For a patient population of 1. I don't know about you, but I love experimenting with my diet and seeing how changes pan out. Of course, I do it in a totally unscientific way, altering multiple things at a time so that it's hard for me to isolate what single thing was the factor in a particular change, but whatever. I don't have the patience for the whole one thing at a time bit.
So, for example, I take fish oil, D3, and K2 on a daily basis and have for about a month. Why? I am D deficient (office drone) I do sometimes eat non free range meat (hello Omega 6s) and I also don't eat foie gras regularly (oh, how I would love to, but my budget will not tolerate it) and I've noticed a major change in my skin. I have mild acne (usually a few small pimples here and there, annoying but not a big deal) and lately, my skin has been totally calm. Love that. Now, is it the fish oil, the D, or the K? Or some combination thereof?
Or when I drink diet soda, my stomach gets extremely sensitive to anything else. I've been diet soda free for a week (YAY me) but I've also cut out all other artificial sweeteners (used to be a Splenda addict, now use liquid stevia on occasion, but far, far less frequently than I used the evil yellow packet) so I can't tell if the carbonation or the sweeteners (or again, some combination) that set my stomach off.
I just find it fun to play around with how my body reacts...