What and how we eat since McDonalds was invented a couple generations ago does not have much relationship to what and how we ate for millions/hundreds of thousands of years.

There are some hints in how we're unable to store vitamin C, so obviously we evolved to rely on a relatively stable source of citrus. On the other hand the gallbladder seems optimized to digest large amounts of fatty meat every couple days at most, rather than none ever or small amounts every meal. Our long term iodine storage is somewhat lacking indicating a bit of coastal living / seafood would be a good idea. Given that ethanol is a systemic poison, our livers seem well evolved to get rid of it compared to other systemic poisons, indicating a modest consumption is probably reasonable, although not drinking is probably wiser. Our unimpressive long term iron storage, at least for women, indicates a reasonable source of iron (meat?) be hunted down and consumed at absolute minimum every month or so.

Now you can use modern high tech living to hack what your body was evolved to do, for moral or ethical or profitable reasons. We've got a ridiculously complicated world wide food production infrastructure, and a pharma infrastructure, and lots of scientific knowledge, so why not hack the system and go vegetarian even if its un-natural. Or occasional weird processed stuff. But the modern ability to hack it, doesn't mean the body doesn't have an inherent set of design constraints WRT nutrition. And occasional fasting does seem biologically part of the design. Otherwise we'd simply keel over and die once the initial blood sugar dropped too low, because it would be evolutionarily simpler to insta-pee out as ketones any fat or excess carbs consumed at the time of consumption... Aside from the obvious evolutionary positives of being lighter and faster. So we're built to pig out for a month and starve for a month.