If you’ve seen the small white ProLon box on someone’s kitchen counter, or heard a friend mention doing “the fasting diet where you still eat,” you’ve run into the Fasting Mimicking Diet — a 5-day nutrition program built to give your body many of the effects of fasting without going without food entirely.
It’s one of the few commercial wellness products that actually grew out of a university research lab rather than a marketing team, which is part of why it keeps coming up in longevity and biohacking circles. Here’s what it actually is, how it works, and what the science does and doesn’t support.
What Is the ProLon Fasting Mimicking Diet?
ProLon is a 5-day, plant-based nutrition program developed by Dr. Valter Longo, director of the USC Longevity Institute, along with the nutrition company L-Nutra. It’s designed around more than two decades of fasting research.
Instead of eating nothing, you eat pre-portioned soups, bars, olives, crackers, and herbal teas in specific low amounts each day. The calorie and macronutrient profile is calibrated to keep your body in a fasting-like state metabolically, even though you’re still putting food in your mouth.
That distinguishes it from two things it often gets lumped in with:
- Water-only fasting, which restricts food entirely for a set period
- Intermittent fasting (like a 16:8 eating window), which restricts when you eat but not usually what or how much
ProLon restricts both what and how much, for five consecutive days, then you return to eating normally.
How Does It Actually Work?
When protein, carbohydrate, and calorie intake drop low enough for several days in a row, the body shifts out of its normal “fed” state and starts pulling from fat stores for energy. Cellular repair processes also become more active — including a process called autophagy, essentially the body’s cellular cleanup system.
Autophagy is well documented in animal studies of fasting-mimicking cycles. In humans, it’s much harder to measure directly, so most of the clinical research instead tracks downstream effects: body weight, waist circumference, blood pressure, blood sugar, and biological age markers. That’s an important distinction — the mechanism is theorized and animal-tested, while the human evidence is built on what that mechanism appears to produce.
What 5 Days Actually Looks Like
Each ProLon kit comes with five individually labeled boxes, one for each day, so there’s no counting or meal planning involved.
- Day 1: around 1,100 calories — eases you in
- Days 2–5: around 750–800 calories per day of plant-based soups, bars, olives, crackers, an algal-oil supplement, and herbal teas
Most people describe day one as the easiest, days two and three as the hardest (mild hunger, low energy, some “food noise”), and days four and five as when energy and mental clarity tend to come back as the body adapts.
What the Research Actually Shows
We think it’s worth being specific about what’s established versus what’s still being studied — not every fasting claim belongs in the same category.
Demonstrated in published human trials:
- Reductions in body weight and waist circumference
- Improved blood pressure and select cardiometabolic risk markers
- Reduced insulin resistance and better glycemic control in adults with type 2 diabetes, in a 12-month primary-care randomized trial
- Measurable reductions in biological age markers across repeated monthly cycles, shown in a two-cohort USC study
- Improved skin hydration and texture over three monthly cycles, in a randomized controlled trial
A landmark 2017 USC-led randomized trial (about 100 participants) provided some of the earliest human evidence that periodic cycles were feasible and safe, and associated with the metabolic improvements above.
https://www.sciencedaily.com/releases/2017/02/170216103923.htm
A 2024 randomized controlled trial published in Diabetologia found that adding FMD cycles to primary care for people with type 2 diabetes reduced the need for glucose-lowering medication over 12 months.
https://gero.usc.edu/labs/longolab/publications/
A 2024 study in Nature Communications, from the USC Longo Lab, found multiple monthly cycles were associated with measurable reductions in biological age across two separate clinical trial populations.
https://stemcell.keck.usc.edu/usc-study-shows-how-cycles-of-a-fasting-mimicking-diet-reduce-insulin-resistance…
Still investigational, not established: use alongside chemotherapy to support tolerability, a supportive role in periodontal treatment, mood-related benefits paired with therapy for depression, and immune support in older adults. These are active research areas, not current uses.
ProLon is a nutrition program, not a medical treatment. Core iV Therapy does not diagnose, treat, cure, or prevent disease, and results vary by individual.
Who Should — and Shouldn’t — Try It
Most healthy adults tolerate the program well, but it isn’t for everyone. It should be avoided, or only attempted with direct physician guidance, by anyone who is:
- Pregnant or breastfeeding
- Underweight or with a history of nutritional deficiency
- Managing a current or past eating disorder
- Under 18
- On insulin or other glucose-lowering medication (risk of hypoglycemia)
- Managing significant kidney disease, a recent heart attack, or another serious chronic condition
- On any prescription medication without having confirmed the program is safe alongside it
Mild hunger, fatigue, or headache in the first day or two is common for people new to any fasting protocol and usually eases as the body adjusts. This is educational information, not individualized medical advice — talk to your physician before starting if you have any underlying health condition.
How Often People Repeat It
Most of the published research uses a repeating pattern: one 5-day cycle per month for three months, then a maintenance cycle every one to three months depending on goals. That’s roughly five days of the program followed by about twenty-five days of normal eating — which is why back-to-back cycles without a break aren’t what the evidence actually supports.
Why We Offer ProLon at Core iV
We’re an official ProLon partner clinic, offering the 5-day ProLon program for clients in Herndon and throughout Northern Virginia. For many of our clients, it fits naturally alongside the other metabolic- and longevity-focused work we already do — our Insulin Resistance support program, NAD+ therapy, and the broader approach we take to stacking therapies for a cumulative effect rather than one-off fixes.
If you’re curious whether the 5-day program is a fit for your goals, our team can walk you through what to expect and help you time it around your schedule.
Ready to Try the 5-Day ProLon Program?
Full details, safety information, and both ways to get your kit — in-office in Herndon or shipped to your door — are on our ProLon program page.
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