The hydropinotherapy intervention consists of the oral ingestion of thermal water combined with bay leaf (Laurus nobilis). Participants assigned to this intervention will ingest 200 mL of Chaves thermal water infused with dried bay leaf (L. nobilis) twice per week. The infusion will be prepared by the research team by adding 5 g of dried bay leaf (L. nobilis) to the thermal water and allowing it to infuse for 15 minutes, followed by filtration through a strainer. All participants will be observed by the research team during ingestion to ensure compliance and safety.

The thermal water used in this intervention is natural mineral water from Termas de Chaves, which emerges at a temperature of 77.0°C. It is classified as gasocarbonic, sodium bicarbonate, fluoride-based, and highly mineralized, with bicarbonate, chloride, sodium, and potassium as the predominant ions.

Change in fasting plasma glucose concentration (mg/dL), measured using standard laboratory methods.

Change in fasting serum insulin concentration (µIU/mL), measured using standard laboratory methods.

Change in glycated hemoglobin (HbA1c, %), measured using standard laboratory methods.

Change in serum aspartate transaminase (AST) activity (U/L), alanine transaminase (ALT) activity (U/L), measured by enzymatic spectrophotometry.

Change in total bilirubin concentration (mg/dL), measured by enzymatic spectrophotometry.

Change in systolic and diastolic blood pressure (mmHg), measured using a digital blood pressure monitor following a standardized seated protocol, with the average of two readings recorded.

Change in waist circumference (cm) and hip circumference (cm), measured using a non-elastic measuring tape according to ISAK protocols.

Change in total fat mass (kg), truncal fat mass (kg), abdominal fat mass (kg), lean body mass (kg), assessed by dual-energy X-ray absorptiometry (DXA).

Change in bone mineral density (g/cm²) from baseline to 16 weeks, assessed by dual-energy X-ray absorptiometry (DXA).

Change in maximal oxygen uptake (mL/kg/min), assessed using a graded treadmill exercise test to volitional exhaustion.

Change in peak torque (Nm) of knee flexors and extensors, hip flexors/extensors and abductors/adductors, and ankle dorsiflexors and plantarflexors, assessed using isokinetic dynamometry.

Change in sleep quality score, assessed by the Pittsburgh Sleep Quality Index (PSQI; score range 0-21, higher scores indicate worse sleep quality).

Change in health-related quality of life score from baseline to 16 weeks, assessed by the Short Form-36 Health Survey (SF-36; score range 0-100, higher scores indicate better health status).

Change in pain intensity score from baseline to 16 weeks, assessed by the Numeric Rating Scale (NRS; score range 0-10, higher scores indicate worse pain).

Change in psychosocial risk classification from baseline to 16 weeks, assessed by the Start Back Screening Tool (SBST; score range 0-9, higher scores indicate higher psychosocial risk).

Change in total energy intake (kcal/day), assessed using a 24-hour dietary recall administered by a trained nutritionist.

Change in macronutrient intake (g/day: proteins, total fats, carbohydrates, fiber), assessed using a 24-hour dietary recall administered by a trained nutritionist.