Time Restricted Eating vs. Caloric Restriction for Obesity

(Time2Eat Trial)

Overseen By Emilee Mickaliger

Age: 18+

Sex: Any

Trial Phase: Academic

Sponsor: University of Colorado, Denver

Must not be taking: Weight loss, Antipsychotics

Disqualifiers: Pregnancy, Diabetes, Cancer, CVD, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: Unknown

Duration: 52 weeks

162 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

The trial aims to explore how different eating schedules aid weight loss in adults with obesity. It compares early and late time-restricted eating (intermittent fasting) with traditional calorie counting (daily caloric restriction) to determine which approach more effectively promotes weight loss and improves metabolic health. Participants will follow one of these eating plans for a year. This trial suits adults with a BMI between 27 and 45 who are not currently practicing intermittent fasting or similar diets and live near the Anschutz Health & Wellness Center. As an unphased trial, it offers participants the chance to contribute to innovative research that could shape future dietary guidelines.

Will I have to stop taking my current medications?

The trial does not specify if you must stop taking your current medications, but it excludes those who have taken medications affecting weight or energy in the last 6 months. If your medication must be taken with food, it may depend on whether it can be adjusted to fit the eating schedule of the study.

Is there any evidence suggesting that this trial's treatments are likely to be safe?

Research shows that time-restricted eating (TRE), whether early or late in the day, is generally safe for people with obesity. Studies indicate that TRE can aid weight loss and improve insulin levels and body composition. Specifically, early TRE has led to improvements in blood pressure and mood. Late TRE has also resulted in modest weight loss and positive changes in body fat and waist size.

Although some studies have demonstrated successful weight loss with TRE, they report no major changes in blood sugar levels, suggesting that this approach is well-tolerated. These studies report no serious side effects, indicating that both types of TRE are safe for improving weight and metabolic health. ^{1 2 3 4 5}

Why are researchers excited about this trial's treatments?

Researchers are excited about this trial because it's exploring new ways to tackle obesity through time-restricted eating (TRE) and caloric restriction. Unlike traditional methods that focus solely on cutting calories, TRE involves eating within specific time windows, either early or late in the day, potentially aligning better with our natural body rhythms. This approach may offer benefits like improved metabolism or reduced hunger, making weight management more sustainable. By comparing early and late TRE with daily caloric restriction, researchers aim to understand which method is most effective and why, potentially paving the way for more personalized and flexible obesity treatments.

What evidence suggests that this trial's treatments could be effective for obesity?

This trial will compare early time-restricted eating (eTRE), late time-restricted eating (late TRE), and daily caloric restriction (DCR) for obesity. Research has shown that eating within a limited time early in the day (eTRE) can aid weight loss and improve health. Studies indicate that eTRE is more effective for losing weight and improving factors like blood pressure and mood compared to eating over a longer period. Participants following eTRE have lost about 3%–5% of their weight over several months.

For eating later in the day (late TRE), evidence suggests it also aids in weight loss and can improve insulin levels. One study found that late TRE led to noticeable improvements in body composition and health markers. Both early and late TRE are promising for weight loss, with early TRE showing slightly better results in some studies. Participants in this trial will be assigned to one of these approaches to evaluate their effectiveness in weight management. ^{2 6 7 8 9}

Are You a Good Fit for This Trial?

Adults aged 18-65 with obesity (BMI of 27-45 kg/m2) who typically eat over a span of more than 12 hours daily, own a smartphone, and can commit to the trial for one year without relocating. They must pass medical screenings and be willing to give informed consent.

Inclusion Criteria

My BMI is between 27 and 45.

Have a primary care physician (or are willing to establish care with a primary care physician prior to study enrollment) to address medical issues which may arise during screening or study procedures/interventions

Live or work within 45 minutes of the Anschutz Health & Wellness Center (exceptions may be made at the discretion of the Study PI on a case-by-case basis for highly motivated subjects)

Exclusion Criteria

Pregnancy or lactation for women (exceptions apply for specific postpartum conditions)

Weight loss >5kg in past 3 months for any reason except post-partum weight loss; weight gain >5kg in past 3 months requires assessment by PI

I have serious stomach or intestine problems.

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Treatment

Participants follow assigned dietary strategy (early TRE, late TRE, or daily caloric restriction) for 1 year with group-based program for instruction and support

52 weeks

Several visits throughout the year for measurements and monitoring

Follow-up

Participants are monitored for safety and effectiveness after treatment

4 weeks

What Are the Treatments Tested in This Trial?

Interventions

• DCR
• Early TRE
• Late TRE

Trial Overview The study is examining how early vs. late time restricted eating (TRE) impacts weight loss compared to daily caloric restriction (DCR). Participants will follow their assigned diet plan for a year with support from group-based programs.

How Is the Trial Designed?

Group I: Late time restricted eating Experimental Treatment 1 Intervention

Participants will be asked to follow late time restricted eating

Group II: Early time restricted eating Experimental Treatment 1 Intervention

Participants will asked to follow early time restricted eating

Group III: Daily caloric restriction Active Control 1 Intervention

Participants will be instructed to follow daily caloric restriction

Who Is Running the Clinical Trial?

University of Colorado, Denver

Lead Sponsor

Trials

1,842

Recruited

3,028,000+

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Collaborator

Trials

2,513

Recruited

4,366,000+

Published Research Related to This Trial

In a study of 43 insulin-resistant adults over 12 months, both alternate-day fasting (ADF) and daily calorie restriction (CR) led to similar weight loss, with ADF resulting in an 8% reduction and CR a 6% reduction in body weight.

ADF was more effective than CR in significantly lowering fasting insulin levels and insulin resistance, with reductions of 52% and 53% respectively, compared to only 14% and 17% for CR, indicating ADF may be a better option for improving glucoregulatory factors in insulin-resistant individuals.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Differential Effects of Alternate-Day Fasting Versus Daily Calorie Restriction on Insulin Resistance. Gabel, K., Kroeger, CM., Trepanowski, JF., et al.[2020]

In a study of 81 participants over 39 weeks, early time-restricted eating combined with daily caloric restriction (E-TRE+DCR) did not lead to significantly greater weight loss compared to daily caloric restriction (DCR) alone, with both groups losing similar amounts of weight.

Both dietary strategies were equally acceptable to participants, showing similar adherence levels and no differences in body composition, dietary intake, or physical activity between the two groups.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Early time-restricted eating compared with daily caloric restriction: A randomized trial in adults with obesity. Thomas, EA., Zaman, A., Sloggett, KJ., et al.[2023]

The ChronoFast trial will compare the effects of early time-restricted eating (eTRE) and late time-restricted eating (lTRE) on cardiometabolic health in 30 women with overweight or obesity over a 2-week period, focusing on insulin sensitivity and other health markers.

This study employs rigorous methods, including real-time dietary monitoring and continuous glucose tracking, to ensure compliance and assess the effectiveness of each eating pattern, aiming to provide clear recommendations for improving health outcomes.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effects of Early vs. Late Time-Restricted Eating on Cardiometabolic Health, Inflammation, and Sleep in Overweight and Obese Women: A Study Protocol for the ChronoFast Trial. Peters, B., Koppold-Liebscher, DA., Schuppelius, B., et al.[2021]

Alternate-day fasting (ADF) is a safe and well-tolerated weight loss method, with 93% of participants completing the 8-week study without adverse effects.

While ADF and a standard caloric restriction diet produced similar weight loss results after 8 weeks, ADF showed more favorable changes in body composition, particularly in fat and lean mass, during the follow-up period.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity. Catenacci, VA., Pan, Z., Ostendorf, D., et al.[2019]

In an 8-week study involving 37 adults with overweight and obesity, both early and delayed time-restricted eating (TRE) combined with caloric restriction (CR) led to significant weight loss and reductions in fat mass, with no significant differences between the two TRE timings.

All groups, including those only on caloric restriction, showed similar improvements in body composition and fasting glucose levels, suggesting that the timing of eating may not be as crucial as previously thought when combined with caloric restriction.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Cardiometabolic effects of early v. delayed time-restricted eating plus energetic restriction in adults with overweight and obesity: an exploratory randomised clinical trial. Queiroz, JDN., Macedo, RCO., Dos Santos, GC., et al.[2022]

Intermittent fasting (IF) may be an effective weight management strategy for overweight and obese adults, but its evidence base in humans is still limited, with only one published systematic review available.

Current guidelines from the National Institute for Health and Care Excellence (NICE) do not recommend very low calorie diets (VLCD) as a routine treatment for obesity, highlighting concerns about potential side effects and the sustainability of fasting approaches.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Intermittent fasting interventions for the treatment of overweight and obesity in adults aged 18 years and over: a systematic review protocol. Jane, L., Atkinson, G., Jaime, V., et al.[2022]

In the CALERIE study, calorie restriction (CR) led to significant weight loss, explaining 41% of the variance in weight loss among participants, but the timing of meals also played a crucial role.

Shorter eating intervals and consistent timing for the first and last meals were associated with greater weight loss and enhanced adherence to CR, suggesting that optimizing meal timing could improve the effectiveness of CR protocols.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Associations between the timing of eating and weight-loss in calorically restricted healthy adults: Findings from the CALERIE study. Fleischer, JG., Das, SK., Bhapkar, M., et al.[2022]

This study is the first to evaluate the effects of time-restricted eating (TRE) on weight loss in a controlled manner, comparing it to a usual eating pattern (UEP) while ensuring both groups consumed the same number of calories and identical diets.

Participants aged 21-69 with prediabetes and obesity were monitored closely, allowing for a rigorous assessment of how meal timing impacts weight change without altering caloric intake.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Design and Implementation of a Time-Restricted Eating Intervention in a Randomized, Controlled Eating Study. White, K., Wu, B., Pilla, SJ., et al.[2023]

Intermittent energy restriction (IER) strategies, such as intermittent fasting and time-restricted feeding, show similar effectiveness in weight loss compared to continuous energy restriction (CER) in adults with obesity, based on a review of randomized trials lasting at least 8 weeks.

Out of 11 studies analyzed, 9 found no significant differences in weight or body fat loss between IER and CER, suggesting that IER can be a viable alternative for obesity treatment.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Rynders, CA., Thomas, EA., Zaman, A., et al.[2021]

In a 12-month study involving 58 low-income women with obesity, time-restricted feeding (TRF) did not lead to significant weight loss compared to a standard hypoenergetic diet, indicating that TRF may not be effective for weight reduction in this population.

However, TRF was associated with a reduction in body fat percentage and waist circumference, suggesting it may have some benefits for body composition, even if these changes are not clinically significant.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effects of time-restricted feeding on body weight, body composition and vital signs in low-income women with obesity: A 12-month randomized clinical trial. de Oliveira Maranhão Pureza, IR., da Silva Junior, AE., Silva Praxedes, DR., et al.[2021]

Citations

1. pubmed.ncbi.nlm.nih.gov pubmed.ncbi.nlm.nih.gov/35939311/

Effectiveness of Early Time-Restricted Eating for Weight Loss ... In this randomized clinical trial, eTRE was more effective for losing weight and improving diastolic blood pressure and mood than eating over a window of 12 or ...

2. jamanetwork.com jamanetwork.com/journals/jamainternalmedicine/fullarticle/2794819

Effectiveness of Early Time-Restricted Eating for Weight ... In this randomized clinical trial, eTRE was more effective for losing weight and improving diastolic blood pressure and mood than eating over a window of 12 or ...

3. sciencedirect.com sciencedirect.com/science/article/pii/S1550413123004540

Time-restricted eating: Watching the clock to treat obesity In participants with obesity, time-restricted eating results in 3%–5% weight loss over 2–12 months, versus controls. Reductions in body weight ...

4. nature.com nature.com/articles/s41430-023-01311-w

Time-restricted eating with calorie restriction on weight loss ... Subgroup analysis suggested that early TRE is more effective in weight loss (WMD: −1.42, 95% CI: −1.84 to −1.01, and I2: 0%) and improving fat ...

5. frontiersin.org frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1664412/full

Effects of time-restricted eating on body composition and ... Our findings indicate that TRE significantly improves insulin levels in overweight and obese women, whereas no significant alterations were observed in blood ...

6. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC11221496/

Time-restricted eating: Watching the clock to treat obesity Results reveal that fasting glucose levels did not change after 2–12 months of TRE in adults with obesity, even when participants achieved 5% weight loss.

7. pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov/articles/PMC12479299/

Effects of time-restricted eating on body composition and ... Our findings indicate that TRE significantly improves insulin levels in overweight and obese women, whereas no significant alterations were ...

8. sciencedirect.com sciencedirect.com/science/article/pii/S2589004224002219

Time-restricted eating improves health because of energy ... The results showed that TRE led to modest weight loss, lower waist circumference and energy deficits. TRE also improved body mass index, fat ...

9. journal-of-hepatology.eu journal-of-hepatology.eu/article/S0168-8278(25)02272-X/abstract

Efficacy and safety of time-restricted eating in metabolic ... Time-restricted eating (TRE) may improve weight loss, insulin resistance, and body composition, which are key factors in the pathophysiology of ...