How much fat can you expect to lose on water fasting?

Hi All,

this is my 15th day of water fasting and I have kept track of my daily weight. I’ve done water fasting several times now and the weight loss follows always the same pattern. First, I lose a lot of weight on the first 3-4 days (about 12 pounds, or 5.5 kg), then the weight loss continues more or less linear, about 1 pound (0.5 kg) a day, but reducing slowly over time.

I understand that the first days, the body losses a lot of water that doesn’t need any more because of the reduce insulin levels, and that would explain why I lose so much water at once when starting the fasting. However, the loss weight I experience over the following days is far more than the expected fat loss as suggested by Dr Jason Fung in his book. He writes that expected fast loss should be about 0.5 pounds per day. I experience twice as much. Has anybody any insight of why might be the case? I play soccer on weekends, but otherwise, I sit all day in a desk, so no meaningful extra calories are burned to explain so much weight loss. I’m wondering whether I’m not just losing fat, but also muscle or if my body continue to get rid of more and more water over time. Or is it reasonable to expect so much fat loss in a single day?


Welcome to our fasting community.

I’m the resident “greybeard” both figuratively and literally as I currently hold the record for longest water fast at 40 days and I’m older than dirt!

As for losing all the “water weight” in the first 3 days of a fast, that’s more due to the fact that the body is burning through its glycogen (stored carbohydrate) stores in the liver (approx 30 to 40 hours) and then turns to the glycogen stored in the muscles. The glycogen molecule is 3/4ths water so when it gets used up it releases the water. Hence the term “water weight”.

As for the .5 lb per day, that’s an average. For myself, I lost an average of 2lbs over the next 8 days starting on Day 5. Then a pound a day. Hit about 3 weight plateaus and near the end it was more like a .5lb a day. The 1st 3 days, I lost 9lbs of water weight.

Hope this answers your questions. Feel free to ask any more or if you need to :scream: for help!

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Hi Alipio, thanks for answering so fast and sharing your experience. Congrats on the 40 day water fast, impressive.

Do you know what makes the difference between those that lose 0.5 lb/day to those that lose 1 lb/day. Is it body composition, or metabolism, or what is it? In addition, do you know if there is any muscle loss as well or it is only fat? According to Dr Fung, muscle creation even increases during fasting, but there are so many other articles out there as well that indicates the opposite, so I never know what to believe here.

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The difference in weight loss has many factors since each human body is different. Base metabolic rate plays a BIG part. Right now I’m wrapping up a 30 workout phase to up my flexibility and add some lean muscle mass (the LBM increases basal metabolic rate) before I start a new 21-day water fast Monday next week.

One of the research scientists I follow is Dr Benjamin Bikman of BYU. At a presentation at Low Carb Denver last year, he presented his findings from a human study of the effect of keytones on preservation of LBM. He found that keytones DO preserve LBM. Also I consult weekly with an endocrinologist with the Keck School of Medicine at the University of Southern California discussing how during a fast that the body maintains its protein needs through autophagy and cell clearance which you would think would allow the adding of LBM. HOWEVER, I contended that the energy cost of creating LBM was too high and that the body instead would use that energy for higher priorities like mental clarity which would be critical in finding a new food source and delay the adding of LBM for ReFeed. The endocrinologist agreed with my contention.

Hope this helps!


I’d opt not to believe most of if any mainstream outlets on this subject matter as it goes against their agenda. They want us fat and lazy and continuing to subscribe to their weight loss programs and the meds and a plethora of other things that are toxic to our bodies. I’m on day 16 and down 32lbs. Not sure how much longer I’ll continue at this rate but I’ll take it as long as it goes on.


Hi, welcome to the forum! :wave::wave: Congratulations on your journey so far!

I’ve tried to make sense of that question myself many times, without finding research that adds up to the results many people have!
I would say that the one thing that many resources are agreeing on is that the more excessive weight a person has, the more their body can afford to lose (Both because a heavier body requires more calories for the organs and muscles to function in a rested and active state, but they also have more fat stores to use as fuel).
Most people has a decrease of weight loss the leaner they get because of their BMR and energy conservation in any type of weight loss method.

In my case I lost less than average during my 30 day fast, since my body preserved more energy!
Dr Alan Goldhamer (at TrueNorth Health Center) always order patients to rest during fasting, to minimise glycogenesis from the muscles and organs, even when you’re far into burning ketone bodies!
Since it takes longer to convert fat into ketone bodies than it takes to convert glucose from protein, the body will use the most efficient method if it’s forced to be very active as a survival method!
But like you guys, I’ve heard others that are suggesting other facts as well!

Two things that you can look out for is a strong ammonia odour from the body or urine, or if the urine is foamy! Those can be a sign of burning protein!


Water fasting could have health benefits. For example, it may lower the risk of some chronic diseases and help you to lose weight. - here you can read more about weight loss. But you have to be careful with water fasting because it has many risks and can be very dangerous if followed for too long.

A look at water fasting, eating no food, and drink only water for a set period. Included is detail on safety, scientific research, and what to expect. Losing weight fast might be your goal, but learn how much weight is safe to lose in two weeks. I have Yoga Burn DVD from which I have yoga poses to lose weight and this I feel relax to lose weight.