[milchek]

I also question if 7 days is safe for most. I don't recall exactly when and a quick search now yields a lot of random gimmicky fasting product sales sites with blog posts written to generate traffic that aren't scientific enough, but I do recall that there is a point (after 72 hours?) where your body starts breaking down muscle and that prolonged fasting is dangerous as your organs get hit next?

Perhaps someone here with medical experience can chime in, but I agree 7 days seems a bit extreme for most people.

[rhinoceraptor]

I haven't seen any convincing evidence that significant muscle loss occurs with a 7 day fast. If you get a DEXA scan before and after, you will have lost a lot of "lean body mass" and your muscles will be smaller, but it's only because you lose about 5-10lbs of water weight.

The only major health risk is refeeding syndrome, and even then it's only really notable if you're an alcoholic or have anorexia. If you're otherwise healthy with normal sodium/potassium/etc. intake and you take it slow when refeeding, I don't think it's particularly dangerous. Obviously, talk to your doctor, and it's probably good to get blood work before doing something like this.

[TimSchumann]

I lost zero noticeable lean muscle mass on my 60 day fast, at least no more than I would have sitting on the couch doing nothing.

There's just not a metabolic pathway for breaking down muscle/organ tissue for energy when you have adequate fat stores. We would have died off as a species a long time ago if that were the case.

In the grand scheme of things, if you have the body fat, 7 days is nothing for a fast.

Edit: To those asking, yes. I fasted for 60 days, water and electrolytes, no calories.

[CamelRocketFish]

When you say 60 day fast, are you saying you didn’t eat for 60 days and just drank water?

[brodouevencode]

https://news.ycombinator.com/item?id=27619297

I remember his post from a few months back - found it rather inspiring.

[CamelRocketFish]

Thanks a lot for linking that @brodouevencode

[pid-1]

Did you exercise or work during this period?

[TimSchumann]

Once-ish a week there was Light lifting, think moving a whole trees worth of firewood or a light day on a family farm.

Quite frequently I hit over 10k steps/day on my step tracker, sometimes double that. I live in the middle of a major city and walk everywhere, and this was before work from home.

If you’re looking for exercise/fasting advice check out my fat per unit time post elsewhere in this thread.

[sedivy94]

Thought experiment...

Humans have weathered long durations of food insecurity for much of their existence. If the default metabolic solution to fasting was harvesting energy from skeletal muscle and smooth muscle... well that strategy wouldn't work for very long, would it? The lowest hanging fruit is muscle/liver glycogen, and fat mass after that.

Breaking down proteins (gluconeogenesis) is a metabolically expensive process, requiring large energy input for low energy output. The body is wholly invested in protecting these vital organs. Skeletal muscle has a reputation for being fickle, subject to change based on stimulus and energy demands, but those adjustments are most significant and relevant to those who are invested in maximizing lean mass (athletes, bodybuilders, statistical outliers).

Fasting is relatively protein-sparing, all things considered. The observations of apparent muscle loss can be attributed to loss of muscle turgidity - a reduction in glycogen, intracellular fluid, and electrolytes. The difference between fed and fasted states, both visual and internal perceptions, are quite extreme.

Are extended fasts ideal, or even generally recommended, for someone with the singular goal of building muscle? Absolutely not. But it is a flexible tool when goals shift towards catabolic outcomes (losing weight). Furthermore, the downstream benefits of fasting can translate to improvements in insulin sensitivity, nutrient partitioning, muscle-building, and body composition... which are relevant to anabolic outcomes.

[SapporoChris]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2495396/

"A 27-year-old male patient fasted under supervision for 382 days and has subsequently maintained his normal weight."

By comparison 7 days is trivial. More to the point, a 7 day fast with medical supervision should be safe, if it is not, the supervisor will advise against it.

[femiagbabiaka]

Not to be snarky, but reading the linked study would be helpful here. Your body is quite intelligent when it comes to drawing on its energy reserves.