Garlic has one of the longest histories of medicinal use of any food plant. Its primary bioactive compound, allicin, is produced when garlic is chopped or crushed, causing the enzyme alliinase to convert alliin to allicin. Allicin is unstable and converts to other organosulphur compounds including diallyl disulphide, diallyl sulphide, and ajoene. These compounds are responsible for garlic's distinctive odour and its biological effects.
Cardiovascular Effects
A meta-analysis of 39 randomised controlled trials found that garlic significantly reduced total cholesterol, LDL cholesterol, and triglycerides compared to placebo. A separate meta-analysis of 17 trials found that garlic supplementation reduced systolic blood pressure by an average of 5.1 mmHg and diastolic blood pressure by 2.5 mmHg in adults with hypertension. These are clinically meaningful reductions comparable to low-dose antihypertensive medication.
Antimicrobial and Immune Effects
Allicin has broad-spectrum antimicrobial activity against bacteria, fungi, and viruses in laboratory studies. A randomised double-blind trial found that participants who took an allicin supplement were significantly less likely to develop a cold and recovered faster when they did. Regular garlic consumption is associated with lower rates of gastrointestinal cancers in epidemiological studies, attributed to its effects on H. pylori infection and carcinogen activation.
- Crush or chop garlic and allow it to rest for 10 minutes before cooking: this maximises allicin formation before heat deactivates alliinase
- Raw garlic in dressings, salsas, and dips preserves more allicin than cooked garlic
- One to three cloves per day is the dose used in most research; this is easily achieved by using garlic generously as a cooking base