What does your dietary lifestyle currently look like?
"On a daily basis: sleep, concentration, physical wellbeing. Some is improvement, some is more about maintenance of what's good."
Believe it or not, fasting alone will drastically help you improve all of those aspects... Have you considered practicing fasting?
Believe it or not, saying it would drastically improve all of those aspects is a total guess and is just well-meaningly extrapolating your personal experience way too far.
I have considered fasting before. I used to do intermittent fasting, not with the concept of "intermittent fasting" in mind, but just because I had an unintended habit of eating all my food in a small window at night. Even now I sometimes do it. Really, some health professionals say eating late can actually make it harder to sleep. Of course the type of food makes a difference too. But in other words, there could be types of fasting that could help someone sleep, but if the fasting involves concentrating all the food intake into a late-night period it might make sleep more difficult for some, if the healthcare sites and nutritionists are correct. It's not something I've looked into that much, but there are studies that support fasting helping sleep and those that don't, so probably it depends on other accompanying factors (either that or all of either the good for sleep or bad for sleep results used bad methodology, which I doubt considering how many different people have studied it and since there's no financial incentive to do bad science about fasting, but it is possible. I suppose there could possibly be a religious incentive to do bad science, since fasting is part of some religions, but studies are done in countries where that's not relevant).
I've also fasted before due to my religious/cultural background (interestingly, even Christians where my extended family's from abstain from food/drink for most of the day during Lent. I've read this "Black Fast" was the norm for Christians elsewhere until around 1000 or so years ago, but it mostly died out). Because the latitude here is high, it can be until past 9pm in the summer.
I wouldn't say I clearly feel any better when it comes to sleep or concentration during fasting. It's possible I do and just don't notice it, since it can be hard to keep track of how you've felt on different days without keeping a journal. Sometimes days where I concentrate best are days when I intermittently fasted, but it's hard to say if the fasting caused the concentration or if it's that the high concentration levels caused me to skip eating and inadvertently fast. Could be both, but it's at least partially the second. And do I concentrate and sleep well on all or even for the majority of the days I fast? No, so I don't think fasting in general is the solution and I doubt it's even a needed part of the solution, considering how many people sleep and concentrate well without fasting.
I didn't talk about physical well-being here, because the type of physical well-being I was thinking of is more to do with physical comfort and musculoskeletal health. Basically staying injury-free or reducing the effects of existing problems. Fasting isn't really relevant, aside from avoiding stomach pains I suppose.
My dietary lifestyle. Well I think my diet is a mix of decent and crap. I'm health conscious (as in the healthiness of my diet is a consideration when choosing food) and I've cooked most of my own food for like 8 years, but I also eat loads of sugar a couple of times a week - mostly ice cream. Otherwise at home (get free food at work, mostly white bread and some cooked chicken/veg) I mostly eat white rice, cheese, nuts, olive or canola oil, tuna/sardines, mixed veg. Things like eggs, white bread with margarine/jam and pasta I might eat for a while too. 95% of what I drink is water. I used to eat legumes every day, but not any more since they hurt my "stomach". Oats aren't great I'd like to eat a higher quanitity of fruit or veg and I'm currently looking for new staples. I take omega-3, vit C, vit D and a supermarket multivitamins/mineral supplement. Might occasionally take iron (it's supposedly in the multi anyway) and for sure if running, since it depletes your iron.