Reader Comments

  1. ooo789456123

    I know several guys on an unhealthy diet, who try to compensate with 1 week of fasting, especially before important events. A whole food plant based 🍅🍠🥒diet with 2 meals per day works best for me. Unfortunately, I'm sitting in the office the whole day 💺

  2. Frank Black

    I did three cycles of the Fasting Mimicking program and found that if I didn't ease back into feeding my blood pressure went through the roof. I already have an issue with blood pressure, so this may not be a common side effect of eating too quickly after an average fast, but if did freak me out. I was not expecting it and thought I might need to go to the emergency room. Lesson learned. Cheers!

  3. Matts Manifest

    Thanks for this Doc. There’s nothing magical about fasting, and if there’s dangers, people really should be informed. If benefits can be attained with safer means- why would you take the risk?

  4. Citizenthirteen

    Ooooh boy. Dr Greger's cohorts who promote fasting and make $$$$ are not going to like this one. LOL. I figured this didn't make sense and I was right. No need to fast on a WFPB diet . Stop destroying your body on non sustainable silly fads.

  5. Bobby Thomas

    Wow, speaking of bullshit to the nth degree. Everything done to the extreme will result in adverse effects even if you eat ONLY kale everyday for a year. So what is your point? Again your studies are mainly from the 60's. Not the best source of data considering the liturgy of science in the past 10 years . You do know we are in the 2000's right? You are still following that dogged tiring theme of skewing information to fit into a neat little box that only you confine yourself to. The point about scurvy in a few days and thiamine deficiency is not beyond the realm of possibility,so is getting hit by an asteroid. Looking at things in black or white is not science, its idiocracy. Any relation to Ancel Keys perhaps? You certainly seem to be going down the same rabbit hole he did.

  6. Yahusha is the Torah made flesh

    Did you find the worst cases for fasting? Fasting is very beneficial for the body. Jesus said when you fast not if you fast. Everyone should do it. Except pregnant or breastfeeding women.

  7. Brett Mason Media

    All of your examples were people who were too stupid to do an extended fasting properly, or were deathly ill to begin with.

    If you fast for extended periods and take electrolytes and supplement with vitamins you will be fine.

    Refer to the fasting fat man channel. He did a 150 fast with no problem this year. And is now about 30 days into another fast. No issue.

    Finally , using papers on starving have no relation to obese people fasting. Obese people do not starve when fasting. They have ample fuel storage to sustain them.

  8. crb2061

    This seems like some questionable science. I have done many water only 2 week fasts over the years. Most Americans are severely malnourished, so it makes sense that fasting would rapidly exacerbate that condition for such people. Also, the usual advice is to rest while fasting which is just bad advice. Lying around for extended periods of time will lead to muscle loss whether you are eating or not. Obviously, you should not engage in activities that result in sweating as the loss of electrolytes could certainly be problematic. I wouldn't advise fasting for more than 2 weeks at a time. There are too many horror stories about that to be worth the risk. For me the benefits have been the slight loss of 10-15 #'s of body fat and to easily reset my diet after the fast. During the course of the year, my habits get corrupted by those around me and I end up over eating and not being nearly active enough. Right now, I am doing less than 20 miles of running a week which is pretty sad.

  9. SWH

    This is classic Dr Greger… Cherry pick a few studies that don't represent the majority of the small community of individuals who fast for health reasons. Using satire to passive-aggressively suggests that people who fast are going to die. Most people who attempt intermittent fasting are healthy individuals who are very health conscious and striving to restrict calories in a reasonable way for longevity. Caloric restriction and longevity are very closely correlated. Vegan or not.

  10. SpiritualVegan

    All types of fasting are unnecessary and idiotic. Both are starvation. It’s like you people are anorexic, thinking you are so fat so you may as well not eat to try and loose weight. Why not focus on healthy foods instead of perceived short cuts.

  11. SpiritualVegan

    Whenever someone in the keto+fasting community has heart issues they shrug it off and say “electrolytes!” As if all their issues will be solved by drinking salt water. The solution is don’t do keto or fasting.

  12. Maro Maro

    I eat OMA plant based food with ocasionaly very small quantity of fish in 4-5 hours window and have no problems.

  13. Cerenade Me

    It is not advised by the experts in this field (Fuhrman, Godhaamer, Klaper, et al) to fast for weight loss. Water only fasting is done for health and healing. Please address those benefits about fasting (of which there are not many studies, but people have been doing it for a millennia). Thanks

  14. Ian Chabot

    As medical supervision during WOF is a must, what testing should we make sure is performed? Is urine analysts enough? mAre blood tests necessary? How soon or often should testing be done? Comas are bad!!

    I know there’s is a center near Montréal (Val Santé) that supervises fasts but it isn’t clear what testing is performed.

  15. so★

    One meal a day is very sustainable. These 7 day starvation people think they've accomplished something but it's really short term. It's not a dick measuring contest.

  16. Courtney HAMILTON

    This is great! However, I would really love videos on intermittent fasting (16 – 20 hours a day) for weight loss/health/cells etc vs long term fasts for days. Pleaseeeeeeeeeeeeeeeeeeeeeeee


    The reasons why fasting longer than 24 hours, and particularly three or more days, should only be done under the supervision of a health professional and preferably in a live-in clinic.

  18. Diana Fleischman

    I don’t think you should conflate deaths from fasting in ghettos, wars, and case studies of fasting deaths from decades ago before people understood electrolyte supplementation and modern day therapeutic fasting. More recent fasting studies have shown adverse events but rarely anything life threatening as you covered in this video. I would like to see fasting compared with gastric bypass for obese patients- I think fasting is likely safer and more effective. Also- a low calorie diet is great but many people find eating very low calorie to make them much hungrier than fasting- the latter is more effective. While I generally appreciate the balance of your videos, the first one was fairly positive, this one was pretty negative and purposefully scary.

  19. Archie

    I watch, much appreciate and promote your vids, however, I have been looking for your research on intermittent fasting and seem to be finding only info on long term fasting. I think few people today are interested in straight, long term fasting.

  20. Yavuz Yorukoglu

    I have been a fan of Dr. Greger for years, but this is probably the worst video I have ever seen.
    Dr. Greger is trying to discredit fasting by confusing the subject with prolonged "starvation".
    Quoting decades old literature on "starvation" and then serving it as the side effects of fasting is absurd.
    Fasting is not starvation !!!
    Very disappointed !!!

  21. Maker’s Persona

    I heard that liver and kidney functions change during fasting. I wonder how this impacts multivitamin consumption during the process? Does the RDI change? Also, I’ve heard that ingesting sodium to taste is recommended in longer fasts, but what about potassium and magnesium?

  22. usma29871

    Dr. Greger's videos on Fasting are very disappointing and not to the level of thoroughness that his videos normally provide. Giving minutes to a subject that has been exercised for decades and even centuries was poorly reviewed. His videos are based on fear and risks of "catastrophic" failures of fasting versus the successes which far outweigh the failures. I would suggest that those interested in therapeutic fasting study the subject by reading the books on how to water fast safely and successfully rather than watch Dr. Greger's poorly done videos. Dr. Greger would have been better served by simply saying in 5 seconds, "The(re are) reasons why fasting longer than 24 hours, and particularly three or more days, should only be done under the supervision of a health professional and preferably in a live-in clinic."

  23. fire7side

    I somewhat agree, but I think a 3 day fast is nothing to worry about either. I'm certainly not going to pay a doctor for something that simple. As usual, it has to do with overall health. Get exercise, eat healthy, and a fast won't be a problem. You can get a wrist bp checker and have a good idea of your overall health. Mine cost 20 dollars and talks. For weight loss, I think a one day fast per week, with a healthy diet has been the most effective for me. I didn't try a longer one, but I didn't need to either. That's the fastest I've ever lost weight.

  24. Aguafria

    Thank you so much for this information Dr. I have been considering fasting as a 'safe' method and followed several people on YouTube who have documented their fasts, so it seemed at first glance to be an acceptable and effective method for weight loss. I have now been educated.

  25. Maro Maro

    Dr. Guido Kroemer on Autophagy, Caloric Restriction Mimetics, Fasting & Protein Acetylation — Dr. Guido Kroemer is a professor at the University of Paris Descartes and an expert in immunology, cancer biology, aging, and autophagy. He is one of the most highly cited authors in the field of cell biology and was the most highly cited cell biologist for the period between 2007 and 2013. Especially notable among his contributions: he was the first to discover that the permeabilization of mitochondrial membranes is a concrete step towards apoptotic cell death. This episode is decidedly focused on autophagy, an important cellular program that is inducible by dietary fasting and has broad implications for aging and cancer. series of interviews on the same topic: Dr. Satchin Panda on Time-Restricted Feeding and Its Effects on Obesity, Muscle Mass & Heart Health

  26. Alenfishman

    so, ive been doing this thing where i fast 1 weekend a month for a couple days to help control my micro biome. its been helping because ive lost most of my cravings for junk food and have no problem eating whatever i should be eating. im a little confused based on what he said. in most of the studies they talk about 5+ days, but in one section specifically any fasts over 24 hours should be monitored. should i be concerned about fasting once a month? does anyone have an extra info on this?

  27. ShaneDeeZee

    This is the first NutritionalFacts vid that made me suspicious. Too many death threat-type case studies for my comfort.

    Still love ya, NF. Just feel like the deep research is where I'll find better answers on fasting, intermittent or otherwise.

  28. Raphael Quaglio

    The Biblical fasts were dry & without water. So clearly 40 day fasts like Jesus' wilderness experience were only possible with magical powers. The Hebrews in the gospels only fasted 'twice a week' which presumably means a length of less than 48 hours.

  29. Fabio

    You are talking about extended fasting lasting several days to weeks.  Agreed that should be done under medical supervision and supplements taken.  I fast one day per week (36 hour period) and have been doing this for 5 years now.  I have no ill effects and in fact can only attest to increased health.  Improved bloods, improved immune system (Ive had two colds in the last 5 years and have recovered very quickly once I caught the colds).  You need to have a serious discussion with Valter Longo regards the aging process, longevity etc. and fasting.  For all your good work I get the distinct impression you cherry pick most of your science articles to suit the agenda you wish to push.  That's not good scientific practice.

  30. Sam V

    So, list off the deaths, these are by people who had known cardiac issues. Also, list of the problems where people did not consider taking supplements and vitamins. Presto, fear mongering.

    Fasting has been done for the entire length of human history. The human body has evolved for periods of no calories. Every single major religion includes fasting. Now that we have more knowledge of what happens to the body, all it takes is to make sure to have electrolytes, some vitamins and minerals, as well as 7.5 to 15 g of sugar (preferably in capsules) to minimize the gluconeogenesis. Also, take salt if one is having low blood pressure.

    It’s amazing what fear mongering is done by the medical industry, but I respected doctors like this channel as well as Dr. Valter Longo. Assume that people are stupid, assume that a few deaths now make fasting too dangerous for us dumb people. of course, we all know that far more deaths occur from pills prescribed by doctors.

    After this video, it is obvious that a person should look into taking thiamin as part of their re-feeding protocol. Wow, instead of educating us, this video is simply saying the entire concept of fasting is too dangerous for us stupid people.

    Instead of emphasizing the list of peoples that should not do fasting on their own, which was listed in a paragraph in the video, they simply use a blanket statement that no one should do it on their own.
    Using fasting to lose weight, should only be done after a person is eating plant-based, whole foods made from scratch, eaten only at their kitchen table, not in their bedrooms, not in their car, not outside the house. By doing it this way, where a persons habits are changed, then implementing fasting makes excellent sense for losing weight in the long term. But, this video suggests that we are too stupid to figure this out. That fasting is not considered useful for weight loss.

    As a case in point dr. Valter Longo considers 19 out of 20 vegans to be too stupid to figure out how to eat nutritionally adequately. As he says one out of 20 vegans eat correctly, and that the 19 out of 20 need to go to a nutritionist. This is how many doctors you are’s uneducated dumb stupid masses. That we are in capable of educating ourselves to the level that these doctors are currently. With Google, with access to research papers with access to the full content of these papers, we can become just as educated or even more educated in these doctors. With access to immediate blood tests, such as the 24 hour continuous glucose meter, blood pressure cuffs, we can safely and effectively do this.

  31. Manuel G

    Hey Doc, but what was the body mass of these patients who died? It makes no sense for lean individual to fast for more than 2 days probably, but if they were big fellas with a lot of fat mass would it still be an issue?

  32. Syris of Lemuria

    For about a year, in my 20s, I pretty much starved myself to lose weight. Ate very little when I did eat- and I did lose weight, but much of it was muscle tissue. I can attest to the fact that starving yourself is no good. I think very limited fasting can be beneficial, maybe a day or two, max- but long term is not healthy.

  33. farorin

    So long fasts = bad.

    Makes sense, starving yourself for extended periods of time never sounded like a good idea in the first place.

    What about short fasts, half a day, a day, 48 hours?

  34. Atom Shucker

    I was planning to buy your book but now I won't. Fasting is usually 24 hours or less. You are focusing on extremely long fasts in your videos. You seem threatened by the intermittent fasting craze. But people are not fasting for weeks on end. All my research on intermittent fasting suggests it is very healthy. I get the impression you are trying to scare people off this approach, in general, using extreme examples. Respect lost.

  35. Maria Wakim

    Hi Dr. Greger. Whats your opinion on the 16/8 method for belly fat loss. I'm a 45 year old female. Other channels prove that it's effective. What about you. Thanks.

  36. rainguynw

    Has Dr. Greger supervised fasting patients? Dr. Jason Fung has, and continues to with minimal problems. Even in elderly patients. I'll stick with Fung on this one.

  37. esteffannyh

    Cannot wait to see intermittent fasting videos :).
    And how about doing exercise in the morning on an empty stomach? I've heard it's good, however, I'd rather to hear this from Dr Greger.

  38. Zett76

    Oh boy. This one fired up all the right people… 🙂
    All he said was: Take vitamins, when you fast.
    (for more than three days)
    What the morons heard: fasting will kill you for sure.

  39. shockwave1986

    Thank you for the video. Can you do one about the fast mimicking diet please ? It’s currently touted by longevity expert Valter Longo as a very effective way to extend healthspan and rejuvenate the body as well as maintaining a healthy weight. The science looks solid but I’m no expert. Thanks!

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