The problem with nutrition is that it's a very sensitive topic for people. Everyone wants to hear that what they eat is healthy, so "science" delivers on that demand.

For myself I decided to go with WFPB diet because pretty much everyone agrees that fruits, vegetables, greens and whole grains are good for you. There's no controversy there.

That doesn't mean it is good for you (or bad). For many years everyone said to avoid eggs for cholesterol. There was no controverse.

Basically without more good science on the subject, we are all just mostly guessing.

See the book How Not To Die. As I see it it is converging quite a bit lately. But it is hard, sure. We know so much, but how to boil it down to something we can practice (that's what WFPB seems to be about to me).

Then there was the 6 glasses of water a day that became dogma but had no basis.

It was based on a misunderstanding: People need the equivalent of 6 glasses of water a day, but a large chunk of that comes in through food and drink you already have. For most, adding one or two glasses of water a day would put you up at the goal.

That said, I don't recall where the target number came from.

They need no such thing. The target number (usually quoted as 8) is pure folk mythology, there never was a study that concluded that that was the right number for some medical/biological reason. This has been in the news.

The correct number depends on individual, weather, activity level, etc. The actual medical recommendation is merely that healthy people should pay attention to their thirst and drink when thirsty, and plan ahead for exertion and desert excursions etc.

Certainly some people don't pay attention to their own thirst, but that's not to say that 6 or 8 are the correct numbers. That may be too much or too little.

Nutrition is a pseudo-science.

I think the problem with it (as with a lot of science) is that control is very difficult. The more you want a controlled experiment, the more abstract and unrealistic you have to be. Eg. (completely made-up illustration) eggs might be good for you if you eat a lot of tomatoes, bad for you if you don't eat a lot of tomatoes, better if you eat tomatoes a couple of hours before the eggs rather than afterwards. Maybe if you have curly hair the rules are reversed... but not if it's red curly hair.

To get any consistency in results you have to control things to a point of being unrealistic, and then the results aren't very useful because nobody's real diet and genetic makeup fits with the fake abstract setting of the experiment.

Then results get simplified and abstracted even more to make easily understandable conclusions... like maybe for 78% of people cacao is good, but for 0.3% of people it doubles the risk of stroke (although this bit doesn't get studied because it wasn't in the initial hypothesis). Results are reduced to "cacao is good for you"... but you might not part of the 78%. Maybe you're in the 0.3%.

I'm not trying to say that science is useless, just that applying it isn't as simple as people like to make out (and a lot of people don't want to accept that life may not be as methodical and predictable as they want it to be). Nuance is too hard.

Well said. This is exactly the problem with nutrition science. Just makes it a bit hard, but not at all impossible.