Cephalic Phase Response and Hunger – Fasting 18

The relationship between fasting and hunger is, without doubt, the #1 concern we hear. Overcoming hunger seems a daunting task, stemming from a misunderstanding of actual hunger. This is mildly ironic, since my guess is that 95% of us have never, truly been hungry in the sense of starvation, where we did not know when we would be able to eat again. However, I also understand that hunger is one of the most basic human drives/instincts known as the 3 F’s (food, fluids, and procreation).

We saw in our last post that much of what we perceive as hunger is actually a learned behaviour, and as such, can be ‘unlearned’. Breaking all the conditioned stimuli of food will help reduce hunger cues. However, there is also a natural need and desire for food. There are unconditioned stimuli – those signals for us to eat – smell, touch, taste, sight of food. The hunger response starts well before food is ingested, and is highly dependent upon hormonal stimuli (gherelin, peptide YY, cholecystokinin, leptin etc). For example, you might think the smell of food increases hunger. But what if you had just stuffed yourself at the All You Can Eat Buffet? The smell of french fries is likely to make you queasy, not hungry.

But, if you are susceptible, then hunger starts in the mind. This is known as the cephalic phase response (CPR). ‘Cephalic’ refers to the brain – so these are measurable physical responses to the suggestion of food and lasts for about 10 minutes. The most obvious of these is the Pavlovian response that we discussed previously. Salivation increases immediately upon the expectation, not the actual delivery of food. Interestingly, the amount of salivation increases when people are shown a picture of a lemon compared to other foods, so clearly the CPR is ‘learned’.

Pancreatic fluid and bicarbonate are also secreted into the stomach well before any food is received. The pancreas also starts to ramp up insulin production and secretion before there is any change in blood glucose levels. Post-prandial thermogenesis – the body heat produced after meals – is also increased. These are measurable responses, although much weaker even in anticipation of food even if no meal is taken afterwards.

The purpose of CPR is to help synchronize the gut response and the incoming food bolus – gut pre-conditioning. If you deliver food directly into the stomach, there is no preparation and subsequent blood sugars are much higher as the body has not had a chance to produce insulin.

Of interest, sweetness itself is not sufficient to start the cephalic response. An unflavored artificial non caloric sweetener by itself did not stimulate insulin secretion. However, when paired with flavour, it may start the the cephalic phase, even if the gastric phase does not proceed (because it has no calories or bulk).

So, why is this relevant?

First, there is controversy whether you can use non-nutritive sweeteners during fasts (Splenda etc.) Even though there are no calories, this does not negate the cephalic phase response. If the flavour and the sweetener is enough to start the CPR (diet soda, for example), then this will naturally stimulate hunger and the desire to eat. You are chumming the shark infested waters of hunger. If you don’t eat soon, somebody’s gonna get their head bitten off. So, yes, artificially sweetened food can make you hungry.

Diet sodas, in my opinion, are generally not helpful to efforts to fast or lose weight. Recent randomized controlled studies back up the point that diet drinks may sabotage weight loss efforts despite the large decrease in consumed sugars. Of course, common sense would have told you the same thing. If sweeteners were the answer, we would not have this obesity epidemic, would we? It’s not like people aren’t eating sweeteners. How many people do you know that have tried sweeteners? 95% of everybody? How many people lost significant weight? 2%? There’s your answer right there. The proof is in the pudding. In our IDM program, we prohibit the use of all artificial sweeteners.

However, if the flavouring is weak and CPR is not activated, then use of artificial sweeteners may be OK. There are certainly those that argue that sweeteners help them lose weight by increasing compliance. If so, great. My best advice is to try to fast without the use of sweeteners. If you cannot, then you can try adding a small amount. However, if it makes fasting harder, or prevents you from seeing results, then stop.

The second practical implication of the CPR is that we must remove ourselves food stimuli. Trying to cook a meal while fasting is almost unbearably difficult. To see and smell the food without being able to eat it is hard. This is not simply a matter of weak willpower. Our cephalic phase responses are fully activated. To stop there is like trying to stop a piranha feeding frenzy. Or like trying to stop peeing after you started. (This is actually the way you are supposed to do a urine test). If you can take yourself out away from food stimuli, then keeping to a diet or a fast is infinitely easier. This, of course is the reason you should not shop for food when hungry, or keep cookies/ snacks in the pantry.

That is why one of our most important tips for fasting is to stay busy. I often fast during workdays, because it fits easily into my schedule. I simply work through lunch. By staying busy, I don’t even remember to be hungry. My cephalic phase response has not been activated. If somebody were to put food in front of me, I often cannot resist. But if there is only a pile of paperwork, I just plow right through and forget to be hungry. Then, I get to go home early because I just saved an hour or so.

Hunger comes in waves

We often imagine that hunger will build and build until it is unbearable and we need to stuff ourselves with Krispy Kreme donuts. however, this is not the case at all. Hunger comes in waves. You just need to ride out the waves.

Remember a time when you skipped lunch. At first, you get hungry. It’s 12:00 noon, but perhaps you are caught up in a meeting and can’t get away. The hunger builds and builds, but there’s nothing to be done. Boss is such a jerk! But what happened at 1:00 or 1:30 or so? The hunger entirely dissipates. The wave has passed. By dinner time, you might remember you missed lunch and eat.

What’s the best way to pass the wave? I find that drinking a cup of green tea or coffee is enough. By the time I’ve finished my cup of green tea, the hunger has passed and I’ve gone onto the next thing to do that day.

Hunger is not predetermined by not eating for a certain period of time. Hunger is a hormonal signal. It does not come about simply because the stomach is ’empty’.  Why is this important? Because that explains how people can fast for days without being hungry. This is a consistent finding throughout the scientific literature on fasting as well as in our own IDM program.

For example, Dr. Gilliland, in his description of total fasting found that

A feeling of well-being is certainly engendered in this way and may amount to euphoria. We did not encounter complaints of hunger after the first day.

Jeez! People weren’t hungry and actually felt ‘euphoric’ during 14 days of fasting. In fact, some felt so good, they wanted to continue. This was echoed by the experience of Dr. Drenick, of UCLA. Hunger comes quite strongly during the first 1-2 days of fasting. After that, the hunger just subsides and then goes away. Some people speculate that the ketones are actively suppressing appetite.

This explains our response to people who feel they cannot go beyond 24 hours of fasting. We advise them to try 3-7 full days of fasting. Why would we do that? Well, this rapidly gets their bodies used to fasting. By getting over the first 1-2 days, hunger starts to disappear and they become reassured that they are not ‘overwhelmed’ by hunger. Most patients feel that day 2 is the worst. Once they know this and expect it, they are able to handle it.

So, the bottom line?

Hunger is a state of mind, not a state of stomach.

Start here with Fasting part 1

Continue to Fasting Part 19 – Circadian Rhythms

2018-08-21T21:12:57+00:0053 Comments

About the Author:

Dr. Fung is a Toronto based kidney specialist, having graduated from the University of Toronto and finishing his medical specialty at the University of California, Los Angeles in 2001. He is the author of the bestsellers ‘The Obesity Code’ and ‘The Complete Guide to Fasting’. He has pioneered the use of therapeutic fasting for weight loss and type 2 diabetes reversal in his IDM clinic.

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Valerie North
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Valerie North

I know a couple of people who fasted for 3 weeks to 40 day, and it is true, their hunger completely subsided. However, once they started eating again, the weight all come back rather quickly. How do your patients avoid this?

Toni
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Toni

I’ve avoided gaining my weight back after a longer fast up to 13 days by not over eating paired with a LCHF diet. I continue a modified fasting schedule of 20 hours fasting daily with a 4 hour eating window. Oddly enough I will gain 2-3 lbs when I begin eating on my daily IF schedule but it will come back off in a few days and a slower weight loss will continue. I imagine if I ate grains as well as a high carb 3 meal a day diet. My weight would bounce right back up plus some added… Read more »

JW
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JW

Maybe they can transfer over to a less intense fasting method such modified alternate day fast (ie Varady or Johnson) or a 5:2 (Mosley)?

Madeleine
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Madeleine

A lot of the weight lost is the initial loss of glycogen stores and the water they tend to hold. This is 5-10 lbs in most people. This will inevitably come back on but the actual fast lost should not. The fast lost should roughly correspond to TDEE*number of days fasted/3500 since a pound of fat contains about 3500 calories.

Madeleine
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Madeleine

Fat lost*

Veronica
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Veronica

Perfect explanation – thank you!

John C
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John C

This is getting really creepy Dr Fung! Once again you have articulated my current thinking on why dietary management is working for me. I believe that my failure to fast much beyond 24 hours is largely psychological, but that there may also be a physical component, as I was saying to Megan during our online meeting at about the same time you must have been posting this blog entry. I am fortunate to be what I think of as being “post-diabetic” with very stable blood glucose and hardly any visceral fat. I find I can shrug off hunger pangs by… Read more »

Ari
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Ari

Maybe you are not just totally adapted to burning fat? Try very low-carb diet for a couple of weeks, say, about 50g/day. When you consume 60-70% of your calories as fat, it is very easy to switch from burning the fat you eat to burning the fat you carry in your stores. No more hunger pangs and no hypoglycemia. I had metabolic syndrome and had same kind of symptoms you describe. Now fully recovered.

John C
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John C

Thanks Ari. Glad it worked for you and it encourages me to keep trying. I can get down to 50g of carb or less most days, but I also need to limit protein intake because of kidney disease. I have to concentrate on keeping the fat intake high because I carry very little stored fat now that I’ve almost halved my weight to 155 pounds and reduced my waistline by twelve inches. Luckily I love the taste of butter (melted over vegetables and stirred into home made soups) and olive oil (mixed with apple cider vinegar as a salad dressing).

stenB
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stenB

I think you are on the right track with the butter! Lots of fat will increase and thin bile flow which will enable a cleaner liver which may be the only thing missing for the kidneys to get back to work: ( Anecdote: A relative was scheduled for liver and kidney transplant. The liver was done first. A few months after it was discovered that the kidneys had normalized with the new liver and the old kidneys could remain. )

JJ
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JJ

Hi Ari,

Fascinating insight.

Any idea why a 70% fat-diet would switch to burning stored fat?

Also what fats were you consuming? Butter, olive oil etc?

Thanks,

Ruthy
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Ruthy

To my horror I just got test results as follows: glucose plasma fasting 16.6 and A1c 11.2. My NP prescribes metformin and insulin and I am feeling a lot of pressure to “toe the party line”. I am afraid to take insulin when I know I already have too much insulin. I just started this week eating LCHF and will start fasting. Should I also take the drugs for now? I live in the Toronto area, so I wonder if Dr Fung can see me? I am highly motivated to get healthy and I need a trail blazing, radical doctor… Read more »

lass lassiter
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lass lassiter

Thanks again for the pertinent information!

Wenchypoo
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Wenchypoo

Is this how the Breatharians can expound the supposed “virtues” of living off nothing but air…right up until they die–the euphoria?

Calvin
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Calvin

Hello Dr Fung!!

Big fan of your site, What do you think of Warrior Diet by Ori Hofmekler: http://www.amazon.com/The-Warrior-Diet-Biological-Powerhouse/product-reviews/1583942009

I am a big fan of fasting but my workday is demanding & i need atleast a fruit or small bowl of veggies to survive the day. I am overweight & my family has a history of T2D. Just wanted to know your thoughts on this.
I only little amount of veggies or couple of boiled eggs or a fruit during daytime, works nicely but still in the first week.

BobM
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BobM

If you’re insulin resistant, fruit is one of the worst things you can eat. I rarely eat fruit, other than berries, and those very infrequently, as a dessert or treat with something high fat to blunt the blood sugar and fructose spike. On the days I fast, I don’t eat anything. I have yet to experience hunger going away. I’ve done a bunch of 3-day fasts and one 5-day fast, and (physical) hunger was present (particularly the day I lift weights) every single day. It does come in waves, though. I’ll have another 3-5 day fast in December (after Thanksgiving)… Read more »

David
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David

It’s absolutely routine- it’s very easy to eat the same way based on the time of day and eating the same kinds of food. It probably comes from picking up routines from family or friends. I also wonder what % of meals the average American has at a restaurant/fast food place. I was going to a restaurant with co-workers, a nicer restaurant, and I happened to look at the menu online. It had a calorie count, there were only a few entrees under 2000 calories, plus I’m sure they used vegetable oil. If I’m in a restaurant, I can’t help… Read more »

Tomairangi
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Tomairangi

I am reading your blog and am excited about freeing myself from my type 2 diabetes. I found you through Diet Doctor adn learning about intermittent fasting. I have had my diabetic medications lowered as I am considered well controlled (according to my blood results). I now take only metformin. I also am on further medication for affective disorder, which is associated with weight gain, also well controlled. However I am still obese and I still have diabetes. I am gaining weight with my blood pressure on the rise. I am told that there is nothing more I can do… Read more »

Jennifer
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Jennifer

I need advice please!

My husband complains my breath gets bad after about 16-20 hours of fasting and basically forces me to eat something (drinking tea/coffee or brushing my teeth doesnt help, it seems to come from my stomach being empty, not my mouth). Anyone experienced the same or have any tips what I can do to minimally affect the fasting? Thank you!!

Amy Berger (@TuitNutrition)
Guest

Jennifer, has no one explained to you that the “bad” odor of your breath when you fast (or are on a very low-carb diet) is acetone? That is one of the ketone molecules the body expels. Acetoacetate comes out in the urine; beta-hydroxybutyrate is on the blood, and acetone comes out in the breath. Take heart — the bad breath is a sure sign you’re in a good ketotic state. 🙂 As to how to get rid of it, it depends on what you would choose to do. Personally, I don’t think a sugar-free breath mint or piece of chewing… Read more »

Steve
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Steve

Greetings Dr. Fungi and Megan: another fantastic post…many thanks. After enjoying a recent prep session with Megan and others via your IDM/ LDP I started a5- day fast and also had NO hunger after day one.

Like Jennifer’s question I too wonder which sugar substitute, in gum or mints, is acceptable. I allowed myself 2-4 pieces of xylitol gum a day, due to extreme ketonix-breath (ketones at 4.7 on day 4).

Thanks again for your ongoing great work. All the best!

Steve
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Steve

….sorry Dr. Fung…not Fungi (darn auto spell)!

Simon Thompson
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Simon Thompson

He is a fun guy though!

Bob Hagan
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Bob Hagan

I like Stevia in my coffee and thought it was a better choice. It seems what you are saying is that the CFR may be initiated either way.

Walter Bushell
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Walter Bushell

Stevia is not an artificial sweetener. Especially if you use the ground up green leaves.
Extracts are not in general real food. Counter example, butter is general considered food, but is a (low tech) extract.

Martin Williams
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Martin Williams

Dr Fung: Since insulin secretion is stimulated only when sweetness is paired with a significant degree of ‘flavour’, does this mean that sweeteners in tea and coffee are reasonably safe, or are the flavours of those beverages sufficient for insulogenesis?

HelenaB
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HelenaB

In no way am I defending the use of diet sodas but, personally I have never felt hungry after drinking it. I do not have a problem cooking or baking for others while fasting, the hunger does not get any worse or different than if I was doing something else. When I started eathing LCHF and after having addressed my sugaraddiction there were so many food items “out there” that simply wasn’t for me. In order to cope with that I had to dissasociate myself from it and that is what I do with food I make that is not… Read more »

Kat Lakie
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Kat Lakie

I get a response from Xylitol exactly as if it were sugar.

corrie
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corrie

“Trying to cook a meal while fasting is almost unbearably difficult. To see and smell the food without being able to eat it is hard. This is not simply a matter of weak willpower. Our cephalic phase responses are fully activated.”

As a mother, cooking several meals a day, this is a major issue for me.

istara
Guest
istara

When water fasting, it was the opposite for me. I enjoyed preparing food and just being around it (though I didn’t even taste it to check it) and the smell of it kind of sated my nostrils and interest.

I was surprised this happened because I would have expected the opposite. But it turned out that many others in the fasting forum I use experienced the same.

Our “nose hunger” was satisfied, and that helped shut our stomachs up.

Lori
Guest
Lori

I agree with you istara, I made dinner for 16 people last night on first day of an extended fast..this will be my first time going more than 36hrs. I have no problem preparing food, and I think it actually helps to smell it!! I have not had much hunger at all and I am at 40 hrs now and not hungry at all today even though everyone has eaten breakfast and I have a huge pot of bone broth going in case i need it. The smell is wonderful and I think just knowing it is there for me… Read more »

Elena
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Elena

As a cook, there are moments when one has to taste to answer simple questions: is it salty enough, is it too spicey, is the chicken undercooked etc. Sometimes I have my daughter around to be my taster, othertimes I have to plunge in to answer myself. I still consider myself fasting, I do not believe a spoon or two of food will change the fact I have not eaten for the last 24 hours.

Kolin
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Kolin

Elena-

I had the same problem while I am cooking & fasting for 24 hours…five days a week. Now I start cooking close to dinner time when I end fast. I agree with you that tasting the food while cooking does not make much difference.

Andrea Sartori
Guest
Andrea Sartori

For the home it’s easy: I do a ‘cookathon’ for the family, when I am not fasting. Then freeze and finish off in the oven. I leave it alone and get myhusband to dish up. It’s my cooking job that scuppers the efforts:-)

Andrea Sartori
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Andrea Sartori

I taste like this: 1/4 spoon of taste and spit out. Swill out with water. Doesn’t help with the CPR though. I still need help with this

Pam
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Pam

I have been LCHF for nearly 5 years. I lost 20 lbs in about 18 mos. Then I lost the last 10lbs by doing alternate day fasting combined with LCHF and it worked like a charm. However, I gradually gained that 10lbs back. My fasting BG is fine but I do think I have been insulin resistent and so after reading your blog I am trying to fast 16-20 hrs per day. I have no problem doing this but I just want to be sure that this sort of daily IF will not lower my metabolism because I have a… Read more »

Simon
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Simon

Pam, this article might be of interest to you. I used to do the same as you daily but after I tracked calories I felt like I wasn’t eating enough as I’m pretty active. That is me in the comments as well.

http://www.nourishbalancethrive.com/blog/2015/06/29/do-experiment/

I’m not diabetic and very lean but have a reasonably high fasting blood glucose (low 100s). I’m going to start doing a longer fast less frequently and see if that helps my insulin resistance. Probably a 36-42 hour fast every month at first and see how it goes. Good luck

Nilda
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Nilda

I am starting the fasting tomorrow. Does anyone have the protocol got me to follow?

Ash
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Ash

“…hunger is one of the most basic human drives/instincts known as the 3 F’s (food, fluids, and procreation).”

Haha, loved this line!

Nicholas Karusin
Guest
Nicholas Karusin

Thank you Dr Fung, since coming across your website, I’ve been following your LCHF combine with IF. Praise God, today my FBS reading is 6.1. My weight is less by 3kg. Looking forward to better health

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[…] Continue to Fasting Part 18 – Cephalic Phase Response […]

Christine
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Christine

Do you have a roster of doctors in the USA who are willing to cooperate with your fasting protocols? I live in Syscamore, IL 60178 in DeKalb County USA .I am on your wait list through Amazon for the Obesity Code. I was hoping that when you book is released and is a best seller you will be inundated with this type of request. Hoping you have plans for expanding our practice or developing a group of like minded doctors who would be willing to see patients living here in the USA.

Marsha Leggett
Guest

I read about what you are doing in the newspaper and cut the article out. I am Type 2 diabetic and weigh 205 lb and I am 5′ 7″. I am also unable to get health insurance for travel due to my diabetes and I also had a stroke 1 year ago. If I could get off the insulin at least I may be able to get coverage. I ordered your book through amazon and will receive a copy once it is released. I found you on line and I am now reading some of what I should be doing.… Read more »

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[…] food may make us hungry. This is not some kind of voodoo, but well described phenomenon of the cephalic phase response, as I’ve written about previously. So, the simplest thing to do is keep things out of sight. […]

Maureen
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Maureen

While fasting, I drank a diet drink with Splenda. An hour later my blood glucose dropped from 78 to 68. Is this cephalic or an indication that I am still insulin resistent even after weight loss and getting my sugar under control?

Priya
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Priya

Dr.Fung… food stimuli.. I own and run a restaurant, and have now started on a OMAD plan, roughly a 24 hour fasting, and you are damn right when you say that the first two days are the toughest.. but whenever I feel like letting go, I either watch one of your videos or reach out to your blog… you are rendering a yeoman service..

Kenny Roy
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Kenny Roy

I’m just starting the 16 hour and 24 hour fast with low carb diet. However; I have a food truck and always think about food, but not necessarily hungry and eating. I also watch food shows at night before I go to sleep. No wonder I never lose weight…my insulin is always increasing.

Kenny Roy
Guest
Kenny Roy

I’m just starting fasting and low carb diet and trying to lose 15 lbs and get healthier overall…(age 52 5′ 8″ 169 lbs). My cholesterol is high and I have a gut that I want to get rid of. I can make it through 16 hour fast daily and 24 hour once a week without eating (coffee and water only) and eat very low carb when I do eat. But my concern is I think about food a lot (I have a food truck side business). Even though I’m going very low carb, fasting and very active, with this insulin… Read more »

Andrea Sartori
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Andrea Sartori

I would like to know how I can fast with a certain set of circumstances that induce CPR. I am a chef and working for persons with eating disorders- Í am around food all the timeª ResultÑ I have put on 30kg weight. I believe fasting and high Ketone content would be the way to go, but how do I control CPR in my case?

Kathy Harmon
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Kathy Harmon

Diarrhea at the end of fasting. What do you recommend to stop it?

Kathy Harmon
Guest
Kathy Harmon

It has happened following a 2, 3 and 4 day fast. I follow a LCHF keto diet.

Keith Breckenridge
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Keith Breckenridge

I am eager to try a longer fast, three weeks or longer. Unfortunately I am the sole cook for my household, and this is pretty non negotiable. I understand that the CPR will make fasting harder, and I am still willing to try. My question is whether the insulin response of the CPR is strong enough to ‘break my fast’, even if I eat nothing. And if this does break my fast, would I be perpetually starting over? Would my body ever ‘switch over’ fully? I have high insulin resistance, and a fatty liver, so I really want to succeed… Read more »

Mike Robb
Guest
Mike Robb

First you say “sweetness alone is not enough to induce CIPR”. But add flavor and voila, CIPR. First, any support for this “flavor” requirement? I can’t find any support for flavor being the deal breaker.
Second, you don’t need to ingest anything at all to have CIPR happen? As in, breathing in aromas is enough? Doesn’t that negate the above point, or having to physically have something with flavor enter your mouth? Any support/studies showing insulin responses to smells?