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Study Design

CALERIE Phase 2, completed in May 2013, was a two-year three-site randomized controlled trial in young and middle-aged non-obese healthy men and women. It compared outcomes in a group assigned a target of 25% CR (i.e., a 25% reduction in energy intake below baseline levels) with outcomes in an ad libitum diet control group. 

CALERIE Phase 2 potential participants were screened during a series of physical and psychological tests and interviews to identify healthy individuals who agreed to make the necessary commitments to participate in a two-year intensive CR-oriented lifestyle modification program.  CALERIE participant requirements included:

  • Absence of significant health problems, including diabetes, cancer, heart and liver disease, and AIDS 
  • Absence of medication use except oral contraceptives 
  • Age from 20 to 50 (inclusive) for men and ages 20-47 (inclusive) for women
  • Body mass index (BMI) of 22-27.9 (lean to slightly overweight) 
  • No recent substantial weight loss
  • No history of eating disorders, behavioral, or psychiatric problems 
  • Use by women of an acceptable form of contraception throughout the study

220 healthy volunteers across three sites (Tufts University, Pennington Biomedical Research Center, and Washington University School of Medicine) were randomized beginning in 2007. The study Coordinating Center was at the Duke Clinical Research Institute. 

The CALERIE intervention employed an intensive behavioral approach coupled with dietary modifications anticipated to enhance adherence to CR. Intervention staff included psychologists and nutritionists who provided individual and group counseling and utilized a centralized interactive database to monitor interventionists’ practices and participant adherence over the course of the study.  The design and methodology of the study are elucidated here.

A unique feature of the CALERIE trial was the objective measurement of caloric intake. To accomplish this, CALERIE used the intake balance method to calculate energy intake from the difference between changes in energy stores (assessed by dual energy X-ray absorptiometry) and total energy expenditure (TEE) assessed by the doubly-labeled water method. The CALERIE data set includes these measures made at baseline and at intervals after the start of the study.