Within this post I present and reflect on Fasting Mimicking Diet results after completing my first cycle.

In my Fasting Mimicking Diet Do-It-Yourself Guide I described the diet, the potential health benefits, and my personal and specific reasons and goals for using it. I offered guidance, tools and resources for others considering it. If you haven’t read that yet I recommend doing so first.

I undertook a FMD cycle in order to assess it as a dietary intervention which I *might* choose to repeat in order to enjoy the health benefits. Preparing for the FMD took significant effort and was my first major ‘quantified self’ practice. I needed to:

1. Select the potential outcomes / impacts that mattered to me
2. Figure out how to measure those outcomes
3. Plan out the food I would eat on the diet
4. Conduct the diet and track the measurements
5. Evaluate the outcomes

There were some significant challenges, not least a motivation crisis on Day Two of the FMD itself. Did my Fasting Mimicking Diet results justify the effort and convince me to do further cycles? The short answer is a yes, with some caveats and with changes.

The remainder of this post will present in sequence my results in summary & detail, learning and next steps, the food I ate on the diet and finally my experience of how it felt. It will be a long post. Enjoy it, and if you have experience or are intending to do the FMD too, I’d love to hear about it in the comments.

Fasting Mimicking Diet Results in Summary

My 5 goals and evaluation criteria for FMD were –

1. Significant (25%+) reduction in IGF-1
2. Significant reduction in C-Reactive Protein (CRP)
3. 72 hours+ within optimal ketosis (ketones of 1.5+ mmol/L)
4. Reduction in bodyfat by 0.5%+ sustained for at least 1 week following FMD i.e. no immediate bounce-back
5. Absence of significant increases in measures of stress, adrenal stress, heart rate variability or sleep quality

I had a very mixed picture of results. I did see the reduction in IGF-1 and sustained body fat reduction. I didn’t have any CRP reduction because as I discovered I had negligible amounts to begin with.

My ketosis target was not met but I think this was due to over consuming net carbohydrates and am keen to put that theory to test in practice. On the measures of stress my cortisol levels cause some concern but may be explained by specific behaviours on the day I completed the test sample.

Fasting Mimicking Diet Results in Detail

Regeneration

FMD trials have shown a reduction in IGF-1, White Blood Cells and Neutrophils, with the latter two bouncing back after the FMD ends indicating cell recycling known as autophagy. Autophagy is literally “self-eating”, and is a normal body process upscaled by interventions such as fasting. Autophagy results in existing damaged cells being recycled and used as the building blocks for new cells. Autophagy is linked to reduction in cancerous cells and lower inflammation.

Measured by Medichecks IGF-1 test, I experienced an almost 25% reduction in IGF-1 between the Day 0 and Day 5 of my FMD. This is pleasing and surprising given that I intermittently fast, exercise regularly and follow a plant-based diet, all things which may lower IGF-1.

However I do supplement with magnesium and zinc and appear to have relatively high cortisol levels, which are things which can increase IGF-1.

Lower IGF-1 is not necessary *better*. There are both upsides and downsides to lower IGF-1. However lowering IGF-1, at least temporarily, was one of my five FMD goals and this one was satisfied.

My White Cell, Neutrophil & Lymphocyte results are puzzling. By Day 5 all my values were increased over my baseline. Notice that my baseline is actually at or below the reference range minimum. In some people this could be a sign of infection or autoimmune disease. However I have had these very low counts for many years whilst also being in great health. In the opinion of a Haematologist who monitored me for several years these are simply my personal *normal*.

The uptick, taking me just above the reference range lows, is curious but I do not understand it. Was there an initial dip and recovery or did the FMD somehow directly trigger an initial increase?

Metabolism

 

The biggest disappointment for me was the failure to reach optimal ketosis (1.5 mmol/L+) during the FMD. When my ketones were highest corresponded with when I felt most vibrant and energetic.

From my intermittent fasting practice I have previously observed that at the 18 hour mark I can sometimes feel hungry, cold and fatigued but this feeling departs and is replaced with energy and even elation around the 20 hour mark. I have also observed that my ketones are reaching 1.0+ around that 20 hour mark, so this might be for me the number I need in order to have sufficient ketones to fuel body and brain.

I believe my failure to get into and stay in optimal ketosis during FMD is due to consuming too many carbs overall and perhaps also too many carbs from sugars, even though those sugars were in the form of whole fruits, berries and dates. Individuals differ but keeping net carbs under 50 grams is an established upper threshold to be sure to enter ketosis and I was consuming significantly more than this.

There is also a difference between having ketones and being keto-adapted, the latter meaning your body and brain is ready to use the ketones for energy rather than glucose. My intent for my second cycle of FMD is to spend the week prior on a keto-diet without reducing calories in order to make it into optimal ketosis and *then* begin the FMD. My hope is that this will make the FMD a more pleasant experience since my body & brain can continue to run on ketones during the period of caloric deficit.

Body Composition

Although less important to me than other goals I was interested to see if FMD would result in a positive change in body composition meaning fat reduction without loss of muscle. Here the outcome was more pleasing than I hoped for. On each day of FMD my bodyfat % decreased and that decrease persisted post-FMD. 4 weeks following FMD, my bodyfat is now at 13%, roughly a 1% decrease from my pre-FMD baseline.

I attribute this to two factors. First is that I inevitably lost some weight during FMD due to the caloric deficit and this appears to have come mainly from bodyfat rather than muscle. Second is that the radical change to my eating patterns enabled me to ‘reset’ some of my habits which had been allowing my bodyfat to creep upwards in preceding months. Monitoring revealed that my bodyfat increases each week day, peaking on Friday, then drops by almost a full 1% over the weekend. I think this is because I am far more active on the weekend and overeat slightly during each weekday, with my evening meal as a *reward* for surviving the day!

In order to maintain my bodyfat at the reset lower level and potentially decrease it further I am now planning an ‘intervention’ day mid-week where I will have a caloric deficit and consume only very easily digestible foods such as soups. I have been at 10-11% bodyfat in prior years and gained several % points following a surgery and subsequent period of reduced activity. One reason for me to re-run FMD therefore is to enable a return to these levels. I would prefer several brief repetitions of FMD to a longer and slower calorie restriction plan.

Inflammation

I was very, very interested in this one. About a year prior to FMD I also had a high sensitivity C-Reactive Protein test which returned a result of 0.93 mg/L. This is not a high result but I was still hoping for a reduction. High levels of CRP indicate an acute infection or chronic inflammation and have also been associated with coronary heart disease risk. Lower is better.

I received my pre-FMD baseline result on Day 2 of FMD. The graph shows 0.3 but my actual outcomes was provided as <0.3 / unmeasurable. Seeing that my hs-CRP is so low already is great and welcome news but does of course mean that FMD cannot possibly improve it! Given that a reduction was one of my five main goals this knocked my motivation to continue especially as it coincided with the day I felt worst during FMD.

The result is however not surprising. Although I have the autoimmune coeliac disease I rigorously follow a gluten free diet. I exercise regularly, have no ongoing health issues and I supplement with curcumin, magnesium, Omega 3 fatty acids and consume probiotic foods such as kefir and sauerkraut, all things which may lower CRP. So whilst FMD cannot help me here, this is a welcome affirmation that my CRP is already low.

Stress

My last FMD goal was for something I did *not* want, namely excessive stress that could impact on sleep quality and therefore general wellbeing. Here I had a mixed picture. Subjectively, I felt absolutely terrible on Day 2 and the first half of Day 3, then felt terrific from Day 4 AM onwards.

Heart Rate Variability is a bit of a ‘magic number’ indicating general wellbeing. It is influenced by very many things, exercise, emotions, food, state of mind, breathing and more. It can be used as a tool to help understand better what things stress you and what things relax you. I intend to continue monitoring and learning about HRV in order to use it to inform my exercise frequency and recovery in particular.

Corresponding with how I felt, my HRV score showed significant upticks on Days 4 and 5. A confounding factor for the spread across the 5 days compared to pre-FMD baselines is that I ceased resistance exercise during the FMD period. The absence of this stressor may have enabled my HRV to increase.

I also saw on the 5th day a *perfect* balance between my sympathetic and parasympathetic nervous systems according to the EliteHRV app. This is something I have not seen before or since.

On the less positive side, I am concerned by the results from my Adrenal Stress Test. My first test was taken about a year prior to FMD and the second on Day 5. I am above the reference ranges on everything except the post-awakening measure. This was the day that I performed High Intensity Interval Exercise (HIIT) in the AM followed by lighter exercise before breaking fast around 1100 and this might help explain the elevated levels. Intense exercise increases circulating cortisol.

I have discussed this outcome with my GP and we agreed that it may or may not be a cause for concern. I will be re-running the Adrenal Stress Test on a day when I am neither fasting nor exercising intensely in order to see what my *true* baseline looks like.

Reflections & Next Steps

The published results of the human trial of FMD note that greater benefits are experienced by those with greater disease risk, for example people that are overweight and people with poor cholesterol or blood glucose profiles. My ‘very healthy’ starting point in combination with regular practice of intermittent fasting made me an unpromising candidate for significant benefits. Nevertheless I was pleased by some of my results.

I will run another FMD cycle within a few months. Prior to doing so I will rerun an Adrenal Stress Test on a day I don’t also exercise intensely in order to get a better baseline for comparison of this one metric which causes concern from my first cycle.

When I do repeat the FMD however I will make several adjustments to how I do so based on my experience, falling into the categories of preparation, Food and Activity.

Preparation

I will begin FMD on a Friday or Saturday, assuming I will be working Monday-Friday. This way if I experience the lethargy and brain fog on Days 2-3 like I did on the first cycle it will not interfere with functioning at work and I will have the ability to both stay active and rest as needed.

I will avoid doing FMD during any period I expect to need to deal with additional stress, such as the run up to a holiday or major work deadline.

I will repeat the practice of partnering with another person to do FMD together and having specific goals in mind to achieve, both of which help reinforce commitment.

Food Choices

I believe ketosis was suppressed by consumption of too many carbs and too many carbs as sugar. I will therefore reduce the carb intake to about 50 grams of total carbs (including fibre).

I think it may be useful to begin a ketogenic diet in the week prior to the FMD itself in order to begin the transition to ketosis prior to the calorie and protein restriction. My expectation is that if I begin FMD already in nutritional or optimal ketosis then there will be a ready source of energy for my body and brain.

I will emphasise soups and broths. These are more satiating and comforting than the solid food I ate. Being able to slowly sip on a big mug of hot soup was so much more pleasant than having a tiny bowl of veggies.

I will also more carefully supplement sodium, potassium & magnesium to see if this helps reduce or eliminate the headaches experienced.

Activity

I think it important to find a way to stay active. I fell into a trap of slumping into a chair, oppressed by lethargy, but when I actually moved and exercised I felt much better. Walking, yoga and light interval exercise are the best candidates in my opinion – refreshing without being draining or challenging.

Food eaten on Fasting Mimicking Diet

Within my publically shared Google Sheets FMD Do-It-Yourself file there is a detailed macronutrient breakdown of the food I consumed throughout.

I ate a lot of greens but also tried to eat a ‘rainbow’ of colours to maximise my micronutrient intake. I favoured nutrient dense vegetables, some fruits, and mostly made use of olive oil for additional fats.

For convenience purposes only I made use of Marks & Spencer packs of vegetables & soup. If you want to use the same they are named in the Do-It-Yourself file and shown in the pictures. They are also very easy to replicate using the vegetable ingredients themselves.

The root vegetable rich soup I started consuming on Day 3 was a minor revelation. Compared to other meals it felt highly nourishing and satisfying. I think this was partly just due to being able to nurse a big mug of hot soup for a long time, rather than very quickly consuming a small portion of solid foods. It enabled my body & mind to realise that indeed, it had been fed, and could now be happy.

Fasting Mimicking Diet Experience Diary

Day One

This day is a gentle introduction to the FMD, coming in from a regular eating day and consuming almost half as many calories as a regular day. Mentally I am excited and anxious, like the feeling before a race. I have prepared well but the preparation is now over and the killer question is, can I really do this?

I feel highly attuned to my body state. Energy. Temperature. Mental clarity. I cycle commute to and from work, about 25 minutes moderate intensity each way. By the time I arrive home in the evening I feel ‘light’ but not faint or dizzy, with blood glucose reading 3.8 mmol/L. I decide to not cycle on the remaining days, fearful that doing so might be too demanding, particularly in the evening.

There is little difference in physical sensation. Instead I am anticipating greater challenge to come in the lower calorie days.

Day Two

After 8 hours of unbroken sleep I feel great and my Elite HRV indicates a ‘perfect’ score of 10 reflecting balance between sympathetic and parasympathetic nervous system stimulation, the first time I have seen this since I began monitoring. I definitely feel ready to cycle commute but wary of how I will feel in the evening, choose not to, instead commuting via a short walk and tube journey.

The day is not pleasant. Feelings of emptiness and hunger grow and concentration and energy levels suffer throughout the day. They are joined by concern about whether my state will stabilize, improve or worsen in future days. I balance hope that higher levels of ketones will transition me to feeling better with concern that as the calorific deficit accumulates I will feel worse.

Other people’s food smells amazing. Someone in my office is having baked chips or potatoes and I feel like a cartoon character able to float through air on the aroma towards the food. On my way to my tube station I walk through an eatery area I have walked through hundreds of times and notice entirely new aromas. My body is clearly helping prepare me to ‘hunt’ so it can end this period of semi-starvation. Thanks for looking out for me body, sorry I am letting you down, hold in there!

My mind generates lots of very good reasons that would justify quitting. One of these is prompted by the receipt of my Well Man Check results which indicate that my hs-CRP is already at a level too low to be detected so I cannot possibly observe any improvement. Three things anchor me. One is going through FMD together with David. Another is to see the impact on IGF-1. The last is intent to complete this experiment and share the results with others. If I did not have these things I would probably quit.

Day Three

Despite solid sleep, I wake up feeling only partially refreshed. I am notably lethargic. At work I struggle to focus. I am not exactly sleepy but I do feel listless and tired and have a dull pain behind and above my eyes. In my adult life I have no memory of suffering a headache so it is only after I google this that I realise what the sensation is. Perhaps I have insufficient electrolytes, or am experiencing the phenomenon of keto flu, or both.

I choose to wear a long sleeved base layer underneath my shirt as a means of staying warmer as body temperature drops. This seems to work well and I am not bothered by chills during the day.

I switch the order of food by consuming a veggie dish first instead of fruit to break my fast. This matches my conventional approach to meal planning which is to always start with low glycaemic index and high fibre foods and if I am going to eat things higher in simpler sugars, eat those at the end of a meal. There is good evidence that the order of foods eaten influences the insulin / blood glucose response.

By mid-day, even before eating, I am feeling stronger and more alert. My confidence is renewed. For lunch I have a very big bowl of salad – cherry tomatoes, cucumber, lettuce and shredded carrot with a tiny drizzle of olive oil – coming in at a tiny 67 calories prior to the olive oil. I follow this with my berries. A very odd thing happens. Post meal, my blood glucose spikes higher than I have ever seen – all the way to 8.8 mmol/L. Seeing this is like reaching the top of a rollercoaster. I brace for the breathtaking plunge down. I reach a low of 3.7 mmol/L by 6pm but do not have accompanying faintness as with other times I have had blood glucose below the 4.0 mmol/L threshold.

For an evening meal I switch to a root vegetable based soup. This just *feels* so much better than other dishes. I am able to savour the hot soup for a long time and it leaves me feeling relatively satiated. I wish I had gone for soups earlier and reflect that I may promote them to a regular go-to for evening meals thanks to their easy digestibility.

Day Four

Sleep was again complete and deep. I am still groggy in the morning but I feel far better mentally and physically than during Days Two and Three. My HRV is also up, 82 compared to 69 on Day Three. I feel no immediate desire to eat and delay breaking my fast until just before midday and performing some gardening and yoga.

Whilst neither weight nor bodyfat loss are my primary goals I am encouraged to see bodyfat % continue to decline. I am already lean but notice that my stomach is far flatter than usual which I expect is due to a mostly empty gut.

After my first meal of soup I actually feel strong, energetic and ready to exercise. In the afternoon I perform a High Intensity Interval Training (HIIT) style workout followed by dynamic yoga.

In the evening I boardgame with a friend and remain mentally alert until around 2100. From there I fade rapidly.

Day Five

On waking I am still not as refreshed as my pre-FMD norm but the grogginess is greatly reduced. My fasting blood sugar is 3.6 mmol/L and ketones are at 0.9, being the lowest and highest respectively so far. Completing the FMD no longer feels imposing or demanding.

Shortly after waking I performed about 30 minutes of HIIT style exercise followed by dynamic then restful yoga. At 1100 I finally break fast. I am not at all hungry and could have continued fasting in comfort. Mental alertness and energy both felt high.

On this final day I also prepare my Cortisol Stress test samples throughout the day. I find producing enough saliva quite challenging and it takes me 5-10 minutes to prepare each sample.

I travel to Central London to get my Day 5 blood draw and walk for about 5k in total. I’ve consumed about 300 calories and expended approximately 700 yet I feel barely hungry by evening and find my ketones are are 1.1, highest yet.

Day Six (refeed day)

Despite poor sleep I feel vibrant and strong within an hour of waking. I appear to have shed more bodyfat, unsurprising given high activity levels and low calorie intake on Day Five.

I perform a fasted resistance workout and my lifts are within 5% of my recent personal bests. I perform yoga after. During neither activity do I feel weak. Remarkable.

On Days One-Three I fantasised and daydreamed about the refeed, imagining lot of my favourite foods and treats. If not for the need to enable refueling and repair following my heavy resistance workout I would, at this stage, happily extend the fasting since I feel so good.

After going for a 10k walkabout and having eaten only a light breakfast I return home and check my ketones again before an evening mean – 1.2. Ironic. I have finished the FMD and *now* I begin to approach optimal ketosis (1.5+)

Thanks to the upbeat mental and physical state beginning Days Three-Six I am absolutely willing to trial FMD again should it be a fit to my goals.