This study is a randomized controlled intervention trial in adults aged 50+ years with overweight or obesity, which will compare three groups with different diet prescriptions: 1) pre-meal water consumption (500 ml, before each main meal) with a hypocaloric diet; 2) 1500 ml water consumed throughout the day with a hypocaloric diet; 3) hypocaloric diet with no instructions regarding water consumption. Smart water bottles will objectively assess water intake timing and volume. Urine osmolality, urine volume, and serum osmolality will be used as objective indicators of compliance with the water intake prescription. We will investigate changes in perceived hunger and fullness and appetite-regulating hormones as potential mechanisms by which premeal water could improve appetite regulation. We will also investigate the impact of water consumption and hydration on executive function capabilities, which may influence intervention adherence. Although increasing water intake could be an effective weight management strategy, no evidence-based recommendations exist for the timing of water intake needed for this benefit.

Inclusion Criteria:

• aged 50+ years
• BMI ≥25 kg/m2
• weight stable (+/- 2 kg) in past 6 months
• willing to provide consent and comply with study protocol

Exclusion Criteria:

• usual plain drinking water intake >1500 ml/d
• uncontrolled hypertension (>159/99 mmHg)
• medical condition requiring specialized diet prescription (eg, T2D, CHF wih fluid restriction)
• medical condition that precludes participating in a physical activity program (eg, orthopedic injury)
• current or history of GI disease (eg, Crohn's), GI surgery, or medications which impact GI function
• allergies or aversions to foods included in the test meals