Four Day Fast-Mimicking Diet: The Results

fast mimicking diet results

The Fast-Mimicking Diet

I first heard about Fast-Mimicking from Dom D’Agostino as a guest on a podcast (Ben Greenfield Fitness). He then popped up in the Tim Ferriss podcast, as did Dr Rhonda Patrick who had this to say:

“When it comes to fasting there are a few things that really differentiate it from a Low Carb High Fat (LCHF) Diet. One of the major benefits of fasting, particularly prolonged fasting, which is around 4 to 5 days in humans, that is not found on a LCHF diet is a dramatic increase in autophagy and apoptosis. This is followed by a massive boost in stem cell production.”

“Autophagy is a genetic program that is very important, it clears away damaged cells to use for energy. Apoptosis is a genetic program that causes damaged cells to self destruct. Both of these processes prevent damaged cells from becoming cancer cells.

dom d'agostino ben greenfield tim ferriss rhonda patrick fast mimicking diet

Fast-Mimicking provides ALL the benefits of true fasting with FEWER negative effects.

If you can get into Ketosis you will preserve your lean muscle mass. Once your glucose reserves are used up you will burn a high percentage of body fat while eating only a few hundred calories a day. This could result in true fat loss of around 1/2 lb per day.

My fast was very closely modelled on the one by Dr Anthony Gustin (pictured left). It involved the use of exogenous ketones in the first few days and a limit of 400 calories per day.

So without further ado, I’m going to share the ups and downs of the 114 hours I spent without a proper meal and the resulting effect it had on my body.

Fast-mimicking Journal

Day Zero

Technically the four FULL days were going to be Monday to Thursday, but I thought I’d get a jump on the calorie deficit by skipping Sunday dinner. Lunch was at 2pm and consisted of swordfish steak and rice. I should note I was on around 200 grams/day of carbohydrate leading up to this fast.

Day One

8.00am: I had my first Keto OS sachet – Orange Dream. It’s around 100 calories and contains ketones for my brain to use as fuel while my glycogen reserves drop. I had 10g of coconut oil in a cup of green tea, and 5g of Essential Amino Acids.

11.00am: As you can see from the video (above) I consumed a very small amount of sea salt that morning. After feeling lightheaded I took a larger dose, around 1/4 teaspoon of it, washed down with a small amount of water.

N.B: Salt intake was something that troubled me through the whole Fasting experience. I had spells of dizziness later on day one having been out sunbathing in the afternoon. I didn’t account for the significant sweat (and electrolyte) loss during sunbathing and so most of day one involved dizzy spells. By day two I was very cautious about sweat loss, ensuring I took cold showers and slept under a thinner blanket than usual. Along with increasing my water intake I aimed to take on three 1/4 teaspoons of salt spaced evenly across the day.

water fast salt intake

2.00pm: My second sachet of Keto OS, with some home-made Bone Broth (salt added) and 10g of Flaxseed. I chose flaxseeds for their high Omega 3 content, and the mixture was actually Ground Flaxseed and Goji Berries. Mental clarity was high. I felt very sharp and focused, which I put to good use reading several items from my list of books.

Hunger: I recorded my hunger levels through the whole experience. It slowly crept up to a 7/10 by late evening. This was the same level I felt the previous night having skipped dinner, so I was certainly aware of it but it wasn’t distracting in any way.

Below are my hunger levels (rated out of 10) across the four days. The red line (above 7/10) was what I perceived to be “uncomfortably hungry”.

fsat mimicking diet hunger
Day Two

6.00am: I weighed in at 70.3kg, one kilogram below what I was on Monday morning. After the initial shedding of ‘water weight’ I was expecting to drop around 0.3kg per day. This would be in keeping with the calorie deficit I had created.

8.00am: I had a Keto OS sachet, a cup of green tea with 10g coconut oil, and 5g of BCAA. Day two mirrors day one, with the exception of not being in the mood for the foul taste of EAA’s. Instead I opted for BCAA tablets. Hunger levels had picked up where they left off the day before but were very tolerable.

12.00pm: My hunger bumped up to an 8/10, which was a significant difference for me as it meant time seemed to slow right down. Between midday and 2pm it was harder to stay fixed on one task. I jumped from reading a book, to listening to a podcast, to writing an article, and back again.

keto os orange dream

2.00pm: Sustenance! My final Keto OS sachet. I likened it to Terry’s Chocolate Orange in flavour, something I despise. The sweetness also meant that I was quite sick of these sachets already. There’s potential GI distress if the sachets are consumed too fast, so having to sip it over the course of 15 minutes was very much a chore. With the Bone Broth and Flaxseed the meal was quite satiating, and hunger levels dropped to a meagre 5/10.

9.00pm: An early night on the Tuesday. This was 55 hours into the fast, hunger had tailed off down to a 4/10 but I was VERY irritable. I watched a film to avoid getting riled up by anything and if I had to be at work in this state I would almost certainly snap at someone.

Day Three

8.00am: This was the first day without the Keto OS sachets. To make up the calories (~100 calories per sachet) I increased my coconut oil to 15g in my morning tea.

10.00am: Hunger levels were back at EIGHT out of ten. Productivity took a dive. Like the previous afternoon I was flitting between four or five projects, not really able to engage with any of them. When I imagined myself fasting this is how I thought the four days would be, so to have been productive on days one and two was a bonus (likely due to Keto OS).

1.00pm: My hunger edged into NINE out of ten. There were very few occasions I could recall of feeling this level of hunger. I moved my Bone Broth, Butter and Flaxseed concoction forward an hour to try and ease my hunger pangs. I took on additional water and salt in case they were at all responsible, and once again hunger dipped to a satisfying 5/10.. for all of one hour.

3.00-6.00pm: Six, Seven, Eight… hunger levels came back very quickly on Wednesday evening. For the first time I doubted whether I would make it to Friday morning without giving up. I had stopped tracking mental clarity, as it’s no use if you can’t apply it to anything. I walked the dog this evening and found my fitness and stamina was very low. This is in contrast to others who have claimed “boundless” energy.

10.00pm: An evening weigh-in, 69.5kg. Down almost 2kg from the first morning, and I was visibly leaner in the mirror. Over the whole day I had only taken two 1/4 teaspoons of salt, one at 11am and one at 2pm. This was all done without any dizzy spells.

Day Four

6.00am: I woke up at 5.40am incredibly alert, though not from being well rested. I found on days three and four that my sleep was being cut short and I was tired through the day. I found a sachet of “Brain Fuel”, 15 grams of C8 MCT oil, which went in my morning tea.

Hunger: This day was HORRIBLE. I was at an 8.5/10 when I woke up and raced quickly into 9/10. You can see in the start of the day 4 video (above) that I am not in the best mood. I’d certainly not want to be around other people in this state for fear of what I might say.

10.00am: Never has a single egg brought me so much joy. It was boiled and chopped up, with 5g of butter mixed in. I think a big part of its appeal was having the texture in my mouth, having drank most of my calories up to this point. The small effect on hunger was overshadowed by its large impact on morale. I was very aware that my macros would allow me one final egg later in the day.

11.00am-1.00pm: I had a nap! This helped me two-fold, as I was 1) sleep deprived and 2) needing a distraction from the hunger.

egg boiled

3.00pm: The second egg was anti-climactic, with the first egg a hard act to follow. Hunger levels were down to 7/10 and that’s where they remained for the rest of the day.

10.00pm: 96 hours on from my very first weigh-in (72.8kg) I tipped the scales at a measly 69.1kg. This is the thumbnail for the Day Four video, as I was recording footage of my torso across the four days.

Day Five – The RE-FEED

7.00am: My choice of 8.00am at the start of this was entirely arbitrary, and I had nothing to gain from waiting an extra hour before tucking into breakfast. An hour earlier I weighed only 68.0kg. I’m the first to point out that this is not a true reflection of my weight.

Breakfast: I took quite comprehensive notes prior to doing this. One point I picked up was not to re-feed with grains or high sugar. I didn’t write down why this is the case but no doubt due to the effect on the body in such a carb-deprived state. I settled on Greek Yoghurt, Berries and Coconut Flakes. This was swiftly followed by a Three Egg Omelette with Green Peppers and Spinach.

spinach omelette

8.00am: With a fine influx of food I was already back to 70.0kg, but there was much more eating to be done. The Yoghurt and Omelette totalled around 500 calories, which is more than I’d eaten on each of the previous four days.

12.00pm: I had no adverse effects coming back to food and tucked straight in to Quinoa and Mackerel with vegetables. The evening meal was prepped at this time too, Sweet Potato and Chicken with more vegetables. Total calories for the day: 1910.

fast mimicking diet chicken sweet potato
Days 6 to 14

 In order to gauge an accurate representation of the weight I’d lost during this fast-mimicking, I ate normally for the next nine days. My average calorie intake over that period was 2000 per day, which is around 13 calories per lb of body-weight. If I’m honest I’d say my eating was more disciplined than an average week of the year. Having suffered from real hunger I was able to deny myself of the usual cravings (chocolate after work).

Results: Below I’ve added a graph of my weight over time. The most comparable numbers are my first evening (72.8kg) and fourteen days later in the evening (71.0kg).

fasting mimicking diet results

I should note a few things:

  • My weight was actually around 74kg in the week prior to this diet. I believe 72.8kg is low for the first evening because I was already fasting and had skipped dinner.
  • How much I weighed straight after finishing the fast was NOT an accurate representation of weight lost. By going back to carbohydrates and re-gaining water weight, I’d put on 2kg just over breakfast.
  • The red circles are daily weigh-ins first thing in the morning. You can see by weighing myself in the morning I can also appear lighter.


While days one and two were pleasant, days three and four were certainly not. It’s possible the Keto OS sachets were fuelling my brain, while after day two my body was unable to do so with the same efficiency. My mood and hunger levels were heavily influenced by salt intake. I found getting the balance right with my salt shots (1/4 teaspoon of salt in water) improved the experience.

If I were to do this again, I would aim for 500 calories per day (this was 400 kcal/day). There’s unlikely to be any added benefit from those extra 100 calories. Additionally, by taking on 25% more it could be the negative experiences could be mitigated. For the same reason I’d also include more solid food, including vegetables. I was strict enough that I don’t actually think purchasing the Blood Ketone Reader would have been worthwhile. I was generally quite confident of being in ketosis beyond day two.

Although I said in the video that I wouldn’t do this again, I am already planning ahead to January 2018 to repeat this protocol (with a few minor tweaks). If successful, I can see myself making it a permanent part of my life on a six monthly basis, if not for fat loss then for the known benefits to health.

Please consult a doctor if you plan to undertake a fasting or fast-mimicking diet similar to mine.

About Fraser_9to5 256 Articles
Site owner. I'm a graduate in Sports Science and have an MSc in Sports Biomechanics. I set up 9to5strength in 2015 as a resource for people interested in strength training, nutrition and fitness. I consider myself a fitness blogger and enjoy creating YouTube videos and trying out workout programs.