White grapefruit vs. red or pink for CYP-3A4 inhibition

[MyDoorsAreOpen]

I can't find the source now (I tried Pubmed) but I could swear I once read that strong cytochrome P-450 3A4 inhibition is a property specific to the white cultivars of grapefruit, and that pink and red and other varieties are not nearly as useful/dangerous, depending on your intentions, because they contain much lower concentrations of bergamottin and naringin. Can anyone verify or falsify this?

I also remember reading that the enzyme-inhibiting chemicals are concentrated in the pulp and the pith rind of the grapefruit, making juice a less effective and more expensive method than eating a whole fruit.

If anyone can tell me definitively that red and pink grapefruits work just as well, I'll be relieved. White grapefruits and their juice seem to be harder to find and more expensive. I once found an urban produce market that had them for fifty cents each -- I got some amazed looks walking up to the checkout counter with two enormous bags of grapefruits. Next time I came, though, I was told they had been discontinued because they weren't popular -- I'd bought the ones I had on clearance.

I actually happen to prefer white grapefruits and their juice. They're lower in calories and just taste more grapefruitty to me; they capture the essence of what a grapefruit should taste like, in my opinion. If I wanted a syrupy sweet citrus fruit, I'd have an orange.

 

[crankfar]

You're correct. White grapefruit will lead to the most inhibition.

 

[sekio]

Alll grapefruits contain significant levels of naringin. Pink/red grapefruit flesh contains, on average, 66% of the naringin content of white grapefruit flesh, though some varieties of pink grapefruit apparently can contain up to 50% flavones as naringin. (!)

The average grapefruit contains 27mg/100g of flavones, avg 17% as active naringin.

http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Articles/jfca19_S74-S80.pdf

Naringin concentration would be expected to be higher in the pith, I'd think. But grapefruit pith tastes nasty, so just stick to drinking fresh, pulp-in juice. It is also seasonally variable, but I don't think the average consumer is going to have much to do with that as most stores don't typically tell you when your fruit was grown.

 

[PerekurPro]

So, Sekio, please just to sum it all, please tell me how many(or what weight) grapefruits I need to eat to singificantly block p450 for potentiating benzos.
I've tried 2-3 at a time, but felt no difference, i'm on medazepam(20-40 mg day) and alprazolam (0.5-1.5 mg).

 

[sekio]

I couldn't tell you, it's going to vary depending on your genetics, the individual ""strength" of grapefruits, etc.

Try a litre of grapefruit juice and see how that goes?

GFJ and compounds are not incredibly effective CYP3A4 inhibitors, though it does work, even the strongest compound in g/f has a Ki of 13 mM, roughly 1000x less potent than you'd expect an enzyme inhibitor.

http://www.ualberta.ca/~csps/JPPS4(3)/S.Wanwimolruk/grapefruit.htm