Iron Metabolism in Obesity

This is a prospective observational cohort study designed to evaluate changes in clinical, biochemical, and dietary variables related to iron status in adult individuals undergoing restrictive bariatric surgery (laparoscopic sleeve gastrectomy or adjustable gastric banding) in the urban area of Monterrey, Mexico. The main objective is to assess whether iron status prior to surgery influences weight loss success, inflammatory response, and overall health-related quality of life in the six months following surgery.

A total of 50 participants (25 with iron deficiency and 25 without, defined according to WHO standards) will be enrolled. Participants will be classified into groups based on baseline iron status measured using routine preoperative laboratory data. Eligibility criteria include age between 18 and 50 years, premenopausal women, BMI between 35 and 45 kg/m², and eligibility for restrictive bariatric surgery according to international guidelines. Exclusion criteria include prior bariatric surgery, severe anemia (Hb < 100 g/L), medical conditions that may affect inflammation or iron metabolism, chronic liver disease, recent pregnancy or lactation, recent significant weight loss (>10% in the last 6 months), shift work, and high levels of physical activity (>10 hours/week).

All participants will be followed for 6 months after surgery. Outcome assessments include anthropometric measurements, laboratory parameters (hemoglobin, ferritin, CRP, among others), dietary intake, and patient-reported outcomes. Dietary intake will be assessed using MyFitnessPal, a mobile app for dietary tracking, with standardized food entries labeled "IRONXL" based on the Mexican food composition database. Participants will be trained to enter food items accurately and consistently. Data from MyFitnessPal will be exported to obtain nutrient intake data.

Quality of life and general health status will be measured using the PROMIS Global Health questionnaire, a validated 10-item tool. A structured case report form will collect demographic, medical history, and lifestyle data. Blood samples will be collected and stored for potential future research purposes, pending optional consent by participants.

The study will be conducted at the Zambrano Hellion Medical Center, TecSalud. The research team includes qualified surgeons and investigators trained in Good Clinical Practice (GCP). Data quality assurance procedures will include double-entry verification of questionnaire data, standardized anthropometric assessments, and laboratory analyses conducted in accredited clinical laboratories. A Manual of Procedures (MOP) guides all data collection processes.

Missing data will be managed through multiple imputation when appropriate, and all analyses will be conducted according to a pre-specified Statistical Analysis Plan (SAP). The primary outcome is change in weight (kg and % of initial body weight) over 6 months. Secondary outcomes include change in hemoglobin, ferritin, CRP, dietary iron intake, and PROMIS scores.

The sampling method is non-probabilistic and based on convenience sampling of patients scheduled for surgery who meet the eligibility criteria and agree to participate voluntarily. All participants will provide written informed consent before any study procedures.

Optional consent will be obtained for the long-term storage and future analysis of biospecimens (whole blood, serum). These samples may be used in future research related to iron metabolism, inflammation, and nutrition. Participants who decline this optional component will still be eligible to participate in the main study.

Inclusion criteria

• Male and female participants aged 18 to 50 years.
• Premenopausal women (defined as no absence of menstruation in the past 12 months).
• Body Mass Index (BMI) between 35 and 45 kg/m² at recruitment.
• Scheduled to undergo bariatric surgery via sleeve gastrectomy or laparoscopic adjustable gastric banding (LAGB), with indications aligned with international guidelines. Bariatric surgery eligibility includes:

• BMI between 35 and 45 kg/m² with the presence of obesity-related comorbidities (medical, physical, or psychosocial conditions), and a history of unsuccessful attempts at sustained weight loss through non-surgical means.
• Adequately informed, understanding and accepting the potential risks and benefits of the procedure, and expressing commitment to adhere to long-term dietary and physical activity recommendations post-surgery.
• Willing to maintain consistent dietary iron intake and refrain from taking any iron supplements other than those prescribed by the attending surgeon throughout the study duration.
• Not pregnant during the study period or in the six months prior to enrollment, and not planning to become pregnant for at least 3 months after the final study visit (at 6 months).
• Not breastfeeding in the six weeks prior to enrollment, nor planning to breastfeed during the study.
• No significant weight loss (≥10% of body weight) in the six months prior to the pre-surgical evaluation.
• Signed informed consent.
• No night shift work during the two weeks prior to the baseline visit or at any point during the study (night shift defined as work performed between 12:00 AM and 6:00 AM).
• Not engaging in strenuous physical activity ≥10 hours per week.

Exclusion criteria

• Participants who have undergone any bariatric procedure other than LAGB or sleeve gastrectomy.
• Severe anemia (defined as hemoglobin <100 g/L).
• History of previous surgical obesity treatments.
• Presence of significant medical conditions that may affect iron status or inflammatory markers independently of obesity, including but not limited to: cancer, HIV/AIDS, inflammatory bowel disease, gastrointestinal bleeding, rheumatoid arthritis, and chronic kidney disease (per investigator's judgment).
• Diagnosed abnormalities in iron metabolism based on routine pre-surgical blood samples and unrelated to obesity (e.g., thalassemia).
• History of frequent blood transfusions.
• Chronic liver disease (e.g., alcoholic liver disease, hepatitis C-related liver disease).
• Use of medications that could interfere with study measurements (per investigator's judgment).
• Women consuming ≥14 alcoholic beverages per typical week or men consuming >21 alcoholic beverages per typical week.