The FastDay Forum

Hello! First time poster here I am looking forward to starting IF but I’m not sure how to time it with shift work... I work 3-4 12 hr overnight shifts per week (usually all in a row, though), which means my sleep schedule is not consistent on days I flip back and forth. Is anyone here and shift worker? Anyone work night shift and do IF? I’m concerned about the 3-4am super-slump when I get sleepy and hungry. How do you time your 16:8’s or 5:2’s? Thanks!

Hello SarahW, welcome to the group!

Shift works is known to negatively affect circadian rhythms but with fasting, it can be an advantage.

Being unpredictable prevents the body from recognizing a consistent routine - to keep it guessing. When it expects another typical feast day, it suddenly encounters what it sees as an unexpected "famine" and vice versa. Eating and fasting at widely different times forces our biology to beneficially adapt in a number of ways to a wider set of conditions.

What's important with fasting is that there's a large period of time between a given meal and the next one - without any snacks in between. This allows our insulin levels to go quiet as the body naturally reduces our glucose level fuel tank in order to power our daily activities. Insulin controls blood sugar - that glucose that rushes into our blood stream from digestion - by forcing cells to use it for energy. It also directs the liver to convert the remainder to fat. Weight loss attempts are immediately stopped because insulin also prevents fats from being burned to ensure efficient blood sugar control. This is why snacks must be avoided.

Energy-wise, there's a real advantage here that most don't expect. Metabolism will actually increase up to 15% in order to handle the perceived famine and to help us catch that next meal. Mental clarity will noticeably increase. Of course those first few fast days will suck as hunger screams at us that we should EAT something! Don't. The first day is the worst. Keep busy, drink water, coffee, tea and sip something salty to get through it. We've all been there.

Hi and thanks for the great reply! I really appreciate your clear and well-explained description of the effects of fasting. I was so preoccupied with timing — fast 9pm to 6pm for a 5:2,, or 6pm to noon for a 16:8, etc— that I hadn’t thought about the underlying physiology and the “why”. The specificity of the times seem to be for our convenience, so I can do any extended time that fits my life and still get the effects? People seem to do it the same every time but if I change when it starts (midnight one time, or 8am another day) it should keep my body guessing more about the feast or famine periods. Do I have that right?

I worked last night so I had a “normal” eating day until midnight, then I fasted from midnight to 6pm today, 18hr, with an 8-hr sleep period during the day. That seems to be about the same as the fast period on a 5:2. And it wasn’t so bad at 3am! I think I can do this. Thanks again for your insight.

Yes and yes.

Other time variations can include 4:3 (often Mon, Wed, Fri leaving the weekends open); ADF (every other day is fasting), and extended fasting. The beauty of the first three (5:2, 4:3 and ADF) is that they leave some slack in the week for those unexpected schedule upsets. What? You can't fast today because ___ happened? No problem, just fast tomorrow instead and carry on. Each of these methods progressively increase the weekly percentage of meals-not-eaten from 20% (for 5:2) to just over 30% for ADF.

BTW, discussions of that last one - extended fasting, "The fast that must not be named..." - are limited to 2-3 days here by (yes, very dated) convention. Any longer than that and we'd have to take the discussion offline.

In any event the first three variations are more than enough to reach most goals. Besides there's much to learn about eating differently that offers permanent weight control and not just a Yee-haa! weight free fall followed by an even quicker trip to a shocking "yoyo" weight blow up. (Splat.)

For everyone reading this - especially newbies - if you see something that you don't believe and would like to challenge it, do so! We're all learning as we go along and requests for facts and sources keeps it all honest.

Hi @SarahW and welcome!

Good to hear that fasting is starting well for you.

Just to clarify the different approach to fasting of 5:2 and 16:8 (and apologies if you are already very clear on these)...

With 5:2, you have 2 days a week where you eat very little (about 500 cal), and the other 5 days where you eat "normally". For someone who isn't a shift worker, on the day before a fast day, you stop eating after dinner; on the fast day you only consume a small amount of cals - most people reserve this for the dinner time meal, but some split it across the day; and then don't eat again until your first meal the day after. So there should be about a 36 hour period during which you only eat about 500 cals.

When you are a shift worker, obviously you have to change the times, but the aim would be to still have a 36 or so hour period with max 500 cals consumed, twice a week.

16:8 is windows eating, where every 24 hours you only eat in an 8 hour window. Many people aim to narrow that window further, eg only eat in a 5 hour window. Some go so far as to only have one meal a day. And you eat within the window every day (you can shift the start times for the window of course).

Different styles of fasting appeal to different types of people. Sometimes you know what will work for you (5:2 worked for me, whereas restricting my eating to only a few hours a day every day never would!), other times you need to try one style for a while - give it at least a few weeks - before trying something else.

Best wishes for whatever method you choose. Good luck!