My Body Ate Itself for 5 Days

My Body Ate Itself for 5 Days

. 7 min read

Sometime deep in the black hole that was 2020, I stumbled upon the Fasting Mimicking Diet (FMD) while reading the book* The Longevity Diet by Valter Longo.

Improve your health by letting your body eat itself? I was intrigued.

Damaged cell buffet? Yum. Count me in.

The Fasting Mimicking Diet (FMD)

FMD was designed to mimic a water fast, hence the name Fasting Mimicking Diet.

The main benefit of a traditional water fast is that your body enters survival mode, which activates cell autophagy. In other words, without food, your body begins to eat itself, starting with the damaged cells first. This is supposed to be beneficial for protecting against diseases like cancer, diabetes, etc.**

The problem with a normal water fast is that it's hard, so people don't do it. FMD was designed to make it easier to achieve the benefits of a water fast, while still being able to eat something. This is possible through severe calorie restriction based on body weight and a specific macro ratio.

How To Do FMD

There are 2 ways of doing FMD:

1. Buy the Prolon fasting meal kit for $250
2. DIY and calculate a meal plan for 5 days

All reviews I've read of the Prolon meal kit are surprisingly decent, but Art and I decided to go for the DIY route since we had time and wanted to control what meals we ate. Also, the kit is expensive and we didn't want to spend that much money on this experiment.


DIY requires a lot of preparation. You'll need to calculate your calorie count, macro composition and meal prep.

To calculate how many calories/macros to consume, we created this Google sheet as a template. Feel free to make a copy and use it yourself.

Calorie count

  • Day 1: 10-16 calories per kg of body weight
  • Days 2-5: 7-11 calories per kg of body weight

Macro composition (protein/fat/carbs)

  • Day 1: 10% | 56% | 34%
  • Days 2-5: 9% | 44% | 47%

For example, I started out at 124.2 lbs/56.3kg, so I ended up eating 550 calories on days 2-5.


Planning the meals took the longest. We input all of the ingredients we planned to use in the template, and measured the exact grams of each ingredient while cooking. We would then adjust if we were slightly over or under our macro percentages.

The diet follows a specific macro ratio and is high-fat, low-carb and low-protein. We mostly ate:

  • Olives - best snack ever
  • Nuts
  • Soup - It was the easiest to make a huge pot in the morning and eat it for both lunch and dinner. We did this for 4/5 days.
  • Zucchini noodles - It's just like spaghetti. Except not.
  • Vegetables - No meat allowed.
  • Supplements - omega-3 fish oil, magnesium, green superfood powder and glycerol.

Tracking Measurements

I highly recommend you track your measurements. Otherwise, you'll come out of FMD and wonder what the point was.

We measured 3 levels daily:

1. Weight - For context, I am a short woman and I usually weigh around 120 lbs / 55 kg. Even though my goal was not to lose weight, it's an interesting metric to track. The Prolon website states that most people lose around 5.7 lbs.

2. Blood sugar - Studies show that blood sugar drops during FMD. We bought a simple finger prick glucose monitor, similar to this one.

3. Ketone levels - Because the diet is low carb, your body starts using fat and ketones for energy instead of carbohydrates. This is the same as in the Keto Diet. In ketosis, people report feeling mentally focused and energized.

We bought ketone measurement sticks that you pee on similar to these. The pee sticks are not as accurate as blood measurements, but it's cheaper and good enough to gauge when you enter ketosis.

Deep purple pee stick showing that I'm in ketosis.

My Experience

We decided to start on January 1st, because we'd been non-stop gorging ourselves during the holiday season and the weeks (ok months) leading up to Christmas.

Actual footage of me in the weeks leading up to the FMD diet.

Day 0 (Pre-FMD):
Weight: 124.2 lbs/56.3 kg
On Day 0 you are supposed to ease into FMD by eating lighter, vegetarian meals. I woke up hungover and we made pho. I'm dreading the upcoming days. We started binging The Handmaid's Tale, which is a great show btw.

Day 1:
Weight: 122.4 lbs/55.5 kg
Blood Sugar: 5.1 mmol/L
Ketone Level: 0
I had a really bad headache the whole day. I'm not sure if it’s the lack of caffeine or the lack of food. Possibly both. I not-so-secretly hate on Art the whole day for getting to eat more than me. I go to sleep with a pounding headache.

Day 2:
Weight: 121.2 lbs/55 kg
Blood Sugar: 4.7 mmol/L
Ketone Level: 1.0
I feel surprisingly good. I check and indeed it's because I've entered ketosis. I still feel very low energy, but mentally much clearer. I can't wait to eat normally again.

Day 3:
Weight: 120.2 lbs/54.5kg
Blood Sugar: 4.8 mmol/L
Ketone Level: 3.9
According to the keto pee sticks, I'm fully in ketosis. Cool! I proudly wave my deep purple pee stick in Art's face. I felt pretty good mentally the whole day, but still very low energy. I get tired walking up the stairs to our apartment.

Day 4:
Weight 119.8 lbs/54.3kg
Blood Sugar: 4.6 mmol/L
Ketone Level: 5.0
I can’t wait for this to be over. I feel overall much better and still very clear mentally. Still in ketosis. I could concentrate a lot better at work and didn't feel hungry. But still, I dream of food.

Day 5:
Weight: 119.2 lbs/54.1kg
Blood Sugar: 3.8 mmol/L
Ketone Level: 5.0
Officially over it by now. I don't feel hungry and my mood/mental state is fine. Still in ketosis. The soup was actually tasty.

Day 6 (Post-FMD Re-feed):
Yay, it's over! I resist the urge to hardcore binge and follow the recommended re-feeding guidelines for day 6:

  • Stick to a vegetarian diet
  • Keep sugar below 10g


I felt worse than FMD round 1. Though, I think it was because of the stark contrast to the Christmas-time binging. I lost 5 lbs, but I think much of this was water/bloat.

Ketosis was again an exciting state to experience. Before trying FMD last year, I always thought it was just bullshit when people mentioned the focused mental state you feel during ketosis. It's real, but I would say it feels more like a state of alertness.

It was also interesting to watch my blood sugar drop. I'd like to do before/after bloodwork next time around to see what other measurements change.

Overall, it's not the easiest 5 days, but I would still do it again. I hope my cells at least enjoyed eating one another.


  • y tho? I figured why not. The potential benefits seemed to outweigh the 5 days of suffering.
  • Did you feel better afterwards? No, but I didn't feel worse. As most of the change is going on in your cells, I think most people would not feel a big difference.
  • Weren't you dying of hunger? Yes and no. The first 2 days were awful and I wanted to eat more. The last 3 days I wasn't physically hungry, I just wanted to eat more.
  • Why not do a juice fast/water fast? I love to eat, so I think a juice/water fast would be torture. Plus, if FMD results in the same benefits, why bother?
  • Did you gain the weight back? I didn't do FMD for weight loss, but from many accounts I've read, many people kept the weight off. The first round of FMD, I gained the weight back almost instantly. This second round, I haven't gained the weight back yet, but I've been eating healthier/haven't been drinking.
  • Would you do it again? Yes. Aside from the purported benefits, I find it a good way to reset as I easily get into Kirby-levels of over-consumption.
  • Were you able to work? Yes. Luckily, I am currently working from home, which made it much easier given the complicated meal preparation and general lack of energy. I would not recommend doing FMD while working if your job requires any amount of physical work.

* I can’t remember how I ended up on this book. I think it may have been suggested in the Cloud Library app, but I really have no idea.

** Disclaimer: I'm not a medical professional or doctor. Please consult your doctor for professional advice before trying out any diet.