Does intermittent fasting lead to muscle breakdown and protein deficiency?

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Does intermittent fasting lead to muscle breakdown and protein deficiency?

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  • Does intermittent fasting lead to muscle breakdown and protein deficiency?

    I recently read a comment in a newspaper by obesity researcher Professor Lau from the University of Calgary. He made the point that “muscle protein breakdown occurs in the first 24 hours of starvation,” and expressed concern that people who fast may be losing crucial muscle mass.

    My response to this is that he is really talking about long term fasting, ie fasting for days or weeks at a time. With intermittent fasting you are not fasting for 24 hours or longer. In the version that I practice, I never go more than 12 hours without eating. If your protein intake is adequate, and we actually recommend an increased protein intake on fasting days, then you are not going to get “muscle protein breakdown”. In fact the evidence from human studies clearly point towards intermittent fasting being better than standard diets when it comes to muscle preservation.

    Dr Krista Varady of the University of Illinois at Chicago has done a number of human trials using intermittent fasting. Her most recent paper was in, Metabolism, Volume 62, Issue 1, Pages 137-143, January 2013. In this study thirty-two overweight volunteers, average age 42, were put on an ADF (alternate day) intermittent fast for 8 weeks. At the end of 8 weeks the volunteers had lost an average of 4kg and seen significant improvements in biomarkers related to the risks of diabetes and coronary heart disease.  Interestingly, the weight loss was all fat, not muscle. As she points out “A similar preservation of lean mass was noted in a previous ADF study conducted by our group.” This retention of lean mass, ie muscle, is not seen with standard calorie restricted diets. “The reason why ADF may assist with the preservation of lean mass is not known at present, but will undoubtedly be of interest in future studies in this field”

    In another study of intermittent fasting (Int J Obes . 2011 May;35(5):714-27), 107 young overweight women were randomly allocated to either a standard low calorie diet or a diet where for two days a week they ate 650 calories a day. At the end of 6 months the intermittent fasting group had lost an average of 6 kg of fat and 3 inches from their waists compared to 4.9 kg of fat and 2 inches from waist for the normal dieters.

    Doing the diet, I have now lost just over 22lbs and my body fat is down from 28% to under 20%. I walk everywhere and do 30 press ups each morning. Keeping muscle mass is important, not just because it looks better but also because muscle is more metabolically active than fat; it burns calories even when you are asleep. Rest assured, the diet will keep you healthy as well as help you lose weight.

    I’d already heard about muscle loss problems before I started the diet so I just keep to the same mix on fast days….just alot less. So, some protein, some carb, some fat. All are essential..just not in the quantities I was taking in before! An egg, a 100g chicken breast, a few slices of parma ham….all sources of protein, around 100 cals each.

    I prefer to go from 6pm dinner the night before a fast day through to a fast day lunch containing protien, eg egg or sardine, giving me an 18+ hour fast. I often go through to lunch time before eating on non-fast days too as I am rarely hungry first thing in the morning. I haven’t noticed losing any muscle tone so presume this regime is healthy for me.

    I’ve lost 5kg using the 5:2 diet and my Fat free mass has stayed constant at 64kg throughout the process indicating that it appears to be only fat that I am losing. I eat a big bowl of porridge in the morning on fasting days and haven’t made an effort to eat more protein but it doesn’t seem to have made a difference. I think I read somewher that Growth Hormone levels are elevated during the first 24 hours of fasting and this has a protein sparing effect.

    Don’t know where else to comment. I found the book very interesting. I am a GP with an interest in diabetes, and I’m afraid that one bit of the book is wrong,where Dr Mosley says that his fasting blood sugar of 7.3 was nearly diabetic. The cut off is 7.0, as stated in the WHO criteria for diabetes – a fasting glucose of 7.0 or above, or a random glucose of 11.1 or above in the presence of classic diabetes symptoms is diagnostic. If there are no symptoms then 2 diagnostic readings on different days are needed. Now the book doesn’t say if he had symptoms, or if he had 2 readings, but as written it implies that a fasting glucose of 7.3 is not diagnostic of diabetes, which is just plain wrong.

    I’ve noticed my muscle tone actually improve, rather than decrease since starting the diet. Though I suspect this is less fat covering them rather than increased muscle size. Given that the fasting is for a fixed period of time there’s no reason why it should eat into your muscle mass – this is more of a problem on low calorie diets which you sustain over several weeks or months – where your body goes into starvation mode and burns muscle which has a detrimental effect on your metabolism and is one of the reasons such diets don’t work in the long term. With IF your eating again before your body needs to start using up muscle, so you should burn mainly fat rather than muscle.

    I am an overweight 57 yr old woman, keen to lose weight and keep it off and I am convinced by the evidence that IF will help me to do this and be good for my body as a whole. However, I am currently recovering from a hip replacement operation and am worried about losing muscle mass at a time when I really need to be building it up in my operated leg. Should I wait until I am fully recovered, or just eat a high protein diet? I am a vegetarian and have been on the diet for 4 weeks with no weight loss!

    I’ve been on a 5:2 regime for a couple of weeks now and happy with the progress thus far and still researching this topic as I go along. I have come across some research published on pub med as follows and wonder if Michael or others have any comments please:

    Calorie restriction is a dietary intervention known to improve redox state, glucose tolerance, and animal life span. Other interventions have been adopted as study models for caloric restriction, including nonsupplemented food restriction and intermittent, every-other-day feedings. We compared the short- and long-term effects of these interventions to ad libitum protocols and found that, although all restricted diets decrease body weight, intermittent feeding did not decrease intra-abdominal adiposity. Short-term calorie restriction and intermittent feeding presented similar results relative to glucose tolerance. Surprisingly, long-term intermittent feeding promoted glucose intolerance, without a loss in insulin receptor phosphorylation. Intermittent feeding substantially increased insulin receptor nitration in both intra-abdominal adipose tissue and muscle, a modification associated with receptor inactivation. All restricted diets enhanced nitric oxide synthase levels in the insulin-responsive adipose tissue and skeletal muscle. However, whereas calorie restriction improved tissue redox state, food restriction and intermittent feedings did not. In fact, long-term intermittent feeding resulted in largely enhanced tissue release of oxidants. Overall, our results show that restricted diets are significantly different in their effects on glucose tolerance and redox state when adopted long-term. Furthermore, we show that intermittent feeding can lead to oxidative insulin receptor inactivation and glucose intolerance.

    Hello Doctor,
    Where are we left with the protein discussion in light of Luigi Fontana’s subsequent increased emphasis on decreasing protein consumption to lower IGF-1?
    If it is now shown that his four day fast results lowering IGF-1 do not last, and that the IGF-1 test results on long term Calorie Restrictors might appear to be no different than couch potatos, how could we view his entire body of reasearch into this subject?

    I’m a student doing a co-op program at a gym, and I was given an assignment to research the IF diet but I can’t seem to find some of the answers I’m looking for. If you workout daily then how are you suppose to have energy for the workout on the fast days? And do you just have your second meal as your post-workout?

    7th day and loving it. Bad knee arthritis feels great, skin really healthy even the hair is healthier I am at my infamous plateau of 200lbs @ 6’2″ have lost 15 lbs which a part of was the Warrior Diet concept but like this far more and really want to get exercising on fast days but nervous…Bike 10-20 mi. swim 1/2 to a 1 mi or stand up paddle or surf for a coupla hours. Obviously not on the same day but would love to hear from anyone that may have that level of exercise and find out how your feeling and how your body has responded.Thanks Mimi and Michael this could be the lifelong answer I have been desperatley searching for.

    I have found that eating one meal daily at 5 pm works best for me with a 23 hour fast M-F, and then 1-2 meals on weekends…I feel fantastic and have so much more energy…..I am thinking (hoping) that this will bring the same results with my IGF levels…I eat normal for my one meal daily, and also take vitamins and a dehydrated veggie/fruit pack every 24 hours with my meal. Cannot tell you how many benefits…sleeping better, improved focus, happier….better quality of life after just two weeks!.

    I recently started doing 2 consecutive days of fasting, 2PM Monday to 2PM Wed with a 500 cal lunch in the middle on Tuesday, so it’s about 48 hours with 500 cal. No one has talked about consecutive days so I am wondering if it is good (faster results?) or bad (muscle deterioration?). It feels much easier to me to do it in one shot, once a week, rather than every few days. What do you think, experts?? and thank you for the inspiration Michael!

    Is there any evidence about the impacts of fasting on the gall bladder? particularly intermittent fasting?

    Michael, How are your lab numbers looking since dropping back to a 6:1 regimen? Once you reach target weight, will switching to a maintenance 6:1 offer the same benefits regarding heart disease, diabetes, etc?
    In the book, you said you’d post the followup on this. Thanks.

    I’ve been on the 5:2 for coming up to a year now (lost about 15lb in the first 6 weeks and about 2-3 since). I’m a keen cyclist and train fairly hard. I have slowly been developing the training I can do on fasting days, starting with 3/4 effort (zone 4/HR) and gradually increasing it to around 90-100%. As long as I keep the ride under 100 mins I don’t feel any side affects, apart from the odd cramp from not having my normal hydration drink (just water). My question is this:

    I regularly get Personal records on Strava segments on fasting day. Any idea why? Is it because I’m a tiny bit lighter on fasting day or is there some other reason why I can push harder for a short segment. I would expect my body to be running on empty?

    I tend to fast from after the evening meal 7pm till 1pm the next day then eat normally. I do this twice a week. I have been doing it for 6 weeks. I have definately noticed loss of muscle mass and fat too (although I was already skinny).

    I lift weights and do cardio several times per week. I started the 5:2 diet 8 months ago and continued the same exercises. In addition I follow a low animal protein diet. I was concerned from the start that I would get weaker, and initially I did lose a little strength as measured by the heaviest weights and repetitions. However, surprising to me is that now even on a strict 5:2 (36 hours with < 600 calories) and low protein I am lifting as much as I ever had before and some weights are higher now than ever. I was thin to start and am now even thinner but muscle definition is very good. I am not doing any of this for appearance but for health. I believe it is important to stay lean, minimize animal protein, and exercise. I feel very comfortable that I am not losing any muscle mass and somehow am getting stronger. Negative side effects besides hunger are tiredness on fasting days, and occasional diarrhea the next day.

    That’s a potenially disturbing study result, but I would note that they used a complete 24 hr fast for the mice which is known to disrupt their nocturnal circadian cycle and could be causing the negative effects. See this…

    I believe intermittent fasting helps in building strong and lean muscles. That is what i have experienced during my training.

    Information source for intermittent fasting:

    So here is my experience with 5:2 muscle loss. Let me start by saying I enjoying IF. However, I have noticed a large decrease in muscle mass. I have been taking Electronic Impedance measurements for the past few years as I have been actively lifting weights. On June 27th 2015 I measured at 230.1 lbs, Body Fat 23%, Body Fat Mass 53.1 lbs. That translates to 177lbs of muscle.
    I measured myself yesterday… Oct. 18th 2015. 214.5 lbs, Body Fat 21%, Body Fat Mass 44.5 lbs. Which means I have lost 8.5 lbs. of Fat & 7 lbs. of muscle.

    I currently fast 2 days a week, and I workout 5 days a week including the fast days.

    My current food intake on fasting days consists of 1 large chicken breast at lunch, and 2 scoops of casein protein (360cal) 6 hours later.

    Any advice to stop the muscle loss?

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    Hello oldestswinger…….The very first part of the title of the study, “Long-term intermittent feeding, but not caloric restriction” doesn’t make a lot of sense. “Calorie restriction improved tissue redox state, food restriction and intermittent feedings did not.” No sense. It doesn’t say how many calories are in calorie restriction, food restriction or intermittent feedings and the difference between them or whether the subjects exercised and how hard they did it or how much protein they consumed during and after their fast. I believe it has been shown that exercise inhibits muscle deterioration. How much it offsets muscle loss from prolonged fasting during IF? Who knows. Just that it does. In the study with Krista Varady, calorie restriction of 400 to 500 calories for women and 500 to 600 calories for men every other day, the fast day meals were formulated based on the American Heart Association (AHA) guidelines (30% kcal from fat, 15% kcal from protein, 55% kcal from carbohydrate) [8]. There wasn’t any lean muscle tissue loss. This has to include fast twitch muscle fibers since they compose a lot of size and have the best adaptation to growth. In other words it would be quite noticeable. I know there is water and glycogen loss in conjunction with IF and this absolutely impacts some muscle size and strength. It must not be a lot. It certainly doesn’t mean the muscle fibers and nerves go away. Nearly anything that impacts your muscles whether larger or smaller, translates into impacts of size and strength. I personally believe short fasts of 24 to 36 hours doesn’t do anything negative on anything except but for a very small shrinkage of fast twitch muscle fibers due to water and glycogen loss but this gets built back up and more once the final weight and waist size reduction is complete and caloric intake is resumed at or very slightly above current maintenance for the newly arrived state. Actually only bodybuilders would be affected because differences in water and glycogen simply has a greater impact and is more noticeable than more sedentary folks. No concern, as long as your getting protein on the days of fasting and feasting, exercise properly, sleeping enough and have your diet overall dialed in.


    “David Lau, an obesity researcher, professor and chair of the diabetes and endocrine research group at the University of Calgary. When glycogen stores in the liver are depleted, the body doesn’t burn fat: It breaks down protein. Lau said starvation will only burn fat as fuel after about a week of starvation.

    “Muscle protein breakdown occurs in the first 24 hours of starvation,” he said. “Muscle protein breakdown [is] not healthy.”

    His concern is that many people are fasting without realizing they may be losing crucial muscle mass. The danger is that as protein in the body breaks down, it could lead to other unwanted side effects, such as altered immunity. In order to fight infections, the body needs to produce antibodies, a type of protein. But when the body is breaking down protein for fuel, it may not send the right signal to make antibodies, Lau said.”

    But… as Dr Jason fung put is in many a video and in this article:

    “Muscle gain/ loss is mostly a function of EXERCISE. You can’t eat your way to more muscle. Supplement companies, of course, try to convince you otherwise. Eat creatine (or protein shakes, or eye of newt) and you will build muscle. That’s stupid. There’s one good way to build muscle – exercise. So if you are worried about muscle loss – exercise. It ain’t rocket science. Just don’t confuse the two issues of diet and exercise. Don’t worry about what your diet (or lack of diet – fasting) is doing to your muscle. Exercise builds muscle. OK? Clear?Macro oxidation

    So the main question is this – if you fast for long enough, doesn’t your body start to burn muscle in excess of what it was doing previously in order to produce glucose for the body. Hell, no.

    Let’s look carefully at this graph by Dr. Kevin Hall from the NIH in the book “Comparative Physiology of Fasting, Starvation, and Food Limitation”. Great title guys. Amazon probably couldn’t keep enough stock on the shelves.

    But anywho, this is a graph of where the energy to power our bodies comes from, from the start of fasting. At time zero, you can see that there is a mix of energy coming from carbs, fat and protein. Within the first day or so of fasting, you can see that the body initially starts by burning carbs (sugar) for energy. However, the body has limited ability to store sugar. So, after the first day, fat burning starts.”

    In my experience, I’ve been IF for five consecutive days midweek throughout Feb and into March. I do gym work, swimming, running and cycling. My lean muscle mass went up in Feb. My running is quicker than when I started 5:2 last Sept. mainly due to the weight loss I think – carrying around 10kg more than I am now when running seems quite extraordinary!

    So from this sample of one I can conclude the Professor is a charlatan (allegedly) or at best mis-guided. I’ve not read the study on the mice, but Dr Fung makes it clear that the natural process of muscle loss and replacement accounts for some of the urine contents, and all that skin that seems to miraculously disappear as we lose weight, (rather than us look like an empty sack of skin) also gets eaten-up.

    And finally, I don’t think I’ve come across anyone on this forum who moans about muscle lost, rather than fat loss!! As the ardent faster Dr Fung says himself, he would have disappeared by now if a large proportion of what he’d lost was protein and not fat. So for heaven’s sake can these Professors think before they pontificate. Let’s remember there are a bunch of very eminent Profs out there who got us all eating high carb-based diets. Even the NHS Healthy Balanced Diet has high carbs, and the evidence in the UK and elsewhere that this is just plain wrong is huge! One big experiment that has led to a rapid growth in Type 2. Or a: “Diabetes Tsunami” – to quote Prof Lau.

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