Is Fasting Beneficial for Weight Loss?


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  • If hunger is the search for nutrients, then the obese are energy rich, and nutrient poor. Fasting will remove the excess energy, but not restore the nutrient levels. Obviously if you return to eating what you did before, you'll resume the previous state or obesity.

  • Very confusing video. It started out saying fasting was good for jump starting weight loss and helping people change their diet to a healthier one after the fast, but by the end the conclusion seems to be that it’s detrimental to fat loss and calorie restriction is the way to go. 🤷🏻‍♀️

  • There are very few people that are going to fast for 2 weeks straight. That's a long time. I can manage to get through a day per week when I am over my top allowed weight. Changing eating habits is the most important and the place to start because I lost a lot of weight doing that alone. Fasting is just an addition for when I plateau. What I found best about a one day fast is after that, it's really easy to wait a couple hours till my normal meal time. I used to think I couldn't make it and had to have a snack. Now it's just a couple hours away, no big deal.

  • I've been waiting so long for this video but it is the complete opposite of what I expected & everything I've researched!! So confused!! What about all the current research on muscle sparing & aotophagy??

  • You do say that exercising while fasting increases lean body mass loss but you don't say anything about the physical activity level of the other people studied. Apart from the second part of the video being directly opposed to the first part: how is it that the patients people like Alan Goldhamer treat with water and other forms of fasting do not lose considerable amounts of muscle mass (I don't remember the exact numbers, but they're in the low single-digit percentage range), if they are kept resting (!)? The same goes for people like Ray Cronise who has conducted a two-week study on himself measuring fat and protein utilization while resting and who lost very small amounts of lean body mass, burning almost exclusively fat or, after a certain time, ketone bodies, respectively. It also doesn't really make sense that the brain would generally and principally cause the breakdown of muscle tissue for the purpose of gluconeogenesis as the brain is able to adapt to the utilization of ketones while fasting for a prolonged time, i.e. depleting all glycogen stores, and while resting. So either the study design and conclusion are misleading or your interpretation of the study has to be wrong.

  • it's interesting how wrong this proves the keto crowd. the body burns up vast amounts of lean tissue before it even thinks of resorting to ketosis. the only reason keto dieters aren't collapsing outright is probably because they supply glucose to the body in the form of broken down protein.

  • But what about the human body's ability to go into ketosis, protecting the lean protein, while continuing to use body fat? I thought that the body converts over to this system after about 48 hours of fasting. Your video is implying that the body is not going into ketosis, and that lean muscle is being eaten up during the entire fasting stage. This is hugely important. Can you pls clarify?

  • I'm beginning to think that Greger has no idea what he is talking about. The "studies" he cites are in opposition to the growing body of evidence from a myriad of experts in the field like Jason Fung. Fasting does not result in muscle loss. If it did, humanity would have died out long ago. Body fat exists for the very purpose of fueling the body during periods of extended of calorie loss – i.e. fasting. Greger should stick to vegetables and leave fasting to actual practitioners and experts in the field.

  • How can it be, that different researchers come to different outcomes? Sometimes I read, fasting is the best thing you can do for weightloss, sometimes I read the opposite. It's so confusing that even "the experts" come to different results. 🤷‍♂️😱

  • I lost 85 lbs on such a diet 30 years ago. I gained back 40 and that was my new set point. 4 years ago I did low carb and lost 40 lbs. I gained back 20 because I had a diet mentality. Recently I dropped that 20 from just skipping breakfast. I need to lose another 20.

  • lol this clown lost me right away when presenting studies from half a century ago … this guy is biased … anything to promote PBWF/veganism … why does he feel the need to bash keto whenever he gets a chance .. check out the video description … He hates keto just because it implies heavy consumption of animal based foods. If health and science is the primary motive of your videos, then just ignore other diets, and be evidence-based as you claim .. why constantly bash keto?! because you have an agenda lol

  • I've always believed that fasting had muscle-sparing effects even if you're out of glycogen, but what you're saying makes sense. I always feel like I lose mass when I fast for 3 days and lift weights, and I usually end up gaining the fat back sooner or later, while having to regain the muscle mass I lost. It seems to me that simply eating whole plant foods, lifting weights, and cardio, is the way to go and no fasting is actually needed; improving metabolism and health for the long run. This is the conclusion I'm coming to after 7 years of fasting and eating plan- based. It really isn't that complicated.

  • But, how much lean mass can an obese person lose before the brain bites the bullet and accepts to run on ketones only? I can't imagine one would die from atrophy of the heart muscles while still having love handles and a beer belly. How about a person that does not have a lot of muscle to start with? And does it matter to lose a bit of muscle that is mostly needed to carry overweight bodies around? Maybe muscle is lost because of less "training" as a person gets lighter. Well well… I am not entirely serious here. I would rather think that that last mentioned "NIH funded study" is not of the greatest quality. The fact that people regained weight while in a caloric deficit at the end of the starvation period shows that they lost water along with their glycogen stores during the fast and gained those back when they ate carbohydrates again, that's not at all sensational. That they got a peak of exactly the same size in the days after the "starvation" even may mean that they just refilled their glycogen stores and effectively did not use up muscle tissue at all during the fast. Right? Can this interpreted differently? Or did they take up intense weight training after the fast to gain 600 grams of muscle a day? Still, why did they drop less fat during the fasting period, their muscle glycogen depots can not have lasted that long? Well, maybe they just lied in bed during the fast, because they are not used to starving hence, burned fewer calories and therefore used a smaller amount of fat. I can't be bothered to read the study myself, but if that were not considered I would join in with the choir of Greger fans that sense biased reporting here and there.

  • So you're telling me if I was in the wild and starving my body is going to go for my muscles which I need to hunt and find food before my fat? I dunno about all that. It seems like keeping muscle would be more optimal for our bodies then keping fat.

  • Wait, was the study Dr Greger was referring to ~5 minute mark the long term benefits of just 1 week of fasting total? to have benefits a year down the line only after a week of fasting is insane. What if the subjects fasted a week every year, then? I think the angle of this video is missing some very important perspectives if they don't go into the benefits of continual intermittent fasting long term.

    Are these long term follow ups looking at people that continued a fasting regimen as a lifestyle change? if not, of course the benefits will fade with time. The same can be said then, looking at WFPBD. It doesn't make sense to compare long term follow up of folks who maintained a WFPBD for years with people who stopped doing fasting years ago…..A better comparison would be long term follow up (years down the line) of those continuing a WFPBD without intermittent fasting vs "healthy diet" intermittent fasters.

    Why not address the most common fasting used, intermittent fasting 16:8? This video is silly for not addressing what people do the most of. Dr Greger should address what is most relevant.

    I direct plenty of patients to But this is ridiculous. Please do better.

  • I have a lot of respect for Dr. Greger and the great public service he provides and yes he is bias because he knows that a whole plant food diet (diverse and done correctly) is the optimal diet for humans period. This video however was very disappointing for me as others have mentioned they are not up to date studies and details around fasting periods or how long a fast is are extremely relevant and important to understanding the benefits of fasting. If you fast long enough of course your body will start to break down muscle. I have been doing one meal a day for about two years now with the occasional 48 hour fast and my weight has remained in the perfect range for my height. In that time i haven't been able to do my resistance training due to a martial arts shoulder injury but have retained my muscle just fine and in addition i feel better than i have ever felt. I don't want to knock Dr. Greger as i feel this is an area (maybe) he has had very little experience with and i agree with others comments that he needs to use the latest research and dive into all the other benefits of fasting not just weight loss. Someone mentioned below that after 72 hours (3 days) you will start to loose lean mass and this is my understanding from all the research i have done in the past but not forgetting everybody's body is different – Anyone else got any thoughts on the 72 hour fast it seems to me it is the optimal for all kinds of benefits before eating in to muscle.

  • This supports my experience that the best diet is the Whole Food Plant Based No Oil, Sugar, or Salt diet and for additional weight loss Partial Fasting is best. I eat the WFPB NoSOS diet and to lose the last few stubborn pounds to get to my ideal weight I will eat once a day in the evening i.e. a partial fast. This works well for me, but it is when I lose my self control and partake of the junk food ever present in the environment that I gain weight again.

  • I think this video should be titled "Long Term Fasting". I would like to hear what you have to say on "Intermittent Fasting" or "Alternate Day Fasting" effects on the body and fat loss.

  • There are a lot of misinformation in this video. I suggest people search for "the fasting fat man" on YouTube. If what this video said about burning protein on a fast is true, then that man would have died! Nonsense.

  • What about intermittent fasting ? 16:8 or one meal a day? I eat Whole Foods plant based and shoot for 16 hours fast per day. I’ve seen great evidence for this, this is actually what the Buddha taught, one meal a day, extended fasts were prohibited for monks/nuns

  • Does this apply to calories restriction too? For example if you go whole food plant based calories restricted vs going whole foods plant based normal. What works better for long term weight loss and diet sustainability?

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