CALERIE

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CALERIE stands for Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy. It is a U.S. study that tests what happens when healthy adults restrict calories for a long time. The research teams are at Pennington Biomedical Research Center in Baton Rouge, Tufts University in Boston, and Washington University School of Medicine in St. Louis. Researchers hope that eating fewer calories could lower the risk of heart disease and cancer and possibly extend life, as animal studies have suggested.

CALERIE is the first large study to look at long-term calorie restriction in healthy people. Participants are non-obese, since calorie restriction in obesity is known to affect health for different reasons. A smaller pilot study finished in 2006: 48 people were split into two groups, and the treatment group reduced calories by 25% for six months. They showed better insulin sensitivity, lower LDL cholesterol, lower body temperature, lower insulin levels, and less DNA damage from oxidative stress.

The main CALERIE trial began in 2007. It requires a 25% calorie restriction over two years with regular health checkups. Participants at the different sites receive payments (about $5,000 at Tufts and Pennington and about $2,400 at Washington University). By October 2009, 132 people had joined, and recruitment continued. Volunteers must be highly motivated and keep a detailed food diary. Before the trial, researchers determine each person’s baseline calories with a two-week lab test that measures carbon dioxide to estimate energy use. Then participants follow a diet of low-energy-density foods like vegetables, fruits (especially apples), insoluble fiber, and soups. Many feel hungry at first but adjust, while some complain about the strict tracking.

Results were posted on the Clinical Trials site in 2018 and a Lancet article appeared in 2019 (paywalled). An MSN article summarized an interview with Dr. Kraus. While calorie restriction has been shown to lengthen lifespan in some animals, results in long-lived primates are mixed. A 2012 study in rhesus monkeys found health benefits but no clear survival advantage, suggesting that the life-extending effect of calorie restriction may depend on study design, care, and diet.