Grapefruit
Food · Fruit · Food, Typed Supps
Grapefruit is packed with vitamin C, but it can also make certain medicines act stronger than they should.
Stage by stage
- Mouth (Chewing & juice release): Chewing ruptures the juicy vesicles of the grapefruit segments, releasing vitamin C, potassium, and bitter flavonoids like naringin along with the furanocoumarins that later drive its drug interactions.
- Stomach (Acid & pectin gel): Stomach acid breaks down the pulp further, and the fruit's soluble pectin fiber begins forming a gel that slightly slows how quickly the meal's sugars move into the small intestine.
- Small intestine (Absorption & enzyme block): Vitamin C and potassium are absorbed here, but so are furanocoumarins such as bergamottin, which irreversibly inhibit the CYP3A4 enzyme in the intestinal wall for up to a day or more.
- Liver & bloodstream (Circulation & drug metabolism): Because less CYP3A4 is available to break down certain medications on their first pass through the gut wall, more of a susceptible drug reaches the bloodstream than the prescribed dose intended -- which is why grapefruit carries a genuine FDA drug-interaction warning.
Timing
Grapefruit's vitamin C doesn't need to be eaten with a meal to be absorbed, but its interaction with certain drugs isn't solved by spacing doses out -- the enzyme-blocking effect can last for days.
Time to effect
- Hours to days: Vitamin C levels in the blood begin rising within a few hours of eating grapefruit, while its inhibition of the CYP3A4 drug-metabolizing enzyme can persist for one to three days after a single serving.
Allergens
None of the fourteen major allergens. Derived from what this food is, not from a product label.
Eating patterns
Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Gluten-free. Depends on the product: Keto, Low-FODMAP.
In season
November to April in the northern hemisphere, May to October in the southern.
Satiety
The satiety index is measured on 240 kcal servings. At 40 kcal per 100 g that is 597 g of this, which is not a serving anyone eats — so the index has nothing to say about it.
Environmental footprint
0.4 kg CO2e and 83 litres of freshwater per kg, matched to "Citrus fruit" in Poore & Nemecek (2018), Science 360.
Cost band
Cheap — roughly £3 per kg, as a band midpoint rather than a price.
Key nutrients
Nutrition per 100g
- Calories: 40.2
- Protein: 0.8g
- Carbohydrate: 7.7g
- of which sugars: 7.7g
- Fat: 0g
- of which saturated: 0g
- Fibre: 1.4g
- Sodium: 1mg
Food vs. supplement
A whole grapefruit delivers vitamin C, potassium, fiber, and (in pink/red varieties) lycopene together, while an ascorbic acid supplement isolates just the vitamin C and carries none of the fruit's furanocoumarin-driven drug interactions.
Kitchen tip
Section the grapefruit (supreme it) to remove the bitter membranes, or broil a halved grapefruit with a little sugar sprinkled on top for a warm dessert.
Common myth
"Grapefruit has a special fat-burning enzyme that melts away fat." In reality: No such enzyme exists; grapefruit's low calorie density (about 42 kcal/100 g) and fiber/water content can promote fullness, but clinical trials find no metabolic fat-burning effect beyond ordinary calorie reduction.
Recipes that use it
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