Does starting with a low-carb versus a low-fat diet change how much body fat you lose?

Diet Order Effects of Low Fat vs. Low Carb Diets on Body Fat Change

This will try whether starting with a low-carb or a low-fat diet changes body fat loss in adults with overweight or obesity over two back-to-back four-week diets.

Quick facts

• Phase: NA
• Study type: Interventional
• Enrollment: 42 (estimated)
• Ages: 18 Years to 50 Years
• Sex: All
• Sponsor: National Institutes of Health Clinical Center (CC) (nih)
• Locations: 1 site (Bethesda, Maryland)
• Trial ID: NCT06325722 on ClinicalTrials.gov

What this trial studies

This is an 8-week outpatient crossover feeding trial in adults with overweight or obesity that randomizes participants to four weeks of a low-carbohydrate diet followed immediately by four weeks of a low-fat diet, or the reverse order, with no washout. Meals are provided while participants live at home, and there are three required visits to the NIH Clinical Center for baseline and endpoint testing including DXA scans. Daily weights and urine collections (and a preparatory special water protocol) are used to monitor adherence and model rate of weight change. The primary outcome is change in total fat mass by DXA between baseline and week 8, with secondary outcomes including rate of weight change and total body weight change.

Who should consider this trial

Good fit: Adults aged 18–50 with BMI ≥25 who can follow provided diets at home, have been weight stable, can attend three visits to the NIH in Bethesda, MD, and have adequate home food storage/preparation facilities.

Not a fit: People with implanted devices that affect DXA, major illnesses that alter appetite or immune function, diabetes or other excluded conditions, inadequate kitchen/refrigerator access, or BMI under 25 are unlikely to qualify or directly benefit from the findings.

Why it matters

Potential benefit: If successful, the results could show a simple sequencing strategy for low-carb versus low-fat diets that improves fat loss and guides diet planning for weight management.

How similar studies have performed: A prior controlled inpatient NIH crossover found greater fat loss when a low-carbohydrate diet was given first over two-week diets, and this outpatient trial seeks to replicate and extend that result over longer periods.

Eligibility criteria

* INCLUSION CRITERIA:

In order to be eligible to participate in this study, an individual must meet all of the following criteria:

1. Stated willingness to comply with all study procedures and availability for the duration of the study
2. Adults aged 18-50 years
3. Weight stable (\< +/- 5 percent over past 6 months) as determined by volunteer report
4. Body mass index (BMI) \>= 25 kg/m\^2
5. Agreement to adhere to Lifestyle Considerations throughout the study duration

EXCLUSION CRITERIA:

1. Subjects with cardiac pacemakers or other implants that may be affected by or affect the DXA measurements
2. Inadequate access to equipment required for the study (e.g., too little refrigerator storage space or a microwave oven that is too small) as determined by discretion of PI and/or study team
3. Evidence of diseases or conditions that may influence appetite (e.g., cancer, diabetes, alterations of smell or taste post COVID-19), diseases or conditions that affect the immune system, or other conditions at the discretion of the PI and/or study team
4. Taking prescription medications or other drugs that may influence metabolism (including but not limited to diet/weight-loss medication, some psychiatric medications, or other medications at the discretion of the PI and/or study team)
5. People unlikely to adhere to a relatively consistent daily and weekly routine and avoid travel during their participation in the study. For example, people with occupations such as pilots, flight attendants, or frequently travel for work or pleasure.
6. People unlikely to abstain from off study food or supplements that may impact metabolism or appetite at the discretion of the study team
7. Positive pregnancy test or lactating as determined by volunteer report (women only)
8. Inability or unwillingness to use birth control between screening and completion of the study (women only)
9. Symptoms or signs of perimenopause or menopause by volunteer report (women only)
10. Regular vigorous exercise \>150 min per week as determined by volunteer report
11. Alcohol consumption \> 3 drinks per day as determined by volunteer report
12. Regular use of tobacco (smoking, chewing, or vaping), nicotine replacement therapy, or illicit drugs over past 6 months as determined by volunteer report. Subjects may also be excluded based on a urine drug test.
13. Psychological conditions as determined by DSM-5 Self-rated Level 1 Cross-cutting Symptom Measure such as (but not limited to) eating disorders, depression, bipolar disorders, that would be incompatible with safe and successful participation in this study, as determined by investigators
14. Volunteers with strict dietary concerns (e.g. vegetarian or kosher diet, food allergies) or a reported dislike of a significant fraction of the study foods
15. Volunteers unwilling or unable to give informed consent
16. Non-English speakers due to unavailability of required questionnaires in other languages

Where this trial is running

Bethesda, Maryland

• National Institutes of Health Clinical Center — Bethesda, Maryland, United States (RECRUITING)

Study contacts

• Principal investigator: Valerie L Darcey — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
• Study coordinator: Nan Zhai, C.R.N.P.

Conditions: Overweight, Obesity, Diet, Body Fat, Nutrition, weight-loss