Can a Fasting-Mimicking Diet Boost Health, Turn Back the Clock on Ageing and Disease?
- Alastair Hunt
- Aug 5
- 8 min read
Updated: Sep 3
In recent years, the idea that we might be able to slow - or even reverse - aspects of biological ageing has captured the imagination of scientists and the public alike. Among the various strategies proposed, fasting has shown remarkable promise in preclinical studies. But prolonged fasting is notoriously difficult to maintain and, for many, not safe without medical oversight. This has led researchers - especially Prof Valter Longo - to explore whether a “fasting-mimicking diet” (FMD) could offer similar benefits in a safer, more practical form.
Two clinical trials (2017 and 2024), led by researchers at the University of Southern California, have investigated whether short, monthly cycles of an FMD could favourably alter metabolic health, reduce risk factors for age-related diseases, and even turn back biological ageing. Their findings suggest that for many people, this form of dietary intervention could offer a powerful tool to promote health and potentially longevity - without the need for constant dietary restriction.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to all studies at bottom of page.
The FMD used in both studies was plant-based and low in calories, protein, and sugars, but high in healthy fats and micronutrients. For five consecutive days each month, participants consumed this pre-packaged, calorie-controlled diet, returning to their normal eating habits for the remaining days. Unlike typical diets that demand daily restriction, the FMD is periodic, aiming to trigger metabolic pathways associated with fasting without full abstinence from food.
The first trial (Wei et al, 2017) involved 100 generally healthy adults aged between 18 and 70. Some participants followed the FMD for three months, while others maintained their regular diets. After the initial period, the control group crossed over to the FMD. Researchers found that those following the FMD experienced reductions in body weight, abdominal fat, blood pressure and the growth hormone IGF-1. These changes were especially pronounced in participants who began the study with elevated metabolic risk factors, such as high BMI, blood sugar or cholesterol.
The second trial, (Brandhorst et al, 2024) built on this work by examining changes in biological age - a more holistic measure of ageing than chronological years. Using a composite of blood markers linked to disease risk and mortality, researchers found that just three cycles of the FMD led to a median reduction in biological age of 2.5 years. Participants who had biological ages higher than their chronological ones showed the greatest improvements, suggesting that the FMD could help realign physiological health with actual age.
Notably, these changes in biological age were not simply the result of weight loss. Even after adjusting for reductions in body mass, participants still experienced significant improvements in markers such as inflammation (measured by C-reactive protein), blood pressure, and blood glucose regulation. This suggests a deeper, system-wide rejuvenation - one that goes beyond shedding a few kilos.
What’s happening inside the body during these fasting-mimicking phases offers some clues. When the body is deprived of calories and certain nutrients - especially protein - it initiates a process known as autophagy, in which damaged cells and components are broken down and recycled. At the same time, levels of growth-promoting hormones like IGF-1 fall, which may reduce the risk of cancer and other age-related diseases. Once normal eating resumes, the body enters a regenerative phase, ramping up stem cell activity and cellular repair. This cycle of cleansing and renewal mimics the biological rhythms of more extreme fasting but in a gentler and safer way.
The FMD also appears to benefit organs that are otherwise difficult to target through lifestyle change alone. In a subgroup of participants who underwent MRI scans, the researchers observed a striking reduction - nearly 50% - in liver fat among those with fatty liver disease. Given the links between liver fat and insulin resistance, this has significant implications for preventing and possibly reversing type 2 diabetes.
Immune function, too, appeared to benefit. Among participants over the age of 40, the FMD increased the ratio of lymphoid to myeloid cells - a marker associated with a younger immune system. This reversal of what’s known as “immunosenescence” may help explain why fasting in animal studies is linked not only to longevity but also to enhanced resistance against infections and cancers.
Interestingly, not everyone responded the same way. Participants with higher baseline risk - such as those with elevated blood sugar, cholesterol, or inflammation - intended to see the greatest improvements. For example, individuals with prediabetes saw fasting glucose return to normal levels. Similarly, those with high CRP saw significant reductions in inflammation. Those with already healthy markers experienced smaller, but still favourable, shifts. This pattern suggests that the FMD may be most impactful as a preventive tool for people on the edge of chronic disease, though it could still benefit the broader population.
To understand the long-term potential of the FMD, researchers ran simulations based on national health data. They modelled what might happen if people undertook three FMD cycles per year over several decades. The projections were striking: a slowing of biological ageing, increases in median life expectancy by up to five years, and significant reductions in the estimated 20 year risk of dying from heart disease, stroke, diabetes or cancer. While these forecasts are not direct evidence and depend on assumptions about long-term adherence, they offer an exciting glimpse at what might be possible with continued use.
So how does the FMD compare with other popular dietary approaches? Intermittent fasting (IF) and time-restricted eating (TRE) are often touted for their health benefits, but these usually involve shorter fasts and may not reach the same depth of metabolic change. Water-only fasting can be effective but it's not practical or safe for many, particularly older adults or those with chronic conditions. Long-term calorie restriction has shown benefits in animal studies but can also lead to muscle loss and other side effects in humans.
The FMD aims to strike a balance: it offers a short-term, intense intervention that can be repeated periodically, with fewer side effects and better sustainability.
For those curious about trying the FMD, it’s worth understanding what the experience entails. Participants in the trials typically consumed about 1,100 calories on the first day, dropping to around 750 calories for the remaining four days. Meals consisted of soups, energy bars, herbal teas and supplements rich in vitamins, minerals and essential fats. Although the plan is commercially available (e.g. ProLon), some people may be tempted to create their own version. However, the nutrient balance in the FMD is specifically designed to trigger fasting-like processes while maintaining safety, so medical or nutritional guidance is advised before attempting it independently.
Read more about the FMD in Longo's 2018 book: The Longevity Diet
In terms of daily life, many participants reported mild fatigue, hunger or headaches - especially on the first two days - but found the regimen manageable overall. Around a quarter of participants dropped out during the FMD phase, a figure that aligns with other dietary trials and likely reflects the challenge of sustaining even short-term restriction. Encouragingly, many of the positive changes - such as lower glucose or inflammation - persisted for several months after the FMD cycles ended, even though participants were not instructed to change their normal diets or activity levels.
Of course, this approach isn’t for everyone. People over 70, those who are underweight, or those with specific health conditions may not be suitable candidates. The FMD should also be avoided by individuals with a history of eating disorders, unless under professional care. For most adults in reasonably good health, however, it represents a well-tolerated option that can be used two to four times a year to help maintain or improve long-term health.
Final Thoughts
It is important to view the FMD as one piece of a larger puzzle. Healthy ageing is influenced by many factors - regular exercise, social connection, adequate sleep and a largely whole-food, plant-forward diet. No single dietary intervention will offset poor lifestyle habits, and the FMD isn’t a free pass to neglect other aspects of health. But as part of a broader strategy, it shows great promise. By temporarily shifting the body into a fasting-like state, activating protective mechanisms and then supporting regeneration during refeeding, the FMD offers a novel way to periodically “reset” the body - potentially slowing the processes that underlie ageing itself.
While more long-term studies are needed to determine how the FMD performs over decades or in those with diagnosed diseases, the existing evidence is strong enough to warrant consideration. For individuals with prediabetes, early-stage metabolic syndrome or concerns about ageing, this structured, science-backed approach may be worth exploring - with guidance from a health professional.
Ultimately, the fasting-mimicking diet does not promise immortality. But it may help more of us reach older age with less disease, greater vitality, and a better quality of life - goals that most of us can agree are worth striving for.
Supporting your body through balanced nutrition, physical activity, stress reduction, quality sleep and meaningful social connection (these are known as the Pillars of Health) are some of the most powerful health 'tools' we have. Changing health for the better is about consistent progress, not perfection, and even small changes can make a meaningful difference over time.
As always, the best health strategy is one you can stick with - one that fits your personal lifestyle profile. Improving health is about finding motivation, prioritising self-care and taking action. If you want to take effective and targeted steps to that fit into your unique lifestyle, The Whole Health Practice is here to help. Whether you want to improve eating practices, beat chronic illness or enhance your overall well-being, our consultations and programs deliver results that are tailored to your needs.
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Stay Healthy,
Alastair
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Related Resources and Studies
Brandhorst S, Levine ME, Wei M, Shelehchi M, Morgan TE, Nayak KS, Dorff T, Hong K, Crimmins EM, Cohen P, Longo VD. Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk. Nat Commun. 2024 Feb 20;15(1):1309. doi: 10.1038/s41467-024-45260-9. PMID: 38378685; PMCID: PMC10879164.
Wei M, Brandhorst S, Shelehchi M, Mirzaei H, Cheng CW, Budniak J, Groshen S, Mack WJ, Guen E, Di Biase S, Cohen P, Morgan TE, Dorff T, Hong K, Michalsen A, Laviano A, Longo VD. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Sci Transl Med. 2017 Feb 15;9(377):eaai8700. doi: 10.1126/scitranslmed.aai8700. PMID: 28202779; PMCID: PMC6816332.
Brandhorst S, Choi IY, Wei M, Cheng CW, Sedrakyan S, Navarrete G, Dubeau L, Yap LP, Park R, Vinciguerra M, Di Biase S, Mirzaei H, Mirisola MG, Childress P, Ji L, Groshen S, Penna F, Odetti P, Perin L, Conti PS, Ikeno Y, Kennedy BK, Cohen P, Morgan TE, Dorff TB, Longo VD. A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan. Cell Metab. 2015 Jul 7;22(1):86-99. doi: 10.1016/j.cmet.2015.05.012. Epub 2015 Jun 18. PMID: 26094889; PMCID: PMC4509734.
Prolon - officially licensed fasting mimicking diet products / nutrition (note: we are not affiliated in any way)
Other
Popa AD, Gherasim A, Mihalache L, Arhire LI, Graur M, Niță O. Fasting Mimicking Diet for Metabolic Syndrome: A Narrative Review of Human Studies. Metabolites. 2025 Feb 23;15(3):150. doi: 10.3390/metabo15030150. PMID: 40137116; PMCID: PMC11943686.
Mishra A, Mirzaei H, Guidi N, Vinciguerra M, Mouton A, Linardic M, Rappa F, Barone R, Navarrete G, Wei M, Brandhorst S, Di Biase S, Morgan TE, Ram Kumar S, Conti PS, Pellegrini M, Bernier M, de Cabo R, Longo VD. Fasting-mimicking diet prevents high-fat diet effect on cardiometabolic risk and lifespan. Nat Metab. 2021 Oct;3(10):1342-1356. doi: 10.1038/s42255-021-00469-6. Epub 2021 Oct 14. PMID: 34650272.
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