Question about fasting

(bambiying2) #1

I’m starting a fast after dinner tonight. I’d really like to go until Saturday morning, but since the longest I’ve done so far is 27 hours, I’m not sure if I’ll last that long. My question is about losing water weight. In The Complete Guide to Fasting, they say how most of the initial weight loss will be water. Is that just for those who are not fat adapted already, or should I expect to lose a bunch of water weight as well? I’ve been keto since July. I was hoping that since I dumped a bunch of water when starting keto, that most of the weight I would lose while fasting would be actual fat and not water. What says the experts??

(Simon Saunders) #2

It really depends on your existing diet, when i did my 4 day water fast i did not loose any weight until the 3rd day, others like Jimmy Moore who is also eating ketogenic lost lots of weight during the first several days which Fung attributed to his water weight.

So short answer is you may or may not have initial water weight, for me is was no but for others maybe.

(G. Andrew Duthie) #3

Not an expert, but my N=1 experience with my current fast (60+ hours at this point) is that I lost 2lbs after the first day, and 1/2 a pound the second day. Both of those are small enough to be within the range of normal day-to-day variability, depending on salt intake, fluid intake, etc.

Try to avoid focusing on the short term. Fasting is good for you, even if it doesn’t result in immediate weight loss. And if you do end up with significant weight loss, be prepared that some of what you lost will likely come back when you re-feed. That’s OK. Two steps forward and one step back still leaves you one step further than you were before. :slight_smile:

(bambiying2) #4

I agree with the two steps forward, one step back. I did 2 egg fasts, a 5 day and a 4 day, and both times I gained on the refeed, but lost overall. You can’t be annoyed with losing overall!!!

(Kathy Meyer) #5

I’m not an expert, although I do fast frequently, but I believe that we can, on average, only lose 1/2 pound of fat per day. I usually assume that if I lose more than that, it’s water, and also assume I’ll be gaining it back – which I usually do. My first two weeks of Keto (back in late February) I lost 18 pounds. Now I assumed that was a big whoosh of water, but I also didn’t gain any of that back. I wonder if the cleaning of cell debris that comes with autophagy is also water?

I guess we’ll wait for the experts.

(Sascha Heid) #6

In my experience the amount of “stuff” i usually carry around with me in my stomach and intestine is easily 1 kg or more. I am guessing that this is for the most part water that your body needs to digest the food (i once weighted myself during a fast and a 300g piece of salmon or meat lead to a 1kg gain in weight). That is probably what people refer to when they tell me that i am “full of sh*t”. So even when fasting in the context of a ketogenic diet i am still losing weight rapidly in the first couple of days.


The water weight you lose when going keto is from the emptying of glycogen stores in the liver. This is a prerequisite for producing ketones. Water is stored with the glycogen.

When fasting, there is water and food in the digestive tract that takes a while to work it’s way out.

There is also glycogen in your muscles (with water) that may become depleted as well, depending on physical activity and your ability to replenish it without food - amount of bodyfat you have plays a role in this - and the duration of the fast.

And then there is electrolyte balance which can be tricky on a fast since you don’t have a normal intake from foods you’re eating. I’ve been known to gain water weight on the first day of a fast with too much salt, then lose it later on.