Due to an injury followed by a stomach virus, I drank a lot (coke, iced tea, and water) but hardly ate anything for 5 days. Now, my weight has dropped by 3 lbs.

I feel like I lost muscle mass. However, my doctor told me that while not eating I would have used up fat, not muscle.

If I stop eating for a week, will I loose muscles or just fat?

Clarification: This was not on purpose, I simply couldn't eat.

  • Your first question is a duplicate of this: fitness.stackexchange.com/questions/4111/… I left the second question in tact.
    – michael
    Commented Jul 30, 2012 at 16:49
  • What did you drink? If it was caloric at all (Such a fruit juice, pedialyte, etc), then that will make a difference in how the body reacts. There is a huge difference between 5 days of no calories vs. 5 days of lower calories.
    – JohnP
    Commented Jul 30, 2012 at 17:54
  • @JohnP: Caffeine free coke, iced tea (with sugar), and water Commented Jul 30, 2012 at 23:48

5 Answers 5


I'll make an assumption that what you're really worried about is how much will your strength be affected in your next workout. That is, how much should you deload when you restart your lifting program?

I had food poisoning that affected my diet for about a week. When I returned to the gym, my squat had dropped from 230 to 215, shoulder press from 95 down to 85.

But, whether or not that is due to actual muscle loss, I don't know. After a week of sickness, you're probably poorly hydrated, you'll have depleted glycogen stores, creatine levels will be low, you'll have missed your super-compensation phase and may have begun deconditioning. You'll definitely feel less strong.

  • Well, I pretty much expect to have to deload the first time back. My question is: Is that one time only, or am I really pushing back a few months? Keep in mind that I lost 3 lbs while out. Commented Jul 30, 2012 at 23:50
  • 3
    I had to deload and re-build strength over several workouts, but it was a few weeks worth of rebuilding to get back to my previous strength, not a few months.
    – user3085
    Commented Jul 31, 2012 at 0:14

Your doctor is closer to being right (but probably not 100%).

The body starts eating muscle when you're out of glycogen. If you're drinking sugary beverages (i.e., not diet) that will delay the onset of chowing down on muscles, at least to some extent.

You'll become marginally de-conditioned after five days, but not radically; most of the issues will be related to not having sufficient fuel stores to bust out a pre-weakness workout.

  • Hello Dave, I would like to politely point out that I believe several of these statements may very well be completely inaccurate. Pages 74-77 of Dr. Jason Fung's "Complete Guide to Fasting" detail a study in which someone who alternate-day fasted for 70 days lost 4.9Kg of fat-free mass, but only 0.1Kg of lean mass. His analogy was something like -- if you gather firewood all summer, and then winter comes and it gets cold, you do not chop up your sofa (ie. functional lean mass) for fuel; you use the firewood (ie. adipose tissue). Commented Jul 8, 2018 at 1:42
  • Other books I have read indicated that drinking sugary beverages will expedite the chowing down on muscles, not delay it. The reason is that the insulin-spike reduces blood-energy levels below basal levels in an over-reaction to the unnatural surge of glucose and insulin also prevents the use of fat stores for energy until insulin levels drop. After glucose levels are depleted by the insulin surge, and fat is no longer an option to the body, it quickly turns to protein to synthesize glucose. As a matter of fact, his doctor may very well be 100% correct. Commented Jul 8, 2018 at 1:47
  • @RyanMortensen ... Okay. One study and "books" don’t mean much on their own, though. Commented Jul 8, 2018 at 1:58
  • Books actually mean a lot; they're written by experts who research their subject and provide a multitude of references. My suggestion for you would be to add sources to improve your answer thus improving the knowledge-base of the site rather than to defend your position by attempting to downplay the credibility of books on the subject (unless you wrote a book on this subject that I'm unaware of and are a generally accepted as an authority on fasting). This shouldn't be treated like "tribalknowledgeexchange.com". Bad info about health/fitness can be dangerous or deadly and should be respected. Commented Jul 8, 2018 at 4:11
  • 1
    @RyanMortensen (My original answer should have read "out of glycogen and at a low body fat percentage".) Commented Jul 8, 2018 at 12:11

Your doctor is correct, see this website: http://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3529354_DMM010009F3.jpg

After about day 5, the energy taken from fat stores is the greatest. If you continue to fast longer than 5 days, the proportion of muscle burnt begins to increase.

  • There is something that should be kept in mind about this chart. It does not declare the body fat percentage of the person who was studied. Maybe if someone is morbidly obese, the rate of fat-energy usage would not decline as rapidly as a normal weight person. Obviously, if an extremely lean person were to fast, they would almost certainly lose lean mass and resort to burning muscle for energy very quickly due to a lack of available fat. Commented Jul 8, 2018 at 4:56

There has been conflict results that have been reported before whether short term fasting has an effect on protein loss. However a number of studies now show that protein breakdown increases during short term fasting so it's very possible that as you are feeling that you actually lost some protein and not fat only. You can follow this article for more evidence. http://ajcn.nutrition.org/content/46/4/557.full.pdf+html

There is also another review which has 3 other studies which also support the aspect of increased protein breakdown during short term fasting.



First thing your body use is carbohydrate (your sugar drinks are high in carbohydrate), then fats, lastly protein. Muscle is protein. And if you're not moving much, your carbohydrate are converted to fats. So you probably just lose some fats.

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