The idea of a 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 a fast mimicking diet 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 fast mimicking 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, but cannot due to financial constraints (note – you can get a big discount using this ProLon coupon code)

In Valter’s book The Longevity Diet, he appears to recognise that some people will still end up doing a DIY fast mimicking diet, despite the warnings and concern. Thus he dedicates a chapter to explaining the details of what a DIY fast mimicking 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 himself started, and hopefully fills in some blanks.

The ProLon Box

Personally I’ve done both – the ProLon box and a DIY fast mimicking diet. Drawing on both experiences, I was pleasantly surprised at how well thought out ProLon is, and I would absolutely recommend it for people starting off. Key reasons being:

  • 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.
  • It gives you a solid idea of what to expect if you later want to create your own.

DIY Fast Mimicking Diet

However, (as discussed above) there are multiple reasons why one might opt for a do-it-yourself fast mimicking 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 2-5

800 calories total

  • 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

Meals on days 1 to 5 can be taken as a breakfast, lunch and dinner, or, taken as 2 meals + a snack.

Day 6 – Transition Diet

For 24 hours following the end of the five-day fast mimicking diet, 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 eating after the fast can lead 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 fast mimicking diet – which I’ve laid out below, in the faith that Valter would want these safety aspects communicated unedited.

Who may do the Fast Mimicking Diet?

Healthy adults in the normal weight range between the ages of eighteen and seventy years may undertake the fast mimicking diet. 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 Fast Mimicking Diet?

  • 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 fast mimicking diet or in therapeutic fasting. The use of the fast mimicking diet 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 fast mimicking diet without the approval of their doctor with input from a dietitian or doctor who specializes in the use of the fast mimicking diet. Although it may be possible to combine the fast mimicking diet with many drugs without side effects, the combination of the fast mimicking diet 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 fast mimicking diet 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 fast mimicking diet, leading to a risk of fainting.

Other Warnings

  • The fast mimicking diet can never be undertaken in association with insulin or medication that reduces sugar levels. The combination could be lethal. At the end of the fast mimicking diet, 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 fast mimicking diet on diabetic patients could be dangerous, it's advised to only do it as part of a clinical trial.
  • Do not combine the fast mimicking diet 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 fast mimicking diet affects you.
  • It's advised to undergo the fast mimicking diet in the presence of another person.

How often to do the Fast Mimicking Diet?

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

  • 1x 6 months = For healthy patients with ideal diet who engage in regular physical activity
  • 1x every 4 months = For healthy patients with a normal diet who are not physically active
  • 1x every 3 months = For average-weight patients with at least one risk factor*
  • 1x every 2 months = For average-weight patients with at least two risk factors*
  • 1x month = For overweight or obese patients with at least two risk factors*

*Risk factors are in respect to diabetes, cancer, cardiovascular or neurodegenerative disease. Examples of risk factors include pre-existing illness, blood biomarkers, family history and genetic mutations.

What day is best to start the Fast Mimicking Diet?

Many people decide to start the fast mimicking diet on a Sunday night so they can engage normally in social eating the following weekend. Note that when you finish on the Friday night (last ProLon meal), you don’t resume your normal diet until you wake up on Saturday.

Prior Preparation

For at least one week before the fast mimicking diet, 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 fast mimicking diet. Others say they feel more energetic
  • Some patients complain of light headaches. This effect is usually greatly reduced by day 4 or 5, and eliminated entirely by the second or third fast mimicking diet cycle.
  • Most people feel hungry during the first few days of the fast mimicking diet. This effect is greatly reduced by day 4 or 5 and on all days during the second or third 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 the fast mimicking diet:

  • 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:

Glycerine Calculator

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 * 1.111)/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 / 8)
Where x = your weight
So for example, 440lbs / 8 = 55 grams

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 familiar with seeing glycerine available in supermarkets, typically in the baking aisle. It’s also available cheaply on Amazon, for example as 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

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 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 takeaway 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 fast mimicking diet, then it absolutely needs to be 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 effects to the NR-3 supplement, it’s likely easiest to use a well formulated multi-vitamin. Examples include 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, as this could increase IGF-1 & mTor, which the diet specifically works to reduce. That being said, it would be very uncommon for off the shelf multivitamin supplements to contain amino acids (certainly the above 2 examples do not). But definitely avoid amino acid supplements (such as BCAAs), unless you decided to go the route of individual amino acid 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 fast mimicking diet:

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

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2 years ago

Thanks for the article. However, the glycerine calculator does not work, neither in Firefox, nor in other browsers. Also, in the calculation it’s said that we should multiply the weight in kilograms with 0.9, however, in the example it is multiplied with 1.111. Perhaps, I am missing something…

Koffee Kloud
Koffee Kloud
1 year ago

Regarding the safety of “Vegetable Glycerine”: does this align with the recent research regarding emulsifier-induced metabolic syndrome?

1 year ago

Thank you so so much for your post. It has been helpful to do a DIY version. I’m on round 4 at the moment. I’m not sure my DIY version is good enough though. I’m using documents provided by GenX life is Good.
Using the glycerine makes a huge difference. I forgot to take it one day and I felt so weak.

Lisa Andiarena
Lisa Andiarena
1 year ago

I normally take Maca, Blackroot cohosh, Evening primrose, and other vitamins. Can I cont to take them during FMD?

1 year ago

Thanks so much for this very helpful article!
One question in the glycerol; the brand I bought contained 15% water. Should I therefore divide the calculated glycerol weight with 0,85? I.e is the calculation based on 100% glycerol? It seemed that the volume of glycerol was less than when I used the Prolon box so I’m guessing this could be the case but wanted to make sure. Felt a bit weaker and a bit more hungry than the last time when I used the box so perhaps this is one of the reasons for it.
Thanks again for a very helpful article!

Trish Gaffney
Trish Gaffney
1 year ago

Hi John, I cannot thank you enough for this article and the breakdown in specifics of the supplements/glycerol. There is nothing like it out there for public use, and I have searched, believe me! This is my 3rd round of a DIY FMD, and at this point I think I have it down to as close as possible to the Prolon. I was missing the glycerine and multivitamin amounts, and I assume that every quantity matters, given what Valter has said about what is ADDED to the macros given, such as glycerin, in the overall effectiveness.

Oh, the calculator is not working again… I appreciate the formula as a back-up.. you’ve just about thought of everything!

1 year ago

thank you so much for your great blog!
Great help!
Only one thing – I can’t find day 2-5 informations – do I oversee something?
You give details for day one, and then about day 6….

El Pi
El Pi
1 year ago

Thank you for a very helpful and well explained article!

10 months ago

Anyone out there experiencing anxiety with the L-Drink? The first three times I didn’t have any problems, but this time I do.

Reply to  John Alexander
10 months ago

I connected the anxiety to the Potassium Sorbate (a preservative). A friend experienced the same symptoms when she drank the L-Drink the week before. (I avoid preservatives so my body is sensitive to them).

10 months ago

My box had the NR-1 supplement, not NR-3. And only taken with lunch, not 2x/day. Also noticed it doesn’t have methionine & cysteine.

Also curious how much of each of these amino acids you take daily.

David Sprouse
David Sprouse
9 months ago

So for the calculator (unless I’m missing something), it’s just body weight in pounds divided by 8. No need to “multiply by 0.5 and then divide by 4”. Just divide by 8, same thing and just one step.