Doctor's Note

For some of the most recent videos on caloric restriction:
Caloric Restriction vs. Plant-Based Diets
The Benefits of Caloric Restriction Without the Actual Restricting

And check out my other videos on memory

Also see my associated blog post, Eating To Extend Our Lifespan.

If you haven’t yet, you can subscribe to my videos for free by clicking here.

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  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on memory. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • becochic

    Well, I’m shocked by this. What about weight loss caused by fasting and making sure to get all your nutrients?

    • Toxins

      Hello becochic!
      One can assume that since the people studied were all elderly, they were not highly physically active. When one is physically active we burn through glucose pretty quickly and need more nutrients to maintain our current stride. Where we get into trouble though is eating when we are not hungry. As Dr. Joel Fuhrman puts it, our body, when not digesting, is the most efficient. Your body cleans out any built up toxins and does the most repairing when not digesting. Dr. Fuhrman also mentions that people who consume a typical western diet eat when they feel “discomfort”, like a headache. This is not true hunger but toxic hunger. Their body is so built up with harmful chemicals that when they finish digestion they feel uncomfortable. They must eat again so the discomfort can go away temporarily. This does not allow their body to adequately heal itself. Before you eat your meal, aim to feel true hunger. True hunger is when you are about to run out of glucose (energy). This is not a craving but an actual feeling in your stomach, mouth and throat. Your taste buds become very sensitive in this state and this is when food tastes so good! Check out some of the most nutrient dense foods here

  • gljohans

    The video seems to be saying that the people were fasting on alternate days, but the linked study seems to say that they weren’t!

    “..intervention was to reduce each subject’s individual caloric intake by 30%, compared with pretrial levels. To avoid cognitive changes due to malnutrition (79), minimal intake was set to 1,200 kcal per day.”

    Am I missing something?

  • susanco

    Yes! You are missing the ADF paper: “Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults” by Varady, Bhutani, Church, and Klempel. Amazing stuff – I am doing it and have lost 5 pounds in a week and feel incredible!

  • There is something against the 3 meal a day thing. We’re the only animal that does this — and we didn’t always.

  • Sarah

     I’m unsure what the take-away message is…I eat really healthy vegan meals but when I miss one I feel drained and can’t think as clearly.  Would these scientists recommend eating much more on one day but nothing the next?   It seems to me that it depends on diet since the time/energy the body requires for digestion varies quite a bit across foods…

  • Dave

    I’m big on fasting and have gone with just water a dozen times for 21 days sometimes more. My body looks forward to it, I do limit my physical activity and can get tired easily, but I generally feel good especially mentally during these fasts. I’m on one now and I am going to go vegan this year after listening to all these videos.

    • Amanda

      I dont at ALL. But they say it is different for females. I keep being hungry and keep thinking about food all days long. I tried it as experiment.

    • Pedro Moisés Camacho Ureña

      I am interested on water fasting but I haven’t found good scientific information about it (I don’t have experience I must say). However there are a lot of big names that backup water-fasting. I got interested after watching doctor Dr. McDougall vouching for Dr. Goldhammer and his True North water fast center. He has a lot of videos on youtube and what he says make sense (he also uses the whole food plant based diet as a treatment). So I will like to see what Dr. has to say about the water-only fasting for long periods of time.

      • I am at True North right now on day 5 of a 12 day water fast. I also water fasted here 3 years ago for 28 days. Both times I have found the facility and the process to be very pleasant, and I experienced improvements in my health. Medically supervised water fasting is very effective for reversing a large number of health issues, but a WFPB SOS-free diet must be followed afterwards to help prevent the issues from recurring.

  • nora

    Instead of alternate day fasting, I’ve been doing intermittent fasting daily…fasting 19 hours and eating vegan during a 5-hour daily window (like 2-7pm). I’ve lost 13 pounds in two months, about 1-1.5 lbs/week with very little effort, and my junk food cravings have stopped completely. I have more energy than ever and feel truly amazing. I think IF, combined with a vegan diet, is the perfect combination.

    • Psych MD

      I am also doing intermittent fasting. I first saw this on the Mercola site a few months ago. There is a wealth of info on It really is amazingly painless. I have some mild hunger pangs around 0930 that I feed with a cup of tea. I also started sprouting a few weeks ago. These measures, along with whole body vibration exercise (which I also learned about from Dr. Mercola) combined with modest strength training on a Chuck Norris Total Gym have me in better shape at 60 than I was at 30.

  • TMR

    I’m vegan. I find when I do intermittent water fasts that I feel lighter, more energetic and it also addresses any food addictions I might have. I try to do a one day water fast at least once a week.

    I read that longer water fasts can address chronic illnesses. I have only done short fasts at this point, but I would like to do longer ones. I would highly recommend water fasting :)

    • sf_jeff

      I am curious about the difference between water fasting and anti-oxident fasting. Eg. Coffee/tea/herbal tea/hibiscus every three hours.

      If the fasting benefits come from protein scavenging or from short ketosis periods, then you would expect antioxidents and even low-calorie vegetables to help. If there is a stress component, like muscle-building, and a digestion component, then maybe the opposite. Thoughts?

  • tavit

    dose it mean water fasting is actually healthy?

    • Toxins

      No, fasting is not at all what Dr. Greger is advocating. He is saying you can get the benefits of fasting primarily from extra DHEA through dietary modifications.

  • Bubby Country

    What does the doctor make of the recent hype over the book, “Grain Brain”? Dr. David Perlmutter claims that carbs cause Alzheimer’s and is recommending huge amounts of red meat and coconut oil.

    • Thea

      Bubby: I don’t speak for Dr. Greger, but in response to your post: I would refer people to “Power Foods For the Brain – An Effective 3-Step plan to protect your mind and strengthen your memory” by Dr. Barnard. This book covers Alzheimer and provides what I consider to be convincing evidence.
      I can tell you that he doesn’t blame carbs on Alzheimers…

      Grain Brain sounds just like another variant of the Paleo/Wheat Belly/etc. diets. All of which have been soundly discredited.

      You might also be interested in Dr. Greger’s book, Carbophobia. It used to be free on-line somewhere as an e-book, but I’m not sure Dr. Greger offers that option any more. But $10 isn’t bad:

      Just some thoughts for you.

    • I would also recommend Dr. Barnard’s book, Power Foods for the Brain. The idea that whole grains causes Alzheimer’s is not the best hypothesis. As Dr. Barnard points out it has been associated with many factors including saturated fats, animal food and certain metals. There of course have been correlations that help reduce the likelihood such as vegetables, fruits, exercise and sleep. The latter make more sense given what we know about our biochemical and anatomical make up plus what we know about the other chronic diseases. The nice thing about Dr. Barnard’s book is that he provides references for the scientific articles that he cites and provides some down to earth recommendations. Given the magnitude of the dementia problem I would expect many more “entrepreneurs” to publish a line of books such as we have seen with the diet industry over the years. The best thing to do is to develop a good understanding of the science which come from reliable sources that are free. For me these include NutritionFacts, Dr. John McDougall, the Physicians Committee for Responsible Medicine and Jeff Novick’s blog.

  • Gabrielle
    Do you know if it is true on whether regular swimming also reduces risk of dying compared to non-swimmers

  • Health

    Hello Dr. Gerger,
    I would like to ask you if you recommend practicing alternate day caloric restriction as I do feel enticed of doing so?

  • vibrant vegan

    Fasting has gotten a lot of attention lately, since it’s supported by vegan doctors like Doug Lisle and Alan Goldhamer… and I’ve always wondered if I should try it. This video touched on the potential benefits for memory, but what about the other physical effects of fasting? Overall, is fasting a good idea? Is it recommended by Dr. Greger?