Long Term Fasting Experiment – Design and Predictions

Lately I’ve been experiencing an urge to fast for longer than the 36 hours per week I’ve been doing over the last month or so, thus I decided to fast for as long as I can (safely and comfortably). Of course, I couldn’t possibly do this without gathering at least a little data, so it will be a bit of a loose experiment as it stands.

Experiment Design

The experiment will have multiple stages, that – except for the beginning and end phase – are not at a set length. They are as follows:

  1. Baseline
  2. Water fasting
  3. Fat fasting
  4. Re-feeding


During the baseline, from September 1st to September 7th I’ll be consuming an ad libitum diet of 73/27 burgers (pre-formed), butter, and commercial pemmican. Beverages will include tea, herbal tea, and flavored sparkling water (no sweeteners). Supplements will include my normal fare of a methylated B vitamin complex, and vitamin D. Electrolytes will be consumed as needed.

1 mile of walking will be done every morning as is my usual.

Water Fasting

During water fasting, no calorie containing beverages or food will be consumed. Supplements, electrolytes, and beverages will be consumed as outlined in the baseline, and exercise will also continue as normal.

This phase will continue as long as I can comfortably maintain it, I suspect around one or two weeks.

Fat Fasting

If I reach a point where water fasting becomes uncomfortable I’ll be adding fat (via homemade broth made from marrow bones, and fat [e.g. cocoa butter and/or butter] added to hot beverages, according to hunger. I’ll continue this phase as long as I can comfortably do so.

Exercise, supplements, and beverages will continue as previously outlined.


After I can no longer comfortably fast, or fat fast, I’ll return to eating by slowly breaking my fast and then returning to the baseline diet. After a week of re-feeding I’ll conclude the experiment. Exercise, supplements, and beverages will all follow the baseline, as well.

Data capture

I’ll be recording the following over all phases of the experiment:

  • Glucose (daily, morning)
  • Ketones/BHB (daily, morning)
  • Acetone (daily, morning)
  • Weight (daily, morning)
  • Measurements (waist, hip, thigh, arm; after baseline, weekly during fasting phases, after one week re-feed)
  • Blood testing (after baseline, weekly during fasting phases, after one week re-feed)
  • Food/Beverages/Supplements consumed (picture logging; constant throughout all phases).
  • Fasting time (via free fasting app, delineated between water and fat fasting)

I’ll be getting 12 tests total during each blood draw. This is pared down from what I’d usually get, but covers many metabolic markers.

  • Comprehensive Metabolic Panel (14)
  • Insulin and C-Peptide, Serum
  • Ferritin, Serum
  • Fatty Acids, Free (Nonester)
  • Complete Blood Count (CBC) With Differential
  • Glucagon, Plasma
  • Uric Acid, Serum
  • NMR LipoProfile
    • HDL-C
    • HDL-P
    • Total Cholesterol
    • LDL-C
    • Triglycerides
    • LDL-P
    • Small LDL
  • Lipoprotein(a)
  • GlycA
  • Oxidized Low-density Lipoprotein (OxLDL)
  • Leptin, Serum

Over the course of the fasting portions I expect the bolded items to decrease and the italicized items to increase. Non-marked items are unknown, or contain multiple tests.

As a side note, I don’t expect GlycA to significantly change over the course of the fast. I expect triglycerides to initially increase and then fall back to normal over the course of the fast. I expect ketones to increase and glucose to decrease over the course of the fasting periods, and weight and measurements will decline. By one week post re-feed I expect blood markers to return closer to baseline levels, with some (although not total) regain in weight and inches.


I’ll be checking in frequently with Dave on how I feel throughout the fast, and in contact with my primary care doctor. If I ever feel unwell, especially any nausea or abdominal cramping, I’ll immediately abandon the experiment and eat. If I ever feel “off” or feel like I should call off the experiment due to any health/safety concerns I will do so without hesitation.


Overall I am very curious to see how things will change over a longer term fast. I’ve previously done a 7 day water fast, outlined here, but this will (hopefully!) extend even beyond that. Adaptions to longer term fasting is definitely something I’m interested in, especially given some studies I’ve been reading recently, and as I’m currently “overweight” I feel I can comfortably take it on. I’m also curious to see what changes may occur comparing water fasting to fat fasting especially in regards to weight, and blood markers.

Given the longer fasting time I’ll definitely be overly cautious about safety and being sure I call off the experiment if I feel it’s necessary for my own health. Other than that, I feel pretty confident overall, especially given I have access to a doctor who has other patients who fast regularly, and am looking forward to sharing back the data.

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19 days ago


maia sutherland
maia sutherland
19 days ago

Sounds great. Me and my mum finished five days with some sashimi today. Divine. Enjoy your fasting x

Robin Rheaume
Robin Rheaume
19 days ago

This is exciting. I look forward to the results. My experience with long term fasting has really varied. Sometimes it has been a breeze. Other times I’ve experienced intense muscle pain as if I was going into ketosis for the first time. Likewise refeeding has either been a breeze or made me never want to eat again.

It really messed up my menstrual cycles so you might experience that. Also, after a few rounds of long term fasting, I developed issues with gallstones which I never had before. I can’t be sure it was causal but the literature indicates it’s a risk.

But wow you can really get a lot of shit done. Focus is 100% and there is no time wasted messing around with food. I wish I knew this hack back in uni.

Last edited 19 days ago by Robin Rheaume
19 days ago

Woohoo!!! Looking forward to hearing your thoughts 🙂

19 days ago

Thank you. I look forward to see the results

17 days ago

Hi Siobhan,

What a fascinating experiment! I’ve been fasting and eating extremely low carb since the beginning of the Covid thing. I’ve lost 25 pounds and have significantly changed my numbers on a 24hr urine test (I have 20 years of kidney stones). My urologist said “whatever you are doing, keep doing it!. That felt great!

I’ve been following along with you and Dave and I’ve been wondering about exactly this type of fasting experiment.

I’ll be following along and cheering for you.

Good Luck!

17 days ago

My only suggestion: take glucose and ketones (at least) twice a day, once in the morning and once in the evening. I find I have the highest blood sugar and lowest ketones in the morning, and lowest blood sugar and highest ketones in the evening.

For me, what happens is LDL, trigs, and TC go up, and HDL goes down during a fast. I’d assume LDL-p goes up, but I don’t have direct evidence of that. LP(a) goes up. I’ll be interested to see what happens with small LDL. Blood glucose is highest in the mornings, but travels downward during the fast. Ketones are opposite: lowest morning, day 1, highest evening day X.

8 days ago

I’ve read that the less insulin we have the less LDL receptors we have. Thus, higher LDL-P in bloodstream when insulin is very low as in the case of severe calorie restriction and fasting.

Muhammad Shariq
Muhammad Shariq
17 days ago

You may factor in ill effects of toxins being released which are stored in fats. They can really make one feel bad and it has nothing to do with no caloric intake.

13 days ago

Any reason not to get a couple of DEXA scans (such as at the start and end of the water section)? Very curious if the limits on lipolysis apply to fasting.


Raphael Sirtoli
2 days ago

any significant trends will be interesting. so are there any bets going on % changes in LBM and/or weight?

8 days ago

I hope you are enjoying the benefits of your fast. I am interested in you LDP – P lab results. I hypothesize it will be significantly higher than your normal.
I believe that severe calorie restriction caused my unusual high results. I am considering ways to increase the LDL receptors because I do believe the science indicating a higher risk of atherosclerosis with higher HDL-P. However, the carnivore diet is so liberating that I do not want to give it up.

8 days ago


This link goes to a YouTube video titled, “The Science of Fasting.” I found it very informative.

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