Fasting and Brain Function – Fasting 24

posted in: Fasting, Health and Nutrition | 34

How does fasting affect brain function? There is very little reliable human data, but some very interesting animal data, as recently reviewed. There are many potential benefits. While I tend to focus on weight loss and type 2 diabetes, there are many other benefits, including autophagy (a cellular cleansing process), lipolysis (fat burning), anti aging effects and anti-seizure effects.IF Effects

From an evolutionary standpoint, we can look at other mammals for some clues. In many mammals, the body responds to severe caloric deprivation with a reduction in the size of all organs with two prominent exceptions – the brain and the male testicles. This suggests that cognitive function is highly preserved.

This makes quite a lot of sense from an evolutionary standpoint. Suppose you had some trouble finding food. If your brain started to slow down, well, the mental fog would make it that much harder to find food. Our brainpower, one of the main advantages we have in the natural world, would be squandered. No, the brain maintains or even boosts its abilities. In stories of Japanese prisoners of war in World War II (Unbroken by Laura Hillenbrand), many have described the amazing clarity of thought that often accompanies starvation.

The preservation of the size of the testicles is also a significant advantage in trying to pass on our genes to the next generation.

In all mammals, one of the highly preserved behavioural traits is that mental activity increases when hungry and decreases with satiation. Of course, we have all experienced this. Sometimes this is called ‘food coma’. Think about that large Thanksgiving turkey and pumpkin pie. After that huge meal, are we mentally sharp as a tack? or dull as a concrete block? How about he opposite? Think about a time that you were really hungry. Were you tired and slothful? I doubt it. Your senses were probably hyper-alert and you were mentally sharp as a needle. That is to say that there is likely a large survival advantage to animals that are cognitively sharp, as well as physically agile during times of food scarcity.foodcoma

Studies have also proven that mental acuity does not decrease with fasting. One study compared cognitive tasks at baseline and after a 24 hour fast. None of the tasks – including sustained attention, attentional focus, simple reaction time or immediate memory were found to be impaired. Another double-blinded study of a 2-day ‘almost total’ caloric deprivation found no detrimental effect even after repeatedly testing cognitive performance, activity, sleep and mood.

What we say we are ‘hungry’ for something (hungry for power, hungry for attention), does it mean we are slothful and dull? No, it means that we are hyper-vigilant and energetic. So, fasting and hunger clearly activate us towards our goal. People always worry that fasting will dull their senses, but in fact, it has the opposite, energizing effect.

These sorts of tests are easy to see in animal studies. Aging rats were started on intermittent fasting regimens are markedly improved their scores of motor coordination and cognitive tests. Learning and memory scores also improved after IF. Interestingly, there was increased brain connectivity and new neuron growth from stem cells. This is believed to be mediated in part by BDNF (Brain Derived Neurotrophic Factor). In animal models, both exercise and fasting significantly increase BDNF expression in several parts of the brain. BDNF signaling also plays a role in appetite, activity, glucose metabolism and autonomic control of the cardiovascular and gastrointestinal systems.CRimprovesMemory

There are also very interesting mouse models of neuro-degenerative diseases. Mice maintained on IF, compared to normal mice, showed less age related deterioration of neurons and less symptoms in models of Alzheimers disease, Parksinon’s and Huntington’s disease.

In humans, the benefits to the brain can be found both during fasting and during caloric restriction (CR). During exercise and CR, there is increased synaptic and electrical activity in the brain. In a study of 50 normal elderly subjects, memory test improved significantly with a 3 months of CR (30% reduction in calories).Memory and Insulin

Neurogenesis is the process where neural stem cells differentiate into neurons that are able to grow and form synapses with other neurons. Both exercise and CR seem to increase neurogenesis via pathways including BDNF.

Even more interestingly, the level of fasting insulin seems to have a direct inverse correlation to memory as well. That is, the lower you are able to drive down fasting insulin, the more improvement on memory score that is seen.

Increased body fat (as measured by BMI) has also been linked to decline in mental abilities. Using detailed measurements of blood flow to the brain, researchers linked a higher BMI to decreased blood flow to those areas of the brain involved in attention, reasoning, and higher function.

Intermittent fasting provides one method of decreasing insulin, while also decreasing caloric intake.

Alzheimer’s disease (AD) is characterized by the abnormal accumulation of proteins. There are 2 main classes – amyloid plaques and neurofibrillary tangles (tau protein). The symptoms of AD correlate closely with the accumulation of these plaques and tangles. It is believed that these abnormal proteins destroy the synaptic connections in the memory and cognition areas of the brain.

Certain proteins (HSP-70) act to prevent damage and misfolding of the tau and amyloid proteins.  In mouse models, alternate daily fasting increased the levels of HSP-70. Autophagy removes these tau and amyloid protein when they are damaged beyond repair. This process, too, is stimulated by fasting.Dementia

There is substantial evidence that risk of AD is related to obesity. A recent population based twin study demonstrated that weight gain in middle age predisposes to AD.

Taken together, this suggests a fascinating possibility in the prevention of Alzheimer’s disease. Over 5 million American have AD and this number will likely increase rapidly due to the aging population. AD creates significant burdens upon families that are forced to care for their afflicted members.

Certainly fasting may have significant benefits in reducing weight, type 2 diabetes along with its complications – eye damage, kidney disease, nerve damage, heart attacks, strokes, cancer. However, the possibility also exists that it may prevent the development of Alzheimer’s disease as well.

The method of protection may also have to do with autophagy – a cellular self cleansing process that may help removed damaged proteins from the body and brain. Since AD may result from the abnormal accumulation of Tau protein or amyloid protein, fasting may provide a unique opportunity to rid the body of these abnormal proteins. We will cover autophagy next week.

34 Responses

  1. I stopped eating breakfast when I was around 10 years old. I just figured out somehow that I felt better and had a better day if I skipped breakfast.
    Over the next 25 years, I earned a degree in electrical engineering, an MBA and co-founded a successful business. (I don’t mean to sound pompous, but I think my brain was functioning OK).

    However in my late 30s I succumbed to the clarion call from all dietitians, doctors, health groups and the media- ” It is the most important meal of the day! Your brain can’t function properly! Etc etc..)

    It was then that my metabolic health started to go downhill.

    Now thanks to LCHF and IF I have regained my health and learned to tune out the silly and dangerous advice you get from the nutritional establishment.

    • Funny, my daughter (now 14) hates breakfast and always goes to school without. Sometimes she won’t eat until 2pm when she comes home. She’s slim, athletic and bright as a button. I tried to force her to eat but she fought me all the way and I’m glad she did! So many of her peers are overweight to obese and she eats loads after her daily fast. Kids do it instinctively as long as we adults don’t interfere 🙂

    • Cool story.
      How low carb do you go as a general rule: are you keto?
      Keep it up.

  2. Greetings again Dr. Fung……another great article. At some point would you post your thoughts on fasting and kidney health. You mention other organs via your insert above. As a kidney Doctor I’m 100% sure you will advise that fasting is good for kidneys and CKD. Robb Wolf also posted a well-written article about Paleo and kidneys a couple years ago.
    The reason I ask is that some articles on fasting warn against doing if someone has diminished kidney function. In my last fasting/ LCHF period my kidney function improved from 40% to over 80%. That said I’d aprreciate your good thoughts. I can’t find much info via “Dr. Google” other than Robb Wolfs good article ( and also a very good Jimmy Moore podcast on the subject).
    Thanks again for the ongoing and highly informative info. All the best!

    • John Caruso

      Yes, I am also very interested in Dr Fung’s view on people with impaired kidney function using both LCHF/Keto diets and fasting, especially extended fasting (10d+). I also encountered and ultimately ignored the warnings about LC diets stressing kidney due to “high protein.”

      After a kidney transplant (due to IgA nephropathy), I maintain a low carb diet, going full keto at times, and since July last year began occasional fasting. My kidney function increased from 40% post transplant, to over 60% after a couple years of low carb, to over 70% after a keto stint, to my highest of 78% recorded 4 days after a 3-day fast.

      During this time, I have also lost weight, however I have data which (to me at least) indicate it’s not solely weight loss as my weight post transplant was ~240lbs and GFR was 41, subsequent GFRs at later dates but around same weight are: 52 (16mo later), 59 (1 yr after that), 68 (3 yrs after that, 6+ yrs post transplant).

      To me, LCHF and fasting appear to be increasing kidney function over time regardless of weight loss.

  3. I’d appreciate your thoughts on the application of fasting as a therapy for both major depression and for so-called post traumatic stress syndrome. I am quite certain that both are triggered by carbs although the mechanism has yet to be fully explained. Insulin resistance, microbiome issues, inflammation, presumably all engage together. Thus it seems lchf plus periodic fasting plus interval training = profound homeostasis, ie, return to evolutionary baseline, ie, health and happiness, our natural states.

    Really great to see you thinking outside of the obesity/diabetes issue; Mental health is certainly embedded in the obesity issue but it stands alone as, in my view, the “job 1” of health pioneers such as yourself. -john d

  4. sten Bjorsell

    Needless to say, another very inspiring article making the case for IF stronger! Looking forward to polish up my grey cells this way, always needed! This is a little off topic, regarding Type 1 diabetics. There is currently a discussion in Sweden in regard of danger of “euglycemic ketoacidosis” for DB-1 if they reduce carbohydrates (too much(?)). The argument against reducing carbs comes from a diabetic paper that (tragically) seems to defend substantial incomes from (overpriced) advertisements by insulin selling pharmaceutical companies, the way I see it. In the cases I have read about there has always been a combination of starvation, low weight and stomach flue with loss of electrolytes, with or without hyperventialtion. Most are causes of metabolic acidosis, and everyone that is not a type 1 diabetic is diagnosed just as usual. But if ketones due to a low carb diet is diagnosed, in the normal range for low carb ketones, the diagnosis of euglycemic ketoacidosis is proposed by many doctors and advocated by this paper together with warnings to their diabetic readers to not reduce carbs. Your take on this Dr Fung, maybe in a future blog post, would be most appreciated.

  5. I have been low carb – real food for about four years now. I was never over weight, and my motivation may be different from a lot of readers here. I went ketogenic (less than 50g carb per day) and confirmed it with blood serum ketone measurements for about 9 months. I went back to eating 40-80g per day just because it takes less meticulous accounting.

    I became interested in fasting after becoming aware of the two competing theories of cancer and reading about Thomas Seyfried’s work on the metabolic theory of cancer. I recently fasted for 72 hours and attempted to track the changes in blood glucose and blood serum ketone level. After 24 hours the ketones rose to about 3 mmolar and glucose fell to the 60’s mg/dl. At 36 hours the ketones rose to 5.1 mmolar and glucose dipped into the 50’s. At 48 hours ketones spiked to over 6 and glucose was in the 40’s – low 50’s. I felt a bit light headed for several hours, but it went away. At 72 hours the ketones fell to 4.9 mmolar and the glucose was back in the 60’s. I felt great, no appetite at all.

    The point of this for all those interested in this from the standpoint of cancer, among other health benefits, is that 72 hours is all it takes to get to some kind of steady state where you feel good, and there are no appetite problems. It is also interesting to note that if you consider blood glucose in the same units as ketones you have affected a huge change in blood serum chemistry. 60 mg/dl translates to 3.33 mmolar concentration for glucose which can be compared to the 4.9 mmolar for ketones that I measured. This is a very advantageous state for cancer treatment – see Seyfried (http://www.bc.edu/schools/cas/biology/facadmin/seyfried.html)

  6. I certainly feel more alert after a fast – even one as short as 24 hours. In fact I rarely fast longer than 24 hours because I don’t feel safe driving with blood glucose levels below 4 mmol/l (72 mg/dl). I have recently concentrated on lowering my carb and protein to less than 50g each per day because of my poor kidney function and have found it easy to keep fasting for 24 hours two or three times a week. I believe that verybody has their own combination of ailments and dietary requirements and it’s important to note what effects changes have and to have a doctor monitor progress.

  7. I did my first extended fast last October and felt fabulous! More energy, clarity, etc. than I had had in ten years. I did keto the next week and then went away for a weekend with friends. I figured this was a “feasting” type of event, so had a fast food meal, and a half hour later, had a tonic clonic (grand mal) seizure. They took me to the ER.

    I have had two other tonic clonic seizures, both precipitated by stress, lack of sleep, and lack of food. (First was in college during finals after staying up all night 26 years ago. The second was during labor 10 years ago (natural childbirth, no pain medication, 18 hours of overnight, hard labor). This time, I had plenty of sleep, plenty of food, and the only stress in my life was the fasting that I had done the day before. Everyone said it was because of the fast, but I disagreed. How could fasting and keto have caused it when they are the therapies that were used before drugs, and still used when people have epilepsy that can’t be controlled by medication?

    I had my first visit with the neurologist yesterday. I went to an Epileptologist in one of the top 10 programs in the country. He supports keto as a therapy, but says that he finds that often it is too hard for his patients to stick to, and prefers modified Atkins. Either are ineffective if the patient doesn’t stick with them (obviously). Even so, he said that extended fasting is a stress on the brain, so while it might be protective while you are doing it, if you come off, you have the stress without the protection. Fasting, but no feasting (at least not on wedding cake, etc.) He said that intermittent fasting is ok, and maybe even a 2 or 3 day fast, but no extended fasting like 7 days.

    My questions for Dr. Fung are: does a 3 day fast and/or ADF have the same efficacy in insulin reduction as a 7 day fast?

    Also, I think that my cortisol does go up during fasting because I find it hard to sleep. I wake up really early (after 5-6 hours of sleep), jittery. and wired (and used to think it was great, but now it’s getting tedious.) Is there anything to do to reduce cortisol while fasting?

    • I don’t know why this posted before I was done. See clarified post below.

  8. I had blood tests performed after a 4.5 day fast, and had fasting blood sugar at 63 mg/dL. I also had some whacked-out cholesterol numbers, relative to a test done a few months earlier. This week, I’m on a 5 day fast and had a blood test done for my cardiologist after about 12 hours of fasting. I’ve paid for a second blood test, which I’ll have after 4.5 days of fasting. I’ll report back after that.

    For me, on longer fasts (3+ days), I can have some mental acuity problems (I’ll have trouble concentrating, for instance), but these seem to be relatively infrequent. I also go through various phases. For instance, both my wife and I (after three days of fasting) were up last night after falling asleep. She was super cold and had leg kicks. I’ve resorting to taking salt, potassium (from no-salt) and magnesium (from powder) to avoid the leg kicks. The same happens with hunger and mental acuity. Most times, I feel great, but every once in a while, I’ll get physically hungry or spaced out. It seems to be transitory, though.

    I do think that 5 day fasts are difficult. I’m on my third 5-day fast, and it takes some mental preparedness and strength to last, especially when our kids are eating things we like to eat, someone is making a good smelling lunch at work, etc. However, IF has really helped me (as gas LCHF) in many ways. And, IF is freeing: if you need to get work done and don’t want to stop for lunch, don’t stop; if you’re traveling in a long car ride and don’t wnat to be concerned about eating or having to go to the bathroom, don’t eat; if you’re on a flight and they’re serving crap food, don’t eat.

  9. I did my first extended fast last October and felt fabulous! More energy, clarity, etc. than I had had in ten years. I did keto the next week and then went away for a weekend with friends. I figured this was a “feasting” type of event, so had a fast food meal, and a half hour later, had a tonic clonic (grand mal) seizure. They took me to the ER.

    I have had two other tonic clonic seizures, both precipitated by stress, lack of sleep, and lack of food. (First was in college during finals after staying up all night 26 years ago. The second was during labor 10 years ago (natural childbirth, no pain medication, 18 hours of overnight, hard labor). This time, I had plenty of sleep, plenty of food, and the only stress in my life was the fasting that I had done the week before (which I had not seen as a stress). Everyone said it was because of the fast, but I disagreed. How could fasting and keto have caused it when they are the therapies that were used before drugs, and still used when people have epilepsy that can’t be controlled by medication?

    I had my first visit with the neurologist yesterday. It takes forever to get into one in my small town so I gave up and went to an Epileptologist a couple of hours away in one of the top 10 programs in the country. He supports keto as a therapy, but says that he finds that often it is too hard for his patients to stick to, and prefers modified Atkins. Either are ineffective if the patient doesn’t stick with them (obviously). Even so, he said that extended fasting is a stress on the brain, so while it might be protective while you are doing it, if you come off, you have the stress without the protection. Fasting, but no feasting (at least not on wedding cake, etc.) He said that intermittent fasting is ok, and maybe even a 2 or 3 day fast, but no extended fasting like 7 days.

    My questions for Dr. Fung are: does a 3 day fast and/or ADF have the same efficacy in insulin reduction as a 7 day fast? Does ADF/IF have the same efficacy as a 3 day fast? I’m trying to figure out the best protocol going forward.

    Also, I think that my cortisol does go up during fasting because I find it hard to sleep. I wake up really early (after 5-6 hours of sleep), jittery. and wired (and used to think it was great, but now it’s getting tedious). Is there anything to do to reduce cortisol while fasting? Does IF and/or keto increase cortisol? Increase it as much as an extended fast? (I have seen at least one study that ties high cortisol to increased seizure activity.)

    • Amberly, I believe that 7 day fasts are “faster” (in terms of insulin reduction, clearing fat from your pancreas and/or liver, etc.) than are short fasts. However, I find longer fasts to be more difficult, so I do these only every once in a while. For instance, this week, I’m doing a 5 day fast. This is my third 5-day fast since starting IF last March. For next week and a few weeks thereafter, I will do a fast from Sunday dinner to Tuesday dinner, then fast Friday until dinner. Note that I don’t eat breakfast anymore, so even on (most) days I eat, I eat in (about) an 8 hour window. A few weeks from now, I might try a different protocol.

      I find that shorter fasts have fewer “bad” effects (like not sleeping, sometimes getting cold, etc.) on me. I also try to mix things up, and will eat breakfast at times(at least every week on Sunday after church). I also listen to my body. I was going to fast last week, but I got a chest cold. Even though I normally do not eat breakfast and don’t eat until noon or later, I felt hungry one day while I had the cold and had breakfast. That day, I swear I ate 5-6 meals! I could not stop eating. (Still ate low carb, high fat.) But that’s what my body seemed to want.

      I personally haven’t had any occurrences of “stress on the brain” (or anywhere else for that matter) while on longer fasts. The only thing that happens to me is that, when I start eating after a longer fast, all the water I drank comes out of me for about 8 hours or so. I haven’t figured out how to fix this, but it occurs a lot less with shorter fasts. My wife also fasts with me and does not have the same problem, at least to the extent I do.

      • @BobM thank you! Those are some really great things to think about. I hadn’t considered a protocol like that, so it gives me some ways I could mix it up on my own.

      • Is headache “stress on the brain”?
        Is it wrong to think there is a time of “switching fuels” from sugar to ketones in the brain? i.e. at that point in time when Alzheimer’s patients become lucid on ketones?

      • Hi Bob, I’m hearing you with the water coming out during a fast. After years of T2D UTIs and the like, it feels fantastic! The most enjoyable passing of fluid. I find this also happens when I enter/re-enter Ketosis.

  10. Dr Fung and Megan…just received my two copies of the Obesity Code Book: one for me and one for local and supportive Korean MD. helping me. My quick scan during my break today suggest that the book was well worth the wait! Many thanks again for all you do!

  11. Wenchypoo

    I just got done devouring the book “The Everything Guide to Nootropics” by Evan Brand (Dr.? I’m not sure–he’s an NPT and CPT, and I don’t know what those initials stand for). After reading your article above, I wonder if it’s any use delving into the world of nootropics for brain improvement–it seems fasting does the same stuff (or almost the same stuff) as drugs/supplements, or even the brain-healthy food nutrients. Am I right?

  12. Debra Griffith

    I also would be interested in a post about kidney function and fasting/low carb.

    I just started on a drug called Topamax for chronic pain (one of 3 meds I take since 2 major back surgeries), which works fantastic, and of which a side effect is weight loss. However, there is a warning that it should be used with caution by people who are on a ketogenic diet because of the increased risk of kidney stones, which I have started to experience, and then after doing more research, have come to find numerous cases of kidney disease and failure being caused by the combination. I hate to stop the drug that helps so much (I did decrease it by half), but hate even more to change my diet which has helped me to lose 45 lbs and done so much for my health in other ways. So the link between our way of eating and kidney function/disfunction would be welcome.

    Also love the book and recommended it on Facebook!

  13. jcm baril

    Sixteen pounds down since November 2015. Feels like an invisible little micro robot is going around to every cell in my body, with a pin, sticking it into each and every one and deflating them. As the old commercial for Alka-Seltzer use to sing:
    “Pop, pop, fizz, fizz, oh what a relief it is!!!”
    Have reduced portions; can’t eat as much as before. Have had to throw spoiled food out, as I did not get around to using it. Am now buying less food, saving a LOT of money!

    Pop! Pop! Fizz, fizz. Oh! what a RELIEF. IT. IS!!

    • jcm, what is your fasting protocol – alternate days, multi-days, missing a meal? Do you have much to lose? Thanks in anticipation.

  14. Deb Rayson

    Hi. Could someone please tell me what they drink on a fast and is it OK to do it once a week? Thank you. Deb

    • Hi Deb, I drink 1-2 cups of black coffee without sugar, plenty of water – 3litres or more (more than the non fasting days), a tbsp of apple cider vinegar in a cup of warm water with salt if I feel gassy in the morning and sometimes 1 cup of coffee with milk without sugar if I feel a headache starting. If the headache persists even after the coffee, I break the fast.

      Dr Fung says its fine to drink bone broth on fasting days and many people do that. For me that didn’t work as I start feeling extreme hunger after drinking bone broth or any kind of thin soup. Even green tea makes me very hungry.. .But it does work for many people to sip on green tea/bone-broth while fasting. Coffee however, numbs my hunger pangs.

      What is the duration of your fast? I do 24 hr fasts 2-3 days every week and sometimes a 3 day fast once in a couple of months. Listen to your body and see what level of fasting is comfortable for you. You can change your fasting routine whenever you feel like as well.

    • Fizzy water with a slice of lime and sprinklings of sea salt. I know Dr Mosley does 6:1 (fasting 1 day) as weight maintenance. I believe you will get better results if you fast for a little longer.

  15. Hi Dr. Wong,

    It was a blessing watching your youtube episode about reversing T2D. I am really motivated and encouraged to follow your regiment. Please let me how to start.

    Thank you very much.

    Regards,

    Johnny

  16. Hi Dr. Fung,

    It was a blessing watching your youtube episode about reversing T2D. I am really motivated and encouraged to follow your regiment. Please let me how to start.

    Thank you very much.

    Regards,

    Johnny

  17. @ Johny-

    You may start your program by joining IDM &instructions are very clear :

    https://intensivedietarymanagement.com/join/

  18. At some point would you post your thoughts on fasting and thyroid gland functions? I’m a woman, 43 years old, and my mother suffers from hypothyroidism. A couple of years ago I went through a small life crisis and also I felt tired, frozen, dropped a lot of hair, slept a lot, gained weight and I tried intermittent fasting 16/8 at the same time. I tested my TSH, T3 and T4 levels and they where not at all perfect. The doctor thought I might be on the verge of getting hypothyroidism just like my mother, but he wanted to do some new tests in another six months. I stopped fasting and 6 month later my T3 and T4 levels were OK. Was it a coincident? Or did my body get stressed from the fasting? Or was it because of my small life crisis, that I felt sick? I would like to start fasting again, because of all the health benefits that I read about, but I’m not sure I dare. What if it were to make me sick instead?

  19. Hi Dr Fung, I am presently doing a 3 week fast in a wellness center in Germany.
    I am thin and fit but suffer from Restless Legs Syndrome.
    I saw a documentary about fasting last year where the benefits to Parkinson’s were mentioned and since the medication I take for my RLS is the same as for Parkinson’s I thought it is worth the try.
    I started week 2 yesterday and feel good. They use the Buchinger method.
    I would appreciate your advice.
    Thank you

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