Extended modified fasting experiment

Last update: 23 January 2021

Between 27-11-2020 and 10-12-2020 inclusive (14 days), I have been undergoing a modified fast. The time was chosen in part because of Advent. My protocol was this:

  • coffee and tea, ad libitum
  • mineral supplements (magnesium, potassium, sodium and phosphorus)
  • multivitamin daily
  • 3 times per day 1 tsp of either lactose or glucose (to ameliorate protein loss1)
  • (almost) daily weight tracking (morning)
  • twice daily (morning and afternoon) BHB and glucose readings (via glucometer)
  • otherwise normal activity, including mental work

On 5-12-2020 I got some basic bloodwork done, and on 3-12-2020 and 10-12-2020, I also got DEXA scans.

The first four days were the hardest – I felt pretty terrible and cold, but afterwards the general malaise went away, and it was tolerable. Hunger per se was not a serious issue until day 13 or so. I maintained full capacity for light activity – such as cycling and walking – though climbing six flights of stairs was more tiring than usual.

Midway through, I had to drastically cut down the dose of mineral supplements, because they were causing me severe diarrhea (at least one of the salts I used is a laxative). I replaced these with a magnesium supplement in pill form (which contained some sucrose, for which I tried to compensate in the CHO doses).


Weight and glucometer readings.
Vitamin B121350pg/ml
Total cholesterol312mg/dl
HDL cholesterol48mg/dl
LDL cholesterol233mg/dl
Non-HDL cholesterol264mg/dl
Total bilirubin1.4mg/dl
Bloodwork results from 5-12-2020.
Fat-free mass [kg]66.735
Fat mass [kg]24.29423.820
Bone mineral density [g/cm2]1.2891.290
DEXA summary.


The alterations in blood energy are as expected from starvation. Weight loss was also expected, but the rate is somewhat different – much more gradual – than what usually happens in water-only fasting2. This can be explained by retention of electrolytes and fluids which would have otherwise been rapidly lost before the system adjusted to it. No doubt the carbohydrate supplementation also helped against some loss of protein1.

The only noteworthy aspect of the bloodwork is that fasting raises lipids3. These were my highest triglyceride and LDL readings ever taken.

The DEXA results suggest very little fat mass loss, but this is spurious, and certainly a result of the inadequate accuracy of the method for this purpose5,6 – it is completely inconsistent with the blood substrate measured, or known fasting physiology. Further, given adequate subjective mood, physical capacity and thermogenesis, as well as an accurate-enough estimate of lean mass, I would estimate – based on known prolonged fasting data1,4 – I was losing 150-250g of fat and perhaps up to 50g of protein per day.


  1. Sapir DG, Owen OE, Cheng JT, Ginsberg R, Boden G, Walker WG. The effect of carbohydrates on ammonium and ketoacid excretion during starvation. J Clin Invest. 1972;51(8):2093-2102. doi:10.1172/JCI107016
  2. Kerndt PR, Naughton JL, Driscoll CE, Loxterkamp DA. Fasting: the history, pathophysiology and complications. West J Med. 1982;137(5):379-399.
  3. Sävendahl L, Underwood LE. Fasting increases serum total cholesterol, LDL cholesterol and apolipoprotein B in healthy, nonobese humans. J Nutr. 1999 Nov;129(11):2005-8. doi: 10.1093/jn/129.11.2005. PMID: 10539776.
  4. Owen OE, Smalley KJ, D’Alessio DA, Mozzoli MA, Dawson EK. Protein, fat, and carbohydrate requirements during starvation: anaplerosis and cataplerosis. Am J Clin Nutr. 1998 Jul;68(1):12-34. doi: 10.1093/ajcn/68.1.12. PMID: 9665093.
  5. Williams JE, Wells JC, Wilson CM, Haroun D, Lucas A, Fewtrell MS. Evaluation of Lunar Prodigy dual-energy X-ray absorptiometry for assessing body composition in healthy persons and patients by comparison with the criterion 4-component model. Am J Clin Nutr. 2006 May;83(5):1047-54. doi: 10.1093/ajcn/83.5.1047. PMID: 16685045.
  6. Van Der Ploeg GE, Withers RT, Laforgia J. Percent body fat via DEXA: comparison with a four-compartment model. J Appl Physiol (1985). 2003 Feb;94(2):499-506. doi: 10.1152/japplphysiol.00436.2002. PMID: 12531910.