We know that B12 needs to be supplemented in people who are deficient, and that medicos sometimes give B12 injections.

We know that pregnant women who take folate supplements have babies with fewer neural-tube defects (spina bifid etc).

We know that we need to put some B vitamins back in the flower after it's milled otherwise the psychiatric wards fill up.

We know that people who ingest less than the recommended daily intake of Chromium (less than 50mcg per day) have more blood sugar disregulation[1].

So why not put these things together in one package, where and when it makes sense to do so.

I'll admit that some multivitamins are badly formulated, and I actively discourage people from taking certain forms of nutrients. Eg. why does any manufacturer put iron oxide or magnesium oxide in their supplements? These things are poorly absorbed and have known negative side effects.

1. https://www.ncbi.nlm.nih.gov/pubmed/9380836

What's the evidence of that?

Right. Our appetite is adapted for pre-industrial times, when craving sweet berries while they are in season would be a good thing. We're not equipped to handle constant availability of sugared and MSG-laden processed foods that are actually designed to defeat natural satiety mechanisms.

I would be cautious of demonizing fats; unprocessed fats haven't been shown to do much harm. In recent years, even Harvard Med School has backed off of low-fat recommendations, instead saying trans-fats ought to be avoided. https://www.hsph.harvard.edu/nutritionsource/what-should-you...

There's one way in which our appetites do point in the right direction: veggies are tastier and more appetizing when paired with butter or sauce, which also make it possible to absorb fat-soluble vitamins from the veggies.