What is 5 Day Fasting Mimicking Diet (ProLon)?

The 5-Day Fasting Mimicking Diet (FMD) is a structured eating protocol developed by Dr. Valter Longo that provides carefully portioned plant-based foods in specific macronutrient ratios — enough to nourish the body, but low enough in calories, protein, and carbohydrates to keep it in a fasting-like state. Unlike water-only fasting, it gives people food to eat each day, making it more sustainable and safer to repeat. The ProLon kit is the commercially available, clinically studied version of this protocol.

How does 5 Day Fasting Mimicking Diet (ProLon) work?

When calories and protein drop low enough, the body shifts away from its normal growth mode and activates a self-cleaning process called autophagy — where cells break down and recycle damaged or old components. At the same time, the body reduces insulin and IGF-1 (a growth-promoting hormone), lowers inflammation, and begins drawing on stored fat for energy. After the 5 days are complete and normal eating resumes, the body enters a regeneration phase, replenishing cells with a fresher, more efficient population.

What forms does 5 Day Fasting Mimicking Diet (ProLon) come in?

The ProLon commercial kit includes pre-portioned soups, bars, crackers, olives, teas, and supplements for all 5 days. A DIY version can be constructed using whole plant foods — primarily vegetable soups, small amounts of nuts and seeds, herbal teas, and minimal fruit — following the same caloric and macronutrient targets. Clinical versions may include medical monitoring for people with metabolic conditions.

Where it comes from:

Dr. Valter Longo spent decades studying centenarian populations, caloric restriction science, and longevity biology at the University of Southern California. He developed the FMD concept in the early 2010s after identifying that periodic fasting — not chronic caloric restriction — produced the strongest longevity-related signals in both animal models and human research. The ProLon product was commercialized following human clinical trials published around 2015–2017.

What does 5 Day Fasting Mimicking Diet (ProLon) help with?

• Weight loss and belly fat: The FMD consistently produces reductions in total body weight and, importantly, in visceral (belly) fat — the type most closely linked to metabolic disease. Most of the weight lost comes from fat rather than muscle, particularly when the protocol is repeated monthly for 3 cycles.
• Blood sugar and insulin resistance: By dropping calorie and carbohydrate intake significantly for 5 days, the protocol lowers fasting blood sugar and reduces insulin levels, improving the body's sensitivity to insulin. People with pre-diabetes or borderline blood sugar tend to see the most noticeable improvements.
• High cholesterol and triglycerides: Clinical studies have shown meaningful reductions in total cholesterol, LDL cholesterol, and triglycerides after 3 monthly FMD cycles. These improvements appear to be driven by the metabolic shift toward fat burning and reduced liver fat production during the fasting period.
• Healthy aging and longevity: The FMD activates biological pathways — particularly autophagy and reduced IGF-1 signaling — that are strongly associated with slower aging and longer healthspan in research models. These are the same pathways that seem to explain why calorie-restricted populations tend to age more slowly.
• Cellular cleanup (autophagy): During the low-calorie, low-protein fasting window, cells ramp up autophagy — their internal housekeeping system that breaks down and recycles damaged proteins and organelles. This cellular renewal process is linked to reduced risk of age-related disease and better overall cell function.
• Inflammation and immune reset: Completing multiple FMD cycles has been associated with reductions in inflammatory markers like C-reactive protein (CRP). Some research also suggests the protocol may partially reset the immune system by reducing aged or dysfunctional immune cells and supporting production of fresh ones.
• Blood pressure: Human trials have observed modest but meaningful reductions in both systolic and diastolic blood pressure after repeated FMD cycles, especially in participants who started with elevated readings. This is likely related to reductions in body weight, visceral fat, and systemic inflammation.
• Metabolic syndrome: The FMD addresses multiple components of metabolic syndrome simultaneously — blood sugar, blood pressure, cholesterol, triglycerides, and waist circumference — making it one of the few dietary interventions studied for its broad metabolic impact in a single short protocol.
• Cancer treatment support (under medical supervision): Preliminary research suggests the FMD may help protect healthy cells during chemotherapy while potentially making cancer cells more vulnerable — a concept called differential stress resistance. This remains an active research area and should only be considered under direct oncology supervision.

What can 5 Day Fasting Mimicking Diet (ProLon) help prevent?

• Progression from pre-diabetes to type 2 diabetes (supported by blood sugar and insulin improvements in clinical trials)
• Cardiovascular disease risk factor accumulation (via improvements in LDL, triglycerides, blood pressure, and visceral fat)
• Biological aging acceleration (via autophagy activation and IGF-1 reduction)

Which foods are rich in 5 Day Fasting Mimicking Diet (ProLon)?

1. Vegetable soups and broths: Low in calories and protein while providing micronutrients and warmth — the backbone of both the ProLon kit and DIY FMD protocols.
2. Olives and olive oil: High in healthy monounsaturated fats that fuel the body during caloric restriction without spiking insulin or IGF-1 — a key fat source in the FMD design.
3. Raw nuts (especially macadamia, almonds, walnuts in small amounts) — Nutrient-dense fat and modest protein source that sustains energy during restricted days without triggering significant insulin or growth-hormone responses.
4. Leafy greens and cruciferous vegetables: Extremely low in calories and protein but rich in fiber, vitamins, and antioxidants — support micronutrient sufficiency during restriction.
5. Herbal teas (chamomile, green tea, hibiscus): Zero-calorie hydration with added antioxidant support; green tea may also mildly enhance autophagy — consumed freely during the protocol.

Practical Tips:

The FMD is itself a dietary pattern rather than a supplement, so there is no single food that 'contains' it. The foods listed above are the core components used in the protocol. Between FMD cycles, a Mediterranean-style diet — rich in vegetables, legumes, whole grains, healthy fats, and modest in animal protein — is consistently recommended by Dr. Longo to extend and maintain the benefits of each 5-day cycle.

What are the side effects of 5 Day Fasting Mimicking Diet (ProLon)?

• Hunger and food cravings (especially days 1–2)
• Fatigue and low energy (typically peaks around day 2–3)
• Headaches (often from reduced caffeine, carbohydrates, or mild dehydration)
• Lightheadedness or dizziness when standing
• Mild nausea
• Difficulty concentrating (brain fog during caloric restriction)
• Irritability or mood changes
• Constipation or changes in bowel habits
• Feeling cold (reduced metabolic output and caloric intake)
• Mild muscle weakness by day 4–5

Good to know:

The FMD is generally well tolerated in healthy adults. Most side effects are mild, predictable, and concentrated in the first 2–3 days as the body shifts into a fasting state. It is not appropriate for pregnant or breastfeeding women, children, people who are underweight, or those with certain eating disorder histories without medical clearance.

How much 5 Day Fasting Mimicking Diet (ProLon) should you take?

• Recommended daily: Approximately 700–1,100 calories per day for 5 consecutive days, structured as: Day 1 (~1,090 kcal) and Days 2–5 (~725 kcal each), with specific macros of roughly 9–10% protein, 44–56% fat, 34–47% carbohydrate.
• Best time of day: Distribute food across the day as desired; many people find eating the larger Day 1 meal at lunch or dinner easiest. Herbal teas and water are encouraged throughout the day.
• With or without food: All intake during the 5 days IS the food — follow the structured meal plan precisely. No additional food or caloric beverages should be added. Black coffee (1 small cup/day) is generally considered acceptable but not officially included in the ProLon kit.
• Time to effect: Cellular and metabolic changes begin within 48–72 hours of starting; measurable metabolic improvements (weight, blood markers) are typically seen after completing 2–3 monthly cycles.
• How long to take it: The most studied protocol is 1 cycle per month for 3 consecutive months, then re-evaluate. After achieving health goals, some people shift to a maintenance schedule of once every 3–4 months. Always return to normal, nutritious eating immediately after Day 5.