I did a 5-day water fast with daily blood glucose and ketones measurements

I have been on Intermittent Fasting (IF) for over a year and I gradually increased my IF from 16/8 to 18/6, 20/4 and sometimes reaching 24 or 25 hours without food. There are so many resources on the web on the benefits of IF such as reversing insulin resistance, weight loss (because one tends to eat lesser with IF and creates a sustainable calorie deficit) and many more.

However, to get some of the better benefits such as fat burn (ketosis) and autophagy, a fast that is beyond 24 hours is required. This is because you may already spend 24-48 hours depleting your glycogen store in your liver and muscle before you can enter ketosis. This is the time that autophagy can also begin. While on a keto diet or IF, one tends to drink black tea / coffee but that is thought to interrupt the autophagy process by stimulating insulin response. As such, I planned to be extremely strict on my 5-day water fast – nothing except plain water.

I started on Sunday, 28 November 2021 at 6:30pm – that is the time I swallowed my last bite of dinner. I at like there was no tomorrow. As a result, I weighed in at 90.45KG that night. Although I started on Sunday 6:30pm and is to break my fast at the same time on the following Friday, let’s take Monday as Day 1 for simplicity.

I bought a tube of ketone urine test strips in advance but I gave it some thought and felt that I should invest in a more precise data collection since I’ll be committing so much to this 5-day fast. It would be a waste if I had to fall back on test strip indicators that are subjective. I will then use Glucose-Ketones-Index (GKI) to see how am I doing in terms of ketosis.

What is GKI (Glucose Ketones Index)

Day 1

I went out to grab blood glucose and ketones strips for my Abbott Freestyle Optium Neo Blood Glucose & Ketones Monitoring System

  • Mood: Totally fine – this is within my usual IF practice anyway
  • Energy level: Great
  • Mental clarity: good
  • Blood Glucose: 4.8 mmol/L
  • Blood Ketones: 0.3 mmol/L
  • GKI: 16 (Not in ketosis)
  • Weight: 88.75 kg
  • Remarks: My body has yet to fully use up the glycogen store due to my high carb meal the day before. I expect this to be depleted within the next 12-24 hours.

Day 2

  • Mood: A little grumpy
  • Energy level: A little lesser than normal
  • Mental clarity: good
  • Blood Glucose: 3.6 mmol/L
  • Blood Ketones: 2.1 mmol/L
  • GKI: 1.7 (Therapeutic ketosis)
  • Weight: 88.25 kg
  • Remarks: I jumped straight into ketosis. The hunger was okay but my mind is

Day 3

  • Mood: neutral
  • Energy level: it’s alright
  • Mental clarity: good
  • Blood Glucose: 3.2 mmol/L
  • Blood Ketones: 3.6 mmol/L
  • GKI: 0.9  (Highest therapeutic ketosis)
  • Weight: 87.2 kg
  • Remarks: Technically hypoglycaemic if based purely on blood glucose level. However, I am burning fats and ketones so this level of glucose is still safe. The body is using protein to produce the little bit of glucose needed by certain parts of the body that cannot burn fat/ketones.

Day 4

  • Mood: grumpy
  • Energy level: lower than usual
  • Mental clarity: great
  • Blood Glucose: 3.3 mmol/L
  • Blood Ketones: 4.7 mmol/L
  • GKI: 0.7  (Highest therapeutic ketosis)
  • Weight: 86.75 kg
  • Remarks: I can’t take my mind of food. Every time I open FB/IG, someone is posting about food they bought / eating or how-to style videos about preparing food. I went into Grab app and attempted to schedule some deliveries for the next day ….

Day 5

  • Mood: surreal
  • Energy level: lower than usual
  • Mental clarity: great
  • Blood Glucose: 3.1 mmol/L
  • Blood Ketones: 6.2 mmol/L
  • GKI: 0.5  (Highest therapeutic ketosis)
  • Weight: 85.4 kg
  • Remarks: I walked for about 2.4km to run errands (Grab groceries and such for my breaking of fast). Because of that exertion, I hit an all time high of 6.2 mmol/L of ketones and 3.1 mmol/L of glucose.

Data Collected

May be an image of text that says "Howard's Ketones, Glucose & GKI Ketones (mmol/L) 8 16 Glucose (mmol/L) GKI 6 4.8 20 3.6 6.2 4.7 3.6 3.2 15 2 2.1 3.3 0.3 1.7 3.1 10 0 29/11/2021 0.9 30/11/2021 0.7 5 01/12/2021 0.5 02/12/2021 Date 0 03/12/2021"

May be an image of text that says "Howard's weight, body fat and muscle mass Weight (KG) 100 90.45 88.85 Body Fat (KG) 88.75 80 Muscle Mass (KG) 88.25 87.5 87.2 60 86.75 58.20 86.05 85.4 58. FI 57.90 40 28:76 57.90 PM 57.70 58.20 27.45 26.89 20 28/11 pm 26.92 26.43 26.16 29/11 pm 25.94 1/12 am 24.70 24.77 2/12 am 3/12pm pm"

My final blood glucose and ketones blood test on Day 5


As you can see, despite not eating for 5 days, my blood glucose level did not drop below 3 (which would have been dangerous). This is no coincidence as the body just produces enough glucose to keep some parts of my body functioning while the bulk of my body ran on fats and ketones. Will I do it again? Yes – twice a year. There is no need to go on a 5-day fast that often. However, I am contemplating going on a weekly 48-hour fast on top of my IF.

A word of warning: if you are diabetic, please consult a doctor first because instead of ketosis, you can slip into ketoacidosis which is potentially life threatening!




Add Your Comment