A Practical Look at the 5-Day Fasting Mimicking Diet

ProLon focuses on fasting mimicking nutrition, a structured programme designed to create some of the metabolic conditions associated with fasting while still providing food. Its flagship product is the ProLon 5-Day Fasting Mimicking Diet (FMD), supported by a growing body of research into fasting-mimicking diets.
This guide explains what ProLon is, how its main products work, what the research says, and who may find the approach useful.

Affiliate and health disclaimer: This article may contain affiliate links. We may earn a commission if you purchase through them, at no additional cost to you. ProLon products are nutritional products, not a substitute for medical care. Speak with a qualified healthcare professional before starting a fasting programme, particularly if you have a medical condition, take medication, are pregnant or breastfeeding, or have a history of an eating disorder.

What Is ProLon?

ProLon is a nutrition brand built around the concept of the Fasting Mimicking Diet. The company was founded around research associated with Dr. Valter Longo and the Longevity Institute at the University of Southern California. ProLon says its programme has been developed from more than 25 years of longevity research and has been studied with multiple research institutions. 

Unlike a water-only fast, ProLon provides specially formulated foods for five days. The goal is to supply controlled amounts of calories and nutrients while keeping the body`s nutrient-sensing pathways in a fasting-like state.

That makes the concept different from simply eating less for five days.

ProLon`s Main Products at a Glance

Product	What it is	Best suited to
ProLon 5-Day FMD	Complete five-day fasting mimicking programme	People wanting the full FMD experience
ReSet 1-Day Fasting Kit	One-day fasting nutrition programme	Those looking for a shorter reset
Fasting Shake	Plant-based shake designed around fasting nutrition	Extending a fasting window
ProLon Nutrition Bar	Fasting-focused snack bar	Convenient intermittent fasting support
L-Biome	Gut-health focused product	Everyday longevity routines
L-Pill	Daily longevity supplement	People building a broader longevity routine

Prices can change, but ProLon UK currently lists the 5-Day Nutrition Programme at around £189, while the ReSet kit starts around £39 and the Fasting Shake around £55.

What Comes in the ProLon 5-Day Kit?

The main ProLon programme is designed to remove much of the planning associated with a fasting diet.

According to the UK store, a five-day kit includes:

• Five soups and meals
• Five nutrient bars and snacks
• Five drinks
• Supplements
• A programme guide

The foods are plant-based and portion controlled, so you do not have to shop for separate ingredients or calculate every meal yourself.
This convenience is arguably one of ProLon`s biggest advantages. Someone interested in trying an FMD can follow a predefined programme rather than attempting to recreate one independently.

What Does the Research Say?

This is where ProLon becomes more interesting than a typical diet product.

A 2017 randomised clinical trial published in Science Translational Medicine studied a fasting-mimicking diet over three monthly five-day cycles. Researchers reported reductions in body weight, total body fat and trunk fat, along with improvements in several markers associated with metabolic and cardiovascular health.

More recent research has continued to investigate FMD. A 2025 randomised crossover trial involving 102 participants with overweight or obesity reported improvements in several cardiometabolic and sensory measures after six monthly FMD cycles.

There is also research specifically examining muscle-related outcomes. A randomised study in healthy young men found that FMD participation did not negatively affect measured muscle volume or maximal force production after repeated cycles. However, the researchers also noted that more research is needed in populations at greater risk of muscle loss.

Importantly, these findings should not be interpreted as proof that ProLon will produce identical results for everyone. Study populations, protocols and outcomes vary, and some research has links to researchers or intellectual property associated with the FMD field. That makes it sensible to view the evidence with context rather than relying solely on marketing claims.

Who Might Consider ProLon?

ProLon may appeal to people who:

• Want to experiment with structured fasting without doing a water-only fast
• Prefer pre-portioned meals over calorie counting
• Want a defined five-day programme
• Are interested in weight-management or healthy-ageing strategies
• Find traditional fasting difficult to plan

The biggest practical benefit is structure. You know what you are eating, when you are eating it and how long the programme lasts.

Is ProLon Worth the Money?

The answer depends on what you value.

If you are comfortable planning meals, calculating portions and following a fasting protocol independently, the price of a ProLon kit may seem high.

However, ProLon is selling more than individual foods. You are paying for a ready-to-use programme, formulation, convenience and the research framework behind the fasting-mimicking approach.

For someone who wants simplicity and does not want to spend time designing a five-day fasting plan, that convenience may justify the cost.

Frequently Asked Questions

Is ProLon the same as water fasting?

No. ProLon provides food and nutrients during the five-day programme. It is designed to mimic certain fasting-related metabolic conditions rather than being a water-only fast. 

How long is the ProLon programme?

The flagship programme lasts five consecutive days. ProLon also sells a one-day ReSet option for people looking for a shorter fasting-nutrition programme.

Can ProLon help with weight loss?

Clinical research on fasting-mimicking diets has found reductions in body weight and body fat in some study groups. However, individual results vary, and ProLon should not be viewed as a guaranteed weight-loss solution. 

Does ProLon contain real food?

Yes. The five-day kit includes formulated soups, meals, snacks, drinks and supplements rather than requiring a complete water-only fast. 

Is ProLon suitable for everyone?

No. Fasting programmes are not appropriate for everyone. If you take medication or have a health condition, consult a healthcare professional before starting. Pregnant or breastfeeding people and anyone with a history of an eating disorder should seek appropriate medical advice before considering fasting.

Final Verdict

ProLon UK stands out because it turns the fasting-mimicking concept into a structured, ready-to-follow programme. The 5-Day Fasting Mimicking Diet is the obvious choice for anyone wanting the complete experience, while the ReSet, Fasting Shake and Nutrition Bars provide shorter or more flexible options. 

The research behind fasting-mimicking diets is promising, particularly around who value convenience, clear instructions and a science-led approach to fasting, ProLon is a brand worth considering. For anyone with medical concerns, however, professional guidance should come before body composition and metabolic markers, but it is still important to separate published evidence from broader longevity marketing claims.

For shoppers who value convenience, clear instructions and a science-led approach to fasting, ProLon is a brand worth considering. For anyone with medical concerns, however, professional guidance should come before starting any fasting programme.

Sources used include ProLon UK`s current product and science pages and peer-reviewed clinical research indexed by PubMed.

2026-05-26