The Fasting-Mimicking Diet: Can Five Days a Month Improve Markers of Ageing and Chronic Disease?
- Alastair Hunt
- Feb 3
- 8 min read
Updated: 2 days ago
Interest in fasting has surged over the past decade, driven by animal research suggesting that periods of low energy intake may switch the body from growth to repair mode. Yet translating these findings into something realistic, safe, and sustainable for humans has remained a major challenge. Here we review the 2017 randomised controlled trial published in Science Translational Medicine that explored whether a carefully designed fasting-mimicking diet (FMD) could deliver measurable health benefits without the risks of prolonged water fasting.
This study, led by Valter Longo and colleagues, examined whether five consecutive days per month of a low-calorie, low-protein, plant-based diet could favourably influence markers associated with ageing, diabetes, cardiovascular disease, and cancer risk in generally healthy adults.
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. Fasting has risks, it can be dangerous. Links to this and other studies at bottom of page.
What Is a Fasting-Mimicking Diet?
Unlike complete fasting, the fasting-mimicking diet is designed to provide limited calories while still supplying essential micronutrients. In this study, participants consumed a plant-based diet for five days each month that was:
Low in calories
Low in protein and sugars
Relatively high in unsaturated fats
The aim was not simply calorie reduction but to reproduce the hormonal and metabolic effects of fasting, particularly reductions in insulin and insulin-like growth factor 1 (IGF-1), while maintaining safety and adherence.
Study Design and Participants
One hundred adults aged 20 to 70 years were enrolled and randomised into 2 groups. 1 group followed their usual diet for three months, while the other completed three monthly cycles of the fasting-mimicking diet. After this initial period, the control group crossed over and also undertook the FMD, allowing the researchers to analyse outcomes in a total of 71 individuals who completed three cycles.
Importantly, participants were generally healthy rather than selected for having diabetes or cardiovascular disease. This makes the findings particularly relevant to prevention rather than treatment.
Key Findings from the Randomised Phase
After 3 monthly cycles, the fasting-mimicking diet led to several statistically significant improvements compared with a normal diet.
Participants on the FMD lost an average of around 2.6 kg, driven mainly by reductions in total body fat and abdominal (trunk) fat. Waist circumference fell by just over 4cm, while lean mass was relatively preserved when expressed as a percentage of body weight.
Blood pressure also improved. Systolic blood pressure fell by about 4 to 5 mmHg, while diastolic pressure dropped by around 3 mmHg. At a population level, reductions of this size are associated with meaningful decreases in cardiovascular risk.
One of the most striking findings was a reduction in circulating IGF-1, a hormone involved in growth and cell proliferation. IGF-1 has been linked in observational studies to ageing processes and increased risk of certain cancers. Levels fell by roughly 20 ng/ml after 3 cycles of the FMD.
Notably, participants following their usual diet did not experience these changes.
Why IGF-1 Matters
IGF-1 plays a central role in growth and metabolism, but persistently high levels in adulthood have been associated with higher risks of cancer and age-related diseases. The reduction seen with the fasting-mimicking diet is particularly interesting because long-term calorie restriction and intermittent dieting have not consistently shown similar effects.
The authors suggest that protein restriction, rather than calorie reduction alone, may be key. The FMD provided substantially less protein than most habitual diets, which may explain its unique hormonal impact.
Effects Were Strongest in At-Risk Individuals
A major strength of this study lies in its post hoc analysis examining participants based on their baseline risk profiles. Those who started the study with elevated risk factors experienced the largest benefits.
For example, participants with raised fasting glucose at baseline saw reductions of nearly 12 mg/dl - around an 11 to 12% drop - bringing many back into the healthy range. Those with elevated blood pressure experienced larger absolute reductions than participants whose blood pressure was already normal.
Similarly, individuals with high cholesterol, triglycerides, C-reactive protein (a marker of inflammation), or very high IGF-1 levels showed greater improvements than those starting within healthy ranges. In contrast, participants with normal values generally saw little change, suggesting the diet may act as a “normalising” intervention rather than pushing markers below healthy thresholds.
Safety and Tolerability
No serious adverse effects were reported. The most common side effects were mild fatigue, weakness and headaches during the 5 day diet periods. Importantly, laboratory tests showed no evidence of harm to liver or kidney function.
However, adherence was not perfect. Around 25% of participants dropped out during the fasting-mimicking phase, compared with 10% during the control period. This highlights that even a relatively short, structured intervention requires motivation and support.
Do the Benefits Last?
A voluntary follow-up conducted around three months after the final FMD cycle suggested that some benefits persisted. Reductions in body weight, waist circumference, blood pressure (particularly in those with high baseline values), glucose and IGF-1 were still evident.
That said, participants were not prevented from making other lifestyle changes after the trial ended, so some sustained effects may reflect improved dietary or activity habits inspired by the intervention.
Practical Takeaways
This study does not suggest that everyone should fast or adopt a fasting-mimicking diet. However, it does offer several practical insights:
First, short, periodic dietary interventions may produce meaningful metabolic changes without requiring constant restriction. Five days per month proved sufficient to shift several key risk markers.
Second, diet composition matters. Lower protein intake, particularly from animal sources, may influence hormones linked to ageing and chronic disease risk, independently of calorie intake.
Third, those with higher baseline risk appear to benefit most. People with excess weight, raised blood pressure, impaired glucose control or high inflammation markers saw the greatest improvements.
Finally, supervision matters. Even though the diet was generally safe, the authors stress that prolonged or multi-day fasting-style interventions should be undertaken with medical guidance, especially for older adults or those with existing conditions.
Limitations to Keep in Mind
The study was relatively small and not powered to assess disease outcomes such as heart attacks or cancer incidence. Many of the most striking findings come from post hoc analyses rather than pre-specified endpoints. Participants were also self-selected and generally health-conscious, which may limit generalisability.
Larger trials in people with diagnosed metabolic syndrome, diabetes or cardiovascular disease are needed before firm clinical recommendations can be made.
Final Thoughts
This carefully conducted trial suggests that a five-day fasting-mimicking diet, repeated monthly, can safely improve several markers associated with ageing and chronic disease risk- particularly in individuals starting from a less favourable metabolic position. While it is not a magic bullet, it offers an intriguing alternative to both continuous calorie restriction and complete fasting.
For now, the fasting-mimicking diet should be viewed as a promising tool under investigation rather than a universal prescription. Since 2017, numerous other studies have replicated its effects. (see Bottom of Page)
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.
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
The study under review:
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.
Other
Mohammadzadeh M, Amirpour M, Ahmadirad H, Abdi F, Khalesi S, Naghshi N, Bahrami A, Hejazi E. Impact of Fasting Mimicking Diet (FMD) on cardiovascular risk factors: a systematic review and meta-analysis of randomized control trials. Diabetol Metab Syndr. 2025 Apr 26;17(1):137. doi: 10.1186/s13098-025-01709-5. PMID: 40287774; PMCID: PMC12032729.
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.
Espinoza, S.E., Park, S., Connolly, G. et al. Effect of fasting-mimicking diet on markers of autophagy and metabolic health in human subjects. GeroScience (2025). https://doi.org/10.1007/s11357-025-02035-4
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.
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.
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.
Other
Prolon - officially licensed fasting mimicking diet products / nutrition (note: we are not affiliated in any way)
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