Intermittent Fasting, Time-Restricted Eating and Aging
What human trials and reviews show about intermittent fasting, time-restricted eating and the fasting-mimicking diet, and why lifespan benefits in people remain unproven.
Content last updated . This page has not been medically reviewed.
What these patterns are
"Intermittent fasting" covers several eating patterns: time-restricted eating (all food within a set window, such as 8 hours), alternate-day fasting, the 5:2 pattern (two low-calorie days a week) and periodic multi-day fasting. [1] A fasting-mimicking diet is a low-calorie, low-protein plan followed for 5 days at a time in research. [2] This page describes research only. It gives no schedules or calorie targets and is not advice to fast.The lifespan question
An NIA review of the research said hundreds of animal studies and scores of human trials show health improvements, but animal lifespan results are mixed, and human trials have been short, so they give no evidence about long-term effects including lifespan. [3] In animals, sex, food composition, age and genetics influenced results. [3] Label: preclinical for lifespan, insufficient evidence in people. See aging in mice, worms and humans.What human trials show
| Question | Finding | Label |
|---|---|---|
| Does 16:8 time-restricted eating beat eating across the day for weight? | In a 12-week trial of 116 adults with overweight or obesity, no: weight change did not differ between groups. In a 50-person in-person subgroup, appendicular lean mass index differed between groups (-0.16 kg/m2), a signal worth watching. [4] | Mixed |
| Over a year, time-restricted eating plus calorie limits versus calorie limits alone? | 139 adults with obesity; weight loss was -8.0 vs -6.3 kg, not significantly different (p = 0.11); adverse events were similar. [5] | No added benefit shown |
| Alternate-day fasting versus daily calorie restriction | In 100 adults over a year, similar weight loss; no better adherence or cardioprotection; more dropouts with fasting (38% vs 29%); LDL cholesterol was higher at 12 months. [6] | No added benefit shown |
| All trials pooled for adults with overweight or obesity | A 2026 Cochrane review of 22 trials (1,995 people) found little to no difference in weight loss versus regular dietary advice, and very uncertain evidence on adverse events. [7] | Mixed |
| Broad umbrella review | Of 103 significant associations across 23 meta-analyses, only 10 were supported by high-certainty evidence. [8] | Promising but limited |
| Fasting-mimicking diet (5 days a month for 3 months) | In 100 healthy adults, lower weight, body fat, blood pressure and IGF-1 and no serious adverse effects were reported; the study measured risk markers, not disease. [2] | Promising but limited |
The umbrella review found small gains in waist size, fat mass and cholesterol in people with overweight or obesity, but fasting lowered systolic blood pressure less than continuous calorie restriction. [8] Most evidence concerns weight loss in adults with overweight, not aging.
Older adults
A 2026 systematic review of intermittent fasting in people aged 60 and over said the evidence in older adults remains limited. [9] NIA's review authors said more research was needed on safety in people at a healthy weight or who are younger or older, because most studies enrolled middle-aged adults with overweight. [3] Muscle and bone loss are particular questions at older ages; see strength training, muscle and aging and bone health and aging.Judging claims
"Autophagy," "metabolic switching" and "cellular cleanup" describe mechanisms proposed from lab work. NIA's review authors argue that ketone signaling, not weight loss alone, may drive benefits, but that is a hypothesis; human lifespan effects are untested. [3] Learn what autophagy is and what is known in humans.Related guides
Frequently asked questions
Does intermittent fasting help you live longer?
Unknown. NIA's review said human trials have not provided evidence of lifespan effects. [3]
Is time-restricted eating better than eating fewer calories?
In two randomized trials, it did not beat eating throughout the day or daily calorie limits for weight. [4][5]
Is it safe for older adults?
Evidence is limited. A 2026 review in people 60 and older found limited evidence overall, so talk with a clinician first. [9]
Who should avoid fasting?
NIH says it is not safe for everyone, particularly people with diabetes, kidney disease or heart problems. [10]
What about the fasting-mimicking diet?
One 100-person trial reported improved risk markers and no serious adverse effects over three cycles; disease outcomes were not measured. [2]
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: promising but limited, mixed, insufficient evidence, preclinical (cells/animals only). A change in weight, cholesterol or IGF-1 is a biomarker, not a longer life.
Who should check first
NIH's MedlinePlus magazine says fasting is not safe for everyone, especially people with diabetes, kidney disease or heart problems, and that it should be approached with a dietitian or physician. [10] The sources read for this page do not cover pregnancy, breastfeeding, eating-disorder history or specific medicines; if any of these apply, or you take glucose-lowering or blood-pressure medicines, discuss it with your prescriber before changing when you eat. See eating disorders and disordered eating and talking with a health professional.
References
- National Institute on Aging. Calorie restriction and fasting diets: What do we know? Research highlight dated August 14, 2018. Read 2026-10-22.
- Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Sci Transl Med 2017. Read 2026-10-22 (abstract on PubMed).
- National Institute on Aging. Research on intermittent fasting shows health benefits (summary of de Cabo and Mattson, N Engl J Med 2019), February 27, 2020. Read 2026-10-22.
- Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med 2020. Read 2026-10-22 (abstract on PubMed).
- Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med 2022. Read 2026-10-22 (abstract on PubMed).
- Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: a randomized clinical trial. JAMA Intern Med 2017. Read 2026-10-22 (abstract on PubMed).
- Intermittent fasting for adults with overweight or obesity. Cochrane Database Syst Rev 2026. Read 2026-10-22 (abstract on PubMed).
- Intermittent fasting and health outcomes: an umbrella review of systematic reviews and meta-analyses of randomised controlled trials. EClinicalMedicine 2024. Read 2026-10-22 (abstract on PubMed).
- Intermittent fasting and healthy aging in older adults: a systematic review of cardiometabolic, mental health and cognitive outcomes with a network meta-analysis of anthropometric measures. Nutrients 2026. Read 2026-10-22 (abstract on PubMed).
- NIH MedlinePlus Magazine. 5 questions about intermittent fasting April 7, 2020. Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.