Completed

Benefits & Risks of Popular Weight Loss Diets

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What is being tested

Data Collection

Who is being recruted

Body Weight+7

+ Body Weight Changes

+ Nutrition Disorders

From 30 to 50 Years
+14 Eligibility Criteria
See all eligibility criteria
How is the trial designed

Treatment Study

Phase 2
Interventional
Study Start: July 2002
See protocol details

Summary

Principal SponsorNational Center for Complementary and Integrative Health (NCCIH)
Last updated: January 27, 2026
Sourced from a government-validated database.Claim as a partner

Study start date: July 1, 2002

Actual date on which the first participant was enrolled.

Obesity is the single most significant, nutrition-related health issue of the new millennium. Several "medical experts" have designed and promoted weight loss diets that dramatically differ from one another and from the USDA Dietary Guidelines. These diets have gained surprisingly widespread and persistent popularity among Americans despite the lack of evidence supporting their claims. This clinical trial will provide preliminary feasibility data for a full-scale study that will examine health outcomes (e.g., benefits, risks, success) of three popular weight loss diets. The study will investigate behavioral and physiological factors that influence adherence and retention to these diet plans. Overweight women will be randomly assigned to one of four diets for 1 year: Atkins (extremely low carbohydrate), Zone (low carbohydrate, high protein), Ornish (very low fat), or USDA/Food Pyramid (high carbohydrate/moderate-low fat). Behavioral and physiological data will be collected. Participants attend study visits at baseline, 8 weeks, 6 months, and 1 year. At these visits, measurements will include that will include weight and blood pressure measurements and blood tests. Participants will be asked to complete ten questionnaires over the course of the study to assess behavior and appetite. Participants will also undergo a DEXA scan to assess body composition.

Official TitleBenefits & Risks of Popular Weight Loss Diets
Principal SponsorNational Center for Complementary and Integrative Health (NCCIH)
Last updated: January 27, 2026
Sourced from a government-validated database.Claim as a partner

Protocol

This section provides details of the study plan, including how the study is designed and what the study is measuring.
Design Details

300 patients to be enrolled

Total number of participants that the clinical trial aims to recruit.

Treatment Study

These studies test new ways to treat a disease, condition, or health issue. The goal is to see if a new drug, therapy, or approach works better or has fewer side effects than existing options.


Eligibility

Researchers look for people who fit a certain description, called eligibility criteria: person's general health condition or prior treatments.
Conditions
Criteria

Female

Biological sex of participants that are eligible to enroll.

From 30 to 50 Years

Range of ages for which participants are eligible to join.

Healthy volunteers allowed

If individuals who are healthy and do not have the condition being studied can participate.

Conditions

Pathology

Body WeightBody Weight ChangesNutrition DisordersNutritional and Metabolic DiseasesObesitySigns and SymptomsPathological Conditions, Signs and SymptomsWeight LossOvernutritionOverweight

Criteria

5 inclusion criteria required to participate
Body mass index (BMI) between 27 and 40 kg/m2

Weight stable for last 2 months

Not actively on a weight loss plan

No plans to move from the area over the next 2 years

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9 exclusion criteria prevent from participating
Pregnant or breastfeeding

Within 6 months of giving birth or planning to become pregnant in the next 2 years

Diabetes (type 1 or 2) or history of gestational diabetes

Renal or liver disease, active neoplasms, or recent myocardial infarction

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Study Plan

Find out more about all the medication administered in this study, their detailed description and what they involve.
Study Objectives

Study Objectives

Primary Objectives

Secondary Objectives

Study Centers

These are the hospitals, clinics, or research facilities where the trial is being conducted. You can find the location closest to you and its status.

This study has 1 location

Suspended

Stanford Prevention Research Center

Stanford, United StatesOpen Stanford Prevention Research Center in Google Maps
CompletedOne Study Center