Food for Thought on a Fast Day – The myth of “starvation mode”

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Food for Thought on a Fast Day – The myth of “starvation mode”

This topic contains 20 replies, has 15 voices, and was last updated by  Stinger 8 years, 3 months ago.

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  • Over the next few weeks, we’ll be posting  10 myths about dieting from the article by Michael Mosley in The Times

    Claim 5. when you stop eating for a while your metabolic rate slows down as your body tries to conserve your fat stores.

    Fear of going into “Starvation mode” is common and yet, at least from an evolutionary perspective, it makes little sense. Our remote ancestors often had to go without food for a while and if, every time this happened, they had simply curled up on the floor of their cave and waited for pizza to be delivered they would have gone extinct. Only during periods of prolonged famine would it make sense to slow the metabolism down, wait for better times to come.

    The myth seems to be based, in part, on the Minnesota starvation experiment, a study carried out during World War Two in which young volunteers lived on extremely low calorie diets for up to six months. The purpose of the study was to help scientists understand how to treat victims of mass starvation in Europe.

    After prolonged starvation there was a drop in body temperature and heart rate, suggesting that their basal metabolic rate (the energy burnt by your body when you are at rest) had fallen. This, however, was an extreme situation.

    A more recent experiment on the effects of short term calorie restriction, Resting energy expenditure in short-term starvation, produced very different results. In this experiment they took 11, healthy volunteers and asked them to live on nothing but water for 84 hours.

    The researchers found that the volunteers’ basal metabolic rate went up while they were fasting. By day 3 it had risen, on average, by 14%.

    One reason for this may have been the significant rise they detected in a catecholamine called noradrenaline, which is known to burn fat.

    If they had continued then, I’m sure, the volunteers’ metabolic rates would eventually have fallen, not least because they would have begun to lose significant amounts of weight. But, certainly in the short term, there is no evidence that starvation mode is anything other than a myth.

    Thanks for addressing this concern in a thoughtful way!

    I wonder about the effects of prolonged, but not extreme dieting. If you lose weight by cutting calories to say 10% below TDEE every day for 6 months or a year or longer would that lower your metabolism. I’ve always expected that it would, but I wouldn’t be surprised if there isn’t any data on that, just because of the difficulty and expense of long term human diet studies. I consider it an advantage of intermittent fasting that you can meet or exceed your TDEE most of the time while still losing weight. I think the non-fast days might be necessary for avoiding the problem of slowed metabolism. But it’s just a conjecture as far as I know.

    It’s good to know that “starvation mode” is a myth, in one way …. but I was wondering if it had happened to me! I started the FD in January 2013 for the health benefits and to lose about 9lbs.

    Everything went brilliantly – I lost the weight, felt great, and was happily maintaining – until I switched from cigarettes to ecigs in January 2014. After a few weeks I noticed I was gaining weight, so exercised more and cut back on calorie intake. I tried the 4:3. Nothing has worked and I am 5 lbs up and fighting.

    I was thinking that “starvation mode” might be to blame …. based on input from other people. So it’s a myth …. back to the drawing board!

    I had my last meal on Sat night at 7 pm . Today I have eaten 400 cals . I wasn’t going to eat again until tomorrow night Monday . is that too long? I have done this on my two fasting days . this is my first week xx

    The 5:2 Fast Diet recommends fasting on non consecutive days. This means during the waking hours of your fast day, you eat up to 500 calories.

    The previous and next waking day are typically a non fast day, so you eat when you are hungry but don’t go overboard — eat up to your TDEE.

    If I were you, I would eat up to 100 more calories today and then normally tomorrow.

    You can go longer if you wish, but you don’t have to do it that way.

    I’ll agree with Micheal on this, however I do feel generation genetics play a role. If some of your recent ancestors have been through famine in childhood? I believe genes are sophisticated enough to pass on traits that slightly alter the rate we store fats. For instance some obese people continue to get larger and larger even unto a 1,000 lbs, while others will hover between 350-and 450 no matter how much and how often they eat. My opinion is this myth will be very difficult to eliminate because of generational variables.
    Often discussed is the ease of losing the first 25lbs, but last 25 is more difficult from diet alone. There must be a reason for this? Yes?

    Want to add that 5:2 or 4:3 doesn’t come close to starvation response. IMO

    Sorry SAMM, I have no idea what you mean by generational variables. If you mean that previous generations have experienced food shortages and we have not – well, yes, that has happened. But genes don’t have a memory a la “oh, your mother went through wartime rationing, you should be prepared – here, get fat”. They do pass on “traits”, that is what genes do, they are our ancestral information on how the body should function; however, changing these traits takes a long time and does not happen as a quick responds to your parents’ living conditions.

    One of the reasons why weight loss slows down is that with diminishing waist lines the BMR changes. It simply takes less energy to get out of bed when you weigh 60 kg than to lob 120 kg off the bed. It takes more energy to move blood around a 120 kg body than around one half that size.
    On long-term calorie restricted diets the body realises that you have lost weight and will reduce BMR to avoid starvation. Michael mentioned this in his post, this is the metabolic adaptation occurring after months of significant calorie restriction.
    I am not aware of studies that look at BMR changes after long periods of intermittent fasting, for example after 6 or 12 months on the 5:2 diet. There are people like Brad Pilon who claim that intermittent fasting fools the body into believing that there is no overall calorie restriction and the metabolic adaptation does not occur even after significant weight loss and years of intermittent fasting.

    I would agree with with Brad also.
    I truly wish I could reference the info. I actually thought it was in the Eat,Fast,Live Longer video!
    About the records kept in Finland. Was from the oldest acesestry records. I thought it pointed to there being an obesity relationship within three generations Hoping someone else may know of what I’m speaking of and have more info on it. I believe the records were kept prior to 1800. So rather than a study it’s statistical. What I mean to say is there may be genetic traits passed that deal with obesity and starvation. I swear to god I didn’t make it up .
    I do have memory issues. Now that thinking on it. I gave a woman advice in 2008 about the video, so it couldn’t have been the Eat, Fast, Live Longer , but much of the info was similar so I associated.

    Again i don’t disagree with what Micheal point is about short term semi fasting not being enough to trigger a starvation response. And I agree that brad points to conditioning. However I will still have the opinion that childhood starvation can effect genes . That may be passed on within a few generations. If I were that recipient I may have issues with weight control that others may not. Just bear with me , because that type of info is above my head. I simply can’t make that kind of stuff up. Give me some time to find it a week or so as it may be on VHS tapes, and haven’t converted my video library unto drives yet. Definitely prior to 2008 , a PBS program geared about obesity.

    I probably won’t find the video I’m think of , but may find reference pointing in this direction.

    Your right Samm, it’s not Lamarckian evolution, it’s caused by methylation of DNA, and in this case, epigenetic imprinting I would guess. I also remember something about starvation possibly having epigenetic effects over a few generations, but I don’t remember any details, or how speculative it is with regard to starvation.

    @marielaem – re swapping cigarettes for e-cigs and gaining weight (I apologise if someone else has remarked upon this in this thread): My mum did the same a good few months ago when she was on a roll of losing weight and exercising. Her weight-loss stalled and she actually gained a few pounds….in complete disbelief she told me about it and I researched my way to an answer: Cigarettes apparently increase your metabolism, so without them presumably your metabolism would decrease – thus the weight gain. Luckily not starvation mode. (Obviously I might be wrong as I’m not an expert, but that’s the answer I found. And it makes sense!) Just keep doing what you’re doing and have a little patience. (And by the by, my mum is losing weight again!) Alex xxx

    I have to agree with alexa5. I stopped smoking 3 and a half years ago, without any aides and I gained 6 kilos. (I weigh in kilos as I don’t really want to know my ‘true weight ha ha)and given I didn’t change anything at all at first, it had to be the metabolism. There just wasn’t anything else it could be.
    Later on, more weight gain could be attributed to my new found crave of peanut butter.That’s why I am on this site now.
    Good luck and keep battling on, Marielaem

    Hi SAMM,
    You can watch the BBC Horizon documentary that features studies here on Epigenetics ‘THE GHOST IN YOUR GENES’:
    In the documentary one such study by Marcus Pembrey, a Professor of Clinical Genetics at the Institute of Child Health in London, in collaboration with Swedish researcher Lars Olov Bygren was particulary interesting. They studied the parish registries of births and deaths in a remote village in Sweden, Överkalix, including detailed harvest records and showed evidence of an environmental effect being passed down through grandparents who were subject to a famine at critical times.

    Hi SAMM,
    You can watch the BBC Horizon documentary that features studies here on Epigenetics ‘THE GHOST IN YOUR GENES’:
    In the documentary one such study by Marcus Pembrey, a Professor of Clinical Genetics at the Institute of Child Health in London, in collaboration with Swedish researcher Lars Olov Bygren was particulary interesting. They studied the parish registries of births and deaths in a remote village in Sweden, Överkalix, including detailed harvest records and showed evidence of an environmental effect being passed down through grandparents who were subject to a famine at critical times.

    Thank you. I am battling on! I have severely restricted carbs to see how that goes, and it seems to be working – I got to the point where I had gained 10lbs. I have now dropped 4. I have also cut back on the vaping a bit. I am still walking, fasting and going to the gym.

    I haven’t found the fasting hard at all – the hard thing for me has been to be fasting, exercising etc etc and still to see the weight increase, especially as the 5:2 was working so wonderfully well for me before I gave up smoking. I did the 4:3 last week, and when I weighed I had gained another 4 lbs. I felt like crying when I saw that I was getting back up to my pre-5:2 weight.

    I’m almost doing Atkins Phase 1 now! Psychologically, it has been a real boost to see the scales go down a little instead of up.

    Hi marialaem, don’t give up… I have been doing this diet since February 14. The results are really slow for me but have been steady I have seemed to of plateaued. Going on 4:3 next week. However I have an under active thyroid I excersise 4-5 days a week at the gym too. It’s noticeable now it’s good. I am pleased with it. Carry on with it and you will see results drink loads of water on your fast days and green tea. Good luck . 🙂

    I understand that the metabolism increases during an intermittent fast yet I was struggling to argue the point with a colleague when she insisted that lost of water is required to tell the body not to “store” while you are fasting. She insisted that you need more than usual whole fasting, while I argued that if you are eliminating clear fluid regularly, then that is enough water, and that happens for me without drinking any more than I normally would (2-3l a day).

    If the metabolism is higher, does that mean that your body is burning, not storing the food you eat?


    First, your ‘metabolism’ does not increase because of fasting – in fact, because you are not expending energy digesting food, it goes down a slight bit. That is why some people get cold on their diet days – the body is not generating heat from digesting food.

    Second, your friend is correct that you usually need to drink more liquid on diet days. That is because a body gets up to 40% of its needs for liquids from food, and if you are not eating much you need to compensate for the water you are not getting from your food.

    You are also right with ‘eliminating clear fluid’ means you are getting enough liquid. Your ‘normal’ amount of liquid – 2-3l a day – is about twice what is necessary for the body to function properly, so if you drink that much on your diet days you are getting more than enough liquid and do not need to ‘compensate’ for the liquid not being ingested with your food.


    Regarding your original post you may be interested in this link on Pubmed that Susan Jebb sent to me recently:

    Hall describes an adaptation scenario where thermogenesis is reduced (organs stop producing as much heat) during weight loss. He did not see a corresponding increase during weight gain though!

    Can this effect be cumulative though? Meaning your body would switch this on after a short time dieting because many weight loss attempts had been made before? An increased response to famine as time goes by?


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