FMD / ProLon
Fasting-Mimicking Diet · 5-Day Protocol
Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.
6 human trials, about 16 studies, ~1,500 participants across trials. The written rationale for this grade is still being prepared.
- FDA
- Sold as food (ProLon)
- WADA
- Not prohibited
Reference only. Not medical advice.
What can go wrong
Cost (a kit runs roughly $249) and the gap between the validated mechanism and the specific branded product. Five days of deep calorie restriction can cause fatigue, lightheadedness, and headache, and is not appropriate during pregnancy or breastfeeding, for those who are frail or underweight, or for anyone with a history of disordered eating; people on glucose-lowering or blood-pressure medication can experience dangerous drops and need medical supervision. This is general information, not a protocol. Anyone considering an FMD, and especially anyone in those groups, should work with a qualified healthcare provider before starting.
The fasting-mimicking diet is a five-day plant-based, calorie-restricted formula engineered to push the body toward fasting physiology, lower IGF-1, ketosis, and autophagy signals, without complete food abstention. It was developed by Valter Longo at USC and commercialized as ProLon through L-Nutra, which Longo co-founded and in which he and USC hold equity. The mechanism is supported by mouse work and a growing set of small human randomized trials reporting improved metabolic markers and, in one 2024 analysis, a lower measure of biological age. Most of those trials, however, come from Longo's lab or are funded or supplied by L-Nutra, and Longo holds the patents; he reports donating his L-Nutra profits to a nonprofit. Independent replication outside that orbit exists but is limited.
Trick the body into fasting physiology while still eating. Real science, real conflict of interest.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
What people get wrong
Often saidProLon is uniquely required to get the benefit
ActuallyThe FMD macronutrient targets are public, not proprietary to the kit. The validated effects are tied to the formula's calorie and macronutrient profile, roughly 800 then ~500 calories per day, high-fat and low-protein, which a home approximation can reproduce at a fraction of the cost. Source: Wei 2017 Sci Transl Med describes the formulation; multiple reviewers note no head-to-head evidence that the kit beats an equivalent home FMD.
Often saidFMD is clinically proven to extend human lifespan
ActuallyHuman FMD trials show improved metabolic markers and, in one 2024 analysis, a lower measure of biological age; none demonstrate extended human lifespan. The lifespan claims rest on mouse data. Source: Brandhorst-Levine 2024 Nat Commun; Longo 2015 Cell Metab (mouse).
Often saidThe human evidence is large and independently confirmed
ActuallyA 2025 narrative review counted 16 human FMD studies in metabolic syndrome, most small, short, and with high dropout (2.3 to 30 percent), and most authored by Longo or his collaborators. Independent, non-company replication exists but is limited. Source: 2025 narrative review, PMC11943686.
Who profits, and who pushes back
Grant Tinsley, PhD
He framed the open question as whether the diet works through unique cellular changes or simply through eating fewer calories, and pointed to the absence of side-by-side comparisons of different fasting programs in humans. Source: STAT News, 2017.
Kristen Gradney, RD
These are only animal studies; there isn't a big body of evidence in humans. It could work, but I can't confidently say that it will. Source: STAT News, 2017.
Mark Mattson, PhD
Broadly supportive of fasting's benefits, he flagged affordability, saying he was thinking about the people who can't afford it. Source: STAT News, 2017.
Dr. Valter Longo
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Inventor of the FMD and co-founder of L-Nutra, which sells ProLon (~$249/kit). Genuine scientist; direct commercial interest in the specific product.
Functional-medicine practitioners
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Many resell ProLon kits; the convenience-and-compliance pitch carries margin.
Where the research comes from
Most of the published research on this comes from one place. 52% of it is from USA. Findings that no unrelated group has reproduced are weaker than the study count makes them look.
| Place | Share of published research |
|---|---|
| USA | 52% |
| Other | 28% |
| Italy | 20% |
Research published from: USA, Italy, Global.
How we got here
Therapeutic fasting is old and global. Ayurvedic medicine in ancient India named it langhana and taught langhanam param aushadham, fasting is the best medicine; classical Greek physicians around Hippocrates prescribed abstinence for the sick; Islamic physicians including Al-Razi and Avicenna used digestive rest as therapy; Buddhist and many other traditions ritualized periodic fasting. The modern fasting-mimicking idea grew from twentieth-century caloric-restriction science. Valter Longo trained under caloric-restriction pioneer Roy Walford and built his early work in yeast, mapping how nutrient-sensing pathways like IGF-1 and TOR govern aging. His insight was that a specific low-protein, higher-fat, calorie-restricted formula could trigger the beneficial fasting state while still feeding the person, avoiding the hardship of a multi-day water fast. A 2015 Cell Metabolism paper in mice, and a 2017 Science Translational Medicine human trial, drew wide attention, and L-Nutra commercialized the protocol as ProLon.
- 1990sLongo's yeast work under Roy Walford maps nutrient-sensing pathways (IGF-1, TOR) in aging
- 2015Cell Metabolism paper: a periodic fasting-mimicking diet promotes regeneration and healthspan in mice, with a small human pilot; L-Nutra commercializes it as ProLon
- 2017Wei et al. human RCT in Science Translational Medicine (~100 randomized) reports lower body fat, blood pressure, glucose, and IGF-1 after three monthly FMD cycles
- 2020sDIY FMD recipes spread as the macronutrient targets become widely known; independent trials begin appearing, including an Iranian breast-cancer chemotherapy RCT with no company tie
- 2024Brandhorst and Levine, Nature Communications, report an average 2.5-year reduction in a measure of biological age across two FMD trials; Dutch FIT RCT shows reduced diabetes-medication need
- 2025GeroScience autophagy pilot (n=30, Cedars-Sinai and UT Health San Antonio with L-Nutra) reports increased autophagy signal in the ProLon arm; L-Nutra launches a next-generation ProLon and cites 37 clinical studies
At a glance
- Duration
- 5-day monthly cycle
- Calories
- ~800 day 1, ~500 days 2-5
- Macros
- High fat, low protein
- Commercial
- ProLon ~$249/kit
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about FMD / ProLon. A short entry is not a safe entry.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
Sources
Original human FMD RCT design and metabolic results, plus NIH grant funding and Longo's disclosed L-Nutra ownership
Foundational mouse evidence that a periodic fasting-mimicking diet promotes multi-system regeneration and healthspan, with a small human pilot
2024 analysis reporting an average 2.5-year reduction in a measure of biological age and improved insulin resistance, liver fat, and immune-aging ratio across two FMD trials
Brandhorst, Levine et al., Nature Communications (2024); USC Leonard Davis summary
12-month FIT RCT (n=100): monthly FMD cycles reduced glucose-lowering medication need and improved glycemic control in type 2 diabetes; L-Nutra co-funded and supplied product; Longo disclosed as founder/shareholder/patent holder
FMD-versus-Mediterranean RCT in hypertensive subjects; L-Nutra sponsored and paid for procedures, Longo holds equity and FMD patents (correction notice with full COI statement)
Mishra, Longo et al., npj Metabolic Health and Disease, publisher correction / PMC (2025)
Independent (non-company) FMD RCT: breast-cancer chemotherapy trial (n=44) using a locally developed FMD, authors declare no commercial relationship
Bahrami, Hejazi et al., Shahid Beheshti University of Medical Sciences / PMC (2024)
Evidence-quality limits: 16 human FMD studies in metabolic syndrome, small samples, dropout 2.3 to 30 percent, short follow-up, many by Longo collaborators
Fasting Mimicking Diet for Metabolic Syndrome: A Narrative Review of Human Studies, PMC (2025)
Named skeptic quotes (Tinsley, Gradney, Mattson), Longo's majority ownership of L-Nutra, his stated intent to donate profits to a nonprofit, and the kit price
2025 GeroScience autophagy pilot (n=30, Cedars-Sinai and UT Health San Antonio in collaboration with L-Nutra): increased autophagy signal in the ProLon arm plus metabolic improvements
L-Nutra company claims: next-generation ProLon, 37 clinical studies, 134 global patents, kit pricing