In Spain, obesity epidemic is one of the leading contributors of chronic disease and disability. Obesity is associated with higher morbidity and all-cause mortality risk especially when fat is stored in the abdominal area (i.e., increased visceral adipose tissue, VAT). Although current approaches such as energy restriction may be effective at reducing body fat and improving cardiometabolic health, their long-term adherences are limited. Time-restricted eating (TRE; e.g., 8 hours eating: 16 hours fasting on a daily basis) is a recently emerged intermittent fasting approach with promising cardiovascular benefits. Results from pioneering pilot studies in humans are promising and suggest that simply reducing the eating time window from ≥12 to ≤8-10 hours/day improves cardiometabolic health. However, currently, there is no consensus regarding whether the TRE eating window should be aligned to the early or middle to late part of the day. The EXTREME study will investigate the efficacy and feasibility of three different 8 hours TRE schedules (i.e., early, late and self-selected) over 12 weeks on VAT (main outcome) and cardiometabolic risk factors (secondary outcomes) in adults with overweight/obesity and abdominal obesity. The final goal of the EXTREME study is to demonstrate the health benefits of a novel and pragmatic intervention for the treatment of obesity and related cardiometabolic risk factors; an approach readily adaptable to real-world practice settings, easy for clinicians to deliver, and intuitive for patients to implement and maintain in their lives.

Inclusion Criteria:

• Aged 30-60 years.

• Body mass index ≥25.0 and <40 kg/m2

• Weight stability (within 3% of screening weight) for >3 months prior to study entry.

• Sedentary lifestyle (<150 min/week of moderate-vigorous intensity exercise) for >3 months prior to study entry.

• Habitual eating window ≥12 hours.

• At least one of the following metabolic impairments:

  • High-density lipoprotein (HDL) cholesterol concentration <50 mg/dL for females and <40 mg/dL for males.

  • Low-density lipoprotein (LDL) cholesterol levels >100 mg/dL (or on medication to treat elevated LDL cholesterol levels).

  • Serum triglycerides concentration ≥150 mg/dL or on medication to treat elevated triglycerides.

  • Systolic blood pressure >130 mm Hg and/or diastolic blood pressure >85 mm Hg or already being treated with anti-hypertension medications.

  • Impaired glucose tolerance is defined as at least one of the following:

    • Fasting plasma glucose (PG) >100 mg/dL and <125 mg/dL.
    • Hemoglobin A1c between ≥5.7% and <6.5%.
    • Insulin resistance as measured by the Homeostatic Model Assessment of Insulin Resistance (HOMA2-IR) >1.8.

Exclusion Criteria:

• History of a major adverse cardiovascular event, clinically significant kidney, endocrine, or neurological disease, bariatric surgery, HIV/AIDS, known inflammatory and/or rheumatologic disease, cancer, or other medical condition in which fasting or exercise is contraindicated.
• Type 1 or Type 2 diabetes.
• Major psychiatric disorders, eating disorders, sleep disorders, or alcohol abuse.

Regular use of medication or compounds that may affect study outcomes (e.g., antidiabetic, steroids, beta-blockers, antibiotics, prebiotics, probiotics and symbiotics).

• Participating in a weight loss or a weight-management program.
• Pregnancy and lactation or planned pregnancy (within the study period).
• Caregiver for a dependent requiring frequent nocturnal care/sleep interruptions. Shift workers with variable hours (e.g., nocturnal). Frequent travel over time zones during the study period.
• Fear of needles and claustrophobia to magnetic resonance imaging (MRI).
• Being unable to understand and to accept the instructions or the study objectives and protocol.