Grapefruit is a hybrid fruit made from mixing pomelo and sweet orange.
There are three common varieties available: red, pink, and white. The names are based on the color of the fruit's pulp.
Effects on Estradiol 17beta-dehydrogenase Type 2
1-2 cups of white grapefruit juice potently inhibits Estradiol 17beta-dehydrogenase Type 2 (17bHSD2). Inhibition lasts approximately 4-8 hours.
Grapefruit juice contains the following inhibitors of 17bHSD2:
- galangin
- kaempferol
- naringenin (31.2 mg/L [12]) is an potent inhibitor.
- quercetin (4.9 mg/L [11]) is an potent inhibitor.
Blocking Psychedelic Action of Allylbenzenes
Anecdotal reports indicate that 2 cups of white grapefruit juice consumed 30 minutes before taking allylbenzenes will greatly reduce the psychedelic effects of allylbenzenes and delay their onset by up to 8 hours. The enzyme 17bHSD2 is required for allylbenzenes to produce psychedelic effects. Grapefruit juice potently inhibits this enzyme for 4-8 hours. See the article Oilahuasca Activation for more information.
Effects on the Cytochrome P450 Enzyme System
Among the varies types of grapefruit, white grapefruit has the strongest effect on P450 enzymes.
1 cup of grapefruit taken 3 times a day by human volunteers was found to inhibit CYP3A4 in small intestine (small bowel) epithelia (enterocytes) by 62%, but had no detectable effect on liver CYP3A4 activity, colon levels of CYP3A5, or small intestine concentrations of P-glycoprotein, CYP1A1, or CYP2D6.[8]
Grapefruit Oil
Grapefruit oil was found to inhibit CYP3A4 in vitro, but not CYP1A1 or CYP2D6.[9] Tests in humans are lacking for grapefruit oil but these results mirror those of grapefruit juice tested in humans.
Cytochrome P450 Enzyme Inhibitors in Grapefruit
P450 enzyme inhibitors found in grapefruit include:
- bergamottin[4]
- 6', 7'-dihydroxybergamottin[4]
- naringenin (31.2 mg/L [12])
- naringin (628 mg/L [12])
- quercetin (4.9 mg/L [11])
Effects on Individual P450 Enzyme Levels From Juice
| Enzyme | Interaction | Dosage | Verified In Humans |
|---|---|---|---|
| CYP1A1 | No Effect[8] | 3 cups | Yes |
| CYP1A2 | 23% Inhibition[3] | 1-2 cups | Yes |
| CYP1B1 | ? | ? | ? |
| CYP2A6 | Potent Inhibition [10] | 1 Liter | Yes |
| CYP2B6 | Potent Inhibition | 1-2 cups | ? |
| CYP2C8 | ? | ? | ? |
| CYP2C9 | No Effect[7] | 1-2 cups | Yes |
| CYP2C19 | No Effect[5] | 300 ml | Yes |
| CYP2D6 | No Effect[8] | 3 cups | Yes |
| CYP2E1 | No Effect[6] | 1-2 cups | Yes |
| CYP2F1 | ? | ? | ? |
| CYP2J2 | ? | ? | ? |
| CYP3A4 [1][2] | 62% Inhibition[2][8] | 3 cups | Yes |