Grapefruit, a citrus fruit eaten for heart and metabolic health, may modestly lower blood pressure, ease artery stiffness after menopause and, as whole fruit, accompany lower diabetes risk; evidence is limited. One serving can raise blood levels of many medications for up to three days; frequent intake is linked to melanoma, a skin cancer. For sun-protected adults on no interacting medications, whole grapefruit is low-risk; on affected medications, interactions dominate. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Blood pressure | Below 120/80 mmHg | Tracks the main vascular benefit |
| LDL cholesterol | 70–100 mg/dL (lower in high-risk people) | Lipid response |
| Triglycerides | Below 100 mg/dL | Most responsive lipid in red grapefruit trial |
| HDL cholesterol | 55–80 mg/dL | Preload trials showed increases |
| Fasting insulin | 2–6 µIU/mL | Insulin sensitivity response |
| HbA1c | Below 5.4% | Long-term glucose control |
| Plasma vitamin C | 0.9–1.5 mg/dL | Nutrient repletion |
| QTc (ECG) | Below 440 ms (men), below 450 ms (women) | Detects QT prolongation |
| CK (creatine kinase) | Within own baseline; typically below 200 U/L | Detects statin muscle injury |
| Immunosuppressant or narrow-margin drug level | Within the prescriber's therapeutic range | Detects interaction-driven toxicity |
| 24-hour urine citrate | Above 640 mg/day | Stone-inhibitor status |
Cadence: Blood pressure weekly for the first month, then monthly; labs at 8–12 weeks, then every 6–12 months; drug levels within one week of any change in grapefruit habits (narrow-margin drugs); annual skin examination