Try it once
ProLon is a five-day boxed meal programme that keeps you eating while your body behaves as though it is fasting. The clinical record is genuine, and so is the €199 list price and the recurring complaint about the food. Worth one cycle if you want a structured reset with published data behind it. Skip it if you would rather improvise cheaply.
How we made this estimate
We compiled this from eight sources between 13 and 16 August 2026: the prolon.it product catalogue and refund policy, the brand's live Italian offers, its Trustpilot Italia profile, three published clinical trials, one dietitian's clinical assessment and one independent first-hand account. We did not run the programme ourselves, so every claim about how it feels to do belongs to the person we name beside it.
What you are actually buying
ProLon is the retail form of the fasting mimicking diet developed by Prof. Valter Longo at the University of Southern California. In Italy it is sold by L-Nutra Italia S.r.l., registered at Via XX Settembre 12/2E in Genova.
The box holds five numbered daily packs. Each contains plant-based soups, olives, kale crackers, a nut bar, herbal teas, a glycerol drink and an algal oil capsule. Calories run from roughly 1,100 on day one down to about 700 for days two through five.
The premise is that this specific composition, low in protein and sugar and moderate in fat, keeps the body from registering that it is being fed while still supplying micronutrients. You eat every day. You do not count anything or plan anything.
Around the core kit sits a wider catalogue: a one-day ReSet kit, an L-Biome gut supplement, the L-Pill, protein products, and the Longevity Nutrition Program bundle. The five-day kit is the product almost everyone arrives for.
What ProLon costs in Italy
Here is the current catalogue as listed on prolon.it in August 2026. The right-hand column is the price the site was actually charging when we checked.
| Product | List price | Current price |
|---|---|---|
| ProLon 5-day kit | €199.00 | €169.00 |
| ProLon ReSet 1-day kit | €49.00 | €35.90 |
| Beginner Bundle | €188.90 | €151.00 |
| Longevity Nutrition Program | €207.90 | €158.00 |
| Fasting Shake | €59.00 | €46.00 |
| L-Biome | €69.00 | €55.90 |
| L-Pill | €59.00 | €45.90 |
Two things soften the number. Shipping is free over €49, which any single kit clears, and the checkout offers three interest-free instalments through Klarna, PayPal or Scalapay. There is also a referral scheme: the person who refers gets a €50 voucher once their friend's first order completes, and the friend gets 20% off.
Sitewide promotional codes run frequently, and the current one is the largest discount available on a single kit. Italian buyers on Trustpilot say openly that they only order during these windows, which seems like the correct instinct.
Run the maths per cycle, not per box. The published trials used three monthly cycles, so the realistic first-year cost is closer to €450 to €510 than to one kit price.
Does the science hold up?
Better than most things sold in this category, with one asterisk we come back to below.
The anchor study is a Phase II randomised trial of 100 participants who ran three monthly five-day cycles, published in Science Translational Medicine. Coverage from USC's Leonard Davis School reports participants averaging around five pounds of fat lost and 1.2 inches off the waist while lean body mass was preserved, alongside movement in cholesterol, triglycerides, blood pressure, inflammation markers, IGF-1 and fasting glucose.
A 2024 analysis from the same institution found the median biological age score of participants fell by 2.5 years after the third cycle. That is a lab-derived score rather than a clinical outcome, and it deserves to be read as a promising signal rather than a promise.
The most useful study for a sceptic is the randomised trial published in npj Metabolic Health and Disease in December 2023, which pitted four monthly fasting mimicking cycles against four months of a continuous Mediterranean diet in overweight and hypertensive patients. Both arms improved cardiometabolic risk factors. The distinguishing result was that the Mediterranean diet group also lost fat-free mass and the fasting mimicking group did not.
That is a real finding and a modest one. It says the kit holds onto muscle better than a good ordinary diet does, not that it outperforms one across the board.
What buyers and experts report
The Italian storefront holds a TrustScore of 4.2 out of 5 on Trustpilot Italia, rated “Molto buono”. Customers there consistently praise three things: results they notice within the first days, the fact that each day arrives pre-portioned in its own box, and the clarity of the digital instructions. Support responsiveness comes up often too.
| Source | Type | Verdict | Date |
|---|---|---|---|
| Trustpilot Italia (prolon.it) | Verified-buyer ratings | 4.2/5, “Molto buono” | Aug 2026 |
| Science Translational Medicine | Phase II RCT, n=100 | Fat loss and improved risk markers, lean mass preserved | 2017 |
| npj Metabolic Health and Disease | RCT vs Mediterranean diet | Comparable gains, no fat-free mass loss | Dec 2023 |
| USC Leonard Davis School | Follow-up analysis | Median biological age score down 2.5 years | Feb 2024 |
| Amy Burkhart, MD, RD | Clinician assessment | Structured and evidence-based, with clear contraindications | Retrieved Aug 2026 |
| The Daily Beast | Independent first-hand account | Manageable, would repeat; five pounds down by day six | Retrieved Aug 2026 |
The writer at The Daily Beast reported being five pounds lighter by day six, attributed most of it to water weight, and noted she had not regained it. She found energy manageable, hunger driven more by temptation than deprivation, and said she would run another cycle. Her single food complaint was the carrot ginger soup.
Amy Burkhart, a physician and registered dietitian, describes the programme as food-based and genuinely researched rather than a fad, and says she has seen improvements in digestive and autoimmune conditions, energy and sleep among her patients. She also states plainly that it is contraindicated in pregnancy, breastfeeding, children, and anyone with a history of an eating disorder.
Where we would push back
The asterisk on the science is a conflict of interest that nobody hides but plenty of write-ups skip. Valter Longo founded L-Nutra, the company that sells ProLon, and a large share of the fasting mimicking literature originates in his lab or in work the company supported.
That does not make the results wrong. It does mean independent replication carries more weight than another study from the same source, and there is less of it than the marketing implies.
The second gap is between what the trials measured and what most buyers want. The trials tracked risk markers over three monthly cycles in supervised participants. Most people buy one box, run it once, and are hoping for durable weight loss. No source we found supports that expectation.
The third is the food, and Italian customers are blunt about it. Trustpilot complaints centre on the crackers and the nut bar, with more than one buyer calling them close to inedible, and one noting the onion flavour lingered well past the meal. Praise for convenience and criticism of taste sit side by side in the same reviews.
The fourth is how demanding the five days are. Some customers report the protocol as easy and barely hungry. Others report severe headaches, stomach pain and weakness, and say it realistically requires clearing your calendar. The clinical trials logged no serious adverse events, but mild headache, fatigue and difficulty concentrating are well documented, usually on days two and three.
The Italian returns policy is narrow. You have 14 working days from delivery to request a return by emailing the company, goods must be intact and in original packaging, and return shipping is at your expense. There is no satisfaction guarantee. If you open the box and dislike the food, that is your cost.
What works and what does not
Strengths
- Published randomised trial evidence, which almost nothing else in this aisle can claim
- Held onto fat-free mass where a continuous Mediterranean diet did not, in a head-to-head trial
- Verified buyers repeatedly credit the pre-portioned daily boxes for making adherence possible
- Clear digital instructions and support that Italian customers rate highly
- Free shipping above €49 and three interest-free instalments take the sting out of one payment
Weaknesses
- Most of the supporting research traces back to the founder's own lab
- Italian customers consistently describe the crackers and nut bar as unpleasant
- A meaningful minority report severe headaches, stomach pain and weakness
- Returns run 14 working days, require original packaging, and cost you the shipping
- The trial protocol is three monthly cycles, so the honest annual cost is several hundred euro
Who it suits and who should skip
It suits you if you want a defined five-day protocol with real published data, you have tried unstructured fasting and abandoned it, and you value a sealed box that removes every decision. It also suits anyone whose objection to water fasting is losing muscle, since that is the one place the head-to-head trial gave it a clear edge.
Skip it if you are pregnant, breastfeeding, or have any history of disordered eating, per Burkhart's stated contraindications. Skip it if you have a medical condition or take medication and have not spoken to your doctor.
Skip it too if your goal is straightforward weight loss on a budget, because nothing in the evidence says a single cycle delivers lasting loss. And skip it if a week where you may need to rest is not something you can arrange.
Cheaper ways to run five days
A do-it-yourself version. Several detailed DIY protocols exist, and their authors report assembling five days of compliant food for roughly a tenth of the branded kit's cost. The catch is real: Burkhart notes that DIY versions have not been clinically validated, and the trial results attach to this specific formulation, not to the general idea. Prefer it if cost is the binding constraint and you accept you are running something adjacent to the studied protocol rather than the studied protocol.
The ProLon ReSet 1-day kit. At €35.90 currently, it is the cheapest way to find out whether you tolerate the food before spending €169. Prefer it as a trial run, not as a substitute; no trial evidence attaches to a single day.
A continuous Mediterranean diet. The npj trial's control arm improved cardiometabolic risk factors too, at no product cost. Prefer it if your aim is long-run metabolic health rather than a periodic reset, and accept the trade-off the trial found on fat-free mass.
ProLon questions people actually ask
Does ProLon actually work?
For the outcomes it has been tested on, the evidence is positive. A Phase II randomised trial of 100 participants running three monthly cycles found fat loss, a reduced waistline and improvements across cholesterol, blood pressure, inflammation markers and fasting glucose, with lean mass preserved. Results for a single cycle are not established.
How much weight do you lose on ProLon?
The trial coverage reports an average of about five pounds of fat over three cycles. The independent writer at The Daily Beast was five pounds down by day six of one cycle and attributed most of that to water weight, though she reported not regaining it.
How much does ProLon cost in Italy?
The five-day kit lists at €199 and was selling at €169 on prolon.it in August 2026. The one-day ReSet kit is €49 list and €35.90 currently. Shipping is free above €49 and the site offers three interest-free instalments.
What are the side effects of ProLon?
Mild headache, fatigue and difficulty concentrating are commonly reported, typically on days two and three. Some Italian customers describe more than mild effects, including severe headaches, stomach pain and general weakness. The clinical trials recorded no serious adverse events.
Who should not do ProLon?
Amy Burkhart, MD, RD, states it is contraindicated during pregnancy and breastfeeding, in children, and for anyone with a history of an eating disorder. Anyone with a medical condition or on medication should speak to their doctor first.
Can you drink coffee on ProLon?
Black coffee was permitted during the programme according to the independent first-hand account we read, alongside low-impact exercise. Check the current guidance in the kit, since the protocol documentation is what governs.
Can I return a ProLon kit in Italy?
You have 14 working days from delivery to request a return by email. Goods must be intact and in their original packaging, return shipping is at your expense, and refunds are processed within 14 days of the return being accepted. The refund policy sets no satisfaction guarantee.
Bottom line
ProLon earns a qualified yes. It is the only product of its kind with randomised trial data attached, it holds onto muscle better than a good ordinary diet in a head-to-head comparison, and the boxed format is the reason people finish it. Our confidence in the evidence is moderate rather than high, because so much of it originates with the founder's own lab.
Buy one kit during a discount window, treat it as a structured five-day reset rather than a weight-loss solution, and decide about further cycles afterwards. If the food descriptions worry you, the one-day kit answers that question for a third of the money.