Fasting Mimicking Diet (Prolon): What Is It? Does It Work?

Last updated April 2026

The Fasting Mimicking Diet is a scientifically developed 5-day program designed to mimic the biological effects of fasting without completely avoiding food. Most people think fasting means going without food entirely, but the Fasting Mimicking Diet (aka The Prolon Diet) turns that assumption on its head, with science backing up the claims. It is not a liquid cleanse or a severe caloric-restriction protocol, but is a structured, food-based program with real science behind it.

It’s the question everyone asks.

Traditional fasting requires complete food avoidance, which comes with predictable side effects: persistent hunger, low energy, headaches, and difficulty sustaining the fast long enough to reap its benefits. Most people abandon fasting before the biological benefits have a chance to kick in.

The fasting mimicking diet takes a different approach. Through a specific combination of foods, precise caloric targets, and nutrient ratios, the ProLon program keeps the body in a fasting state even while food is being consumed. The body essentially doesn’t register that it has been fed, so the beneficial cellular processes triggered by fasting still happen.

This means you get the benefits of fasting with significantly fewer of the physical downsides that make traditional fasting so difficult to maintain. Keep reading to learn how it does this.

It relies on specifically formulated meals

The fasting mimicking diet was developed by Dr. Valter Longo, a longevity researcher who has spent more than 20 years studying fasting, aging, and disease. His research team at the University of Southern California focuses on how the body responds to nutrients, specifically through what are known as nutrient-sensing pathways.

Instead of complete food avoidance, the fasting-mimicking diet uses specifically formulated, plant-based meals that provide some calories while keeping the body in a fasting state, biologically, by preventing activation of nutrient-sensing pathways. 

Nutrient-sensing pathways function like biological gauges.

After a typical meal, these pathways detect the incoming nutrients and signal the body that it’s in a “fed state”, activating growth, energy storage, and cell replication. The ProLon fasting mimicking diet is engineered to stay below the threshold that triggers these signals. Through a precise combination of caloric content and macronutrient ratios, the nutrient-sensing pathways are prevented from being triggered.  The body never receives a clear “fed” signal. Because of this, metabolic activity continues to mirror a fasted state, even with food present.

We want autophagy to be active.

One of the most important effects of blocking nutrient-sensing pathways is the activation of autophagy, the body’s internal process for breaking down and recycling damaged, dysfunctional, or aging cells. This is a good thing.  It is the way the body “eats up” old, damaged cells, lowers inflammation, slows aging and helps prevent cancer cells from forming.

Autophagy is always running at a baseline level, acting as a continuous maintenance crew for your cells. Think of it as a garbage truck operating inside every cell, collecting cellular debris, clearing out worn-down proteins, and making room for healthier structures to take their place.

When the FMD stops nutrient-sensing activity, autophagy shifts into a higher gear. This accelerated cellular housekeeping has important health benefits.

• Damaged cells that contribute to chronic disease and accelerat aging are cleared more efficiently
• The cellular environment becomes less welcoming to the conditions that allow cancer cells to persist
• Overall cellular function improves, which translates to measurable effects on energy, recovery, and long-term health

When your cells clean better, your body operates better, and your risk for developing future disease decreases.

Nutrient-sensing pathways affect your genes/DNA

Nutrient-sensing pathways don’t stop at autophagy and metabolism. They reach deeper into epigenetics, the field that studies how lifestyle and environmental factors determine which genes are activated and which remain dormant.

Your genetic code is fixed, but gene activity is not. Two people can carry the exact same gene yet have entirely different health outcomes, because that gene is turned on in one person and effectively silenced in the other. This is why one individual with a genetic predisposition to an autoimmune condition develops it while another doesn’t or why twins can yield different responses to diet, stress, or aging.

Factors that act as biological switches turning specific genes on or off are what are studied in the field of epigenetics. Nutrient-sensing pathways are among the most influential of those switches.

The ProLon fasting mimicking diet is the only program of its kind specifically designed to activate fasting biology without requiring complete food elimination.

A Fasting Mimicking Diet Is Specifically Designed

On a fasting mimicking diet, you eat a precise combination of plant-based foods, including soups, crackers, and nutrition bars specifically formulated to keep the body in a fasting state while still consuming real food. All meals and snacks come exclusively from the ProLon kit, the only clinically researched fasting mimicking diet program currently on the market.

Each day’s food is pre-portioned and organized in numbered boxes (1-5), removing any guesswork from the process.

Fasting Mimicking Diet Food List by Day

Day 1: Appx 1100 calories

• Plant-based soups
• Nut-based crackers
• Nutrition bars
• Plant-based protein, healthy fats, and low-carbohydrate sources

Days 2-3: Appx 725 calories

• The same categories of food as Day 1, in smaller portions
• Calorie and nutrient ratios are maintained to maximize autophagy effects

Initial Phase (1-3 months)

The Prolon research team, the primary group behind FMD clinical research, recommends completing the 5-day plan once per month for 3 to 8 months. The majority of published FMD research is based on this 3-month repeating cycle.

Maintenance phase (ongoing)

After completing the initial protocol, practitioners generally follow the 5-day cycle every 1 to 6 months, depending on individual health goals, to sustain the diet’s benefits over time.

Why 5 days?

The 5-day duration is specifically designed to optimize autophag, the cell clean-up we discussed earlier.

• Program length: 5 days
• Initial frequency: once per month for 3-8 months
• Maintenance frequency: every 1-6 months
• Primary mechanism: autophagy with muscle preservation
• Most studied protocol: 3-month consecutive cycle

The ProLon fasting mimicking diet kit is available without a prescription

The kit ships directly to your door. You can make a one-time purchase, which I recommend starting with, unless you want the discount of buying a bundle, and if it is a good fit for you, auto-ship programs are available. For optimal results, complete the 5-day program once a month for at least 3 consecutive months.

• For convenience, you can view pricing and purchase ProLon products using the button below. All purchases made through this link include an up to 40% discount or more, depending on the number of products or kits purchased. It also offers significant savings on all ProLon products. The discount at the button is reusable for repeat purchases.

   

• Prolon Discount & cost-saving tips are found here.

• The ProLon Fasting Mimicking Diet is the only fasting-mimicking meal program currently undergoing clinical trials.

• Each Prolon kit provides all the food you need for the 5-day plan

• The cost of the Prolon kit varies by quantity purchased with options to buy individual kits or discounted bundles of 3 or 4.

• Clinical studies on fasting-mimicking diets are done with the ProLon kit.

• Research suggests using the kit once a month for 3 months to achieve optimal results.

A DIY fasting mimicking diet is not the same as the clinically researched Fasting Mimicking Diet (FMD).

While numerous DIY versions circulate online, none have been scientifically validated to replicate the metabolic and cellular effects of the official ProLon protocol.

The official fasting mimicking diet is backed by over 20 years of research and is precisely engineered with specific vitamins, nutrients, and macronutrient ratios to keep the body in a metabolic fasting state. This level of formulation cannot be replicated by simply reducing calories or following a generic low-calorie meal plan.

A DIY fasting mimicking diet may still offer some health benefits. Eating fewer calories and prioritizing whole foods is generally positive, but those results are not equivalent to the proven outcomes of the scientifically formulated FMD protocol. Equating the two is not scientifically supported.

For the full FMD benefits, the kit is the only scientifically validated option.

If the cost of the ProLon kit is a barrier, a low-calorie, whole-food diet may still support general health improvements. However, to experience the full, proven benefits of the fasting mimicking diet, including autophagy and cellular renewal, the official ProLon kit is currently the only validated option. Research on standardized DIY versions is ongoing and may provide more guidance in the future.

Time vs. Specific Foods

Intermittent fasting involves cycling between designated periods of eating and not eating throughout the day. It does not prescribe specific foods; it prescribes timing.

The most common IF protocols include:

The 16:8 method: This is the most popular approach. Individuals fast for 16 consecutive hours, consuming only calorie-free beverages such as water or plain tea, followed by an 8-hour eating window. Food choices during the eating window focus on healthy options without strict calorie counting. The timing windows are flexible, but maintaining a continuous 16-hour fast is essential.

5:2 method: Individuals eat normally five days per week and fast completely for two non-consecutive days, consuming only water or calorie-free beverages on fasting days.

The key distinction is that intermittent fasting controls when you eat. The fasting-mimicking diet controls what you eat and, in what precise combination, and simulates fasting biology without abstaining from food entirely.

Unlike intermittent fasting, the FMD does not rely on timed eating windows or periods of complete food restriction.

Here are some other frequently asked questions that I did not address in the article. When you purchase a kit, Prolon does offer access to group coaching  with their trained health coaches who can answer other questions that may arise.

Can I take supplements and medications while I’m on the fasting mimicking diet?

Basic vitamins and electrolytes in ( without sweeteners or calories) are usually OK. If you are unsure, ask your healthcare provider or avoid them if they are necessary. Prescription medications should not be stopped during the fasting mimicking diet. Always consult with your provider before starting the fasting mimicking diet to ensure there are no contraindications with other health conditions.

Will I lose muscle on the fasting mimicking diet?

The fasting-mimicking diet aims to minimize muscle loss by allowing small amounts of nutrients. Minor muscle loss can’t occur with any calorie restriction, but compared with traditional fasting, the fasting-mimicking diet is associated with less muscle loss.

Can I drink coffee on the fasting mimicking diet?

Yes, limit caffeinated coffee to one cup per day; drink it black; avoid sweeteners, cream, or protein additives such as collagen or other protein powders.

Will I feel hungry or tired?

In my clinical experience, if symptoms of a calorie drop occur, I find that men experience them more often than women. Most people have very mild or no symptoms on the first day. If symptoms do occur they are more common on day 2 or 3. Hunger, fatigue, and headaches are the most common symptoms and tend to decrease during the final days of the diet. They are not as significant as those that occur with other forms of fasting. 

Can I exercise during the FMD?

I recommend avoiding intense exercise since calorie intake is limited. Light walking, stretching, or yoga are encouraged, just don’t overdo it.

What are the biggest mistakes that people make on the fasting mimicking diet?

• Not eating everything in the kit One of the most common things I see is people limiting their food intake beyond the diet. It is recommended that you consume everything in your diet; not doing so will increase the risk of side effects and elevated stress hormone levels. 
• Cheating Some people”cheat” with small snacks, thinking they are insignificant. I remind people that if you were going to pay for the tie and optimize its benefits, you need to stick precisely to the program. 
• Adding protein to beverages. This often happens because many online sources say that protein powders and collagen don’t break a fast. If you do that on the fasting-mimicking diet, it negates the program’s positive effects.
• Doing too much exercise, I also see people trying to do too much exercise while they’re on the program, because it is their routine. I encourage avoiding strenuous exercise and focusing on more moderate exercise options.
• Ignoring their hydration and electrolyte needs. A hydration beverage is included with the kit, and I encourage people to use it to minimize side effects and maintain hydration.

There are nearly 240 completed or ongoing studies examining how the fasting-mimicking diet affects the body.  Many projects are in progress, looking at the effects of FMD on conditions such as autoimmunity, longevity, cancer, fertility, inflammation, weight loss, and more. Thus far, research has identified a range of important health benefits, which include

• Support for autoimmune conditions
• Measurable improvements in depression symptoms
• Rebalancing of the gut microbiome
• An estimated increase in healthy lifespan of up to 2.5 years
• Anti-cancer cellular activity
• Below are a few brief explanations of some of the research on common conditions and the FMD.

Prolon FMD & Depression

A study showed that using a fasting-mimicking diet in conjunction with therapy for depression resulted in significantly better outcomes than therapy alone.

Fasting Mimicking Diet & Aging

A 2024 study in Nature showed remarkable results regarding the FMD’s effect on diet and aging.  Three rounds of the FMD lowered the biological age by 2 1/2 years compared to the actual age. More studies are needed but it may get us one step closer to a fountain of youth.

Fasting Mimicking Diet & Weight Loss

A large randomized trial* compared FMD with a typical calorie-restriction regimen. Both approaches achieved comparable weight loss and improvements in risk factors for cancer, diabetes, and cardiovascular disease. Both appeared equally beneficial for weight loss and disease risk reduction. *human study

Fasting-mimicking Diet & Multiple Sclerosis

All mice had improved symptoms, and 20 percent of mice with MS had complete resolution of symptoms. No meds, no side effects! The FMD reduced markers of inflammation and promoted a healthier gut microbiome.

FMD Improves Sense Of Smell & Taste

A 2025 study showed significant improvement in the sense of taste and smell, which is often decreased in obesity.

FMD & Parkinson’s Disease

In this animal study, the fasting-mimicking diet was helpful in improving Parkinson’s disease symptoms and slowing disease progression.

Alzheimer’s & FMD

The results of this animal study show that periodic protein restriction cycles protect against age-related changes.  A 2023 study on the FMD and Alzheimer’s showed improvement in cognitive function, biomarkers and well being in Alzheimer’s patients when using the FMD.

FMD & Diabetes

In this human study, FMD was found to help blood glucose control in type 2 diabetics.

Inflammatory Bowel Disease & FMD

The fasting-mimicking diet decreased gut inflammation and increased the number of stem cells and the number of “good” gut bacteria in people with inflammatory bowel disease. A 2026 study in patients with Crohn’s and the fasting mimicking diet showed it to be superior to a regular diet in helping control Crohn’s and promote remission.

Cancer & FMD

Can a fasting-mimicking diet help in the fight against cancer? That can’t be said yet, but early results are promising. One research study in mice found that a fasting-mimicking diet could reverse tumor growth. Yes, this is in mice, but wow! Couldn’t this be a fantastic addition to cancer therapy if it pans out in humans? A 2024 study on the FMD and CLL shows promising results for the most common leukemia in adults.

Other studies have looked into how fasting-mimicking diets might work on people with cancer, but they are still preliminary, and more research needs to be done before we can say for sure. See the bottom of this article for other studies on FMD and cancer.

• The fasting-mimicking diet is a specific meal plan formulated to simulate the fasting state while providing some nutrients and calories. It does this by not triggering pathways that make the body think it is in a fed state.
• The fasting-mimicking diet is not the same as restricting daily calories.
• The FMD appears to be as effective as calorie restriction for weight loss. More studies are needed.
• Many human trials are in progress using the fasting-mimicking diet for various health conditions.
• The diet has the potential to provide an alternative to more restrictive forms of fasting.
• The FMD aims to provide the benefits of fasting without the common side effects, such as headaches, fatigue, and muscle loss.
• In my clinical experience with the FMD, I have seen patients have improvement in digestive and autoimmune conditions, energy levels, mood, inflammation, and sleep.
• If you are considering the fasting-mimicking diet, please consult a medical professional before you begin. Fasting is not appropriate for everyone. Learn here: who should not fast?

Disclosure: I earn a small commission on purchases made through links. This does not affect my honest assessment of the science and my clinical experience with the product.

Listen here to a PODCAST on the fasting mimicking diet with Dr. Valter Longo.

Body Of Wonder Podcast Featuring Dr. Andrew Weil and Dr. Victoria Maizes

This is a fantastic podcast covering research-based topics in the field of integrative medicine.

• Cyclic Fasting-Mimicking Diet in Cancer Treatment: Preclinical and Clinical Evidence
• Effect of Fasting-Mimicking Diet on Markers of Autophagy and Metabolic Health in Human Subjects
• Effects of the Periodic Fasting-Mimicking Diet on Health, Lifespan, and Multiple Diseases: A Narrative Review and Clinical Implications
• Fasting-Mimicking Diet Causes Hepatic and Blood Markers Changes Indicating Reduced Biological Age and Disease Risk
• Fasting Mimicking Diet During Neo-Adjuvant Chemotherapy in Breast Cancer Patients: A Randomized Controlled Trial
• Fasting Mimicking Diet Extends Lifespan and Improves Intestinal and Cognitive Health
• Fasting Mimicking Diet for Metabolic Syndrome: A Narrative Review of Human Studies
• Fasting-Mimicking Diet Modulates Microbiota and Promotes Intestinal Regeneration to Reduce Inflammatory Bowel Disease Pathology
• Fasting-Mimicking Diets Reverse Accelerated Biological Aging in Multiple Sclerosis
• Fasting Mimicking Diet and CLL
• Fasting Mimicking Diet and Aging
• Fasting Mimicking Diet and Weight Loss
• Fasting Mimicking Diet and Metabolism
• Fasting Mimicking Bar Extends Ketosis
• Fasting Enhances the Response of Glioma to Chemo- and Radiotherapy
• FMD Decreases the Inflammatory Response in Autoimmune Disease
• FMD Improves Response to Breast Cancer Chemotherapy
• Impact of Fasting Mimicking Diet on Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Control Trials
• Integration of a Fasting-Mimicking Diet Programme in Primary Care for Type 2 Diabetes Reduces the Need for Medication and Improves Glycaemic Control: A 12-Month Randomised Controlled Trial
• Neuroprotection of Fasting Mimicking Diet on MPTP-Induced Parkinson’s Disease Mice via Gut Microbiota and Metabolites