Caloric restriction is the oldest and most robustly validated longevity intervention in non-human animals. CALERIE is the closest thing to a definitive human RCT — and what it found is more nuanced than "eat less, live longer."
CALERIE 2 (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) randomized 218 healthy, non-obese adults to two years of 25% caloric restriction versus ad libitum eating. Participants in the restriction arm achieved an average of roughly 12% restriction — well short of the 25% target, a real-world adherence pattern that is itself informative.
This is the largest and longest RCT of sustained caloric restriction ever conducted in healthy humans, and remains the primary human evidence base underlying caloric restriction's status as a geroscience reference intervention — the standard against which pharmacological "caloric restriction mimetics" like rapamycin and metformin are often conceptually compared.
Even at roughly half the target restriction level, the intervention group showed significant improvements in multiple cardiometabolic risk markers — LDL cholesterol, blood pressure, insulin sensitivity, and CRP (a key inflammatory marker) — sustained over the full two years. A widely cited secondary analysis also found a slowing of a validated biological-age measure (the DunedinPACE epigenetic clock, applied retrospectively to trial biosamples) in the restriction group relative to controls.
CALERIE was not statistically powered for and did not measure hard outcomes like mortality or major cardiovascular events — two years is far too short a follow-up for those endpoints in a healthy, non-obese population with low baseline event rates. What it demonstrated is sustained, real biomarker and epigenetic change from modest, real-world-achievable caloric restriction.
Perhaps the most practically important finding of CALERIE is not biological at all: healthy, motivated, closely supported trial participants — with dietitian counseling and structured support — still only sustained about half the targeted restriction over two years. This is a meaningful data point for anyone extrapolating from animal caloric-restriction studies (which typically achieve and maintain the full targeted restriction under controlled housing) to real-world human feasibility.
CALERIE provides genuine, sustained human evidence that moderate caloric restriction improves cardiometabolic biomarkers and may slow a validated epigenetic aging measure — real surrogate-endpoint evidence, not a hard mortality outcome. It also demonstrates, empirically, that sustained restriction is difficult to maintain even under ideal support conditions, which is directly relevant to how much weight to place on caloric-restriction-mimetic drug candidates as a more feasible alternative.
This information is provided for educational reference only and does not constitute medical advice or a treatment recommendation.