Who pays for the research? Pharmaceutical companies a lot of times. That's just one factor to consider.
Another thing to consider is the bioavailability of the multivitamin you are taking. You pay a bit more for plant based ingredients that are bioavailable, or the processing are supplementary ingredients required for the particular supplement needed to make it bioavailable, and one can find the bioavailability of a product if one looks. So far what I see on drug store shelves doesn't address bioavailability. The money goes into television advertising, and shiny foil labels, not quality ingredients. I see them using the cheapest, not the best ingredients, in order to get the most profit, since the drug stores have a captive audience, as the average person won't look beyond their local drug store. Especially so many "studies" implying that all vitamins are useless (or bad!). Which cannot be true.
But what is the validity of the studies, anyway? That can be looked up, with a little bit of effort, but the vast majority of people will accept the results they are told to accept without checking further to see if the study has any worthwhile validity. I expect the people in the multivitamin studies you mentioned took ONE multivitamin every day for years as if it was a magic pill that should account for everything they might have missed in their diet and/or lifestyle.
My Naturopath says EVERYONE needs to take a multimineral supplement because our soil is so depleted from factory farming that one can't thrive even if one ate only things labeled "organic". And I want to thrive, not just survive. And I think it is possible to thrive, because whenever I have sought natural alternatives for a problem that was supposed to be a "forever" sort of medical problem, I fixed it without pharmaceuticals or over the counters but with vitamins and supplements, and reversals came quickly.
One vitamin cure-all many times is magnesium. Lots of people are deficient, and lots of people get medical care, surgery, or on a lifetime of prescriptions for the very common actual core problem of magnesium deficiency. And it's an easy fix. Like it can work in a day or two.
If you have an ailment, it's a good idea to google the ailment and "natural alternatives" or "supplements", and see what is working for others.
I started my interest in vitamins and supplements before my son was born, when teaching. It was a job that took a LOT of energy and I wanted to still have energy when I got home. Several teachers in my building had begun to go to the same health practitioner who used applied kinesiology to determine what their particular body needed at that particular time, and I realized they ALL looked more alert, relaxed and focused now. Also the one in the school who looked the most old and tired now looked alert and happy. So I went, and it solved my energy problem quickly and thoroughly. I had no intention at that time of changing my lifestyle, or avoiding medical care, but it worked powerfully, and I have sought and found natural alternatives for every need since.
Now I am teaching again and have found that in the years between these two parts of my career they have not just increased the pay but they have piled on the teacher work load and responsibilities to such a degree that I would have never thought it possible. Everyone would have quit! But increase the pay, and constantly and incrementally increase the work load, and people will find a way. And I don't want to be a quitter. I am determined to do well. The new supplements I started this September really did the job. But now I want to also try red light therapy, which some say is even more beneficial that supplements. (When used properly). I am thinking of looking into Written's "Energy Blueprint", as itsounds like solid research, but I hate his super hawking ways).
Fruit and veg - I think you can truly do too much. Lierre Keith's Vegetarian Myth book is a solid case in point. (Here is a short video with her speaking of her experience and learning:
https://www.youtube.com/watch?v=rNON5iNf07o. Also I recently (can't remember where) read some very convincing research that too much veg is bad - basically, too much fiber is a big problem. Better to peel the potatoes and fruit like our parents and great grandparents did! They knew something. And oatmeal and whole grains wreck havoc in the intestinal tract. Also the fruitarian fad exposes problems of too much fruit.
Re: fruit/veg powders - I went through a couple jars of Miracle Greens at one point, starting each day with the proscribed amount mixed in juice. I think that is the sort of thing you mentioned. It did noticeably increase my feeling of well-being at the time, and if you feel those things have been missing from your diet you might feel the same good results, too.
