I’ve been reading a lot about fasting, I’ve been writing a lot about fasting, I’ve been doing a lot of fasting.

In fact, I have recently finished my first ever 3-day fast (well 72 hours anyway) and I wanted to give you my reasons for doing it and relay my experiences – in brief. So here goes. 

Reasons for doing it:

The science around fasting for a range of health benefits is compelling, and includes benefits for weight loss, blood sugar control, immunity, anti-ageing and more. For me it was mainly about four aspects:

  1. Mental clarity that comes with being in deep nutritional ketosis.
  2. Benefits of “Apoptosis” and “Autophagy”, essentially cell death and cell clean-up and rejuvenation of cells that have passed both their best before and use-by dates. I believe this is something I can do a couple of times a year along with the other things I do more regularly (eat well, sleep well, live well) as well as shorter fasts to ward off degeneration of the brain and any cell-waywardness.
  3. Longevity and anti-ageing properties. There are only a few things we can actively do for anti-ageing, so I’m taking this one.
  4. Simply, just to experience it. The value in exploring your relationship with food (even if you think you have an ok one) is a total eye-opener and is very worthwhile – if you are a reflective person that is.

My experiences and musings for those who care…(written in the present tense – purely for dramatisation ;))

Day 1.

This is easy (as I’ve done it before). I actually started off doing a planned 24-hour fast. But now I’m thinking well, I’m 1/3 of the way there, I might as well. I really want to do a 3-day, but I don’t actually want to do it. The environment is not right, I’m working at home, by the kitchen. Oh stop making excuses and just do it. I can’t stop thinking about what I’m contemplating to do. Just do it! Ok, I’m doing it!

Night 1:

Husband Mark makes an omelette for dinner, no problem for me, I feel fine, but dreading tomorrow as I believe day 2 is hard. Still obsessing that I’m actually doing this. Keep thinking about the next day and the next day.


Not a great sleep as I woke up a few times stressing about what I was doing.

Day 1 Blood ketones: 
9am: 0.1 (not in ketosis)
3pm: 0.4 (on the cusp of ketosis)
9pm: 1.1 (in ketosis)

Day 2:

Working like a trojan. I’m totally coping, don’t listen to what they tell you, everyone is different. It’s now 2pm, and oh no, here comes a hunger wave. 10 minutes later: It’s over, ok not so bad. Brisk walk with dog – Pepper, I feel good, great even.

Night 2:

Mark cooks dinner. Lamb, my favourite. Hmmm, now it feels hard. I see a chocolate tasting on TV, oh dear, now my mouth is watering. Then Mark eats chocolate. Mini-torture. Ok, just move to another room temporarily (out of sight, out of mind). It works. No problem. Come back for cuppa tea and some Netflix. All back under control.


Better sleep as I stopped stressing about it.

Day 2 ketones: 
3pm: 1.2 (in ketosis)
9pm: 2.1 (deep in ketosis)
(only two readings as I had to ration ketone strips, as I only had a few with me).

Day 3:

Wake up. Feel tired and have headache, maybe I should stop. No, just have more salt and fluid. What do you know? Headache is gone, and by 10am I feel great.
All day 3: No hunger, what..so..ever, just feeling empty. (Empty- not hungry, an interesting feeling). Again working well, keeping busy.

Day 3 at 7pm

End of 72 hours – I could’ve continued as there was no hunger at all, but social activity arrived and I was only psyched up for 72 hours, so that’s where it ended.

Day 3 ketones: 
8am: 2.4 (deep in ketosis)
7pm ketones: 4.1 (deep in ketosis)
Followed by a delicious, super-nutritious meal!

Parting thoughts:

  • Did I get more clarity? I might have, but I’m not totally convinced of it – just being honest here, but that might be because I generally eat LCHF and feel energised when I work a lot of the time, because I love my work, it energises me. I’m also never tired during the day, despite getting up most days at 5:35am. I worked well over the last 3 days, for sure, but then again, I always do when I work from home and I get no disturbances. So maybe…maybe not.
  • Did I reflect on how often I usually eat and why? I sure did, a fascinating, introspective experience, even for me who doesn’t have any real food issues (apart from knowingly eating too much chocolate). From this perspective, it was a profound learning experience.
  • Was it hard? On the whole, it was tough, but a lot easier than I expected.

Bottom line: It’s really interesting what you can do when you put your mind to it. Apart from talking, reading and writing about food every day, I really love eating food and going without it for 3 days was a real challenge for me, not physically, but mentally. I wasn’t hungry at all, just “psychologically hungry”, an incredibly interesting concept.

Would I do it again? yes, but not for a couple of months. Back to the short stuff, where it’s easy, you still get some great benefits and it’s not so taxing on the psyche.

The best piece of advice I can give when doing longer fasts? Just don’t overthink it!

Join the discussion 10 Comments

  • miss lena says:

    lam not used to fast because I try it but its hard I will try again thank you for sharing with us

  • Annette says:

    Hi Caryn

    I’ve heard and read different things about whether fasting is unhealthy for women of childbearing age. Most of the studies I have seen don’t really have a focus on long-term effects on women and fertility. Do you have any information on this?

  • Aaron says:

    I started doing it too, there are ways to turn it into a lifestyle. Just gotta make a few tweaks. Not easy but I feel better overall, more energetic and healthy.

  • Emma Calveley says:

    Hi there,

    Thank you for this.
    I’m trying as I’m sure it can’t hurt!
    But what is the latest research around this? Are there some journal articles you could point to? Really curious to know if there has been anything conclusive…. mostly because my husband is challenging me on this and it would be good to have a fuller understanding from the source of the info.

    Many thanks

  • Simon Thompson says:

    Great article Caryn. You probably don’t have enough body fat to justify longer fasting. I found my glucose levels of interest fasting… day 3 of fasting ketosis 2.6 pg with 2.8 Ketones. One prick- two readings. I generally sum glucose with ketones to estimate the brain fuel available (i.e. that example is like having a non ketosis pg of 5.4) .Certainly eating behaviour is largely social cues and habit. Have not seen many dietitians promoting therapeutic fasting, even I saw it all the time in the surgical wards post op before the days of laparascopic surgery. A typical cholecystectomy patient was nil by mouth for 5-6 days!

  • .marie lockie says:

    If you had gone 4 or 5 full days off food you would have been right to find out if you have an hidden enemies, i.e. food intolerances. 3 days is not long enough.
    But I am addressing a dietitian. In 1947. Diet and Disease we were told- no- food never made one ill.
    I used to get up on the 4th day after 3 prostrating days in bed with migraine several pounds lighter. Tea and toast and the new energy would get a lot of work done. By lunch I was depressed again. Eventually i ate bacon and egg alone and the wellbeing continued.

  • Tanya O'Neill says:

    Hi Caryn, great info on your first three-day fast, thanks. I have done a few OMD fasts, but never more than that, have been eating LCHF for three years now. My question is, number two related, what happens if you are on a three day fast? You go as per usual day one then what? Thanks in advance, Tanya

    • What The Fat? says:

      Hi Tania. Simple story, you go as needed (if I am thinking about the same thing you’re meaning, number 2 as in bowel habits?) If there is no food going in, there is none to come out. Sometimes on day two or three there can be some residual content from the days before, but nothing substantial. Hope this helps.



  • Paul Evans says:


    I have been fasting from 9pm before bed through to 1pm the following day. I only have consumed water, some non flavored Metamucil and black coffee in this time. this has been ongoing for 1 week. I have also been very light on the carbs.
    what is your opinion/advice?

    kind regards

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