results, with X2=92.7%>50%. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 20 studies with a high risk of bias and 24 studies that did not meet the GRADE and AMSTAR-2 criteria. It was concluded that hair loss related to obesity and post-bariatric surgery hair loss can have a significant impact on individuals, including emotional distress that should not be underestimated. Further investigation is needed on the relationship between obesity/bariatric surgery and hair loss. Laparoscopic vertical sleeve gastrectomy alters the serum amino acid profile in obese patients, and the serum leucine concentration at 3 months post-operatively is an influential factor in post-operative alopecia. Hair loss is a frequent condition after vertical sleeve gastrectomy. In most cases, iron and zinc levels are within the normal range. The variable composed of the sum of zinc and iron is a good predictor of hair loss.