While autophagy does correlate with fasting and some studies link it to health markers, it should be noted that it usually takes at least 18 hours of continued fasting to even start and only goes into full swing after 48 to 72 hours. It is also an extreme cell response that is associated with high levels of cellular stress, which might have understudied long term detrimental effects. A simple calorie reduction either by eating fewer highly processed meals or regular intense exercise is much more universally accepted as longevity boosting, because it combats overweight, which is by far the most common disease that shortens general lifespan in the western world. There's really no good reason to force your body through these extreme diets. Don't be overweight, don't smoke, don't drink alcohol, maybe go easy on junk food and maybe do some exercise. And get your regular medical check-ups. Then you're already at the pinnacle of clinical longevity science. There is no actual anti aging drug yet that has a proven effect on humans. Best we have are some moderately promising monkey and small mammal studies, but they generally don't translate well.
Autophagy research is all over the place and its hard to understand this stuff or make blanket statements, instead we just have to be flexible with it. Autophagy is always working and the ramp up happens pretty quickly for a lot of people. I think aiming for the 48-72 hour peak isn't helpful. Most people cant or wont fast that long. A lot of people on 16-18 hour daily fasts see benefits that suggest autophagy working well.
Also biology isnt computers, its not exact and all our bodies are very different. For example, say your standing autophagy rate is 3. 16-18 hours fasting its 7 out of 10. But at 48 hours its 10. The difference between 7 and 10 might not even be very meaningful on a practical health level. The difference between never getting to 7 because of "it takes 48 hours" thinking and never trying is then huge. Just a couple hours a day at level 7 autophagy or whatever could be life changing. I do about 14-16 hours a day and am happy I made that decision for myself. I do see benefits that are real seeming to me.
From what I've seen there's no real downside to 14-18 hour daily fasting and in theory incredible benefits. Its also worth mentioning for a lot of people just sleeping with an empty belly means a higher quality of sleep, so there's secondary benefits as well. Your gut 'taking a break' during those hours may also be another benefit in terms of gut health as well, but I'm more skeptical of that claim.
Personally I'd add 'consume and make tons of fermented food' to that list and also eat lots of prebiotics. Gut health is key to so many aspects of a healthy life - I have to imagine it helps with longevity (and lower stress). Nobody likes having stomach pain!
People love their probiotic pills but I'm not convinced - the amount of beneficial microbes is measured at bottling or production and who knows how many survive by the time they get to you. Not to mention how many survive into your gut once consumed.
Homemade sauerkraut or natto though? Pretty much guaranteed to be teeming with the stuff. And your grandparents and their parents were probably eating it their whole lives. It's a whole forgotten art / science that is thankfully making a comeback.
Anecdotally (obviously sample size of 1 so big grain of salt here) every person in my personal life who I saw live to a super long age and also maintain good mental fitness followed what you are saying above plus made their own fermented food into their elderly years.
At the worst it does nothing for longevity and you end up with more unique tasty food for yourself and your friends :-D
Probiotics fall into the same category as all other supplements: i.e. they can have some short term effects if your diet is really bad or you are recovering from GI disease, but there is not much evidence regarding general health improvement. And you also have the same issues as with all food supplements in that they are not FDA regulated or approved. So even if you think you actually need a particular dosage, you can't rely on what is written on the packaging. A balanced diet is a much better and healthier approach without any downsides.
Even stuff like "don't be overweight" is a maybe. This meta-analysis famously found that being overweight actually has a moderate protective effect: https://pmc.ncbi.nlm.nih.gov/articles/PMC4855514/
This is a BMI-only study and should be treated carefully. They also found a protective effect for one of the obese categories, which seems extremely weird (unless you consider bodybuilders or strength athletes, in which case it would be reasonable). If you replace "don't be overweight/obese" with "don't have excess amounts of fat" (in particular vascular fat) it is certainly not a maybe.
