Consensus on muscle maintenance vs loss while extended-fasting?

I’ve read conflicting studies. Anybody know if there’s a scientific consensus on whether or not it’s possible to maintain muscle mass while doing an extended (2+) day fast? I’ve read that growth hormone surges after around 24 hours, and that this helps to protect muscle mass. (I’ve read that GH values are higher in fasting men than fasting women , but increases in GH have been found in both genders). I’ve been bulking for the past few months, and I’d like to lose some of the extra fat I’ve gained without losing muscle. My preference is for fasting over dieting (largely because of the other benefits associated with fasting), but I really don’t want to lose muscle mass.

Answer

Make sure you get enough potassium. 4700mg a day. That’s around 1 tsp of potassium chloride powder spaced out throughout the day.

https://www.ncbi.nlm.nih.gov/m/pubmed/2819012/

But otherwise, for a 48-72 hr fast you have hardly anything to worry about. It’s when you do longer and repetitive fasts that you start to lose muscle.

I like doing bulk-fast cycles. 3 weeks bulking and then a 5-7 day fast. I strongly believe you need a calorie surplus to really build muscle effeciently, and you need to fast to burn fat effeciently. So cycling between them is the ultimate way to get big but not fat.

Answer

There’s no doubt that you lose protein every day that you fast. The loss is the highest in the first couple of days, and then slowly drops a bit.

I’ve seen average values of around 60-70 grams of protein/day. This can be measured fairly easily by measuring nitrogen in urine, which is the result of breaking down proteins.

Now the big question is where this protein is coming from. I don’t know of any quality research with the answers, especially not for humans.

As far as practical advice, I think 2-3 days of fasting, alternating with high protein recovery days should lower your fat, while minimizing muscle loss. If you notice that you’re losing muscle, add some more days of recovery.