How long should I wait before starting fasting?

(Max Scotthorne) #1

Hi to all fellow ketoites,

Just wanted to ask how long should I wait before I begin fasting? I’m well into my keto flu now and feel like I’m coming out of the other side of it. I am hesitant to start fasting cycles as I don’t want to make it super hard.


(Joey) #2

Greetings @Max147 Great question and many on this forum have different views. Here’s mine…

Don’t get involved in fasting unless/until you sense that your hunger levels are generally reduced enough to comfortably do so. Trust your hunger sensations after you’re fully fat-adapted (i.e., your mitochondria are burning fat to produce your body’s energy levels).

Unless you’re battling a specific serious ailment (e.g., cancer), there’s no rush to introduce fasting, beyond perhaps skipping the occasional meal you’re just not hungry enough to care about. That’s when your body is telling you that fasting would be easy and manageable. It’s NOT supposed to be hard if/when your body is ready to miss meals, perhaps for a more extended period if you wish.

(Chuck) #3

I was doing intermittent fasting long before I started my keto/low carb diet. For me I was instantly hooked on the fact I was no longer hungry at all. I have since starting keto I have been able to do longer fasts.


Whenever it feels okay for you… I hadn’t stopped intermittent fasting when I went keto but I never could do EF on low-carb without real determination and effort unlike on high-carb (where it just happened very occasionally and naturally. I imagine my body wanted a break now and then).

You may try if you feel ready, you can stop any time if it gets hard - unless your attitude is different. I am not familiar with that, I only fast until I am fine and not hungry too much :slight_smile: I may put some extra effort into it when determined but if my body wants food, my body gets food.

And of course, don’t fast if that triggers undereating! That’s not good.

This is just my hedonistic approach, I am aware others are different but I am still very much against forcing ourselves and SUFFER. I frequented a fasting forum at some time and it was horrible, there was no extreme problems where the others (except me) didn’t advised “being strong”. That’s not a healthy attitude.
But it’s individual (I don’t mean only the person but the situation) if you should fast when you are hungry.

Why do you want to fast? It’s an important question. Don’t feel you EVER need to do it just because you do keto (some people seem to think that keto must results in eventual fasts. nope). I understand experimenting, in that case it’s up to you to decide if you feel ready… It needn’t to happen automatically, all the (very little) EF I did on keto needed effort and it was fine, I didn’t go too far. I like to push things a bit here and there :wink: Really just a bit, I don’t actually force things. Anyway, I tend to eat way before I get hungry (no idea how to wait even after years… it doesn’t mean I don’t do that sometimes but very often not) so trying a bit harder is something I really should do.

(Allie) #5

When you’re naturally not hungry, it’s not something that should be forced.

“Keto flu” is usually a lack of sodium, easily avoided.

(Bacon is a many-splendoured thing) #6

All keto “flu” is, is a lack of enough sodium. It is easily preventable by using a bit more salt on your food.

As far as fasting is concerned, the easiest way to get into it is down the road, when you find yourself forgetting to eat. But there’s no reason not to try earlier. Just don’t force it if it seems too difficult.


Do you mean intermittent fasting or extended?

Depends if you’re adapted to living on your fat? Like Paul said do you easily miss meals?

I’d think about your reasons. Do you want tho lose weight or achieve autophagy or for Mental Health?

Experimenting with time restricted eating can help you learn whether to go 16/8 or however long you can fast daily. I build for a week of IF then I can EF. It works for me to have a goal when IF or EF and to be aware of danger signs like feeling cold. You can avoid hunger by keeping yourself busy or exercising when you’re normally getting hungry.

I haven’t been able to keep the weight off but have realised good relief from stress and better awareness of tension levels. I believe it does rejuvenate too. In autophagy the body looks very very healthy.

Watch out as you might not sleep as much as you did previously too. The first meal after an EF normally passes v quickly so don’t eat much and then eat afterwards,

None of this might apply to you but some of it could. I’ve seen someone at work come out of IF and put weight on too. Be aware you can obsess about food and not many people can beat the hunger. I can’t.

Before you consider this stuff, I’m me, not you, Im not trying to lose too much/any weight (more MH now) and after 18 months Im still trying to get it right.

(Alec) #8

I would recommend you get thoroughly fat adapted before you fast. How long does fat adaptation take? It varies, but estimates range from 6-8 weeks to 6-8 months. My view is that it is a 6 month process. Of course fat adaptation is a gradual process… in 2 months you have some fat adaptation and it becomes stronger and stronger the longer you go with very low carbs.

So I would recommend you wait 6 months before you start fasting. Why does fat adaptation matter? If there is no fuel coming in, then the body needs to be able to have good access to bodyfat. Your body will access some bodyfat if not fat adapted, but probably not enough. Result? You may decrease your metabolic rate, which is not what you want.

My experience is if you keep carbs really low, the fat loss just happens without fasting. It may be fairly slow, but you have time… let it happen slowly, don’t be in a rush.

(Chuck) #9

I was reading and researching about fat burning and fasting and came across something that has stuck in my head. “Fasting 16 hours per day has been found to be the key to weight maintenance and management.“ But it added that a person still could gain weight as I did by eating a standard American diet. I have fasted most of my life for between 12 and 18 hours a day. And I have noticed that if I eat lower carbs I either lose or maintain my weight, but if I eat high carbs even an extremely low calorie high carb diet I gain weight.

(Bacon is a many-splendoured thing) #10

This is the primary observation underlying the carbohydrate-insulin model of obesity. Insulin, among its many other functions, instructs adipose tissue to store fat. It also inhibits the action of hormone-sensitive lipase inside the adipocyte, so that once the triglycerides are inside, they cannot be broken down and are therefore trapped. (Intact triglycerides are too large to pass through the cell wall.)

The reason that low-calorie high-carb diets can work (at least for a time) is that usually the reduction of calories leads to a reduction in high-glycaemic, highly-processed foods, which helps the process. But people are highly variable. One of the executives at DuPont profiled in a series of case reports by the company physician was so sensitive to carbohydrate that even a single extra apple would cause him to put on weight. (I imagine that today we would describe him as highly insulin-resistant.)


Well I surely can’t store negative calories so I need to overeat for a gain on high-carb as probably most people… Some people work in tricky ways though… (And it’s not negative for them as the body manages to lower metabolism if it “must”, scary.)


Why are you doing Keto? If it is for weight loss then I would start out planning your meals and getting the macros right. Start with the 16/8 protocol but not every day. As you become adapted you can do longer fasts. 24 hour or even longer. IF can help with weight loss. Think of it as, once your body burns through its sugar stores for energy, the body now will release fat to burn. Dr. Jason Fung has mentioned that some of his patients have a blood lactate level above 2 (burn almost 100% sugar) just from walking, even with a lower heart rate. The fasting helps with this process.

(Chuck) #14

I have a question, but first a little information. I am not diabetic, but my grandmother on my mom’s side was diabetic. My sister is pre diabetic due to her weight. Even at my heaviest my fasting blood sugar levels were low normal. Now after 3.5 months of keto/low carb, I only work to keep my total carbs below 50, my blood sugar was still in the low normal range. My total cholesterol was below normal and my triglycerides HDL ratio was 1:1. How does that even say I am insulin sensitive or resistive? I am just trying to understand. And by the way I am still approximately 25 pounds overweight, by the BMI standards. Now when I turned 21 and before I went in Navy boot camp I weighed 167, since I left the I once managed to to get down to 170, that was on the Atkins diet back in the early 1980s. I managed to get down to 188 for a while in 2017-2018 on the standard eat less move more by speed walking close to 8 miles a day. My goal and vision now is to hopefully get down to about 175 to 180, this is within the BMI normal weight for my height. But I am only able anymore to walk and hike the trails around here for about 3 to 5 miles at a time and not everyday as I was doing back in 2017.

For general reference I average 400 mg of cholesterol per day.

(Bacon is a many-splendoured thing) #15

It is possible to have normal serum glucose and still be insulin-resistant. The most sensitive measure of insulin resistance is the insulin-response pattern shown during an oral glucose tolerance test. The late Dr. Joseph Kraft identified five patterns, four of which indicated that diagnosis of Type II diabetes was likely in the future. Dr. Kraft maintained that this actually already was diabetes, even though serum glucose was not yet out of control, and possibly wouldn’t be until as much as twenty years in the future. Since for good or ill, the loss of glucose control is the official diagnostic of Type II diabetes, today we would simply call it pre-diabetes or insulin-resistance.

As for your ratio of triglycerides to HDL, I am assuming it is in U.S. units (mg/dL), which means it is very good and probably indicative of good insulin sensitivity.

It may not be helpful to use BMI as a guide. Very fit body builders often register as obese by BMI, which to me indicates limited usefulness. Better to use a DEXA scan or the caliper measurement of body composition as your guide to fitness or the lack thereof.

As for trying to exercise off poundage, that is probably not worth the effort, according to various studies. It is easier to shed excess fat (assuming that’s what those 25 pounds actually are) by staying in ketosis. But there are a number of factors that regulate body weight, and we used to use the term “Phinney weight” here on the forums, in recognition of Dr. Phinney’s advice to get to a weight that would could achieve and maintain reasonably, without too much effort. Arguing with our body is difficult, and in any case Dr. Phinney says that he and Prof. Volek have typically seen a fat loss on keto amounting to about 20-25% of starting weight. Further loss can sometimes be seen, after the body has spent some time at the new settling point. Sometimes eating more helps, and sometimes cutting out carbohydrate entirely leads to the loss of more fat.

It was Ancel Keys himself who showed that our cholesterol intake has nothing to do with the level of cholesterol in the body.

(Marianne) #16

I would wait at least 4-6 weeks, just to give your body a break and let it adjust to your new way of eating.

In the beginning, I did a 24-hour fast once a week. No great shakes compared to how long many people do it, but I just didn’t like it. It wasn’t hard and I wasn’t hungry, but I just didn’t like going through a day without eating. Everybody’s different. You are at the beginning of your journey; let your body repair a little. Fasting is not a requirement for those who decide it doesn’t suit them.

Good luck.

(Doug) #17

Hi Max. I’d say do what you want - give it a try. It sounds like you’re getting used to burning fat for energy, so all good there. We’re all different, but you don’t know until you go.:slightly_smiling_face:

I was used to eating one meal a day, most days, so perhaps I was somewhat ‘fat-adapted’ even while eating lots of carbs. I slammed into a 4.5 day fast right away (the day the doctors office called me and annointed me as a Type 2 diabetic). Only stopped because I chickened out on Sunday night, thinking I might be ‘weak’ or some dang thing at work.

(BuckRimfire) #18

That shows that your pancreas and glucose uptake systems was able to handle the amount of carb you were eating, but to really know if you were pre-diabetic, you’d needed to have tested your fasting and post-glucose-challenge insulin. A “Kraft Test” or even just a pre- and 2-hour post-glucose insulin measurement. This is very much NOT that standard of care, but Kraft argued that you could identify diabetic tendencies many years earlier with his test than the usual glucose test.

Supposedly after being low-carb for a while, you can’t really do the Kraft test without going back to high-carb eating, although how long is needed, I really don’t know. Seems like some people have suggested it’s as little as one day.

OTOH, your trig/HDL-C ratio is reassuring.

KraftAssay.pdf (467.6 KB)

(BuckRimfire) #19

I’d probably give it a couple of months, at least. See what’s happening with a regular low-carb eating schedule, first.

I forget exactly, but before we started “fasting” and after a year on low-carb, we had a period of a couple of months at work that were horribly busy. (Lab work, so not completely sedentary but not strenuous activity.) Some days I suddenly realized that it was after 5 PM and I’d had nothing since a big breakfast except a couple of cups of tea, and I wasn’t really that hungry. In contrast, when I used to have big high-carb brekkies I’d be ravenous by 11:30 and a little dizzy soon after.

So, you might try skipping lunch at some point and see how you feel, once you are comfortable with the low-carb program. If that goes well, try a big breakfast then nothing until breakfast or lunch the next day.

I’ve started 36-48 hour fasts by stopping eating after dinner or after breakfast, and for me having breakfast as the last meal is a little easier. When I have dinner last, the next afternoon/evening I find not eating a bit annoying, but I wake up on the second morning uninterested in food. It seems like the hard part is roughly the 18-26 hour phase, so if you have breakfast as the last meal, you’re asleep during that time. This works for me, anyway!

(Bacon is a many-splendoured thing) #20

Bikman talks about this in a couple of interviews I’ve seen. The “problem” is simply that after long enough on a low-carb diet, the pancreas stops storing insulin for ready release. This is needed on a high-carb diet, but the body doesn’t like to maintain such things unnecessarily. So the upshot is that when people on a low-carb or carnivore diet are hit with a sudden glucose load, the first-phase insulin response does not occur, since the pancreas has to manufacture insulin to deal with the glucose. This gives a false impression of poor glucose control. Bikman says, however, that it only takes 24 hours for the pancreas to build up a supply of insulin for the first-phase response. This is why ketonians who are going to be taking an oral glucose tolerance test are advised to eat carbohydrate a day or two before the test, so that their insulin response doesn’t look abnormal.


I would start skipping breakfast, just as a “playful experiment”, and see where that leads you. When you start feeling miserable or get a headache you stop the fast and adjust on that level for some days (you will see you adapt fast). Then you increase gradually, keeping it a pleasant experience so it does not feel “hard”. You will one day be able to fast for 40 or 50 hours without it feeling a terrible experience (my record is 70 hours, I always interrupt because of headaches, never because of hunger).

This is how I did it, and it worked for me because I never push it hard and am, therefore, ready to push it a bit further a bit later.

Of course, it slows the pace and it will take a while before I can do regular extended fasts of 48-72 hours (first wet, then dry). But I will not feel miserable in the process, which is important to me.

For dry fasting, I interrupted at the point of headache appearing, gradually extending. Now I can do a dry fast of 22 to 23 hours (my normal “one meal a day” as I am a slow eater) without any discomfort. Next year I’d like to get to the point where I can extend to 36 hours without headaches, and so on.

If it were a “tour de force” that makes the experience unpleasant or outright miserable, I know I would start looking for excuses to postpone it again, and again, and again…

Your mileage may vary…