Fasting and longevity

Of all the claims made about fasting, living longer is the most exciting, and the hardest to prove. Nobody can run a trial that follows thousands of people on a fasting plan for 50 years. So scientists piece the answer together from animal studies, long human trials of eating less, and newer tests that try to measure how fast the body is aging. Each tells part of the story.

What animals tell us

In most species studied, eating less without malnutrition extends lifespan and delays age-related disease ². A widely read review in the New England Journal of Medicine brought together the evidence on fasting, aging and disease, from these animal studies to the first trials in people ¹.

The longest human trial: CALERIE

CALERIE is important because these were young and middle-aged people who were already healthy, and the benefits still appeared ³. Researchers later analysed their blood using DNA-based measures of aging. Eating less slowed the pace of aging on one of these measures, called DunedinPACE, but didn't change estimates of biological age from other well-known clocks, and the effects were small ⁴. It's an intriguing signal, not a fountain of youth.

Fasting-mimicking diets

Some researchers have tested a "fasting-mimicking diet": five days a month of a plan low in calories, sugar and protein but rich in unsaturated fats, then normal eating. In a trial of 100 adults, three monthly cycles reduced weight, body fat, blood pressure and IGF-1, a growth hormone linked to aging in animals ⁵. A later analysis of blood samples estimated that three cycles lowered median biological age by about 2.5 years ⁶.

Healthy aging needs muscle

As we get older, losing muscle and strength becomes one of the biggest threats to a long, independent life. Reviews of fasting trials show that weight loss from intermittent fasting includes some loss of lean mass ⁷. And a large observational study of US adults over 60 found that those with daily fasts longer than about 12.4 hours had a higher risk of death from heart disease; that study can't prove cause, but it's a reason for older adults to be careful with long fasts ⁸. European experts recommend at least 1.0 to 1.2 g of protein per kilo a day for people over 65 ⁹.

Sources

1. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019;381(26):2541-2551. doi.org/10.1056/NEJMra1905136
2. Mattison JA, Colman RJ, Beasley TM, et al. Caloric restriction improves health and survival of rhesus monkeys. Nat Commun. 2017;8:14063. doi.org/10.1038/ncomms14063
3. Kraus WE, Bhapkar M, Huffman KM, et al. 2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial. Lancet Diabetes Endocrinol. 2019;7(9):673-683. doi.org/10.1016/S2213-8587(19)30151-2
4. Waziry R, Ryan CP, Corcoran DL, et al. Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nat Aging. 2023;3(3):248-257. doi.org/10.1038/s43587-022-00357-y
5. Wei M, Brandhorst S, Shelehchi M, et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Sci Transl Med. 2017;9(377):eaai8700. doi.org/10.1126/scitranslmed.aai8700
6. Brandhorst S, Levine ME, Wei M, et al. Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk. Nat Commun. 2024;15(1):1309. doi.org/10.1038/s41467-024-45260-9
7. Patikorn C, Roubal K, Veettil SK, et al. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open. 2021;4(12):e2139558. doi.org/10.1001/jamanetworkopen.2021.39558
8. Zhang Z, Zhao H, Tao Z, et al. A National Study Exploring the Association between Fasting Duration and Mortality among the Elderly. Nutrients. 2024;16(13):2018. doi.org/10.3390/nu16132018
9. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542-59. doi.org/10.1016/j.jamda.2013.05.021