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Background

The CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) clinical trial was the first study to focus on the effects of sustained caloric restriction (CR) in humans. CALERIE demonstrated the feasibility of sustained human CR (for at least two years) and the favorable effects on predictors of longevity and cardiometabolic risk factors. No previous clinical study of non-obese individuals attained the degree of CR nor the resulting sustained weight loss that was achieved in CALERIE.

Other noteworthy features of the study are the substantial size of the trial, the comprehensive physiologic, psychologic, Quality of Life (QOL) and cognitive assessments conducted, as well as the extensive collection of biological samples, which include serum, plasma, urine, and biopsies from skeletal muscle (vastus lateralis) and adipose tissue (subcutaneous abdominal). The publicly available CALERIE data sets and biospecimens are a unique and invaluable research resource for the investigation of innumerable hypotheses about the biological mechanisms underlying the effects of CR on human aging biology and for translational research to develop strategies for promoting health span.

Specific Aims

CALERIE 2 tested effects of a two-year randomized clinical trial (25% CR vs. Ad Libitum (AL). The longer intervention period allowed the study to distinguish long-term CR effects after weight has stabilized from the acute effects of weight loss.

CALERIE Phase 2’s specific primary aim was to test the hypothesis that CR in humans causes sustained metabolic adaptation as defined by: 

  • Reduction in core body temperature
  • Reduced resting metabolic rate (RMR) corrected for changes in body composition

CALERIE Phase 2 secondary aims were to test the hypotheses that CR in humans: 

  • Reduces serum triiodothyronine (T3)
  • Reduces inflammation as reflected by plasma concentrations of tumor necrosis factor-α a (TNF-α)

In addition, the study pursued numerous exploratory aims.

Study Design

CALERIE Phase 2 was a two-year, multi-site randomized controlled trial completed in May 2013, investigating the effects of a 25% calorie restriction (CR) in healthy, non-obese adults aged 20–50 (men) and 20–47 (women) with BMI between 22–27.9. Participants were screened for physical and psychological health, with exclusions for major diseases, recent weight loss, or psychiatric issues. A total of 220 volunteers from Tufts University, Pennington Biomedical Research Center, and Washington University School of Medicine were randomized starting in 2007, overseen by the Duke Clinical Research Institute. 

The trial compared outcomes between a group assigned to 25% caloric restriction and a control group on an unrestricted diet. The intervention featured intensive behavioral and dietary support by psychologists and nutritionists, with adherence monitored via a centralized database. Notably, the study objectively measured energy intake using the intake balance method, combining dual energy X-ray absorptiometry for energy stores and doubly-labeled water for total energy expenditure, with measurements taken at baseline and follow-up intervals. 

Summary of Findings

In CALERIE Phase 2, participants achieved 12% caloric restriction and maintained a 10% weight loss over two years. The intervention had no significant effect on core temperature and only reduced resting metabolic rate in the first year. However, it significantly lowered T3 and TNF-ɑ levels, along with various cardiometabolic risk factors.  

CALERIE Contacts

If you are a researcher interested in collaborating on caloric restriction studies or require assistance with statistical analysis of CALERIE data, please reach out via email at calerie@duke.edu. We welcome scientific engagement and collaborative inquiries regarding the CALERIE project and its data resources. Please note: We do not provide specific dietary or clinical advice about CR or other diet interventions. 

Protocols & Procedures

Essential information used in conducting the CALERIE Study found here. These documents, including those detailing the aims of the study, screening of participants, and follow-up procedures will assist Network Investigators in understanding the details of the interventions and conditions under which study assessments, data, and samples were collected.

Calerie Centers

CALERIE Centers include:

 

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