thanks, interessting idea. Quercitin and maybe coffein may be a good try if Rapa is metabolised on other pathways then CYP3A4. I’ll have a look.
But some thoughts and concerns:
GFJ is a irreversible inhibitor, that means it just “kills” the CYP enzyme so it has to be build up again by the liver.
I don’t think that more substances that inhibit CYP3A4 will be more effective because if its not there, it won’t have any further effect.
We know that Ketoconazole is more effective then GFJ. It is possible that 350ML GFJ doesn’t irreversible inhibit all of the CYP3A4 enzyme (so I try just to eat more grapefruits). But it is also worth thinking that Ketoconazole has got another effect I don’t know.
I also don’t know if they tested ketoconazole in people with active CYP3A5. 3A5 is most common in asians, but some europeans have also an activated 3A5 so it just doubles the metabolisation.
And taking more substances always mean that you propably get serious drug interactions you don’t want.
But taking Rapa with more GFJ then 350ml equivalent just means that I have to do a blood test to get the answer if its working. And the least I want to have is more Rapa then I need.
But a combination of some substances may still be possible. One have to keep an eye on:
a) some effects dont last very long and others will only work if you consume something for 10 days in higher doses.
b) most of the substances that inhibit CYP3A4 (or other enzymes) also induce them and vice versa
They class inhibitors only as inhibitors if the effect is more inhibiting then inducing.
The question here is: in which timeframe you get the effect you want. Some substances inducing CYP3A4 at first and then they inhibit it. Its just one GFJ-box short of a sixpack. 
c) its highly individual and we just don’t know if our CYP3A5 is active or not. Maybe we have to test ourselfs.
If someone tries to combine substances, one should also keep an eye on what causes the effect of the inhibition. For example:
Grapefruitjuice is effective because of the special furanocumarin-combination. I wrote about it some time ago.
Long story short: You need a specific mixture of furanocumarins to get the effect. If you chance the mixture, it will be propably lesser effective.
st. johns wort’s (Hypericum perforatum) effect is also caused by one specific furanocumarin. If you mix st. john with GF, you will maybe change the balance of the furanocumarines in GF.
I cant remember which furanocumarins are in GFJ. If Hyperforin is in it, I wouldn’t combine them.
Btw: Just don’t eat some inducers like garlic and leek (i eat a lot of them) doesn’t mean that I have a higher CYP3A4 activity. I actually get rid of it if I drink GFJ. So it I think it doesn’t matter.
And the last thing is:
taking more substances always mean you get a higher risk of serious drug interactions. So I would try not take any extracts just to be safe.
Its frustrating. I’ve been reading for a while about the biology behind it. In some cases biologists and pharmacists only have a guess about the bioplausibility. It means nothing. But nevertheless the list of CYP3A4 affecting substances is long and still incomplete as the list of substances that increases the bioavailability of Rapa.
And BTW, I am also not a biologist. I doesn’t even know about the different pathways my body matabolises Rapa.
