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Wellness Center

Fasting and starvation mode



If I go on a one day fast for religious purposes (such as eating before bed on tuesday and breaking the fast on thursday morning) does my body go into starvation mode or does that take longer? What about a three day fast?


Thanks for your question. During a three-day fast (without stress of surgery, car accident, or other hypermetabolic condition), your body will initially use carbohydrate from glycogen stores.

Glycogen is carbohydrate that is stored in your liver and muscles and is used when you are fasting (not eating).  Your body may mobilize some protein from circulating amino acids as well as muscle for calories as well.

After three days, your body will start to mobilize fat for calories to spare protein. However, protein will eventually be used for energy as well if the fast continues.

The bigger risk in fasting is dehydration. Water is vital to every organ in your body to help maintain blood pressure, respiration, body temperature, etc. Never go longer than three days without water or other fluids.

I hope this information is helpful.

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Response by:

Lisa Cicciarello Andrews, MEd, RD, LD Lisa Cicciarello Andrews, MEd, RD, LD
Adjunct Faculty
University of Cincinnati