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Experience: Strict fasting for 8 days

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  • I did near zero calories fasting for 8 days - here's what happened

Motivation#

  • Fatty liver: simple calories deficit doesn't help - deep ketosis e.g. through fasting necessary 3
  • Experience how deep ketosis & autophagy feel
  • Reset salt, sweetness, insulin and food volume desensitization as well as breaking habits of e.g. regular snacking or eating out of boredom rather than hunger
  • Get a bit leaner

The plan#

Prep#

Digestion / Detox#

  • Laxative: Glauber salt (~5€ at the pharmacy) for a "clean" fasting start and stomach pain prevention
  • Tea
    • Dandelion "Löwenzahn"
    • Nettle "Brenessel"
  • Apple vinegar (for tea): mild, low in calories and inhibits insulin spike

Supplements#

  • Vitamins: 1
  • Electrolytes, especially Magnesium & Potassium "Kalium" 2

"Food"#

  • Tea
  • Soup veggies, e.g. 400g / 2 days
  • Veggie broth powder: basically salt, but healthier due to part veggies
  • Erythritol and stevia: two of the few zero calories sugar substitutes that don't lead to insulin spikes and are not known to impact gut health and thus e.g. insulin resistance 3

Equipment#

  • Hot water bottle / grain pillow etc.: to calm the stomach and feeling cold due to low energy and bad sleep
  • Optional tracking
    • Body scale
    • Body fat caliper
    • Heart rate monitor (e.g. watch, to enable monitoring during sleep)
    • Blood pressure monitor
    • Continuous glucose monitor 4

Daily routine#

veggie soup

  • 2-4L Water
    • Veggie soup (lasts for 2 days actually)
      • Boil 400g veggies in 1L for 40-60min
      • Strain liquid from veggies
      • Add as little salt as possible, up to 6g
      • Compensate evaporated water up to 2l again
    • Teas
      • 1x bag Dandelion + 1x Nettle per day to support detox
  • Supplements
    • Intake according to product recommendation
  • Training
    • Strength training to prevent muscle loss
    • At least 4k steps to support digestion and counter metabolic adaption

To avoid#

  • Portions with calories >10-20kcal
    • Will not only inhibit autophagy & ketosis, but can also lead to insulin spike and thus hunger
  • Protein, as it might inhibit ketosis
  • Any food with intense flavor, e.g. also coffee - not needed for the fat-reduction or detox related benefits, but would reduce the desensitization benefits and might lead to other issues like cravings or drinking more than necessary to experience flavor
  • Too much salt, as it increases thirst and thus further promotes electrolytes loss

Timeline#

2 weeks before#

  • Get used to eating less, e.g. 100-250 kcal daily deficit
  • Order prep stuff

1 week before#

  • Reduce calories down to 500-1000 kcal till last day before fasting start
  • Not much fiber the day before, e.g. only curd, yoghurt etc.

Day 1#

  • Glaubersalz 30-40g 500ml in 15min
    • to ensure there's nothing left to digest in the stomach and prevent discomfort or cramps, as without new food to push, old food is kind of stuck
  • Cardio to exhaust carbs

Day 2-4#

  • Timing: ideally on a weekend
  • Prioritize strength training, cause risk of muscle loss with no food and without ketosis is the highest here
  • Prepare for "fasting crisis"
    • Hunger might be high, mood and concentration especially bad
    • Increases risk of pain due to adaption to ketosis and e.g. release of bound toxins in fat tissue

Day 5#

  • Vacation day for rest

Day 7-10#

  • Prepare for ending the fasting based on personal goals and how fasting that long feels

Day 14-16#

  • Measure again after ~1 week of eating normal to learn about short term recovery

Day ~30#

  • Measure again to learn about longer term (persistent) effects

My actual experience#

Energy/Endurance#

  • How easy it was to exercise or even move (motivation wise)
  • Low energy levels make prolonged cardio in particular very hard and lead to higher heart rate at same output
  • Low energy doesn't mean potential strength output is low, but it get's very uncomfortable and requires a lot of discipline
  • Low energy levels are maybe the main factor that make fasting feel hard to endure, especially if you need to stay productive and active
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Energy" [5, 3, 2, 3, 3, 2, 3, 2, 1, 3, 4, 4, 4, 5]
        bar "Energy" [5, 3, 2, 3, 3, 2, 3, 2, 1, 3, 4, 4]
  • Personally the hardest part for me about fasting was knowing that skipping strength training would mean sacrificing hard earned muscle at a potentially fast rate and thus needing to find the motivation for daily training as much as before - while fighting against increasing discomfort to finish sets strong and later even starting sets at all
  • When energy hit a new low on day 8 and going shopping felt like hiking uphill, I decided that considering needed buffer/ramp up for recovery I should rather start eating again to be fit for work next week
    • same as the days before, after ~10-30min of walking/activity: energy levels actually recovered noticeable and the activity didn't feel so uncomfortable anymore after building some momentum
    • this again showed that activity wasn't impossible, but rather the body just "strongly discouraged" activity to conserve energy
  • Even after eating normally again, especially during training (gymnastics) I noticed energy wasn't back to the levels before
  • Energy preservation was also noticeable through indoor temperature feeling 2-5°C lower and warmer clothes didn't help so much as cranking the heating up
  • Might be due to needing to establish a proper sleep routine again or due to being very careful about gaining any unwanted fat back, but my energy levels only really recovered fully after about 1 month (also with 1 week vacation during that time)

Power/strength output#

  • Maximum strength set volume output during strength training compared to before
  • Lower power levels mean maximum set volume was lower even at maximum discipline 
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Power" [5, 3, 4, 4, 3, 3, 4, 3, 4, 4, 4, 4, 4, 5]
        bar "Power" [5, 3, 4, 4, 3, 3, 4, 3, 4, 4, 4, 4]
  • As expected, maximum set volume almost didn't suffer at all except maybe on the worst days and during exercises with more pronounced endurance component (e.g. L-sits)
  • On day 11 I even set a new personal record, increasing my handstand-against-wall time from 180 to 240 seconds

Dizzy#

  • Dizziness while standing but also sitting as well as "brain fog"
  • Inhibited mental work similarly as low motivation
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Dizzy" [1, 1, 1, 2, 4, 2, 2, 2, 3, 3, 2, 1, 1, 1]
        bar "Dizzy" [1, 1, 1, 2, 4, 2, 2, 2, 3, 3, 2, 1]
  • The dizziness was comparable to what I feel during a fever
  • Especially combined with mental fatigue in the late afternoon this was impacting concentration required for mental work
  • Balance during exercise wasn't impacted noticeably
  • Luckily the dizziness mostly came only in short spikes and I barely noticed them longer than 30min at a time

Mood#

  • General mood, e.g. considering feelings of sadness and irritability
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Mood" [5, 4, 3, 4, 3, 4, 4, 4, 3, 2, 4, 4, 4, 5]
        bar "Mood" [5, 4, 3, 4, 3, 4, 4, 4, 3, 2, 4, 4]
  • More than anything, mood seemed mostly related to cravings and e.g. not being able to do cooking as a hobby

Motivation#

  • Motivation to be productive and active
  • Low motivation will lead to e.g. excessive doom scrolling and make non-intrinsically motivated (mental) work quite hard to keep up
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Motivation" [5, 1, 2, 3, 3, 3, 4, 2, 3, 2, 3, 4, 5, 5]
        bar "Motivation" [5, 1, 2, 3, 3, 3, 4, 2, 3, 2, 3, 4]
  • I really needed day 5 as a vacation day to recover some motivation - not sure I'd have managed without it and not appearing like a slacker at work

Hunger#

  • Feeling of hunger as in actually needing to eat, as e.g. indicated by stomach growling
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Hunger" [2, 2, 3, 2, 1, 1, 1, 2, 4, 3, 3, 3, 2, 1]
        bar "Hunger" [2, 2, 3, 2, 1, 1, 1, 2, 4, 3, 3, 3]
  • On day 0 hunger wasn't at its lowest due to the ongoing fasting prep of eating less for several weeks
  • As expected, probably keeping insulin very low at all times by staying at almost zero with calories helped with keeping hunger in check so that it was only a minor inconvenience - pretty unimportant e.g. compared to lower energy levels

Craving#

  • Simply "wanting to eat" or tasting something flavorful independent of a feeling of needing to eat
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Craving" [1, 2, 3, 4, 5, 4, 3, 4, 3, 4, 5, 3, 4, 1]
        bar "Craving" [1, 2, 3, 4, 5, 4, 3, 4, 3, 4, 5, 3]
  • Here I really failed the idea of fasting to avoid intense flavors, especially sweetness and salt
  • On day 2 I began to use more erythritol and stevia tabs e.g. in my tea, where I think especially the erythritol but maybe also the carriers ingredients in the stevia tabs lead to regular bubbling in my stomach, though e.g. not uncontrolled diarrhea or gassing
  • On day 4 I bought some artificially sweetened lozenges
  • On day 5 I switched out some tee with heavily diluted (20 kCal) DIY hot chocolate
  • On day 6 I increased the sweetened consumption yet again, making it hard to fall and stay asleep
  • Before going into calory surplus on day 11, I still felt strong cravings at intake levels that should have been around maintenance level (and I didn't feel hungry)
  • After about a month and working through my "want to cook and taste pipeline" I tried to focus 1) on only eating when hungry 2) reducing salt and sweetness in cooking in general 3) reducing snack frequency and size, which after time toned down my cravings and eating out of habit or boredom

Pain#

  • Any kind of kind which seems directly related to fasting
  • Starting the fast with a laxative is recommended to prevent fasting pains
  • Stomach (region) pain is probably most common (as it was more me), but e.g. muscle aching due to limited regeneration could also be considered here
  • This excludes e.g. non-painful bubbling in stomach
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Pain" [1, 1, 3, 4, 1, 2, 4, 1, 1, 1, 1, 1, 1, 1]
        bar "Pain" [1, 1, 3, 4, 1, 2, 4, 1, 1, 1, 1, 1]
  • I felt both pain spikes (day 3 + 6) from somewhere in lower liver region
  • They were sharp enough to prevent me walking with a straight spine - - The 1st spike I could remedy by laying down for 3min, which seemed to get some water out of a spot where it didn't belong especially during sitting it seemed
  • The 2nd one was even sharper but went away quickly after a toilet break and without needing to lay down
  • Interestingly, binging 1600 kCal at day 8 6pm in 3-4h only caused me only minor issues. I started off again with a veggie puree made of veggie soup liquid remains and frozen veggie soup "leftovers", which caused a minor and short discomfort in the stomach. After that my stomach didn't complain much, though I also tried to keep volume in check with higher calory food like soy bean flakes

Sleep quality#

  • Perceived sleep quality of that night going into the next morning
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar [5, 5, 5, 5, 4, 3, 2, 1, 4, 3, 3, 2, 4, 5]
        bar [5, 5, 5, 5, 4, 3, 2, 1, 4, 3, 3, 2]
  • Beyond the first days where hunger was still noticeable, sleep quality later mainly deteriorated due to increased consumption of sweetened drinks
  • but also late night walks I tried to cram in before sleep to counteract not moving enough during the day

Sleepy#

  • Feeling of sleepiness, without differentiation whether caused by low energy levels or poor sleep quality
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "1 to 5 (highest)" 1 --> 5

        bar "Sleepy" [1, 2, 3, 2, 3, 2, 4, 5, 4, 4, 3, 3, 2, 1]
        bar "Sleepy" [1, 2, 3, 2, 3, 2, 4, 5, 4, 4, 3, 3]
  • Unsurprisingly, sleepiness increased with decreasing sleep quality and I feel this was the main factor here, even considering decreasing energy levels

Weight#

  • Measured after getting up, going to the toilet, in underwear only
  • Weight differences should always be evaluated carefully and rather averaged across no less than a week, e.g. considering that muscles in the average person can store ~2kg of water and drinking 2-4l daily during fasting is recommended
  • Rather, consider that 1kg of body-fat can provide 7000 kCal, so assuming e.g. a 1500 kCal deficit should result ~200g fat loss per day
  • Anything beyond that must largely be water based differences to happen so quickly
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "kg"

        bar [66.4, 66.1, 65.5, 65.2, 65.2, 64.7, 63.9, 63.2, 62.8, 62.8, 63.4, 64.1, 65.4, 64.0]
        bar [66.4, 66.1, 65.5, 65.2, 65.2, 64.7, 63.9, 63.2, 62.8, 62.8, 63.4, 64.1]
  • Kind of in line with expectations, considering the bodies energy savings attempts maybe reducing my base metabolic rate from ~1600 to maybe below ~1300 or lower, final weight loss was about 1kg to 2kg (through fasting alone)
  • It's worth to note that when I started to eat less already 2-3 weeks before the fasting, my weight was around 68kg
  • The last weight of 64kg was after switching to a more low-carb, low-volume and less watery diet (and after day of generally eating less calories on top)
  • My suprailiac skinfold 5 measured via caliper went from 6.5mm to 5.5mm (day 8) to just shy of 6mm (day 27)

suprailiac

Resting heart rate#

  • Measured by Huawei Watch Fit 3
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "bpm" 30 --> 51

        bar [51, 45, 48, 37, 38, 37, 37, 47, 43, 47, 45, 49, 56, 54]
        bar [51, 45, 48, 37, 38, 37, 37, 47, 43, 47, 45, 49]
  • The very low RHRs were usually measured during sleep of course
  • It didn't really give me distinct feeling as far as I could tell - much unlike low blood pressure strongly correlating with dizziness for example

Calories intake#

  • Total kCal intake, incl. e.g. supplements
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "kCal"

        bar [1000, 20, 20, 20, 20, 80, 80, 140, 1500, 1800, 1800, 2400, 1900, 1300]
        bar [1000, 20, 20, 20, 20, 80, 80, 140, 1500, 1800, 1800, 2400]
  • Due to cravings I also starting adding diluted hot chocolate to the menu from day 5 (on top of ~20kCal from supplements)
    • How much those calories and potentially insulin lead to the sharp breakdown of energy and e.g. blood pressure levels would be interesting to know
  • After eating again normally on day 8 - 10, I wanted to set a signal of "there's enough food, provide energy please" to my body (and also address constant cravings honestly) on day 11, so I went into a distinct calory surplus

Water intake#

  • Rather accurate during fasting, else estimated intake through raw liquids + food water content
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "ml" 0 --> 3600

        bar [2000, 2400, 2400, 2400, 2000, 2400, 3000, 3600, 1700, 2000, 2000, 2000, 2000, 1500]
        bar [2000, 2400, 2400, 2400, 2000, 2400, 3000, 3600, 1700, 2000, 2000, 2000]
  • Due to cravings, I consumed more sweetened tea and hot chocolate from day 6
  • by day 5 it felt like individual drinks passing through the body in 30 - 120min tops

Blood pressure#

  • Measured by Omron RS7 Intelli IT
  • Sys on top, Dia below
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "mmHg"

        line "Sys" [99, 98, 94, 100, 99, 97, 101, 99, 91, 94, 97, 93, 92, 93]
        line "Sys" [99, 98, 94, 100, 99, 97, 101, 99, 91, 94, 97, 93]
        line "Dia" [66, 61, 59, 65, 69, 64, 68, 63, 55, 64, 58, 60, 57, 63]
  • Even though I exercise a lot, I guess due to low body weight my blood pressure is generally low, giving me not a lot of buffer before other circumstances that lower pressure even further lead noticeable dizziness
  • Blood pressure seemed fine though until I started to get short black outs on day 7 and then especially day 8 when trying to stand up from sitting too quickly. I didn't want to get to a place were there was a risk of collapsing while standing, so I took this as a sign to quit the fasting
  • The reduction blood pressure by around 5% seem to stay after 1 month, also showing my experience from other diets again on how weight affects blood pressure rather directly
    • This might also explain why perceived energy levels took so long to recover - my absolute values are just really low especially now

Stress / HRV#

  • Proxy of heart rate variability
  • Measured by Huawei Watch Fit 3
xychart-beta
        x-axis "Day" [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 27]
        y-axis "Value" 0 --> 31

        bar [33, 24, 26, 23, 28, 21, 23, 27, 29, 26, 31, 32, 34, 34]
        bar [33, 24, 26, 23, 28, 21, 23, 27, 29, 26, 31, 32]
  • Doesn't tell me much, other than it seemed to decrease during fasting and then increased again

Learnings#

  • Potentially went into an electrolyte deficit due to reading the label wrong
    • the supplement only provided 15% of recommended daily Potassium and 40% Magnesium
    • on the one hand I took at least 10g of added salt per day and the daily 1L of veggie soup is also intended provide electrolytes
    • on the other hand on the later days the 4L of liquid intake also lead to constant liquid and electrolyte on the toilet
  • Didn't feel any "fasting high" or sign of increased serotonin levels - or it didn't unfold due to my lack of control of cravings
  • This is also connected to maybe the most interesting open question: how much did giving in to cravings later e.g. via hot chocolate "ruin" the later phases of fasting by disturbing ketosis?
  • Fasting could be an interesting alternative to the classical e.g. 1000kcal deficit mini-cut, as science suggests that only the first days without food and out of ketosis are really harmful for muscle mass. My strength performance even during fasting barely decreased, maybe even rather increased a bit (of course less weight needs to be lifted for bodyweight exercises), suggesting that ketosis/fasting at least no longer than maybe 10 days isn't harmful here, but the weight/fat loss is definitely there
    • Thus I also wouldn't recommend e.g. eating 250g lean curd per day as some recommend - the 30g of protein aren't a lot given the deficit and I guess potentially disturbing ketosis would do more harm than good in this regard
  • Weight loss yet again directly reduced my blood pressure (by ~5%)
  • Considering very low levels of hunger, even without direct comparison I'd recommend a near "zero diet" with supplements over classical Buchinger fasting with fruit/veggie juice for lunch, as I don't think this would have helped with the cravings, but likely would maybe have rather increased them or added hunger to the mix via increased insulin
  • Regarding bad eating habits
  • as somebody who exercises weight control through high volume meals, feeling more full and satisfied even with smaller meals was noticeable and an unexpected benefit
  • reestablishing a recent reference point through restraint of eating only when hungry, not letting snacking escalate and especially also not needing to season/flavor boost food right from the start considerably helped with not having thoughts regularly revolve about eating
  • Unsurprisingly, due to giving into salt and sweetness cravings, the customary fasting break apple wasn't so much more exciting flavor-wise, though eating some solid was nice apple
  • I really not only missed the flavors from eating but maybe even more not being able to meaningfully have fun with cooking. I spent the next 1-2 weeks cooking and baking all sorts of old and new dishes, though starting of course with one of my favorites: Teriyaki chicken salad wrap. Just leaving it here... wrap

  1. E.g. https://www.dm.de/mivolis-vegetarier-und-veganer-vitamine-mineralstoffe-tabletten-30-st-p4066447336986.html ↩

  2. E.g. https://www.dm.de/mivolis-elektrolyte-20-sticks-p4066447788426.html ↩

  3. https://www.l-iz.de/bildung/forschung/2020/02/interview-peter-schwarz-iss-so-viel-du-willst-aber-beweg-dich-noch-mehr-317267 ↩↩

  4. E.g. https://www.freestylelibre.de/produkte/freestyle-libre-3-sensor.html ↩

  5. https://legionathletics.com/body-fat-calipers/ ↩

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