According to Deuteronomy 9:9, Moses did not eat or drink anything for 40 days.

When I was gone up into the mount to receive the tables of stone, even the tables of the covenant which the LORD made with you, then I abode in the mount forty days and forty nights, I neither did eat bread nor drink water.

Is this possible from the scientific point of view? My guess is that no water for that long time must be impossible. How about no meals?

  • 2
    The better-known Bible passage featuring a 40-day fast is the one where Jesus fasts, in Matthew 4:2. Aug 22, 2011 at 12:04
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    According to some old (although not biblically old) interpretations of Jewish law, it was considered fine to chew a food as long as one spit everything out before swallowing, including one's saliva. I am not sure, but it might be possible that one could get some amount of nutrition/hydration from chewing food.
    – ESultanik
    Aug 22, 2011 at 12:19
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    The NKJ translation to "neither did eat bread nor drink water" does not necessarily mean "did not eat or drink anything" (but...I don't know Hebrew so I can't tell you if "water" literally means "water" or "water, wine, goat's milk, and all other liquids."). Also, I know someone who did the no meals thing for 40 days; he looked terrible at the end. Aug 22, 2011 at 15:20
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    This instance of fasting, was to show that Moses while in the presence of god needed no food or water, for gods presence himself sustained him, later when he comes down from the mountain the people could not look upon moses as he glowed and had to be covered, however most of the other instances of fasting in the bible did still include water, such as jesus's fasting in matthew as well as john the baptists fasting. so it was literally ment to show an impossible situation that he lived through, while the others were about simple discipline
    – Himarm
    Dec 10, 2014 at 22:57
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    Very lawyer-esque language by Moses there. "neither did eat bread or drink water" does not necessarily rule out leg of lamb washed down with wine. Aug 2, 2018 at 18:26

4 Answers 4


"Comment in passing"—the biblical term "40 days and 40 nights" or similar can be used to mean "a long time". Whether this is the case in any given passage would need to be understood, but is outside the scope of this question.

In any normal circumstance you'd be dead long before 40 days without water.

But hunger strikers regularly live beyond 40 days and purposeful fasting for that period is not unknown.

As an example of what this may do to the body, assume that a person fasting is largely immobile and can survive on a 500 kcal daily energy budget. Available calories from food are about 4 kcal/gram for carbohydrate, 5 kcal/g for protein and 9 kcal/g for fat. Start by assuming that body resources can return say 6 kcal/gram if "living off your own body.

  • 500 kcal per day requires 500/6 ≈ 85 grams of body mass.
  • 40 days requires 40 x 85 ≈ 3400 grams ≈ 3.4 kg of body mass.
  • Even doubling that to 1000 kcal/d requires about 7 kg of body mass.

Obviously there are many other factors to consider, and the above mass loss seems 'rather low' compared to expectations, but is an indication that energy availability is not the major factor involved.

This document—Adult Malnutrition in Emergencies—advises that hunger strikers experience "severe metabolic disturbance after 3 to 4 weeks" (ie 21 to 28 days) and death in 6 to 10 weeks (42 to 70 days). ir 40 days would be "pushing your luck".

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    Nice answer. Can you add a reference to where you found the cal/g figures? if the source is the document, could you mention that it is the case in the answer?
    – Sklivvz
    Aug 22, 2011 at 12:13
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    +1 can you also explain why 40 days without water is a certain death?
    – Fitri
    Aug 22, 2011 at 14:12
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    @Sklivvz: I know, but this is a skeptics site :P Also, the answer apparently assumes body nutrition is converted 100% to energy. Is such efficiency normal?
    – Fitri
    Aug 22, 2011 at 14:27
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    @James, it doesn't matter what base the number system is; if the average person has the equivalent of a second-grade education, there's a limit to how high people can count.
    – zzzzBov
    Aug 22, 2011 at 20:32
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    @zzzzBov Then why would they choose 40 rather than a maximum of one digit in the number system?
    – James
    Aug 22, 2011 at 20:36

Wikipedia has different articles in English and German about hunger strikes. The English version talks about people dying after 52 to 74 days of strike and it looks as if it is the lower bound. One Person, Swami Nigamanand, is reported to have died after being on a hunger strike for 115 days. There are several other numbers in between, and not every incident ended in the death of the hunger strike performer.

The German Wikipedia talks about 50 to 70 days strikes, which can be survived, but this sounds like an upper bound. The article is much shorter and concentrates on well known cases in Germany.

But there is a link to the medical aspects of hunger strike and a english version too. To summarize them: In the beginning, a typical weight loss is about 1kg/day, later 0.5kg/day.

Normally, a person will die without water after 3-4 days, but depending on weather circumstances, this can be shorter (1d, hot, dry) or longer (10d, cold, wet). Without food, but with water, healthy persons should survive 30 to 200 days. A critical question is, whether you get minerals and vitamins, or not even that.

One kg of body fat can be used like 30 MJoule or 7.000 kcal energie.

Afaik, we don't know much about the kind of diet which Moses or Jesus would have performed, and in which physical condition they started. Did they drink, and if they did, just water, milk or juice? If I remember correctly, the Bible claims that John Baptist ate locusts, which have a lot of proteins; did Jesus too?

My conclusion from this information is, that - apart from being just a written story - a 40 day fastening is hard, but possible - not a miracle, but a stunt of discipline. But 40 days without water is impossible; that's a lie.

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    The main problem with the passage is hydration -"nor drink water". I think it is hyperbole or translation error from the original Hebrew text. Aug 23, 2011 at 21:20
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    I don't think it is translation error. Hundreds of theologians have nothing to do than argue about translation and interpretation of the text. I put more emphasize to the 'no! impossible' in the last sentence. Aug 24, 2011 at 20:33
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    You might want to check Will we be able fast like the fasts described in Bible ? on †.SE as this is a good answer and would answer the other question, too! Sep 24, 2011 at 19:20
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    No, thank you, but you already linked this entry. I don't like to repeat myself, and I don't like to argue whether the bible is therefore talking about a miracle, is lying, talking about an illusion, is bad translated or a metaphor for something else. :) No, thanks. Sep 25, 2011 at 21:41
  • I believe John ate this kind of locust: en.wikipedia.org/wiki/Locust_tree and some translations say "pods"
    – WGroleau
    Aug 2, 2018 at 0:49

There was a single study published in 1973 in which an obese man, under close medical supervision, fasted for over a year. He took water and some vitamin or mineral supplements but no food.


Yes, it is possible to fast for 40 days. (for food, not water)

Here is a list of about 2 dozen IRA prisoners who participated in a hunger strike in 1981. https://en.wikipedia.org/wiki/1981_Irish_hunger_strike#Participants_who_died_on_hunger_strike

The shortest it took one of them to die was 46 days, the longest someone lasted who didn't die was 70 days.

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