While body weight reduction can be achieved through various interventions in people living with obesity, most patients regain a substantial proportion of the lost weight within the following months. There is a lack of effective interventions to prevent this regain, making weight regain one of the most pressing challenges in obesity management. The goal of this clinical trial is to determine whether adhering to time-restricted eating (TRE; a form of intermittent fasting) during and after a dietary weight loss intervention, promotes weight maintenance to a greater extent than consuming all daily meals within 11 hours or more. Additionally, the study will address other questions, such as whether TRE improves body composition, insulin sensitivity, and cardiometabolic risk factors; whether the TRE intervention produces effects on different components of energy balance or related behaviors; and whether prior exposure to the TRE intervention influences eating window duration and weight change over the subsequent 24 months.

The study will compare participants who concentrate all their food intake within 8 hours or less with those who consume all their daily meals within 11 hours or more. All participants will follow a calorie-restricted diet designed to induce an 8-10% weight loss over 12-16 weeks and will be followed for several months after the weight loss intervention.

Inclusion Criteria:

• Have a body mass index of 30-45 kg/m2.
• Have safety laboratory test results (general biochemistry and complete blood count) within the normal reference range or with abnormalities considered clinically insignificant by the medical research team and that do not require the initiation of drug treatment.
• Have sufficient venous access for the blood sampling required by the procedures described in this protocol, and not have a phobia of needles or blood.
• Maintain a usual intake window of 11 hours or longer at least 5 days a week and have a response rate greater than 85% during the self-recording carried out during the screening process.
• Willingness and ability to consume all foods provided during the outcome assessment and dietary intervention.
• Being able to understand and undergo the procedures that are part of the study, in the opinion of the research team.
• Availability to participate in the study.
• Be willing to complete the study regardless of the group to which they are assigned.

Exclusion Criteria:

• Having received a diagnosis or presenting signs or symptoms that, in the opinion of the research team, could contraindicate TRE intervention or any of the procedures included in the study.
• Having been diagnosed with or having a history of metabolic (including a diagnosis of any type of diabetes mellitus), hematological, pulmonary, cardiovascular, gastrointestinal, neurological, immune, hepatic, renal, urological or psychiatric diseases that could interfere with the study results or compliance with the protocol.
• Having undergone any surgical procedure that, in the opinion of the research team, could alter energy metabolism or digestive function during the course of the study.
• Taking drugs or supplements that are likely to alter body weight or appetite.
• Have experienced weight loss of more than 10% in the last two years, or more than 5% in the last 6 months, unless all the weight lost has been regained.
• Follow unconventional eating patterns, such as vegan or fasting diets, or be unable to tolerate the foods provided during the study.
• Being pregnant or planning to become pregnant within the next two years.
• Being in the postpartum phase (within 12 months of giving birth) or breastfeeding.
• Being in the perimenopausal stage, defined as meeting the criteria of irregular menstrual cycles, hormonal changes indicative of perimenopause, or the presence of menopausal symptoms.
• Participating in a nutritional intervention or treatment or having done so during the previous 3 months.
• Having been diagnosed with or showing signs or risk factors for the development of an eating disorder.
• Experiencing frequent interruptions in the sleep-wake cycle.
• Having clinically significant gastric emptying abnormalities, a current diagnosis of any form of diabetes, blood pressure greater than 160/90 mm Hg, or heart rate below 50 or above 100 beats per minute (sitting), with or without stable doses of antihypertensive medication.
• Have an active or untreated malignant disease or be in remission from a clinically significant malignant disease for less than five years prior to the time of evaluation.
• Having a history of drug or alcohol abuse or testing positive for drugs, unless due to medication prescribed by a healthcare professional.
• Smoking, vaping, or regular use of tobacco products, unless there have been periods of at least 24 consecutive hours without consumption during the last 4 weeks.
• Regular consumption of caffeine in excess of the equivalent of 3 espressos per day (225 mg/day).
• Being a direct relative or cohabitant of research team personnel.
• Any other condition that, in the opinion of the research team, makes participation in the study inadvisable.