Valter Longo’s Fast Mimicking Diet has been clinically proven to provide many of the same benefits of a water fast, without requiring participants to abstain from food entirely. In the post below we look at the details of the diet, including the macronutrient composition, vitamin contents etc.

Prolon – Fast Mimicking Diet (DIY)

The Prolon fast mimicking diet is designed so you get the benefits of a 5 day water fast, whilst still being able to eat something each day. Valter and his colleagues at USC (University of Southern California) have patented and designed an out of the box 5 day ‘fast mimicking diet’ (FMD) called Prolon. This can be purchased in the USA from for $249 (use coupon code TAKE25 for $25 off), and in UK from for £225. For many people, the easiest way to do the fast will be to simply purchase it and follow the instructions. See below for information on a DIY version.

DIY Fast Mimicking Diet

I think overall, buying and using the Prolon FMD diet is a great idea, for the following reasons:

  • The exact calorie and macro compositions are laid out for you, and you know that by only eating what they provide, you will 100% stay on target. 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.
  • The contents have been carefully constructed to support your micronutrient needs (for example it includes multivitamins, fortified potassium drink and omega-3 DHA oil).

However, I can think of at least 3 possible reasons why you might opt for a do-it-yourself FMD diet:

  • You live in a geographic location that Prolon do not (yet) ship to.
  • You would like to customize the foods you consume, and eat fresh, home made ingredients or custom ingredients
  • You are financially constrained, and can’t justify $249 on 5 days of food. Totally understandable – $249 buys a lot of groceries!

In those cases it’s definitely possible to create a DIY FMD diet. In order to replicate the same diet and results, you will want to start by knowing the exact calorie and macronutrient composition of the diet.

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).

Since that paper was written, Valter and his team created the “off the shelf” FMD diet box called Prolon (discussed above).

Beyond calories and macros, the Prolon FMD box adds:

  • Days 2 to 5 adds a daily “energy drink” (they call it L-Drink), which contains vegetable glycerine, potassium sorbate & flavouring. Each L-Drink bottle contains 118ml, but you don’t need it all. Instead, you use the measurement guidelines on the side, to measure out the correct quantity based on your weight, add it to the provided plastic water bottle, which then gets topped up with water, to be drunk by the end of the day.
  • Days 1 to 5 add a multivitamin daily
  • Days 1 & 5 add 200mg DHA oil each day


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). If there isn’t enough glycerol, the body can end up breaking down muscle. Valter notes 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, you can use the coupon code TAKE25 to get $25 off your order.

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. 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.


  2. 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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