Fasting Periods Varying -- Does it matter?



This year I began a new diet regimen involving both keto and intermittent fasting. So far I’ve gotten some promising results – down 15 pounds since Jan 1.

One thing that has happened as I’ve adapted – fasting for longer periods has become easier. I’ve been less hungry which is obviously one of the benefits.

As a result, what started as a 16:8 fasting window has often been extended. I’ve gone 18, 20 and the last few days even 23 hours (OMAD).

I’m curious – are there any issues fluctuating how much I fast? Are there benefits to “consistency” in terms of my schedule? Will going from 23 to 16 hours have any negative effects.

Thanks in advance for any responses.


I don’;t think so. I always do whatever I can. I prefer OMAD or a small eating window, at least - but if I need 5 meals, so be it. Getting my nutrients and satiation is the most important for me and I don’t think forcing me to eat or fast would do any good, in the contrary…
I like similar days but some flexibility is needed. If my days are too crazy and different, I probably need to think about choosing my food better… But that has its limits so fluctuations are normal.

(My macros can’t stay put either. It’s very normal for my macros to get doubled from one day to the other sometimes, I consider it’s normal.
And to a smaller extent but my percentages varies too. Yesterday 78% fat, today 59%… That’s life to me.)

So I am all for just doing what feels best even if it gives very different days.

(Joey) #3

@UntouchableCrew Sounds like you’re doing great in just a few weeks. Congratulations on heading down this path to your better health!

Having lost 15lbs (avg 5lbs/week) I’d caution you not to expect this pace to continue. No doubt much of it thus far is water weight as opposed to adipose tissue (fat), as your body is still in its early stages of converting over to becoming a fat-burning metabolism.

The point of fasting is not to starve yourself … on the contrary. You must continue to feed your body the nutrition it needs (healthy fats + proteins) so that (a) it converts over to fat-burning and (b) does NOT begin to shut down your metabolism in response to a “starvation” signal.

PLEASE don’t under-eat. Too much focus on fasting - especially early on - can lead you down an unhelpful path.

Over the longer run, the point of fasting is all about giving your body a chance to have a healthier insulin cycle by providing “breathing” room between intake and digestion/metabolic usage of the food you’re eating.

If you are not hungry, don’t eat. But please eat when you are genuinely hungry.

For now: don’t worry about how often that happens to be. Some days it’ll be surprising how hungry you’ve grown, other days quite the opposite.

The best answer to your question: listen to your body and pay little attention to the clock or to the bathroom scale. You’re off to a wonderful start! :+1:

(Alec) #4

That’s spot on…. Exactly where I am right now… there’s no logic to it, sometimes you’re hungry, sometimes not.

OP: I don’t think it matters how long your fast is: as others have said, in the early days, just don’t stay hungry.


Most of the fasting influencers recommend mixing up your fasting protocols.

You are doing very well. Congrats.


No - quite the opposite. Fasting experts like Jason Fung and Megan Ramos regularly advise to keep mixing things up, rather than sticking to the same TRE/IF schedule each day. Keeping the body “guessing” seems to elicit greater benefits.

You might find the 2 Keto Dudes’ pod with Megan of interest in this regard:


My body doesn’t guess, it demands food and gets food :slight_smile: But it doesn’t want it with the exact same timing every day…

(Ross) #8

Phinney and Volek have some concerns about fasting


  1. The current practice of intermittent fasting has outpaced the published human data supporting its use, particularly in weight control and promoting nutritional ketosis.
  2. There is the strong potential that lean tissue losses can become significant when full fasting days are more frequent that once or twice per week (and this caution may apply to resting metabolic rate as well).
  3. Medications for diabetes and high blood pressure require prompt and expert management when initiating a fast longer than 24 hours. Improper medication management carries significant health risks.
  4. Rather than pursue acute and dramatic weight loss by fasting—even if it is just ‘intermittent’—it is better to take the long-term view and avoid doing things that can compromise lean tissue and function. Health is defined by where you will be 1 year or 1 decade from now, not where you will be in 1 week or 1 month.

They are two of the smartest guys in Keto/LCHF, so it’s worth reading.

Jack Lalanne practiced two meals a day without snacking while maintaining muscle mass (was a body builder in an era prior to PEDs) with amazing body compositing and lived to be well into his 90s, so take that for what it’s worth. (he ate high protein (mainly eggs, fish and turkey), lowish fat, moderate carb including lots of fresh fruits, raw vegetables, juice and a bit of whole grain)

(Bob M) #9

They do have concerns about fasting, but I think they can be misplaced. Dr. Fung has treated thousands of patients with fasting, and some of what Phinney and Volek have been concerned about don’t appear. Particularly the “lean muscle mass loss”.

I’d personally go with Dr. Fung’s experience rather than rely on a few studies.

Having said that, I do think it’s possible to overdo fasting. Like everything else, too much of anything can be bad.

(Ross) #10

Fung is a smart guy but in science, the lack of studies is a red flag and anecdotal info isn’t a good substitute. Fung (a nephrologist) is also trying to treat some extreme situations (morbidly obese diabetics at risk of losing limbs and kidney function) so his recommendations may not be appropriate for everyone? As P&V point out, we have fat reserves we can draw upon for energy, but we have no protein reserves other than our lean tissues to draw upon thru the day.

Personally, having fasted myself (OMAD and TMAD), even for amateur endurance swimming (I’m not good but I try LOL), I tend to drop some muscle mass on OMAD, but less so when I try to gorge and pound in all my daily calories/content from two or thee meals into one single meal, but that takes some practice, isn’t always comfortable and makes it difficult for me to include all the nutrients I need. Right now, I’m favoring TMAD for me, but that’s just me. Plan-Do-Check-Act.

(Bacon is better) #11

I have observed before that the public positions of Dr. Fung and Dr. Phinney are not that far apart, if you listen carefully to what they are saying. For example, neither of them recommends fasting longer than about 72 hours without medical supervision.

(Robin) #12

@ggv… thanks for this quote. I tend to always lean in the direction of slow, steady, and consistent. Otherwise I can take just about anything to the extreme. Also, I remember Plan-Do-Study-Act from my years in education. Can’t remember who promoted it. But I liked it. For life in general.

(Bob M) #13

Disagree. Thousands of patients versus a few studies is a lot.

Moreover, I believe the studies I’ve seen referenced do not prove anything. If one does DEXA scans after 7 days of fasting and loses “fat-free mass”, what does this mean? Volek assumes it means muscle. That’s not clear to me. And if Fung has hundreds/thousands of patients who do not lose muscle mass, do we just ignore that?

I fasted many 4.5-5.5 day fasts while gaining fat-free mass and losing fat mass. Do I just disregard this info because Volek has a study in which he interprets this as not being true?

(Ross) #14

Hi Robin!

The PDCA cycle is attributed to both Deming and Shewhart (probably came from the latter) in the field of Quality Engineering (may have come from Bell Labs?) and is a way of applying the scientific method to smaller single systems, like us! :slight_smile:

I think it works well for diet and exercise because I don’t really care how this or that impacts a larger population. I care how it impacts ME!

(Robin) #15

Same. And thanks for the source.

(Ross) #16

Very possibly true. I this article on Diet Doctor, Fung is referencing studies in support of fasting that cycle OMAD days ever-other day with ad-libitum eating days. He does, however go on to discuss longer fasting periods whereas P&V would seem to warn against such.

As in anything, Cavate Emptor.

(Ross) #17

No need for controls?
Not worried about various biases that might be present in the population Fung is treating?

(Michael - When reality fails to meet expectations, the problem is not reality.) #18

Just my 2 cent input. I think we evolved to the capacity not to eat for relatively ‘short’ time spans without deleterious consequences. Short time spans would be up to as long as a week or two. As an example consider me. Total weight 145 pounds - consistent for 4.5+ years - and 14-15% body fat - about 22 pounds. That’s about 70k plus calories which would get me through a month of no food without dire consequences. Sure, my metabolism would slow a bit to adjust but not much and it would ramp up again as soon as the next meal. After glycogen is gone I might lose a little lean mass but probably not much as long as I’ve got fat to burn. What I’m getting at is that we evolved to thrive in a life situation where food was intermittent and even the leanest of us - like me - do not suffer much until you get much longer term or greater frequency of lo/no input.

(Stickin' with mammoth) #19

I think Michael nailed it. Life, literally and figuratively, is changeable and our whole survival mechanism hinges on adaptation, especially nutritionally.

Finding general rules of engagement with fuel that allow for constantly shifting variables isn’t as simple or clean as rigidly and doggedly doing the same danged thing every day and forming a neat line of progress on a chart that you can draw with a ruler, but life ain’t like that. I think the ones braggin’ about straight lines are liars. Or androids.

The humans (the ones who’ve figured out what that means) are flexible, patient, and focus on the long-term. The only point on the chart you need to think about is this: Do you feel better now than you did this time last year? Well, then…

(Allie) #20

I think, if anything, the opposite as the variances will help prevent your metabolism from adapting. I’m currently doing IF during the week but not at weekends for the same reason. Normally this means I don’t eat from 1300 until I have coffee or a shake early the next day, but know my body well enough to recognise when more fuel is needed which yesterday resulted in me eating during the afternoon.