I think optimizing the exercise part of the wellness equation is great, but it's obviously only part of it.
I'm not sure which factor matters more (and maybe it varies not only person-to-person but also within a person depending upon age, immune health, mental health, sleep, inflammation, etc.) but I think it's clear it not only matters how you use your body as a physical machine but also what you fuel it with.
I am a sucker for thinking back about "what our ancestors did". Even if you only look at the time modern humans have existed, which is at least 300,000 years - we've only had agriculture and what has spawned since for the last 10,000 or so. That is, even if you ignore all the hominin programming that went into who we are today before we broke away from chimps and bonobos and everything in between, the time modern humans were hunting and gathering dwarfs modern behaviors and consumption patterns. So what were humans doing and eating for those first 290,000+ years? It obviously worked as they survived^. They probably walked a TON (collecting water, foraging) and ate what they gathered and hunted. I'm guessing this didn't involve much, if any, dairy after being weaned and probably was a lower proportion of carbs* overall. So my rudimentary analysis would say to keep up the great job on the walking and make sure you're staying on top of your leafy greens, other fruits and veggies, and proteins (bonus points if your calories are not coming from a feedlot or monocrop ag).
^ If you've ever looked at historical pictures of crowds at sporting events or wherever large groups of thousands would congregate, if it was taken prior to the 1970s, you probably wouldn't see many obese people. This is not to say that I'd want to live back then or that obese people did not exist at all in the past or that obesity is an immediate death knell or even the cause of chronic issues (it could be a symptom!), but *something* has radically changed in the last 50 years and I'm pretty confident that modern humans (especially the ones living in "developed" areas) at their current rate of change with regard to health aren't going to make it 300,000 more years if we keep eating McDonald's dipped in Roundup with microplastic frosting en masse.
* If that is not accurate and ancient humans DID consume a percentage of carbs comparable to many cultures today, then at least they would have been carbs that wouldn't spike the insulin response in the same ways that many of the foodstuffs found in the interior aisles at a grocery store can.
Also, thanks for the topic. Now I'm motivated to go for a walk!