A couple of additional points:
If you take something like aspirin or ibuprofin, you can take it either with or without food, but you’ll feel the effect a lot faster if you take it without. So there’s a distinction to be made between how well something is absorbed and how fast something is absorbed. If you want to get rid of a headache, I’d imagine that you’d want the quickest response possible in the case of the above.
As TT pointed out, you’ll get different effects out of a given supp depending on when you take it. Example: wobenzyme. When taken with food it helps digest the protein contained in the meal. When taken on an empty stomach, it will “search” the body for protein and thus can help to alleviate tendonitis and other conditions. (Somebody correct me if I’m wrong on the specifics here.)
In the case of fish oils, there was a good discussion not too long ago and it was pointed out by Joel and Heb that they are probably most effectively taken in one lump right before bed so as to avoid having them get used for fuel (= better absorption). Simply taking them with food won’t really prevent them from being used as fuel - especially if you’re on a low-carb diet.
Finally, let’s look at Tribex. When it first came out the recommendation was to take it with food. If you’ve ever taken Tribex, you know why - it helps eliminate the famous Tribex Burps. But then about a year ago suddenly Biotest started saying that you should take Tribex on an empty stomach.
Why? Well, I’ve asked this question several times and haven’t received a real answer, but here’s what I think. The testing that is done on most supps has to be done on an empty stomach in order to isolate the effect of the supp from whatever else you’re eating. So when a company then says, “We got X results”, it then more or less has to recommend that the supp be taken on an empty stomach so that the conditions for taking the supp match those under which the original results were obtained. Doesn’t necessarily mean that the supp HAS to be taken on an empty stomach in order to work - only that the company has to SAY that it should be taken that way (probably in order to protect itself from lawsuits).
I know that in Tribex’ case, it works just fine if you take it with food, and that’s how I’m going to continue to take mine.
Hope this helps.