Calorie Restriction and Aging Research
What animal studies, the two monkey trials and the CALERIE human trial show about calorie restriction and aging, including what is unknown about lifespan and the safety limits.
Content last updated . This page has not been medically reviewed.
What it is and why researchers study it
Calorie restriction means eating fewer calories than usual while still getting the nutrients the body needs. The National Institute on Aging (NIA) separates it from ordinary dieting: it is studied as a way to learn about aging, not as a weight-loss plan. [1] This page describes research only. It is not advice to eat less, and it gives no calorie targets.Animals: the origin of the idea
In many experiments in worms, flies and rodents, eating 10 to 40 percent fewer calories delayed age-related disorders and sometimes extended lifespan. But some studies did not show the benefit, and in some mouse strains calorie restriction shortened lifespan. [1] Label: preclinical. See why mouse results do not prove an effect in people.Monkeys: two long studies, two answers
Two long rhesus monkey studies used about 30% fewer calories. The Wisconsin study reported a survival benefit; the NIA study found no significant survival effect. [2] The NIA team reported that its regimen "has not improved survival outcomes," and suggested that study design, husbandry and diet composition may strongly affect results. [3] A later Wisconsin report said the restricted monkeys had better age-related and all-cause survival. [4] Both studies found fewer age-related conditions such as cancer, heart disease and diabetes in restricted monkeys. [1] Label: mixed. Monkeys are not people.Humans: the CALERIE trial
CALERIE is the main randomized trial in people. Adults aged 21 to 50 with normal weight or mild overweight (218 started) were assigned 2 to 1 to a 25% calorie-restriction goal or their usual eating for 2 years. [5] They did not reach 25%: intake fell by a mean of 11.9% and weight by 7.5 kg, about 71% of it fat. [5]| Outcome | What the trial found | Type of outcome |
|---|---|---|
| Cardiometabolic risk factors | Lower LDL cholesterol, blood pressure and C-reactive protein; better insulin sensitivity [5] | Biomarker |
| Mood and quality of life | Some positive effects and no negative effects reported [6] | Self-reported |
| Pace of aging (DNA methylation) | A small slowing on one measure (DunedinPACE); no significant change on PhenoAge or GrimAge clocks; post hoc analysis [7] | Biomarker |
| Telomere length | No difference from baseline to 24 months; authors could not say whether trends reflect harm, adaptation or error [8] | Biomarker |
| Bone density | Lower at spine, hip and femoral neck [9] | Biomarker with possible clinical meaning |
Nothing in CALERIE measured lifespan, disease or death. NIA states that there are no data in humans on calorie restriction and longevity, and that the longest trial lasted 2 years. [1] Whether the small DunedinPACE change would translate into healthier aging was left open: the authors say conclusive tests need long follow-up of disease and mortality. [7] Label: promising but limited for biomarkers, insufficient evidence for lifespan.
How to judge claims
Ask: was it people or animals? How long? Was the outcome lifespan, disease or only a blood marker? Who ran the study? Claims that restriction "slows aging in humans" go beyond the evidence read here. NIA concluded there is not enough evidence to recommend any such eating regimen to the public. [1]Related guides
Frequently asked questions
Does calorie restriction make people live longer?
Not shown. NIA states that there are no human data on calorie restriction and longevity; the longest randomized trial lasted 2 years. [1]
Did the monkey studies prove it works?
No. One monkey study found better survival and the other did not, and the teams point to differences in design and diet. [2]
What did CALERIE show?
Two years of moderate restriction improved several cardiometabolic markers and slightly slowed one DNA-methylation measure, but it was not designed to test lifespan or disease. [5][7]
Is it safe?
In CALERIE it was well tolerated under monitoring, but bone density fell and anemia needed watching. It is not tested in everyone. [10]
Should I try it?
This page cannot advise that. Ask your clinician, especially if you are older, underweight, pregnant, or have a history of disordered eating.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: preclinical (cells/animals only), promising but limited, mixed, insufficient evidence. A biomarker change (such as blood pressure or a DNA-methylation score) is not the same as living longer or avoiding disease.
Risks and who should not try it
- Bone loss. The CALERIE bone analysis called bone loss at fracture-prone sites a potential limitation of prolonged restriction. [9]
- Other findings. A safety analysis found the regimen well tolerated, with three people withdrawn for safety concerns, and advised close monitoring for bone loss and anemia. [10]
- Extreme practice. People who restrict heavily on their own had very low heart and diabetes risk markers but also reduced sexual interest and reduced ability to keep warm in cold environments. [1]
- Not studied. NIA notes trials mostly enrolled adults aged 60 or younger, so results may not apply to children or people over 60. [1] The sources read do not cover frailty, low body weight, eating disorders, pregnancy or chronic illness; talk with a clinician before changing how you eat. See eating disorders and disordered eating and older adults and safety.
References
- National Institute on Aging. Calorie restriction and fasting diets: What do we know? Research highlight dated August 14, 2018. Read 2026-10-22.
- Caloric restriction improves health and survival of rhesus monkeys. Nat Commun 2017. Read 2026-10-22 (abstract on PubMed).
- Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. Nature 2012. Read 2026-10-22 (abstract on PubMed).
- Caloric restriction reduces age-related and all-cause mortality in rhesus monkeys. Nat Commun 2014. Read 2026-10-22 (abstract on PubMed).
- 2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial. Lancet Diabetes Endocrinol 2019. Read 2026-10-22 (abstract on PubMed).
- Effect of calorie restriction on mood, quality of life, sleep, and sexual function in healthy nonobese adults: the CALERIE 2 randomized clinical trial. JAMA Intern Med 2016. Read 2026-10-22 (abstract on PubMed).
- Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nat Aging 2023. Read 2026-10-22 (abstract on PubMed).
- Effect of long-term caloric restriction on telomere length in healthy adults: CALERIE 2 trial analysis. Aging Cell 2024. Read 2026-10-22 (abstract on PubMed).
- Effect of two-year caloric restriction on bone metabolism and bone mineral density in non-obese younger adults: a randomized clinical trial. J Bone Miner Res 2016. Read 2026-10-22 (abstract on PubMed).
- Safety of two-year caloric restriction in non-obese healthy individuals. Oncotarget 2016. Read 2026-10-22 (abstract on PubMed).