What is the Fasting Mimicking Diet?
The Fasting Mimicking Diet (FMD) is a 5 day diet plan designed by longevity researchers and tested on yeast, mice and humans with encouraging results. Positive impacts of the diet include multi-body system regeneration, enhanced cognitive performance and healthspan. It is expected that the biomarkers that the FMD impacts upon can lead to reduced risk for diabetes, coronary heart disease and some cancers.
Full fasting or long term calorie restriction could also produce similar benefits but both are highly challenging and intolerable for most people and come with their own significant risks and downsides. By contrast the unique feature of the Fasting Mimicking Diet is the mimicking part. It is designed to deliver benefits similar to those achieved by fasting but also be far more tolerable and avoid the risks and issues presented by fasting.
The 5 day Fasting Mimicking Diet itself is a nutrient dense, calorie restricted protocol with very low protein and low carbohydrate content. The 5 day diet is intended for repetition between 2-12 times per year to fully enjoy the healthspan benefits. This means on the most frequent regimen the FMD would be followed for 5 days followed by 25 days of normal eating. Less frequent repetitions, such as 3-4 times per year, may be sufficient to enjoy many of the benefits.
Since it involves a caloric deficit the FMD does produce weight loss and this appears to be accompanied by decreases in abdominal fat and even increases in lean body mass. However this is only one of the outcomes of the diet, and it is not designed or intended to be used for weight loss alone.
Fasting Mimicking Diet Research
As of April 2017 outcomes from the first human intervention trial have been published and a larger trial is underway which will attempt to compare the FMD against other protocols which also produce weight loss to determine whether the FMD offers incremental benefits compared to weight loss achieved via any means.
The outcomes of the first small scale human trials of FMD are reported as including –
- Reduction in blood glucose and large increase in ketones
- 25%+ reduction in circulating Insulin Growth Factor-1 (IGF-1)
- Reduction in C-Reactive Protein (CRP)
- Positive changes in cholesterol and triglyceride levels
- Reduction in body weight
Fasting Mimicking Diet Do It Yourself Guide
The lead researcher for the FMD, Valter Longo advises “not to do FMD at home” and I repeat that warning here. Don’t do this if you have any health issues. If in any doubt do consult with a trusted medical practitioner. That said, this guide will provide you with everything that *I* did to prepare for my first FMD cycle and what I learned from my first cycle.
There is a commercial product named ‘ProLon’ available already in US, UK, Australia and an expanding list of other Countries. ProLon is a package of soups, snack bars, crackers and drinks that can be consumed over 5 days in order to follow the FMD as designed by the researchers. I do not believe that use of ProLon is necessary to perform FMD safely and effectively however as ultimately, it consists of fairly conventional food, supplements and tea.
I used a ‘Do it Yourself’ approach rather than wait for the commercial ProLon product and believe on the basis of my experience and that of others that this is entirely feasible.
Why follow the Fasting Mimicking Diet?
Here I explain my very *personal* reasons. There are certainly others. I love life and wish to live as healthily as possible for as long as possible. I think of this as ‘healthspan’ rather than ‘lifespan’.
I am aware of the correlation between age and disease risk. I cannot control everything but I can take some certain actions to mitigate these the risks where possible. I am therefore very interested in anything I can do to reduce the risk of neurodegenerative disease (such as alzheimer’s) metabolic syndrome leading to diabetes, and coronary heart disease, and cancers.
My starting points are –
- I don’t smoke or drink alcohol, ever (I simply do not enjoy alcohol)
- I exercise frequently both aerobic and anaerobic
- I maintain a weight at the lower end of the normal BMI range and a bodyfat around 13-14%
- I have excellent sleep hygiene and practice meditation for relaxation
- I follow a whole foods and plant based diet with minimal processed foods and added sugars
- I enjoy the company of friends regularly and am happy with my social life
With all these in place, the basics are covered. For me to further improve my current and long-term health requires something special. I already also practice intermittent fasting / time restricted feeding. I am aware of the potential benefits of calorie restriction but am unwilling to pursue it partly because of the certain downsides and risks but also because food is a major source of pleasure I am unwilling to reduce.
Enter the Fasting Mimicking Diet. This is the first intervention I have discovered that appears to offer genuine promise. It’s key and differentiating characteristics are –
- It is designed to provide benefits to people that are *already* generally healthy
- There is intervention study evidence for those benefits, mainly in rodents but also in humans
- The benefits can be obtained by short 5 day periods of dietary intervention
- It is possible to verify positive outcomes via (mostly) consumer available tests and tools
Fasting Mimicking Diet Goals
I was keen to experiment with the FMD as a pure quantified self practice and challenge. However before beginning I also set out the specific outcomes on which I would base a decision to repeat the FMD or not in future. Note that I picked these in advance by reference to both what the FMD is designed to deliver and what is of value to me personally. My top 5 hoped-for outcomes were –
- A significant (25%+) reduction in IGF-1
- A significant reduction in C-Reactive Protein
- 72 hours+ within optimal ketosis (ketones of 1.5+ mmol/L)
- Reduction in bodyfat by 0.5%+ sustained for at least 1 week following FMD i.e. no immediate bounce-back
- Absence of significant increases in measures of stress, cortisol, heart rate variability or sleep quality
Overall I was mainly interested in the longevity related outcomes whilst a friend I partnered with to practice FMD, David, was more interested in weight loss and bodyfat.
5 Steps to Prepare for FMD
There are five key steps to preparation. I offer direct advice based on my own preparation and first FMD cycle. I also offer a publicly shared Google Sheets FMD Do-It-Yourself file which features templates for preparation, planning and tracking. The file will open into View Only access. Make a copy of it within Google Drive to edit it as you wish.
1. Establish an outcomes measurement plan
Here are the key things you need to decide:
- Which of the potential FMD outcomes interest you, these are the ones you should measure
- The tools and tests you will you use to measure your selected biomarkers
- When you will begin and end measurement and the frequency and timing
- For self-administered measurement how you will maximise consistency, for example, by always taking blood glucose immediate after waking, prior to breaking fast
- For lab tests, when you will visit a lab or complete a home-use kit
The biomarkers I selected along with the measurement test or tool and frequency are all described in the ‘Metrics Protocol’ sheet within the Google Sheets FMD Do-It-Yourself file and in the picture below.
2. Source the measurement tools and tests
If you are UK based the tools and tests shown in the Metrics Protocol sheet of the Google Sheets FMD Do-It-Yourself file could be repeated in full. If you are based outside of the UK you will need to search for locally available lab tests.
It is *critical* to use the same tool at the same time and state in order to gain consistent data. I would favour consistency over accuracy given the choice so that the *change* can be observed. This is the reason I used home body composition scales rather than a more accurate BodPod or DEXA scan. My Taotronic scales are low cost and uncomplicated but also terrifically consistent.
Taking blood glucose and ketone samples using finger-prick tests is very quick and simple. I recommend combining a little practice at the same time as establishing your pre-FMD norms.
Taking Heart Rate Variability (HRV) is also very straightforward. Understanding it takes more time and connecting the readings to how you feel and what has impacted on that longer still. The more you practice, the more you will understand the context for your results and be confident that changes during FMD are *caused* by the FMD.
3. Plan ALL the food to be eaten on the diet
I emphasise the need to plan *all* the food you will eat during the Fasting Mimicking Diet. FMD is really not something you can carry out ad hoc as most readily available convenience and restaurant foods would not be suitable. Here the mantra “if you fail to plan you plan to fail applies”. You should have your food planned out for all 5 days and also make sure you have it in stock or know for certain where and when you will be buying it during the FMD period. This avoids the risk that you find yourself outside of the protocol and deny yourself the potential benefits.
There are two options here. You could copy the ProLon commercial FMD package, if you do this, the calorie and macro counts are as follows.
Alternately, you could follow the calorie and macro counts featured within a Fasting Mimicking Diet Patent. In contrast to ProLon the calorie count varies according to bodyweight. I think this is *probably* a superior approach. The ‘one size fits all’ approach used by ProLon is probably a compromise to provide a simple, standard consumer product. The bodyweight based variation works like this –
Day 1: 10 to 16 calories per kg bodyweight, 10% protein, 56% fat, 34% carbs
Days 2 – 5: 7 to 11 calories per kg bodyweight, 9% protein, 44% fat, 47% carbs
I consider the fat % as the only macro safe to exceed. Too much protein or carbohydrate will prevent or delay progression into ketosis. Too much protein is likely to interfere with reduction of IGF-1. Therefore if you struggle to match the macros precisely, go over with fat, don’t go over on protein or carbs. Note that the researchers also emphasise unsaturated fats in their design, which means choices like olives, rapeseed and macadamia nut oil rather than butter and coconut oil.
Based on my learning I also recommend limiting carbohydrate to 50 grams total. This is in order to enable progress into ketosis. Go higher only if you know you can enter and maintain ketosis.
The most challenging macro limit is that of protein. On Days 2-5 it is so low that most vegetables and even some fruits are too high in protein to include. Those veggies that are low in protein are often high in carbohydrate instead. The implication is that many foods are unsuitable to including in significant volumes, again making careful planning necessary.
My Google Sheets FMD Do-It-Yourself file shows almost exactly what I ate on my first FMD and under the Resources section further down, I provide links to alternative approaches for the food.
4. Establish the pre-FMD baseline measures
If like me you are willing to incorporate FMD into a longevity regimen but *only* if you see significant benefits then you need pre-FMD baseline values to compare to the post-FMD outcomes. Make sure you have the necessary tests completed before starting the FMD.
For some measures, like Blood Glucose, Heart Rate Variability and Bodyfat % you should ideally have at least several weeks of data since these fluctuate from day to day and time to time. I also highly recommend getting into a consistent routine of measurement prior to beginning FMD so that you do not have to begin everything at once.
For two weeks prior to my first FMD I established a routine. At 0600 I woke, hydrated with 2 cups of water and then:
- Took a weight and body composition reading using my Taotronic scales
- Returned to a lying position and took a Heart Rate Variability (HRV) reading using a Polar H10 and the EliteHRV app
- Measured my fasted blood glucose using an Abbott Freestyle Libre
3 days prior to beginning FMD I visited a Medichecks lab to have blood draws for my IGF-1, Cholesterol profile, White Blood Cell profile and high sensitivity C-Reactive Protein. I recommend having these done as close to the beginning of the FMD as possible so that there is a proximate point of comparison to the second set of measures you will take at the end of FMD for comparison.
5. Emotional & Environment Support
Preparation steps 1-4 are purely physical and practical. Don’t skip over this one. When you read about my experience, you will see that I might have quit on Day Two if I had not partnered with David for this first FMD practice. Here are my do’s and don’ts for success:
- DO tell friends and family what you will be doing, why, and how they can help you succeed
- DO write your desired outcomes down, visualise them, define why they are important to you
- DO prepare your environment too. If you know you are likely to struggle with the temptation of snack foods, remove them
- DO ensure you will be able to take plenty of sleep, you may be more tired than normal
- DO ensure you will have opportunity to be active with light exercise, such as walking, interval training or yoga
- DO consider your workload and stress
- DON’T do FMD for the first time if you will also need to manage higher than normal work, family & social demands
- DON’T perform heavy exercise such as lifting weights that will place significant demands on your recovery ability
- DON’T do FMD if you have any unresolved health issue which fasting might worsen
Thats it! You should be ready to undertake the Fasting Mimicking Diet. For further help, refer to the resources below.
Results, Learning and My Experience
Jump to my Results & Reflections post to read about my experience, outcomes and learning from my first FMD cycle. The spoiler is yes, I will repeat it, but with some very important modifications to how I ran it the first time thanks to lessons learned.
Tools & Resources
Google Sheets FMD Do-It-Yourself file is my personal preparation file with details for biomarker tracking and food planning, all the further resources mentioned below are also captured in this file.
CRON-O-Meter is the most comprehensive food logging tool available, going far beyond the likes of MyFitnessPal by tracking almost all micronutrients in addition to the macronutrients.
Medichecks is the UK based lab test service I used for C-Reactive Protein, Cholesterol and Blood Count tests
Freestyle Libre is the device I used for blood glucose monitoring as it offers an adhesive which enables quick and convenient readings. I used a Freestyle Optium Neo for ketone monitoring and this also offers blood glucose readings, both via finger prick blood tests. You need both the device(s) and either a Glucose Monitor (Libre) or test strips and lancets (Optium Neo).
I used a Polar H10 heart rate monitor and the EliteHRV app to track Heart Rate Variability. There are other options but this combination is one I gained confidence in and EliteHRV provide some wonderfully educational articles to accompany the app.
Genova Diagnostics is the service I used for an Adrenal Stress Test. Note they do not sell the test kits direct to consumers, you will need to procure this through a practitioner. Many Nutritionists are able to order this test.
Original Cell Metabolism paper describing FMD in mice and humans (free full text)
Abstract only (full text behind paywall) of the published outcomes from the first human trial
Quantified Bob N=1 – Bob followed the FMD using the low end of the FMD patent calorie counts for his body weight and presented his outcomes along with reflections, a great read.
Quantified Body N=1 – Damien provides a fantastic article with lots of information about FMD. Be aware that he did not actually follow the FMD and instead did a water fast.
Narrative from a BBC Journalist who was part of the earliest human trials of FMD