Refeeding syndromes – Fasting 20

posted in: Fasting, Health and Nutrition | 31

Complications with refeeding were first described in severely malnourished Americans in Japanese prisoners of war camps in World War 2. It has also been described upon treatment of long standing anorexia nervosa, and alcoholic patients. It is important to have an understanding of these syndromes if you are attempting an extended fast – usually greater than 5-10 days at a time. Re-feeding refers to the period of time immediately after an extended fast when you are just starting to eat again. We’ve touched upon this briefly with ‘how to break a fast’.  The two main syndromes are refeeding syndrome and refeeding edema.DavidBlaine

In 2003, David Blaine, the magician, emerged from a 44 day water only fast. Opinions abounded regarding whether or not he was cheating, although he was in plain sight the entire time. Doctors recorded every measurement they could think of afterwards during his hospitalization. He lost 24.5 kg (25% of his body weight) and his body mass index (BMI) dropped from 29 to 21.6. Blood sugars and cholesterols were normal. Free fatty acids were high (expected during fasting).

He developed both refeeding syndrome and edema after this stunt. His phosphorus levels fell and required intravenous replenishment.

Re-feeding Syndrome

Refeeding syndrome has been defined as the “potentially fatal shifts in fluids and electrolytes that may occur in malnourished patients”. The key clinical marker of this is hypophosphatemia – very low phosphorus levels in the blood. However, lowered potassium, calcium, and magnesium in the blood may also play a role. Calcium, phosphorus and magnesium are all primarily intra-cellular ions – that is, they are kept inside the cells and blood levels (which are outside of cells) tend to be quite low compared with concentrations inside cells.

Adults store 500-800 grams of phosphorus in the body. Approximately 80% of the phosphorus in our bodies is held within the skeleton and the rest in soft tissues. Almost all of the phosphorus is inside the cell, rather than outside, in the blood. The blood level of phosphorus is very tightly controlled and if it goes too high or low, can cause real problems. Average daily intake of phosphorus is 1g/day, meaning that it often requires many months of undernutrition to produce these syndromes. Protein rich foods, as well as grains and nuts are good sources of phosphorus. 60-70% of the phosphorus is absorbed, mostly in the small intestine.

Refeeding1Much of the calcium, phosphorus and magnesium in our bodies is stored in the bones. If the body needs more or these intracellular ions, it will take it from the bone ‘stores’. If there is too much, these get deposited into the bone.

During prolonged malnutrition, blood levels of phosphorus remain normal and the deficit is taken from the bones. This can last for a very long time, as was proven with severe malnutrition imposed on the Japanese prisoners of war during World War 2.

But there are some problems that can happen once food is given, particularly carbohydrate containing foods. During the refeeding period, insulin and other hormones are activated. This causes the movement of the major intracellular ions (phosphorus, potassium, calcium and magnesium) into the cells. However, due to overall depletion of body stores, this becomes excessive and too little of these ions are left in the blood. This is what causes the major symptoms of the refeeding syndrome, some of which are rarely fatal.

Phosphorus is used in all cells for energy. The basic unit of energy (ATP) contains 3 phosphorus molecules so severe depletion of phosphorus may cause your entire body to ‘power down’. This typically happens when the serum phosphorus level drops below 0.30 mmol/L. The symptoms include muscle weakness as well as breathing difficulty as the diaphragm (the large muscle powering the lungs) weakens. Outright muscle breakdown (rhabdomyolysis) has been described, as well as heart dysfunction (cardiomyopathy).

Magnesium is a co-factor in most enzyme systems in the body and severe depletion can result in cramps, confusion, tremor, tetany and occasionally, seizures. Cardiac rhythm abnormalities are also described – classically the pattern known as Torsades de Point. Most magnesium (about 70%) taken orally is not absorbed but excreted unchanged in the feces.

Potassium may also be shifted into cells, leaving dangerously low levels in the blood. This, too can cause heart rhythm disturbances or even outright cardiac arrest.

Insulin stimulates glycogen, fat and protein synthesis which requires many ions like phosphorus, magnesium, and cofactors like thiamine. The insulin surge puts an enormous demand on phosphorus stores which have been depleted. In essence, the stores of all these intracellular ions has been severely depleted and once the signal is given to replenish, too much phosphorus is taken out of the blood leading to excessively low levels.

So you can see that one of the key pre-requisites for refeeding syndrome is severe, prolonged malnutrition. How common is it? A study of over 10,000 hospitalized patients only found an incidence of 0.43%. These are the sickest of sick people, but still was found rarely. This is actually on overestimate since it also included diabetic ketoacidosis, which is a different mechanism entirely. The main groups that had this disease? Severe malnourishment and alcoholics.

Refeeding syndrome is most often described in the situation of parenteral (intravenous) refeeding in the intensive care unit. These patients are often intubated and cannot eat for weeks. In the setting of relative malnourishment, extremely calorically dense and nutrient rich fluids are introduced directly into the vein. A setup for re-feeding syndrome.

The main risk factor for re-feeding syndrome is prolonged malnutrition. When we use fasting as a therapeutic tool, most people have never missed a single meal in over 25 years! This is hardly the situation that we deal with currently. However, it is important to understand that patients that are severely underweight or malnourished should not fast. This is important because re-feeding syndrome is mostly found in the condition of starvation (uncontrolled, involuntary restriction of food) or wasting (starvation to the point of severe malnutrition) rather than fasting (controlled, voluntary restriction of food).

Vitamin deficiencies have also been described, again mostly with prolonged malnutrition. The most important is thiamine, which is an essential coenzyme in carbohydrate metabolism. Typically, this has been described in alcoholics with the syndromes of Wernicke’s encephalopathy (ataxia, confusion, visual disturbances) and Korsakoff’s syndrome (memory loss and confabulation). Confabulation is a symptom whereby people have a complete lack of short term memory. They therefore ‘make up’ everything when they are talking because they have no memory. There is no intent to deceive. Traditionally, it has been taught to treat alcoholics and other malnourished people with thiamine (intravenous if needed) before treating hypoglycaemia. Theoretically, the glucose may stimulate acute thiamine uptake and precipitating Wernicke’s.

Re-feeding Edema

Insulin acts on the proximal tubule in the kidney to reabsorb sodium and water. Higher insulin levels will result in salt and water retention. Low insulin levels will result in loss of salt and water by the kidney. This has been well described for over 30 years.

During fasting, insulin levels go down quite significantly. This may lead to loss of salt and water. In some extreme cases there is up to 30 pounds of water weight lost, as George Cahill described in his article “Starvation“. The body is not able to hold on to salt and water due to low insulin levels. During re-feeding, especially with carbohydrates, insulin levels start to go back up, and the kidney starts to hold onto salt and water extremely tightly. Sodium excretion may fall to less than 1 mEq/day.Refeeding2

In extreme cases, you may actually see gross edema. This can occur as the legs and feet start to become very swollen. Occasionally retention of fluid in the lungs leads to congestive failure in those with heart disease.This has been called”refeeding edema”.


Obviously the mainstay of treatment is prevention. Box 3 identifies those at risk of re-feeding syndrome. Obviously the key is to avoid fasting a malnourished person, but that should have been pretty obvious already.

The mainstay of treatment is to start feeds very slowly. Generally this means 50% of the needed food intake with slow increase in rate if no problems are found. This is reflected in the traditional advice to break a fast gently. This is more important the longer the duration of the fasting period. We have often seen people who eat too much as soon as the fasting period is over. Most complain that the food gives them a stomach-ache, but this usually passes quite quickly. I’ve never seen or treated re-feeding syndrome personally, and I hope never to need to.DavidBlaine2

What happened in the Blaine fast?

There were some differences in the fasting done by Blaine and the ones we use in the IDM program. First, it was a water only fast. Generally, we only use those in severe cases. We allow the use of bone broth during fasts, which is not technically a fast, but provides phosphorus and other proteins and electrolytes. This reduces the chances of developing the refeeding syndrome.

Second, you can see that Blaine is suspended in a Plexiglas box for the duration of his fast. He is not able to do any of his usual activities and does not even stand up for 44 days. This is far more than a fast. His muscles and bones will actually develop significant atrophy during that period. He was losing far more than fat. He lost significant lean weight – muscle and bone, but this was NOT due to fasting. It was due to being cooped up in a box for 44 days.

During fasting, we encourage our patients to do all their usual activities, especially their exercise program. This helps to maintain their muscles and bones.

Start here with Fasting part 1

31 Responses

  1. Daniel Flichtentrei

    Dear Dr. Fung: I am cardiology from Argentine. I need help about a question: what strategies are effective for breaking adaptive thermogenesis (plateau) which produces the plateau in weight reduction with low-carb diets? Is there any role og T3 and T3R?

    Dr. Jason Fung: I have not used T3 or T3R. I generally try to change the diet or fasting routine to shake things up.

  2. Dr.

    When training or the the rise highly physically active, does fasting need to be more of the 16:8 variety to be beneficial or intermittent as in missing a meal or a day here and there?

    In other words for a training recreational athlete is there a fasting strategy that can be helpful and is there one that is not recommended?

  3. Would a partial fast like Dr. Longo’s Fasting Mimicking Diet – where you can eat 700 calories a day – prevent Re-feeding Syndrome/Edema?

    • I’d really like to see a conversation between Dr. Fung and Dr. Longo. Though they have really different objectives (and Dr. Longo is a research scientist not a clinician), I think an exchange between them could be really fantastic.

    • sten Bjorsell

      Derwood: Seems a lot more sensible to me to follow Dr Fung’s advice and use bone broth and water to keep blood levels of minerals from dropping too low. The 700 calories per may need maybe 5 times longer fast to achieve the same as what Dr Fung advises.
      Reason must to keep the cleansing action of fasting – autophagy or breaking down damaged proteins into useful spare parts, fuel and trash – going most of the time. At every refeeding event this process is interrupted and may take half a day to restart, every day. Bone broth maybe once every day seems a lot better and safer. For veggies extra sea and/or rock salt, but have no idea if any phosphorous in that.
      Also note that there are “electrolytes” one can get from pharmacies, but the ones I have seen are loaded with sugar, something that immediately spoils any fasting. Fung also implies limiting carbs and proteins during refeeding with reference to that quickly raised insulin is a damaging factor.
      Not surprised he never came across refeeding syndromes!

  4. This is why I drink and cook with purified water with added cal, mag, and potassium all the time–even during fasts. I am hypertensive, and this water is my medicine (cheaper than pills). It also assures me of adequate electrolytes. No, the cooking does not destroy the minerals.

  5. If you are 100 pounds overweight do you have to worry about refeeding syndrome? Also would I have to worry about it if I supplement magnesium potassium etc during the fast?

  6. Dr. Fung, for 6 days now, I eliminated sugar, dairy and processed food in my diet since I joined an online challenge. While I lowered my carbs intake, I am also trying to lengthen the “fasting window” to 14 hours so that I will eventually shift to IF (16/8). My last meal last night is at 7:30 pm; at 9:30ish in the morning, I experienced hypoglycemic symptoms- mild palpitations, blurry eyes and shaky. (I experienced this when I did a 24 hr fast a couple of weeks ago.) My question is- what do I eat when I become hypoglycemic due to lowered carb intake or IF? And should I continue with my attempt to do IF? Or should I just focus on lowering my carbs? I read in a ketogenic website site that what I experienced is “reactive hypoglicemia”–seems common to those who are starting to lower their carbs intake. (I plan to see a doctor to check my blood sugar, etc. but I am concerned that the doctor will advise me to eat often and eat carbs!) Thanks, Dr. Fung.

    • Joy-

      While we await response from Dr.Fung let me narrate my experience when I started 16/8 IF along with LCHF & HIIT. My fasting blood sugar went down within a week but I did experience palpitations during day time as well night time & I used to check blood sugar every time while having palpitations but I found every time that it was not within the range of of hypoglycemia.This happened as my body was getting used to new lows & after a week or so palpitations disappeared. I suggest you to check your blood sugar every time you have such symptoms.

      • @Devduttas, thanks. I’ll check it out. I still have 7 weeks into the challenge; will try monitor everything!

  7. Has anybody experienced diarrhea after short fasts, immediately after the first meal? (24-48 hour fasts) Do you have any recommendations to avoid this? Thanks.

    • Hi David, yes I have experienced diarrhea most times i do a fast longer than 24+hours. I find it helps to eat something small to break the fast (boiled egg, piece of cheese, veggie sticks, soup or similar) 1-2hours before continuing with a bigger meal.

    • Absolutely. If I fast for three days (eat Sunday evening, eat again Thursday at “lunch”), I will expel all the water I’ve had for those three days within about 8 hours or so after eating. I’ll go to the bathroom 8-10 times easily within that time frame. And it’s 100% water. I used to stop longer fasts in the evening, but I don’t do that anymore, as I have to get up to go to the bathroom too much. My wife has something similar happen to her, but not to the extent I do. She’ll go to the bathroom once for every 5 times I go. I haven’t figured out how to stop this, although it’s gone from 1.5 days or so to about 8 hours of basically expelling water. So, it’s gotten better, but I haven’t cured this.

      I note that even if I have a 24 hour fast (eat dinner day 1, don’t eat again until dinner day 2), I have a much smaller effect, but have some stomach/intestinal discomfort. If I just skip breakfast (which I do always now), I don’t have similar problems. This may be because I’m eating more in a shorter period of time (trying to eat all my calories for “dinner” rather than split them between lunch and dinner).

      I’ve been using resistant starch on the times I eat to try to help with this. It’s unclear whether it’s helped, but I believe it has helped a bit. It’s difficult to tell, though.

      • I also skip breakfast every day, and do not have an issue – unless I try a fast greater than 24 hours. Thanks for your suggestions.

    • I get this too! Within an hour or two of breaking the fast I get diarrhea. And at the risk of TMI often I recognize some of what comes out as what just went in to break the fast. How is that even possible??

    • Thanks for the feedback. Next time I’ll try breaking the fast with a snack, and having a regular meal later.

  8. Hi,
    I have tried the IF . I am o.k. With only having dinner….but I eat rotis, veg n sometimes chicken…if I take my B.S. it is in the range of 6. I am doing this so I don’t enter into fully blown Diabetes…Any, suggestions as to what do I replace in place of the wheat rotis…


  9. Lexie Boomer

    Dr. Fung, are your patients weightlifting during fasting or that’s too intense activity?

  10. I have a problem with too much fibre – I constipate! Even on normal LCHF days (2 meals a day), if I eat more than 1 serving of salads or greens, and more than 2 servings of vegetables, I constipate the next morning.

    I’d forgotten this when I broke my 5-day fast with 1 serving of mushrooms and 1 serving of stir-fried vegetables. The next morning, I had constipation accompanied by bleeding.

    During my fast, I drank coffee with cream, green tea and bone broth.
    By my own, rather simplistic reasoning, bulk laxatives during the fast may not help, simply because I constipate on fibre. Please correct me if I’m wrong.

    Grateful to Dr. Fung for the series on fasting. I love fasting and its benefits, but breaking the fast is almost traumatic.
    Can you please advise me on
    – what could be the reason I react quite the opposite to fibre than most other people
    – what kind of foods would be advisable for refeeding?

    • Sorry… forgot to mention

      I drank lots of water during the fast. Around 3-3.5 litres of water.
      (I weigh 57kg. I’ve read that normal water consumption of 1 litre per kg of water is advisable… and what I drank during the fast is much more.)

      Should I drink more? I really don’t mind.

    • re: constipation after fasting with fibre
      I had constipation for years…only after have a full body chemistry balancing test did I find out I was low in magnesium. Magnesium is used by the intestinal muscles for movement…this was the sources of my constipation….get a good magnesium supplement…say goodbye to constipation.

    • re: constipation after fasting
      I had constipation for years…only after have a full body chemistry balancing test did I find out I was low in magnesium. Magnesium is used by the intestinal muscles for movement…this was the sources of my constipation….get a good magnesium supplement…say goodbye to constipation.

  11. S. Kafune

    I am finishing a 10-day water fast (water, black coffee, decaf tea; no bone broth). I took a multi-mineral supplements (no sugar) on days 6,8. I feel great. Thinking I can go longer but I want to stop fasting so I can eat socially again, and it’ll take a few days to breat the fast. I’m 165cm tall, was 72 kg and now I’m 66kg.


    Any suggestions to break the fast smoothly? As I understand it, start small, stay away from carbs/sugar/sugary juices. Just go for the broth, non-starch veggies (cooked – like bac choy), bits of meat, and take fiber supplements (like flax?). How long? Can I take protein powder?

    Uktimately, I want to apply my new outlook on food to my eating habits going forward. Moderate my eating and appreciate food more. As well, I still want to lower more body fat while building moderately more muscle.

    Any tips, stories, or advice is much appreciated.

  12. Julie Tann

    Can strictures in the pylorus and distal bulb/duodenum lead to this?

    This is what I have at the moment & am really struggling to eat solid food.

    I’d really appreciate any help.

    Thank you.

  13. […] sticking to seven days or fewer. In his article he says fasts over 14 days bring increased risk of refeeding syndrome – which can in severe cases be fatal. I’m doing this for my health, so I’d rather […]

  14. Didi Lima

    I have been fasting for years at the Buchinger Clinic in Marbella, Spain. My largest period was 39 days, if you want real results you must do at least 21 days. Never a water fast, never stimulants like caffeine or juices containing sugar. Only vegetable broths and herbal teas. It is truly amazing to see your body eliminate toxins. Prep for the fast is rice 2 days, to break the fast, 1 apple, next day brown rice. Only. It must be slow and based on veggies not carbs. Longevity is the intent, this is normal in Europe, Americans are not really familiar with the process. Pavlov and Buchinger are the Fathers of fasting.

  15. […] ali zbog potencijalnih opasnosti – nepredvidivih hipoglikemija kod dijabetičara, ili zbog re-feeding sindroma kod dugotrajnijeg gladovanja i raznih drugih, teško predvidivih reakcija u različitim […]

  16. Dr Fung, my close up vision gets blurry. I am diabetic and introduce carbs back in when I fast.

    Is there a solution to this challenge?

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