Randomized Controlled Experiment of Dieting in Pairs

This study examined how dieting with a partner affects weight loss, diet adherence, psychological well-being, and cortisol.

Study Overview

• Status: Completed
• Conditions: Dietary Modification
• Intervention / Treatment: Behavioral: Mixed Diet Condition; Behavioral: Both Diet Condition

Detailed Description

The goal of this study was to understand how different types of diet "buddy systems" affect diet success and outcomes related to dieting. Pairs of non-romantic cohabiting female dyads (i.e. roommates) were randomly assigned to one of the following three-week manipulations: (a) neither roommate dieted, (b) one roommate was assigned to a 1200-calorie/day diet and the other ate normally, (c) both roommates were assigned to a 1200-calorie/day diet. Both pre- and post diet, participants were weighted and measured, filled out psychological questionnaires, and provided two days of diurnal salivary cortisol samples. During the three-week manipulation period, participants who were assigned to diet recorded all calories consumed on each day. This study tested whether dieting in a pair would lead to improved diet outcomes in terms of adherence and weight loss, changes in psychological well-being, and changes in cortisol.

• Study Type: Interventional
• Enrollment (Actual): 164
• Phase: Not Applicable

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (ADULT, OLDER_ADULT)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: Female

Description

Inclusion Criteria:

• Female
• Over 18 years of age
• Interested in dieting in the coming 12 months
• self-reported BMI over 18.5
• < 5 kg weight change in previous 3 months
• Have a university meal plan
• Have a roommate also willing/eligible to participate

Exclusion Criteria:

• Recent/current history of major medical disorder
• Pregnancy/lactation
• History of eating disorder
• Use of lipid-lowering medications
• Use of weight-altering/metabolism-altering medications
• Smoking

Study Plan

How is the study designed?

Design Details

• Primary Purpose: BASIC_SCIENCE
• Allocation: RANDOMIZED
• Interventional Model: PARALLEL
• Masking: NONE

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: Control Condition; Neither roommate dieted.
Experimental: Mixed Diet Condition; Low-calorie diet: One roommate in each pair was randomly assigned to a 1200-calorie/day diet, while the other roommate was instructed to eat normally.	Behavioral: Mixed Diet Condition; One roommate dieted and the other ate normally.
Experimental: Both Diet Condition; Low-calorie diet: Both roommates in each pair were randomly assigned to a 1200-calorie/day diet.	Behavioral: Both Diet Condition; Both roommates dieted.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Psychological well-being measured via electronic questionnaires	~3 days after end of 3-week manipulation
Weight loss measured via pounds	~3 days after end of 3-week manipulation
Diet adherence measured via daily calorie counts	up to 3-week

Secondary Outcome Measures

Outcome Measure	Time Frame
Cortisol measured via 2 days diurnal cortisol	1 day after end of 3-week manipulation

Collaborators and Investigators

• Sponsor: A. Janet Tomiyama
• Investigators: Principal Investigator: A. Janet Tomiyama, PhD, University of California, Los Angeles

Publications and helpful links

General Publications

• Cohen S, Kamarck T, Mermelstein R. A global measure of perceived stress. J Health Soc Behav. 1983 Dec;24(4):385-96. No abstract available.
• Fairburn CG, Beglin SJ. Assessment of eating disorders: interview or self-report questionnaire? Int J Eat Disord. 1994 Dec;16(4):363-70.
• Spielberger CD, Gorsuch RL, Lushene RE. State-trait anxiety inventory (self-evaluation questionnaire). Consulting Psychologists Press: 1970.
• Radloff, L. S. The CES-D scale a self-report depression scale for research in the general population. Applied psychological measurement, 1(3): 385-401, 1977.

Study record dates

Study Major Dates

• Study Start: October 1, 2013
• Primary Completion (Actual): December 1, 2014
• Study Completion (Actual): December 1, 2014

Study Registration Dates

• First Submitted: September 8, 2016
• First Submitted That Met QC Criteria: September 12, 2016
• First Posted (Estimate): September 13, 2016

Study Record Updates

• Last Update Posted (Estimate): September 13, 2016
• Last Update Submitted That Met QC Criteria: September 12, 2016
• Last Verified: September 1, 2016

More Information

Terms related to this study

• Keywords: weight loss; cortisol; psychological well-being; dieting; dyads
• Other Study ID Numbers: 13-000666

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED