The “Fast Mimicking Diet”, developed by Valter Longo and his colleagues, has been clinically proven to provide many of the same benefits of a water fast, without requiring participants to abstain from food entirely. The diet has been clinically tested and commercialised by a company called L-Nutra, with the goal to take this from a fringe idea, to something that can be used in many different clinical settings.

Their product is called “Prolon”, and for safety and efficacy reasons they strongly recommend not to make a “homemade” version of this diet, which could be ineffective and potentially harmful.

I 100% agree with their cautionary stance, because there are many situations in which an FMD could be dangerous – and below we’ll discuss these situations more.

I would re-iterate L-Nutra’s warning by requesting readers exercise extreme caution around a DIY FMD diet, and if they are going to do it, they read this article completely (or Chapter 6 of Valter’s book The Longevity Diet), and ensure they fully understand the risks. Including whether or not they’re in an “at risk” category (such as those with diabetes or those taking blood pressure medications).

That being said, there are a number of reasons that someone may wish to create their own version, including:

  • You live in a geographic location that Prolon does not ship to. Which is a large chunk of the world.
  • You’ve done the Prolon diet once or twice previously, and for your next one, would like to customize the foods you consume. Perhaps moving towards fresh, home-made ingredients, rather than long life packets.
  • You do not like, or your body does not agree with certain ingredients of the Prolon diet.
  • You would like to use Prolon on a regular basis, but cannot because of financial constraints.

In Valter’s book The Longevity Diet, he appears to recognise that some people will still end up doing a DIY FMD diet, despite the warnings and concern. Thus he dedicates a chapter to explaining the details of what a DIY FMD diet would look like, and who would be at risk, and what some of the risks are (discussed below).

In that vein, this post is a continuation of that discussion Valter started, and hopefully fills in some blanks.

The Prolon Box

Personally I’ve done both – the Prolon box and a DIY FMD. Drawing on both experiences, I was pleasantly surprised at how well thought out Prolon is, and I would recommend it for people’s first time. Key reasons being:

  • It gives you a solid idea of what to expect if you later want to create your own.
  • The exact calorie and macro compositions are laid out for you, thus if you only eat what’s provided, you will 100% stay on target to reap the health benefits. Minimizing temptations to “eat a bit much” of something.
  • There’s no time/energy spent preparing foods, and all ingredients can be easily thrown in your bag for the days activities. Bare in mind for the soups that you will need access to a hot water source (worst case you could pack Thermos).
  • Given the extremely low calorie content (compared to what we’re used to), the foods are actually tasty, and relatively filling.

Prolon can be purchased in the USA from for $249 (For $25 off, use this coupon code), and in UK from for £225.

DIY Fast Mimicking Diet

However, (as discussed above) there are multiple reasons why one might opt for a do-it-yourself FMD diet. Thus you’ll need to know the macronutrient and caloric restrictions in order to emulate it.

The “original” 2015 Cell Metabolism paper that described the diet quoted the composition as:

Day 11,090 calories10%56%34%
Day 2-5725 calories9%44%47%

To quote the specific section in the paper:
“The human fasting mimicking diet (FMD) program is a plant-based diet program designed to attain fasting-like effects while providing micronutrient nourishment (vitamins, minerals, etc.) and minimize the burden of fasting. It comprises proprietary vegetable-based soups, energy bars, energy drinks, chip snacks, chamomile flower tea, and a vegetable supplement formula tablet. The human FMD diet consists of a 5 day regimen: day 1 of the diet supplies $1,090 kcal (10% protein, 56% fat, 34% carbohydrate), days 2–5 are identical in formulation and provide 725 kcal (9% protein, 44% fat, 47% carbohydrate).

Then in Valter’s book ‘The Longevity Diet’, he goes into more detail for how to perform a fast mimicking diet:

Day 1

1,100 calories total

Which includes:

  • 500 calories from complex carbohydrates (vegetables such as broccoli, tomatoes, carrots, pumpkin, mushrooms, etc.)
  • 500 calories from healthy fats (nuts, olive oil)
  • 1 multivitamin and mineral supplement
  • 1 omega-3/omega-6 supplement
  • Sugarless tea (up to 3 to 4 cups per day)
  • 25 grams total of plant-based protein, mainly from nuts (this is included within the 1,100 calorie total, rather than in addition)
  • Unlimited water

N.B. The total calorie limit is 1,100 – with 500 coming from complex carbs, and 500 from healthy fats. That leaves 100 calories that could come from things like fruit or legumes. You have more freedom with that last 100 calories!

Days 2 to 5

800 calories total

Which includes:

  • 400 calories from complex carbohydrates (vegetables such as broccoli, tomatoes, carrots, pumpkin, mushrooms, etc.)
  • 400 calories from healthy fats (nuts, olive oil)
  • 1 multivitamin and mineral supplement
  • 1 omega-3/omega-6 supplement
  • Sugarless tea (up to 3 to 4 cups per day)
  • Unlimited water
  • The above components can be divided between breakfast, lunch, and dinner, or they can be taken as two meals and a snack.

Day 6 – Transition Diet

For 24 hours following the end of the five-day FMD, patients should follow a diet based on:

  • Complex carbohydrates (vegetables, cereals, pasta, rice, bread, fruit, etc.)

Minimizing consumption of:

  • Fish, meat, saturated fats, pastries, cheeses, milk, etc.

This is to give the stomach a chance to adjust again to eating normally.

*From personal experience I can say that over eat after the fast can leak to stomach distress (!). You want to avoid overburdening the stomach for the next 2 days (6 & 7) following the fast – easier said than done when you’ve been starving!

As you can see from Valter’s description of the diet, he has simplified it a bit from the highly prescriptive 2015 Cell Metabolism paper. However, it retains the same basic key hallmarks. 100% plant based, and 1100 calories day 1, and 800 calories on days 2-5 (slightly up from the 725 calories in the study).

Valter also goes on to give specific guidelines around safety for the FMD – which I’ve laid out below, in the faith that Valter would want these safety aspects communicated unedited.

Who may do the FMD?

Healthy adults in the normal weight range between the ages of eighteen and seventy years may undertake the FMD. A few genetic mutations, however, are incompatible with long-term fasting. If any side effects occur other than slight weakness, tiredness, or a headache, you should contact your doctor. Drink a small quantity of fruit juice for immediate relief.

Who may NOT do the FMD?

  • Pregnant women.
  • People who are underweight, have very low body mass index, or suffer from anorexia.
  • People over the age of seventy, unless in superior health—and then only with a doctor’s approval.
  • Anyone who is fragile.
  • People with liver or kidney diseases.
  • People affected by pathologies, unless they have the prior approval of their specialized doctor. In the case of serious or relatively serious illnesses (cancer, diabetes, or cardiovascular, autoimmune, or neurodegenerative diseases), it is important to seek permission and approval from a disease specialist as well as from a dietitian with expertise in the FMD or in therapeutic fasting. The use of the FMD for disease treatment should for the moment be limited to clinical trials unless the doctor determines that there are no other viable options and the patient cannot wait until the conclusion of appropriate clinical trials and FDA approval.
  • Patients who take medication should not undertake the FMD without the approval of their doctor with input from a dietitian or doctor who specializes in the use of the FMD. Although it may be possible to combine the FMD with many drugs without side effects, the combination of the FMD and certain drugs could result in severe side effects.
  • Patients who have low blood pressure or who are taking medication for hypertension should not undertake the FMD without the approval of a specialized doctor.
  • Patients with rare genetic mutations that block the organism’s capacity to produce glucose from glycerol and amino acids (gluconeogenesis).
  • Athletes during training or competition. High muscular effort requires levels of glucose not available in the blood during the FMD, leading to a risk of fainting.

Other Warnings

  • The FMD can never be undertaken in association with insulin or medication that reduces sugar levels. The combination could be lethal. At the end of the FMD, the patient may still be sufficiently insulin-sensitive to have below normal levels of glucose in his or her blood. Because the use of the FMD on diabetic patients could be dangerous, we advise to do it only as part of a clinical trial.
  • Do not combine the FMD with very hot and lengthy showers, especially during hot weather. There could be a risk of fainting.
  • Drive with caution—or better yet, don’t drive at all—until you know how the FMD affects you.
  • It’s advised to undergo the FMD in the presence of another person.

How often to do the FMD?

This is a decision that ideally should be made with input from a doctor or registered dietitian, but broad guidelines are as follows:

  • Once a month for overweight or obese patients with at least two risk factors for diabetes, cancer, or cardiovascular or neurodegenerative disease
  • Once every two months for average-weight patients with at least two risk factors for diabetes, cancer, or cardiovascular or neurodegenerative disease
  • Once every three months for average-weight patients with at least one risk factor for diabetes, cancer, or cardiovascular or neurodegenerative disease
  • Once every four months for healthy patients with a normal diet who are not physically active
  • Once every six months for healthy patients with an ideal diet who engage in regular physical activity

What day is best to start the FMD?

Many people decide to start FMD on a Sunday night so they can end the following Friday night. This decision is based purely on social considerations, allowing them to return to the transition diet on Friday night and to a normal diet on Saturday night.

Prior Preparation

For at least one week before the FMD, Valter recommends following the Longevity Diet, with 0.36 grams of protein per pound of body weight per day, preferably obtained from vegetables and fish. Multivitamin supplements of omega-3 should be taken at least twice during this preparatory week.

Side Effects

  • Some people feel weak during parts of the FMD. Others say they feel more energetic
  • Some patients complain of light- or average-intensity headaches. This effect is usually greatly reduced by day 4 or 5, and eliminated entirely by the second or third FMD cycle.
  • Most people feel hungry during the first few days of the FMD. This effect is greatly reduced by day 4 or 5 and on all days during the second or third FMD cycle.

Positive Effects

In addition to the production of stem cells, the reduction of abdominal fat, and lower levels of risk factors for various illnesses, many people report the following beneficial effects during or after FMD:

  • Glowing skin, which many describe as “younger looking.”
  • Stronger mental focus.
  • An ability to resist bingeing once they resume a normal diet. Many reduce their consumption of sugar and calories, and are less prone to excess in their consumption of coffee, alcohol, desserts, etc.


The fast mimicking diet is low in a number of things, including total calories and protein. Valter notes in the below video that it’s not just what the diet lacks, it’s also about what the diet contains, that gives it the positive results.

The Prolon box contains a 118ml (4 fl oz) bottle of liquid, called L-Drink, for each of days 2 to 5. Based on your bodyweight, you decant a specified amount of the L-Drink into a water bottle, and dilute the rest with tap water. Then you aim to drink the whole thing throughout the day.

L-Drink Function

Valter describes the function of the L-Drink as being to provide an external source of glycerol. People who are in a fasted state naturally produce glycerol, and this is used for gluconeogenesis (the production of glucose (energy) from non-carbohydrate substrates like fat and muscle). Valter notes in the video below that after 3 Prolon cycles, when measured, people are found to have lost minimal amounts of muscle – and one of the reasons could be due to the L-Drink.

See the video below for more on Valter Longo discussing the role of glycerol:

L-Drink Ingredients & Functions

  • Purified water: Unlikely to form any function, other than as a base to mix the rest of the ingredients into, and then bulk them up for measuring out quantities
  • Vegetable glycerine: As mentioned above, this provides the body with an external source of glycerol to aid in gluconeogenesis
  • Natural flavor: To make more interesting to drink, and perhaps mask any uncomfortable taste from the glycerine
  • Potassium sorbate: Whilst potassium is an electrolyte, it doesn’t seem common to choose it in sorbate form for electrolyte purposes. Therefore it’s most likely that potassium sorbate is included for preservative reasons – to extend the shelf life of L-Drink

How Much Vegetable Glycerine to Use

I haven’t been able to find the exact measurements of glycerol used in the L-Drink. Instead what we can do is to calculate, based on the L-Drink’s nutritional information, approximately how much glycerol we should take. I’ve turned this calculation into a calculator, which you can use below:

Below are the calculations I've used for glycerine quantities:
According to the L-Drink label it's formulated to provide 50Kcal per 45kg/100lbs of bodyweight, with (presumably) almost all the calories in the drink coming via the glycerine. According to myfitnesspal, 1gram of glycerine = 4 Kcal. So we can calculate that it's about 12.5 grams of glycerine per 45kg/100lbs of bodyweight.

To figure out how much glycerine you'd need per day, to emulate the L-Drink, the formulas for kg & lbs are below:

Measuring your weight in Kilograms
You want to do (x Kg * 0.9)/4
Where x = your weight
So for example, 200Kg * 1.111 = 222.2, 222.2/4 = 55.55 grams

Measuring your weight in lbs
You'd want to do (x lbs * 0.5)/4
Where x = your weight
So for example, 440lbs * 0.5 = 220, 220/4 = 55grams

Once you have calculated how much vegetable glycerine you would need per day, you can then:

  • Measure this out each day on days 2, 3, 4 & 5
  • Add it to a water flask, and shake to mix. If it’s not mixing due to the water being cold, using warmer water may help with initial mix
  • Optionally add a calorie free flavouring. The L-Drink does this to improve palatability

Is Vegetable Glycerine Safe?

Vegetable glycerine is commonly used in food & cosmetics. For example in food, it’s used to prevent icing setting too firm, and for making ice cream softer to scoop.

In a 2012 study into the effectiveness of glycerol for sports performance, they used a dose of 1.2 grams per kilogram of bodyweight for each study participant, with no noted adverse health effects1. 1.2g/kg is a much higher dose than is used in Prolon, which is around 0.3g/kg. Just to re-iterate, glycerine/glycerol are the same thing, however commercially it’s often referred to as glycerine, and inside the body as glycerol.

Where can I buy vegetable glycerine?

Many will be familar with seeing glycerine available in supermarkets, typically in the baking aisle. It’s also available cheaply on Amazon – NOW Vegetable Glycerine.

NR-3 Vitamin Supplement

In addition to the food contained in the Prolon box, there is also a multivitamin called NR-3. This is taken twice daily, at lunch & dinner. The majority of the ingredients for this supplement are vitamins. However it also contains:

  • Two amino acids; Methionine & Cysteine
  • Methylsulfonylmethane (MSM)
  • The minerals Zinc, Selenium & Copper

Nutritional Information – per 1 capsule (serving size 2 capsules)

per 1 capsule % NRV Type?
L cysteine 79.8mg Amino Acid
Zinc gluconate 5.5mg 55% Mineral
Methionine 19.8mg Amino Acid
Vitamin C 19.8mg 25% Vitamin
Selenium-enriched Yeast 28mcg 51% Mineral
Vitamin E 3.3mg 27% Vitamin
Methylsulfonylmethane (MSM) 6mg
Vitamin PP (B3/Niacin) 6mg 37% Vitamin
Vitamin B12 0.6mcg 24% Vitamin
Vitamin B2 0.5mcg 24% Vitamin
Vitamin B1 0.46mg 42% Vitamin
Beta-carotene Vitamin A 10% 0.2mg 25% Vitamin
Folic Acid 67mcg 33% Vitamin
Vitamin H (Biotin) 0.05mg Vitamin
Copper gluconate 0.6mg 60% Mineral
Vitamin B5 2mg 33% Vitamin
Vitamin B6 0.7mg 50% Vitamin

And a picture of the actual ingredients list:

What can we learn from NR-3?

In the above list, the bulk of the ingredients are vitamins (11), which are all essential to regular cellular processes. Then there are two amino acids; methionine & cysteine.

(As a reminder, amino acids make up what we call “protein”, and there are 9 essential amino acids (of which methionine is one), which are the building blocks for the human body)

It’s interesting to note the ratio of methionine to cysteine, which is approx: 1:4. Apparently it’s possible to reduce the body’s need for methionine, by adding more cysteine2, thus I’d hypothesize that is the strategy here – provide a minimum level of methionine, through the addition of cysteine. It could be that too much methionine triggers cellular functions that detract from the fasting process, but adding cysteine does not cause the same trigger. The benefit of this could be to help keep IGF-1 & mTor activation low.

Methionine is generally found in plentiful quantities in animal products, thus given Prolon is formulated of vegan ingredients, this may be a reason to supplement some additional methionine. Note, they also add vitamin B12 which is a common deficit in vegan diets.

One thing they add is MSM, for which I don’t have any hypotheses for its inclusion – but I would note that the amount is very low. Most off the shelf supplements are in the range of 100mg+ whereas NR-3 contains 6mg per capsule.

Probably my biggest takeway from the analysis of NR-3 is the deliberate intention to keep methionine levels adequate, but low. This suggests to me, that if one tries to formulate a DIY FMD, then it’s best done using vegan ingredients (to keep as true to the original formulation as possible). It’s possible that if we formulate using animal ingredients (even whilst sticking to the same macros), we end up over-doing it with regards to certain amino acids.

NR-3 Alternative?

In order to achieve similar affects to the NR-3 supplement, it’s likely easiest to use a well formulated multi-vitamin such as Thorne’s 2 / Day or Pure Encapsulations – ONE – which don’t contain anything extra beyond vitamins and minerals. That being said, most multivitamins contain much greater levels of vitamins and minerals than NR-3 – and it’s not clear if that would interact negatively with the fasting process.

What we can be sure of, is that adding a greater level of either of the amino acids found in NR-3; methionine & cysteine – would be counter-productive. This could increase IGF-1 & mTor, which the diet specifically works to reduce. Therefore I would avoid any amino acid supplements, unless you decided to go the route of powders, in which case you could measure out the exact quantity that NR-3 uses.

Further Info

Additionally I’ve mentioned both of these links above already, but will mention them again in case they help you formulate your FMD diet:

  • The first is a set of tables that provide the blow by blow macros and calories for each day of the official FMD diet.
  • The second is details of the individual products in the FMD diet, with their respective nutritional information.

If you’d like to try out the Prolon FMD, use this coupon code for $25 off.

See Post Sources Below:

  1. The Effect of Glycerol Supplements on Aerobic and Anaerobic Performance of Athletes and Sedentary Subjects – J Hum Kinet (2012)
  2. Minimum methionine requirement and cysteine sparing of methionine in healthy school-age children – Humayun MA (2006)

Posted by Alex


  1. I attempted a DIY version of this last Fall. I was looking for relief from mild IBS symptoms. Other than my stomach woes I’m a healthy,fit woman in my 30s with normal markers for everything. I’m not on any medications and I’ve never been diagnosed with any disorders. I decided to try to DIY this because of financial constraints.

    From the first day of the diet I developed a severe headache that did not subside. Day 1 &2 otherwise seemed fine. Day 3 sometime after I had eaten the allotted “breakfast” I started to feel dizzy. I got really muddle headed confused/dizzy and sat down on the floor of my kitchen. I had to have my son mix me sugar water (we didn’t have juice). I intuitively felt I had to have sugar. I felt like I was going to die if I didn’t have some. After I felt my blood sugar recovering I had a severe attack of, let’s say, “stomach distress” where I must have been compelled to use the bathroom 10 times in the next 2 hours.

    I stopped the diet and felt perfectly normal the next day.

    I’m not really sure why my body reacted this way. I wasn’t drinking a glycerol solution as it was the only thing I couldn’t source. Maybe that was it? I thought I’d just put it out there to add a cautionary tale. This diet can indeed be risky. Not that I wouldn’t try it, but be mindful of your blood sugar dropping too low.


    1. Alex

      Hi Cirelo. Thanks for sharing this experience – I think it’s important for others to read. A 5-day fast mimicking diet is a strong dietary intervention, and should be treated with caution.

      I have a few thoughts based on what you’ve said, but first would want to ask what your experience is with fasting prior to this?


      1. Thanks for responding, I hadn’t ever tried an extended fast. I have done 1 day fasts a few times a year for religious reasons for about the last 15 years.


  2. Hi Alex, another comment from me. Could you please write about the refeeding part? Prof Longo says most of us seems to know what to eat. Like to have your thoughts on how you go about T+1 day FMD and how many days you consciously re-feed?
    For me, I take about 1 week to re-feed mindfully…no smoking, junk food etc, and take mostly high quality protein, vegetables, good fats and good carbs.


    1. Alex

      Hi Jason. Thanks for this message. That’s a great point about refeeding, I’ve messed up that part myself a couple times (typically by either eating too much in one go, or eating too many carbs and having a huge crash). I’ll make a note to revisit this post and go into more details on refeeding – at least a few guidelines on what NOT to do, hehe.


  3. I am a female five feet one inch who weighs 220 and has thyroid condition. I want to know if I can fast for two weeks.


    1. Alex

      Hi D Yueng. With regards to your thyroid condition and fasting, that is a question best left to your doctor. Especially if you’re looking to do an extended fast in the region of 2 weeks. I could imagine a number of possible complications when combining thyroid issues (and its medication) with long periods of not eating. So yes, as I mentioned, do seek specialized medical advice for this question.

      For anyone relatively new to fasting, I would suggest taking it in stages. Start off with a 2-3 day fast, perhaps repeat that a couple of times, then move to 5 days, and so-forth. Firstly, like anything that is practiced, it does get easier over time. And secondly, this gives you adequate experience to learn how to manage your time, energy and wellbeing as you go deeper into the fasting territory.

      Jumping straight to a 7 or 14 day fast could come with unnecessary risks.


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