I was just speaking from personal experience.
However, to get technical, when I first started blazing, eating after the high didn't affect it at all. I was just as stoned after eating as I was before. But as time progressed I noticed that when I would blaze, then eat, my high would diminish (I used to be one of those people that would blaze purposely before a meal to enjoy it more). I don't know why this happened. It doesn't make sense to me either. I don't get how the digestive system would affect the THC, as was mentioned above. All I know is that in all my experience, this was the case. Whether or not it is scientifically provable is irrelevant to me. This is how my body is. Sure it'd be nice to know why my body does this, but I could really care less, I doubt there's anything I could do to change this.
I'd like to note that the only exception to this (for me) is when I get stoned to the MAXIMUM. Like that point where you know if you smoke another joint, you won't get any higher. If I'm stoned like that, and I eat a meal, I'll still feel the same. However if I smoke like a 0.1g bowl, then eat, my high diminishes.
EDIT: And yes lets distinguish between munchy snacking here and there, compared to eating a complete meal that FILLS your stomach (aka, no more munchies).
Even if it did effect your high, it would depend what kind of food you ate. Mangoes increase the duration of your high (look it up!). I think the main reason people think that weed makes them less high is because eating takes time, and time reduces a high. Even if eating did decrease a high it would be so small a difference that it would be barely noticeable.
I'd like to point out that when I'm high I can devour an entire meal in under 10mins (and still be full). I don't think that 10mins plays a significant role in reducing my high to the extent that I would notice it actually reduced. If that makes sense.