Fasting-Mimicking Diet: Valter Longo's Protocol

Of all the dietary interventions studied for longevity, the fasting-mimicking diet (FMD) is the one with the most elegant scientific story. Developed by Valter Longo at the University of Southern California's Longevity Institute, FMD is a 5-day, low-calorie, low-protein eating protocol that tricks the body into a fasting-like state — triggering the regeneration and autophagy benefits of prolonged water fasting, but with food on the plate.

The protocol sounds too good to be true: eat a carefully designed plant-based mini-diet for five days, return to normal eating for 25 days, repeat 3–12 times per year, and apparently reset multiple markers of aging. But the science, while still emerging, is more credible than most "anti-aging" interventions. This guide explains what FMD is, what the research shows, what to eat, and how to decide whether it belongs in your longevity protocol.

What is the fasting-mimicking diet?

A fasting-mimicking diet is a low-calorie, low-protein, moderate-fat, plant-based eating pattern that produces the physiological effects of a water fast — without requiring you to eat nothing. The defining features:

• Calories: ~1,100 on day 1, then ~700–800 on days 2–5 (roughly 40–50% of normal intake).
• Macros: very low protein (~10% of calories, mostly plant), moderate complex carbs (~45% from vegetables and nuts), moderate fat (~45%, mostly from olive oil and nuts).
• Duration: 5 consecutive days.
• Frequency: once a month for 3 months as an induction, then every 1–3 months for maintenance.
• Composition: plant-only — vegetables, nuts, olives, seeds, small amounts of fruit, no animal products, no refined sugar, no caffeine (in the commercial version).

The macronutrient profile is the secret. By keeping protein very low (especially low in methionine and other amino acids that activate mTOR), and calories low enough to deplete glycogen and lower insulin, the body shifts into a fasting-like metabolic state — even though you're still eating. Longo's research shows this state is enough to trigger the key longevity pathways: AMPK activation, mTOR suppression, autophagy induction, and stem cell activation during refeeding.

Valter Longo and the science of FMD

Valter Longo is one of the most credible longevity researchers in the world. He directs the Longevity Institute at USC, has published hundreds of peer-reviewed papers on aging, and authored The Longevity Diet (2018). His research focuses on the connection between nutrient sensing, fasting, and regenerative biology.

Longo's key insight: prolonged water fasting (5+ days) produces remarkable regenerative effects in animal models — but is dangerous, miserable, and almost impossible to sustain in humans. FMD was his solution: an eating pattern that reproduces the cellular effects of water fasting with a small amount of food. The food is engineered to keep protein low enough to suppress mTOR and IGF-1, while providing enough calories and nutrients to avoid the risks of starvation.

His lab published the foundational FMD paper in Cell Metabolism in 2015, showing that periodic FMD cycles in mice extended lifespan, reduced cancer incidence, improved immune function, and promoted regeneration of multiple tissues. A human trial followed in 2017 (Science Translational Medicine), showing that 3 monthly cycles of FMD reduced body weight, body fat, blood pressure, fasting glucose, IGF-1, and C-reactive protein in healthy adults.

How FMD works: autophagy, IGF-1, stem cells

FMD triggers the same cellular pathways as prolonged fasting:

1. mTOR suppression and autophagy

By keeping protein extremely low for 5 days, mTOR (the cellular growth sensor) is suppressed. When mTOR is suppressed, autophagy — the cellular recycling process — ramps up. Autophagy clears damaged proteins, malformed organelles, and other cellular garbage that accumulates with age. This is one of the core longevity mechanisms. See our mTOR vs AMPK guide for the deeper biology.

2. Lower IGF-1

Insulin-like growth factor 1 (IGF-1) is a growth hormone that declines when protein intake is restricted. Lower IGF-1 is associated with reduced cancer risk and slower aging across species. FMD reliably drops IGF-1 by 10–20% after a single cycle.

3. AMPK activation

The calorie deficit activates AMPK (the cellular low-energy sensor), which shifts cells into maintenance mode and triggers mitochondrial biogenesis. See our AMPK guide.

4. Stem cell regeneration

The most striking finding from Longo's mouse work: prolonged fasting depletes old immune cells, and refeeding triggers stem cell-based regeneration of new immune cells. The same effect appears to occur in human trials of chemotherapy patients (Longo's group showed FMD before chemo protected normal cells while sensitizing cancer cells). The regeneration of the immune system is one of the most exciting potential longevity benefits of FMD.

5. Ketosis

By day 2–3 of FMD, most people enter mild nutritional ketosis, which provides an alternative brain fuel and has its own anti-inflammatory and autophagy-inducing effects.

The 5-day protocol: calories, macros, foods

Here is the canonical FMD protocol as specified in Longo's published research:

Specific foods allowed on FMD:

• Vegetables: leafy greens, broccoli, cauliflower, zucchini, cucumber, tomatoes, mushrooms, onions, garlic.
• Nuts and seeds: walnuts, almonds, macadamia, hazelnuts, flaxseed, chia (in moderation — they're calorie dense).
• Olives and olive oil.
• Small amounts of fruit: berries, apple, citrus.
• Complex carbs: small amounts of quinoa, sweet potato, or brown rice.
• Herbal tea and water.

Foods to avoid during FMD:

• All animal products (meat, dairy, eggs, fish).
• Soy protein (Longo recommends against it due to methionine content and concerns about processed soy).
• Refined sugar, refined flour, ultra-processed food.
• Caffeine (the commercial ProLon version excludes it).
• Alcohol.

ProLon vs DIY: how to actually do it

There are two main ways to do FMD:

Option 1: ProLon (the commercial product)

ProLon is the branded, pre-packaged FMD kit sold by L-Nutra (Longo's company). It contains 5 days of pre-measured, plant-based, low-protein food — crackers, soups, nut bars, olives, kale crackers, tea, and a supplement drink. You eat only what's in the box, in the prescribed order. Cost: ~$150–250 for the 5-day kit.

Pros: convenient, mathematically precise, no meal planning, no shopping. Cons: expensive, the food is shelf-stable and not gourmet, and some users find the portions small and the food repetitive.

Option 2: DIY FMD with grocery-store food

You can replicate the FMD macronutrient profile with whole foods at a fraction of the cost. Longo has published the macronutrient targets; the food choices are flexible as long as you hit the calories and macros. A typical day's DIY FMD menu:

• Breakfast: handful of walnuts + 1 cup green tea + small bowl of berries.
• Lunch: large mixed greens salad with 1 tbsp olive oil + lemon, cucumber, tomato, 5 olives.
• Snack: 1/4 cup almonds + vegetable broth.
• Dinner: vegetable soup (broccoli, kale, zucchini, mushroom, onion cooked in olive oil) + small portion quinoa.

Pros: cheaper, fresher food, more flexibility. Cons: requires planning and tracking calories/macros carefully, easy to accidentally over-eat protein (e.g., too many nuts) and miss the mTOR-suppression effect.

Either way, the key is hitting the macro targets: very low protein, modest calories, plant-based. ProLon just removes the guesswork.

What the human trials show

Longo's 2017 human trial (Brandhorst et al., Science Translational Medicine) tested 3 monthly FMD cycles in 71 healthy adults. Results after 3 cycles:

• Body weight: average 2.6 kg reduction.
• Body fat: reduced, particularly trunk fat.
• Blood pressure: systolic dropped ~5 mmHg, diastolic ~4 mmHg.
• Fasting glucose: reduced by ~10 mg/dL.
• IGF-1: reduced by ~15% (a key anti-aging marker).
• C-reactive protein: reduced (lower inflammation).
• Stem cell markers: increases in markers of regeneration and mesenchymal stem/progenitor cells.

Subsequent trials in metabolic syndrome, inflammatory bowel disease, and multiple sclerosis patients have shown similar benefits, with FMD reducing disease severity markers and improving metabolic health. Larger RCTs are ongoing.

For comparison with shorter fasts and time-restricted eating, see our intermittent fasting protocols guide.

Who should not do FMD

FMD is not for everyone. Do not do FMD if you:

• Are pregnant, breastfeeding, or trying to conceive.
• Are underweight (BMI < 18.5) or have a history of eating disorders.
• Are over 70 or frail (without medical supervision).
• Have type 1 diabetes or are taking insulin or sulfonylureas (serious hypoglycemia risk).
• Have type 2 diabetes on multiple medications — only with physician supervision.
• Have a history of severe low blood pressure or fainting.
• Are undergoing surgery or recovering from surgery.
• Are an athlete in heavy training (the calorie deficit will impair recovery and adaptation).

If you have any chronic medical condition, talk to your physician before attempting FMD. This is a substantial metabolic intervention, not a casual cleanse.

How often to do FMD

Longo's protocol for healthy, normal-weight adults:

• Induction: once a month for 3 consecutive months.
• Maintenance: once every 2–3 months thereafter.

For overweight or metabolically unhealthy adults, more frequent cycles (monthly) may be appropriate. For athletes or already-lean individuals, 2–4 cycles per year is plenty.

Don't do FMD more than once a month. The cycle of depletion and refeeding is what triggers regeneration — chronic depletion just causes muscle loss and metabolic slowdown.

What to eat on the refeed

The refeed (day 6 onward) is just as important as the fast itself. This is when stem cell regeneration occurs. Don't break the fast with junk food. Longo recommends:

• Day 6: transition gently with vegetable soup, cooked vegetables, small amounts of fish or legumes, fruit.
• Day 7: resume your normal Mediterranean-style diet, with extra protein if you strength train.
• Avoid heavy, fatty, or sugary meals immediately after FMD.

For the broader dietary context, see our longevity diet guide.

Supplements that support FMD

FMD itself requires no supplements — the protocol is food-based. But three supplements are commonly used alongside FMD cycles to support the fasting state and recovery:

Electrolytes

During the low-calorie phase, sodium, potassium, and magnesium intake can drop. A sugar-free electrolyte supplement helps prevent headaches, fatigue, and muscle cramps. LMNT is our preferred clean electrolyte product:

NMN (for refeeding recovery)

NAD+ levels rise during fasting (which is one mechanism of FMD's benefits). Some practitioners supplement NAD+ precursors during refeeding to support stem cell regeneration and metabolic recovery. Liposomal NMN from Renue By Science is our top pick:

Spermidine (for autophagy support)

Spermidine is a polyamine that induces autophagy via mTOR-independent pathways. It complements FMD's mTOR-suppression effect and may amplify the cellular cleanup. We like DoubleWood's spermidine for a clean, dosed supplement:

For a complete longevity supplement stack, see our supplement stack guide.

The bottom line

The fasting-mimicking diet is one of the most credible dietary interventions for longevity. Valter Longo's research shows that periodic 5-day low-calorie, low-protein cycles reduce body fat, blood pressure, fasting glucose, IGF-1, and inflammation — while triggering stem cell-based regeneration. The effects resemble prolonged water fasting but with food on the plate, making it safer and far more sustainable.

If you're a healthy adult with metabolic risk factors (overweight, elevated blood pressure, elevated fasting glucose, elevated IGF-1), 3 monthly FMD cycles followed by quarterly maintenance cycles is a reasonable, evidence-based protocol. If you're already lean and metabolically healthy, 2–4 cycles per year is plenty. Either way, get the diet right between cycles — FMD is a periodic reset, not a substitute for daily good nutrition.

For a broader look at how FMD fits into a complete longevity protocol, see our beginner protocol, our guide to lowering biological age, and our longevity diet guide.