Wait. Why is it possible fasting has upsides, but it is not possible it has downsides?
This is a relatively new phenomenon for humans - starting in the 1700s. Feast/famine is how we used to live. The Romans ate one meal a day and frowned upon breakfast, for instance - their default was what we would now consider OMAD fasting. [1]
It could be better, worse, or the same.
We don't know. And there's no reason to assume that it might be better while it is definitely not worse (and therefore an obvious choice).
There's a lot of compelling studies being done at the moment, including the interaction of fasting with the immune system. [3]
> Last week, in a paper just published in the New England Journal of Medicine [4], Rafael de Cabo and Mark Mattson reviewed multiple strategies for fasting that have been tested in the years since Longo's study. The news continues to be very encouraging: intermittent fasting is good for you.
I'm not saying it's conclusive but to suggest there's no reason to think it might be better is disingenuous.
There's been some pretty interesting studies over the last few decades (few and far between, but interesting) - and the idea of fasting for heath is enjoying something of a renaissance in nutrition research these days.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC329619/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5990470/
[3] https://www.forbes.com/sites/stevensalzberg/2020/01/06/can-i...
I didn't say there's no reason to assume it might be better!
I said there's no reason to assume it might be better AND that it is definitely not worse.
The biggest takeaway that I’ve gotten recently is that our bodies are literally designed to take fasting into account. Specifically, our vascular system is terrible at doing cleanup and nutrient delivery at the same time. So it needs ample time to do both.
I'd not heard this before, sounds cool. Do you have a reference handy? Thanks.
Fasting absolutely can have downsides. The link in the comment you are replying to, for example, recommends a five day fast which is a lot longer than I've ever seen recommended.
The first obvious downside is that people with health conditions like diabetes, underweight, immunocompromised, etc. need to consult a doctor first. They would probably call a 5 day fast with zero intake of food or electrolytes needlessly reckless with little evidence to support it over a shorter fast.
Medical studies also tend to be of poor quality and don't stand up to meta-analysis by organizations like Cochrane. For example:
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD...
https://www.cochrane.org/CD013496/VASC_does-limiting-times-y...
The Mayo clinic also argues theres not enough high quality evidence even on intermittent fasting at this point to recommend for or against it in weight loss (where you think it would be of obvious benefit):
https://healthletter.mayoclinic.com/issues/july-2020/is-inte...
Speculating on in-vitro effects and microbiological mechanisms scaling to result in things like cancer prevention or life extension seems like a fools errand.
People saying "oh but it's natural" are also making a naturalistic fallacy. It was also "natural" for much of human history to be infested with parasites and ravaged by disease. Natural is not necessarily good.
I think you are committing a fallacy here too. The naturalistic appeal is not about how things were before, but in what conditions we evolved. For example, we could try to eliminate every single germ everywhere, but that would make our immune system weaker, because our immune system can adapt itself. Vaccines are a way of leveraging that knowledge about our immune systems. Same thing about light: we spent most of our evolution time following the Sun cycles, and now we see that people that work shift hours are in a worse condition than people that don't.
A big difference between the way we fast today and the way people may have faster before is that we don't have to hunt or gather for our food, we have certainty about the presence of food at the end of a fast. Though by writing that, I wonder if early humans felt constantly the need for food and the fear of not finding it. I don't even know if animals do.
I remember reading somewhere that anorexia used to be more common in highly religious communities where ritual fasting was encouraged: the devout would fast so long that they would find themselves unable to eat again when the fast was over. If you go too long without eating, you can actually lose the ability to do so. I don't suppose that can happen after just a two-day fast, but it does seem like a "possible" downside to me.
They were not designed to survive 7-8 decades regardless of diet, because by this time reproductive success (and therefore fitness and pressure) is zero for women and almost zero for many men.
Devil's advocate against this point: Grandparents might increase the reproductive success of their children's children, helping their genes propagate in accordance to Kin theory.
Devil's advocate against Devil's advocate of this point: Grandparents might also decrease the reproductive success of their offspring, since they must care for their own children as well as their parents. Hence, the near inescapable phenomena of dementia as age increases into the 100s, and the trait of Senicide (ex. Ättestupa) in many cultures.
My point being, maybe it is best to avoid categorical statements about "evolutionary perspectives."
edit: Correction, Ättestupa is mythological and not a good example of Senecide. The wiki for senecide has many other examples, however.
From an evolutionary perspective, “vessels to propagate our genes” carries a lot of baggage with it, including the need to be healthy enough to take a baby to term, care for yourself/other family/group members, and raise it until it reaches sexual maturity, all of which require efficient energy gathering, storage, and usage strategies.
Indeed, it's a wide, complex topic that I only know a little about, and I only had time for a brief comment.
BTW love your chain of devil's advocate statements. More people should think/counter that way.
Also I think about how young we are as a species that uses the scientific method to question our reality.
Maybe all of my knowledge today will not stand the test of time, and will be considered just as silly as someone from the 1600s seems to me today? (ex. A natural philosopher that believes in abiogenesis)
But a mutual respect and bond can exist if we both strive to prove ourselves wrong, adapt, and grow.