The goal of this randomized controlled trial is to learn how the time of day when calories are eaten affects weight loss in the long-term (12 months). The main aims are to learn:

1. The influence of time-based energy intake goals on longer-term weight loss.
2. The influence of time-based energy intake goals on eating temporal patterns, sleep regularity, and appetite regulation.

Researchers will compare whether goals to eat most of a person's calories in the morning or evening work to treat obesity.

Participants will:

1. Eat a reduced-calorie, low-fat diet (some participants will have goals to eat their calories at certain times of day based on their group)
2. Be physically active at least 200 minutes
3. Receive a cognitive behavioral intervention

This randomized controlled trial investigates the longer-term (12 months) effect of time-based energy intake goals on weight loss. It also explores whether enhanced appetite regulation is a mediator of the relationship and if chronotype moderates the effect. Adults with overweight or obesity are randomly assigned to one of three, 12-month lifestyle interventions: 1) Morning; 2) Evening; or 3) Standard. All conditions receive a reduced-energy, low-fat dietary prescription (1200-1500 kcal/d, < 30% energy from fat), physical activity goals (> 200 min/wk of moderate- to vigorous-intensity physical activity [MVPA]) and a cognitive behavioral intervention. To minimize the effect of other eating temporal variables on outcomes, guidance on the eating window length and the number of eating occasions in the day are consistent across all three conditions. Thus, the three conditions are instructed to have their first eating occasion < 60 minutes of awakening, and eat their three meals and one snack within a 12-hr eating window. Morning group has time-based energy intake goals of 70% of kcal within the first 6 hrs of the eating window and 30% of kcal within the last 6 hrs of the eating window (a morning-loaded energy distribution). Evening group has the opposite time-based energy intake goals (an afternoon/evening-loaded energy distribution). Standard group receives no guidance on energy intake distribution (standard lifestyle intervention). Assessments occur at 0, 3, 6, and 12 months on anthropometrics, diet (24-hr recalls with time-stamped digital images verifying timing of intake, combined with continuous blood glucose monitoring [CGM] to objectively assess for length of the eating window and number of eating occasions), sleep regularity (actigraphy supported by sleep logs collected via ecological momentary assessment [EMA] using smartphones), appetite regulation assessed via EMA using smartphones, chronotype (self-reported midpoint of sleep on work-free days), and MVPA (actigraphy).

The primary aims are to determine:

1. The influence of time-based energy intake goals on longer-term weight loss.
2. The influence of time-based energy intake goals on eating temporal patterns, sleep regularity, and appetite regulation.

The exploratory aims are to consider:

1. If appetite regulation mediates the relationship between time-based energy intake goals and weight loss.
2. The moderating effect of chronotype on weight loss and changes in eating temporal patterns, sleep regularity, and appetite regulation in the three conditions.

Inclusion Criteria:

• Body mass index (BMI) between 27 and 45 kg/m2.

Exclusion Criteria:

• Report not regularly (>/= 5 days/wk) consuming energy (>/= 100 kcal) prior to 12 pm, and not being able to consume energy every day (>/= 50 kcal) within one hour of awakening.
• Report taking sleep medication or not regularly (>/= 5 nights/wk) getting at least 6 hrs of total sleep.
• Report being a shift workers/alternative shift workers that work outside of 7 am and 7 pm.
• Report being diagnosed with type 1, or type 2 diabetes and taking medication that requires eating to occur at certain time periods.
• Report a heart condition, chest pain during periods of activity or rest, or loss of consciousness on the Physical Activity Readiness Questionnaire (PAR-Q). Individuals reporting joint problems, prescription medication usage, or other medical conditions that could limit exercise will be required to obtain written physician consent to participate.
• Report being unable to walk for 2 blocks (1/4 mile) without stopping.
• Report major psychiatric diseases or organic brain syndromes.
• Report currently participating in a weight loss program and/or taking weight loss or appetite regulation medication or lost >/= 5% of body weight during the past 6 months.
• Report having bariatric surgery for weight loss/planning to have bariatric surgery in the next 12 months.
• Report being pregnant, lactating, < 6 months post-partum or plan to become pregnant (next 12 months).
• Report planning to move outside of the metropolitan area within the time frame of the investigation.
• Do not have daily access to PC with internet or smartphones (needed for self-monitoring).

Types and amount of scientific data expected to be generated in the project:

Demographic, anthropometric, dietary intake, sleep and physical activity from actigraphy, appetite regulation collected via ecological momentary assessment, and chronotype data will be collected from 174 adults with overweight or obesity (described in detail in section c.3. of this application) at four time points (0, 3, 6, and 12 months). Raw data will be transformed by processing software (diet and actigraphy) and will generate 4 data sets (data organized by timepoint), which will be no more than 100 gigabytes. These four data sets will be used for statistical analyses and be placed in the repository. All data will be de-identified prior to receipt by the repository, and individual-level data will be made available for sharing.

Data will be made available as soon as possible or at the time of associated publication, whichever comes first. Data on Dryad are retained indefinitely.

Dataset(s) resulting from this research will be shared via the generalist repository Dryad, which provides metadata, persistent identifiers (i.e., DOIs), and long-term access. Dryad is the institutional data repository supported by the University of California and all data is shared under a CC0 waiver, which makes the dataset(s) publicly available. Data will be made available as soon as possible or at the time of associated publication. Dryad datasets are backed up to Merritt, the UC's CoreTrustSeal-certified digital repository, for long-term storage and accessibility. Procedures in place to ensure dataset preservation include storage of data files in multiple geographic locations, regular audits for fixity and authenticity, and succession plans in the event of repository closure.

Meetings will be 60 minutes and led by an interventionist with training at the M.S.- or Ph.D.-level in nutrition, exercise physiology, or behavioral psychology blinded to study hypotheses. Dependent measures will be assessed by a trained researcher blinded to treatment assignment at 0, 3, 6, and 12 months, unless otherwise indicated. The research assistant (blinded to treatment condition) will review all assessment data for accuracy and completion.