My priest told me that an important thing about rules like the lenten rules is not to get legalistic about them. That would defy the entire point. I've read some early Fathers, and it seems that many of them had various traditions. I recall one that even just did no food at all for 3 days before Easter. I think many of the specific canon rules were developed in part because mankind likes rules, generally, and likes to have a standard to follow. I think this easily leads to legalism though, and is akin to what happened with the Pharisees and Judaism.
For me, the goal of fasting is to learn discipline, sacrifice, to get in a proper spiritually-focused mindset, and to also promote health bodily. I personally think it is silly to disallow a few drops of olive oil and allow tahini, which would contain far more oil. If you're point is to avoid fat, eat only vegetables. But it is pointless to just substitute an "allowable" fat for a "disallowed" fat simply because of some canon that isn't even in line with what the earliest Fathers and Apostles followed.
So some days I avoid meat. Some days I avoid dairy. Some days, alcohol. And some days I just avoid food altogether. But if I am eating that day, I never avoid fats. It is just what works for me... and I think everyone has to come up with what works for them spiritually and physically.