Does diet really matter much for anything in your experience?

as a farmer, there is a pretty solid but not widely used theoretical understanding of plant health, which posits that that health largely relies upon an alive and balanced soil -- the figurative and in-some-ways literal stomach of the plant -- to provide the minerals a plant needs for optimal genetic functioning. that is largely done through fungal/mychorrhizal root associations that the plant tunes.

when a plant has all of the minerals it needs for the co-enzymatic production of its basic to advanced structure -- think phytochemicals of all flavors, and actual flavors -- the plant is largely immune to disease and insect pest predation, broadly speaking. the plant can pretty easily produce its simple sugars, but to get into more complex sugars, proteins, fatty cuticles, and secondary metabolites, it needs an alive soil that will provide it access to all of the enzyme co-factors for their production -- selenium, cobalt, zinc, etc.

a plant and its fruits can look fantastic on a conventional farm when sprayed and fed with chemicals, but its like a body builder about to have a heart-attack. in my estimation, they are just the ghosts of their genetic potential, lacking all of the phytochemical and trace minerals that made them what they were when they lived in a more natural system.

when we eat these ghosts of a carrot -- for instance -- that lack the selenium, etc. and phytochemicals our body evolved with and genetically expects, we are just ghosts of humans. yup.

we are the ghosts of our genetic potential on a sub-optimal diet, and a sub-optimal diet is the absolute easiest thing to eat in our modern culture, and in some ways also the hardest thing to achieve.

While I eat very healthy, I try not to make myself illusions it improves my running performance by more than at most a few percent. Even at the elite level, runners just load up on any carbs and protein. I eat healthy for long term health. If you feel worse after eating unhealthy food, I’d say it’s either expectation bias, a sugar crash, constipation or more likely even; your own guilt. Eating an unhealthy meal does not ’tire’ your body or create nutritional deficiencies…this takes a long time to happen.

Eating whole grains, legumes and vegetables do not improve running speed, no relevant authorities say so. It seems mostly YouTubers, magazines and Netflix documentaries recommending to ‘clean up your diet’ but the short term benefits are never substantiated with more than anecdotal evidence and pseudoscience. People eat it up anyways.

Yes.

Beyond not eating things that upset your stomach diet does not matter.

The OP's question wasn't "does eating healthy foods increase speed or improve performance?"

What about the effect on your nervous system, cardiovascular system, endocrine system, musculoskeletal system, and immune system?

Until recently (last few hundred years) few humans have lived to be anywhere near 70 years old, so there probably hasn't been enough time to evolve those traits.

OP here: I’d like some simple thumbrule like this to be true, but this can’t be literally true because if you locked someone up and gave them only chips and coke, they’d likely get their stomachs used to it fairly quickly but their bodies will slowly deteriorate because of protein and mineral deficiency.

I’d say it is safe to assume that malnourished individuals or those eating far too few calories will perform worse. But to be malnourished to the level where symptoms start to show, even subtly, is far rarer than Healthline, YouTubers and podcasters might make it seem. Even in those eating badly.

Now the argument is easily made that if one were to increase intake of vitamins, minerals, phytochemicals etc. 200%, surely our bodies will be supercharged and there will be benefits in perfomance? This however seems not to be the case, provided minimum requirements are met. Only in the long run, our health will suffer, say in 20 years, if we eat badly.

Obviously extreme cases are exceptions, as with any rule. But the exceptions do not make the rule. Put another way, the refined carbs and processed food currently in the diet of Kipchoge, you and me do not hurt our performance. So worry about others things if you want to improve.

I mean... it obviously does matter from a pure health perspective.

From a performance perspective I've found it affects me less when I'm out of shape, and when I'm in race shape I notice the difference a lot more.

FWIW, this article linked below on “intuitive eating” popped up on my news feed today and seems balanced about its pros and cons. It captures the “eating without thinking” part of my OP, but it’s focus is too much on weight control that wasn’t my point. It has 10 principles, but I think we need just two “eating well” principles to get most of the benefit there is:

1) Be tuned to your body’s hunger signals, so eat when hungry and stop eating when no longer hungry.

2) Eat a variety of foods by intuitively following your innate desires for different tastes, textures, colors, preparation methods etc.

Caveats: If the above makes you obese, your hunger system is broken, and if your innate desires tell you to eat 95% donuts, then your desires are broken; :) so you need to figure out how to fix what’s broken.

It doesn't matter if you eat loads of sugar and crap, you just need to be getting in your important nutrients. Get your healthy fats, carbs, proteins, water, and whatever veggies you enjoy and then you are free to gluttinously demolish whatever else you want.

Unrelated sidenote: for other vegetarians or people who avoid red meat, an iron supplement is super important for good running

Now look what you've done. All the 'healthy eating' nutjobs of letsrun are chiming in with their food preference obsessions.

Listen to this guy. I have spent 50 years of my life thinking Vegan was a joke. Thinking it was for lefties or all about denying yourself of what you love. I run every day and figured that gave me latitude to eat what I want.

10 days ago, I did this guys 7 day test. I was wrong. Going Plant based is a game changer. I have no cravings for Pizza, Cheesburgers, fried etc. Your taste buds quickly change and you desire plant based food. And Plant based food is simply much better for you. More energy, better sleep, good mood. Immediately lowered my blood pressure to perfection. Perfect digestion now. I could go on and on.

Prove it to yourself by trying it. You will never know for sure if you dont try.

How old are you? I'm curious because I'm basically doing the exact opposite. Going from eating carb based, plenty of fast digesting carbs to focusing on protein. I've been feeling really good doing this, put on a little muscle, recovering super fast, runs feel good. For carbs I'm eating mostly whole grains, with the occasional sweet. Not too much alcohol lately.

When I was 25-30, the high carb diet absolutely worked, could eat whatever and drink a ton of beer and as long as I worked out a lot and I'd be pretty lean. If I eat like that now at 40 yo, I get fat, doesn't matter how much I train. I've tried to use the same diet/training plans, and what worked then does not work at all now. I'm certain this is age related, but the focus on protein seems to be helping.

To answer the original question, its been my experience that diet doesn't matter much when you are under 35, but once you hit that its super important. You need to be doing everything possible to hold off the inevitable decline, that includes a lot of things you could skip when you're younger....diet, stretching, strengthening, etc... You have to take recovery way more seriously, all those little things add up.