Intermittent Fasting, Cortisol and Blood Sugar | Chris Kresser

Intermittent Fasting, Cortisol and Blood Sugar

by Chris Kresser

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There’s been a lot of discussion about the benefits of intermittent fasting (IF) in the paleo community lately. Paul Jaminet mentions it’s role in boosting the immune system in his book, The Perfect Health Diet, and IF can also be helpful for those trying to lose weight and tune their metabolism.

From an evolutionary perspective, intermittent fasting was probably the normal state of affairs. There were no grocery stores, restaurants or convenience stores, and food was not nearly as readily available or easy to come by as it is today. Nor were there watches, schedules, lunch breaks or the kind of structure and routine we have in the modern world. This means it’s likely that our paleo ancestors often did go 12-16 hours between meals on a regular basis, and perhaps had full days when they ate lightly or didn’t eat at all.

So, while I agree that IF is part of our heritage, and that it can be helpful in certain situations, I don’t believe it’s an appropriate strategy for everyone.

Why? Because fasting can elevate cortisol levels.

One of cortisol’s effects is that it raises blood sugar. So, in someone with blood sugar regulation issues, fasting can actually make them worse.

I’ve seen this time and time again with my patients. Almost all of my patients have blood sugar imbalances. And it’s usually not as simple as “high blood sugar” or “low blood sugar”. They often have a combination of both (reactive hypoglycemia), or strange blood sugar patterns that, on the surface, don’t make much sense. These folks aren’t eating a Standard American Diet. Most of them are already on a paleo-type or low-carb diet. Yet they still have blood sugar issues.

In these cases, cortisol dysregulation is almost always the culprit. When these patients try intermittent fasting, their blood sugar control gets worse. I will see fasting blood sugar readings in the 90s and even low 100s, in spite of the fact that they are eating a low-carb, paleo-type diet.

That’s why I don’t recommend intermittent fasting for people with blood sugar regulation problems. Instead, I suggest that they eat every 2-3 hours. This helps to maintain stable blood sugar throughout the day and prevents cortisol and other stress hormones like epinephrine and norepinephrine from getting involved. When my patients that have been fasting and experiencing high blood sugar readings switch to eating this way, their blood sugar numbers almost always normalize.

I don’t think eating every 2-3 hours is “normal” from an evolutionary perspective. But neither is driving in traffic, worrying about your 401k, or staying up until 2:00am on Facebook. The paleo template is there to guide us, but it’s not a set of rules to be followed blindly. This should also be a reminder that there’s no “one size fits all” approach when it comes to healthcare. Successful treatment depends on identifying the underlying mechanisms for each individual and addressing them accordingly.

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  1. Can anybody give me some ideas?
    Ihave gallbladder polyps and need to get them checked every few months as they can turn malignant, have also fatty liver, borderline high cholesterol, BG around 100 and 130 post prandial sometimes 110 even. Overweight 107kg need to be at around 73kg (ideal weight) Viceral fat 15, bodyfat 30%.

    I do intermittant fasting and up to 22hrs but usually round 18hrs and then start eating, I tried keto but failed many times seeing as I have GERD/Hiatal Hernia and so an increase in Fat = reflux hell, I even made keto bread myself as I figured the coconut flout in the bread or almond flour may help to bind the acid, Nope!

    I find that I have little energy whilst in a fasting state in the mornings and afternoon and have energy, thats right … after Ive eaten, and so doing cardio or resistance type exercise whilst fasting would be like climbing a mountain, whereas its easier when I eat. I aslo feel more nervous/anxious in a fasted state and this makes sense, higher cortisol/adrenaline etc cause you are being pushed to find food, or kill, woe betide anybody gets in my way whilst Im driving in the am … this is what I dont like and need to carb up to calm the heck down.

    My idea was to help shrink those polyps by getting my body to get into autophagy and this is achieved (hopefully) after the 15hr period with some cardio help to deplete liver and skeletal muscle stores, I think the increased cortisol is not so bad unless it gets too high, i.e. unless I add insult to injury and do daily coffee enemas, drink coffee and tea then yes I get wired and ratty as hell.
    Im taking serrapeptase, curcumin and vitamins and selenium too.
    in 2000 I slashed my weight by 30kg in 3 months and came off 2 meds, I went back to my old ways and here I am now.
    I did this by eating 3 meals a day drank sugary green tea beverage throughout the day and walked a LOT, didnt eat friut or veg only tiny amount of veg and meat during the day and ate simple carbs like bread and noodles, this totally worked for me at the time but now I have acid reflux and have to be careful with green tea etc as they weaken the sphincter muscle in the stomach and allow acid to reflux, I need to tweak and try that again or combine the two (IF and my China protocol)

    • Please research relationship between H.Pylori bacteria in stomach causing lowered stomach acid/GERD…even triggers morning sickness as bad as hyperemesis gravidarum.
      GERD is dominantly a problem of deficient stomach acid.
      The body is off-loading what it cannot process. It will do that in 2 ways: throw it up, or sudden fast-transit out the back (for those who tend towards that).
      Some Remedies that usually work well: take 1 or 2 Tablespoons of ACV (real apple cider vinegar in water, with each meal; take something that kills bad germs, or controls sudden over-growths of them, like GSE, colloidal silver, or specific antibiotic to kill-back the H.Pylori….usually one serving of GSE (about 10 to 20 drops in water with citrus juice to buffer the bitter taste); or, a couple ounces of a 30 or 45 ppm colloidal silver, does it…one-time serving.).
      Then, take a really good probiotic…one that has a long list of different kinds of them, as well as high colony counts. We’ve often used Garden of Life Ultra, because that one contains at least one kind that helps make vit. K2, so important for overall health benefits.
      Some have successfully only used daily large amounts of same probiotics only, to crowd-out/kill-back overactive h.pylori….that usually translates to 4capsules daily, on empty stomach, about 30 minutes before eating, to give them best head start to establish themselves.
      Pharma has gone to extreme great lengths, over the past approximately 45 years, to relabel certain symptoms as-if those were stand-alone diseases…they aren’t.
      Symptoms indicate underlying root-causes, which the industries governing and directing how medicine is practiced, have increasingly promoted, to very effectively increase profits, among other things. There are other factors, but that’s the worst, as it has been usurious of human behavior weaknesses.
      But you can look up stomach acid deficiency, and those remedies. We’ve used them often, for ourselves, family and friends, as well as non-related patients, with good success rates.

    • Of course there are other triggers which should be better controlled, such as figuring out why the foods consumed are triggering it.
      That can happen due to how the food was grown, what chemical residues are on it, and things like food sensitivities or allergies. …Allergies/sensitivities indicate underlying conditions that need corrected, too…often, it’s related to trace mineral deficiencies…which is how AgriBiz/CAFO grown foods trigger more frequent and worse digestive upsets than if one only ate organically grown foods (real ones, not all the industry faked-organics ).
      Also, how, when, and what one eats, can matter. Eating fast=bad; combining some foods with certain others, can matter.
      Some get relief using sequential eating: eat the stuff more easily digested, first…in this order:
      First simple sugars/starches, then more complex starches, them proteins, last. That order, “primes the system”, so that by the time it gets to digest the proteins, it’s ready to do it. Though some may need to start by only eating one type of food at a sitting, to start retraining the system, for a time.
      Paying attention to maintaining peace and pleasantness while eating, avoid eating when stressed, etc., matter, too.

  2. I usually disagree with what Kriss has to say, but this I have to agree he has some good points.
    Ive been doing I.F. for 6 months to a year and fast for 18 to 22hrs and was pushing for the 23hr mark and one meal a day, Ive noticed when I do go for the one meal I tend to feel sleepy and HAVE to nap afterwards, maybe the insulin spike? This doesnt happen if I eat 3 meals a day.
    Also in the am I do coffee enemas, if I eat its okay as long as I dont drink too many coffees or teas I dont get jittery, but on my fasting days I DO get more nervous, anxious and woe betide you get in my way, whilst driving Im more nervous, kids tantrums seem worse (my reaction to stress is terrible) easier to anger, I have to a ‘ride’ the morning/afternoons and wait for that evening window.
    Now Im thinking its the cortisol that normally rises in the morning, but in a fasted state doesnt adrenaline and other stress chemicals increase to make you move your ass and find food, its no wonder my brain is more stressed, smells are more intense, sounds seem louder, this is all stress for the human body, and I have less energy (duh) to exercise cardio or resistance, whereas if I eat breakfast I have the energy to walk and do some movement.

    • Gerald, I do the same but no such effects. But it is probably due to that I eat a high fat, (saturated and monounsaturated stable fats) diet combined with low carb and low protein. It enables the fat burning BEFORE fasting so that there is no real fuel change, only change from food to body fat. My 5 cents.
      See also Jason Fung!

    • Checked all labs related to iron in body?
      Serum ferritin, CBC, Tibc, etc., together, can show iron levels in blood, as well as stored iron. One can have a CBC in normal limits, but a low ferritin means borderline anemia.
      Automated lab tests’ accuracy DEPEND on the person being decently hydrated, too! An Automated CBC , from a dehydrated person, can show “normal range”, yet, doing a copper sulfate test on a drop of blood, same person, at same time, will reveal anemic….because the automated lab depends on seeing a certain number of blood cells floating in a certain amount of serum.
      If there’s low fluid volume, the machine thinks there’s more blood cells in ratio to serum, than actually exist; but the copper sulfate manual test, is based on a chemical reaction, not a picture, so reveals the anemia when machine cannot.
      I wonder how chronic dehydration might also cause erronious results on other mechanized labs…worse, how many people have been mis-treated, due to this kind of erronious results!?

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