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Comment by Engineering-MD | Hacker News Reader

Just a word of caution, after 7-10 days of fasting, you can get refeeding syndrome. This can be pretty unpleasant and dangerous, and is best avoided.

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Hey man, sorry to call you out. I want you to find where you heard that, and maybe post it here so that we can review.

I have fasted many times for that length, and I happen to already be thin. Never even got close to refeeding syndrome.

I've read a variety of books on the subject. I've spent some time on PubMed. I don't know everything about fasting -- absolutely not -- but I know enough to say that you might be misremembering the time it takes to get refeeding syndrome.

I personally believe the number is closer to 30 or 40 days. We are talking Christ-level fasters, hunger strikers, performance artists, or concentration camp victims.

I downvoted your comment because I consider it to be spreading misinformation, and because your tone indicates that you have expertise or experience on the matter.

You can definitely get refeeding syndrome after 7-10 days of fasting. It depends on your your fat reserves, health, and lifestyle.

Say I'm 192cm and 69kg. My BMI is 18.7, which is definitely low, but perfectly healthy. I have an active lifestyle and burn 3500kcal per day. If I fast for 7 days without changing lifestyle, I lose roughly 7*3500/7700=3.2kg of bodyweight. By that point my BMI is 17.9. According to this paper[0] with 632 citations, anyone with a BMI <18.5 who's not eaten for more than 5 days is at high risk of refeeding syndrome.

If you think the numbers are fictional: those are my numbers from ~5 years ago.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440847/

Cool, if it’s that clear cut I’m sure you can find a few cases to make your point.

It is rare that eating after fasting causes critical illness. Just check online. People do this stuff all the time.

I wasn't making "my point". I just knew your comment about 30-40 days and the random mentioning of concentration camp victims was absurd, and it clearly is according to official clinical guidelines. So no, I won't "just check online".

> Historically, some of the earliest reports of the refeeding syndrome occurred in starved patients in wartime such as Japanese prisoners and victims of the Leningrad or Netherlands famines. In general, those individuals with marasmus or kwashiorkor are at risk for the refeeding syndrome, particularly if there is greater than 10% weight loss over a couple of months. Patients are at risk if they have not been fed for 7 to 10 d, with evidence of stress and depletion. However, more specifically, this syndrome also has been described after prolonged fasting, massive weight loss in obese patients including after duodenal-switch operations, chronic alcoholism, prolonged intravenous fluid repletion, and anorexia nervosa. Anorexia nervosa is one of the more common modern clinical presentations of the refeeding syndrome, as are oncology patients undergoing chemotherapy, the refeeding of malnourished elderly individuals, and certain postoperative patients.

https://www.hopkinsmedicine.org/gim/_pdf/consult/refeeding_s...

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